Phosphor and light-emitting equipment using phosphor

This application is a continuation of U.S. patent application Ser. No. 13/775,334, filed Feb. 25, 2013; which, in turn is a continuation of U.S. patent application Ser. No. 11/441,094, filed May 26, 2006, now U.S. Pat. No. 8,409,470; which, in turn is a continuation-in-part of International Patent Application No. PCT/JP04/17895, filed Nov. 25, 2004, the disclosures of which are incorporated herein by reference in their entireties. This application claims priority to Japanese Patent Application No. 2003-394855, filed Nov. 26, 2003, Japanese Patent Application No. 2004-041503, filed Feb. 18, 2004, Japanese Patent Application No. 2004-154548, filed May 25, 2004, and Japanese Patent Application No. 2004-159306, filed May 28, 2004, the disclosures of which are incorporated herein by reference in their entireties.

The present invention relates to a phosphor mainly composed of an inorganic compound and applications thereof. More specifically, the applications relate to light-emitting equipments such as a lighting equipment and an image display unit as well as a pigment and an ultraviolet absorbent, which utilize a property possessed by the phosphor, i.e., a characteristic of emitting fluorescence having a long wavelength of 570 nm or longer.

Phosphors are used for a vacuum fluorescent display (VFD), a field emission display (FED), a plasma display panel (PDP), a cathode ray tube (CRT), a white light-emitting diode (LED), and the like. In all these applications, it is necessary to provide energy for exciting the phosphors in order to cause emission from the phosphors. The phosphors are excited by an excitation source having a high energy, such as a vacuum ultraviolet ray, an ultraviolet ray, an electron beam, or a blue light to emit a visible light. However, as a result of exposure of the phosphors to the above excitation source, there arises a problem of decrease of luminance of the phosphors and hence a phosphor exhibiting no decrease of luminance has been desired. Therefore, a sialon phosphor has been proposed as a phosphor exhibiting little decrease of luminance instead of conventional silicate phosphors, phosphate phosphors, aluminate phosphors, sulfide phosphors, and the like.

The sialon phosphor is produced by the production process outlined below. First, silicon nitride (Si 3 N 4 ), aluminum nitride (AlN), calcium carbonate (CaCO 3 ), and europium oxide (Eu 2 O 3 ) are mixed in a predetermined molar ratio and the mixture is held at 1700° C. for 1 hour in nitrogen at 1 atm (0.1 MPa) and is baked by a hot pressing process to produce the phosphor (e.g., cf. Patent Literature 1). The α-sialon activated with Eu obtained by the process is reported to be a phosphor which is excited by a blue light of 450 to 500 nm to emit a yellow light of 550 to 600 nm. However, in the applications of a white LED and a plasma display using an ultraviolet LED as an excitation source, phosphors emitting lights exhibiting not only yellow color but also orange color and red color have been desired. Moreover, in a white LED using a blue LED as an excitation source, phosphors emitting lights exhibiting orange color and red color have been desired in order to improve color-rendering properties.

As a phosphor emitting a light of red color, an inorganic substance (Ba 2-x Eu x Si 5 N 8 :x=0.14 to 1.16) obtained by activating a Ba 2 Si 5 N 8 crystal phase with Eu has been reported in an academic literature (cf. Non-Patent Literature 1) prior to the present application. Furthermore, in Chapter 2 of a publication “On new rare-earth doped M-Si—Al—O—N materials” (cf. Non-Patent Literature 2), a phosphor using a ternary nitride of an alkali metal and silicon having various compositions, M x Si y N z (M=Ca, Sr, Ba, Zn; x, y, and z represent various values) as a host has been reported. Similarly, M x Si y N z :Eu (M=Ca, Sr, Ba, Zn; z=⅔x+ 4/3y) has been reported in U.S. Pat. No. 6,682,663 (Patent Literature 2).

As other sialon, nitride or oxynitride phosphors, there are known in JP-A-2003-206481 (Patent Literature 3) phosphors using MSi 3 N 5 , M 2 Si 4 N 7 , M 4 Si 6 N 11 , M 9 Si 11 N 23 , M 16 Si 15 O 6 N 32 , M 13 S 18 Al 12 O 18 N 36 , MSi 5 Al 2 ON 9 , and M 3 Si 5 AlON 10 (wherein M represents Ba, Ca, Sr or a rare earth element) as host crystals, which are activated with Eu or Ce. Among them, phosphors emitting a light of red color have been also reported. Moreover, LED lighting units using these phosphors are known. Furthermore, JP-A-2002-322474 (Patent Literature 4) has reported a phosphor wherein an Sr 2 Si 5 N 8 or SrSi 7 N 10 crystal phase is activated with Ce.

In JP-A-2003-321675 (Patent Literature 5), there is a description of L x M y N (2/3x+4/3y) :Z (L is a divalent element such as Ca, Sr, or Ba, M is a tetravalent element such as Si or Ge, and Z is an activator such as Eu) phosphor and it describes that addition of a minute amount of Al exhibits an effect of suppressing afterglow. Moreover, a slightly reddish warm color white emitting apparatus is known, wherein the phosphor and a blue LED are combined. Furthermore, JP-A-2003-277746 (Patent Literature 6) reports phosphors constituted by various combinations of L Element, M Element, and Z Element as LxMyN (2/3x+4/3y) :Z phosphors. JP-A-2004-10786 (Patent Literature 7) describes a wide range of combinations regarding an L-M-N:Eu,Z system but there is not shown an effect of improving emission properties in the cases that a specific composition or crystal phase is used as a host.

The representative phosphors in Patent Literatures 2 to 7 mentioned above contain nitrides of a divalent element and a tetravalent element as host crystals and phosphors using various different crystal phases as host crystals have been reported. The phosphors emitting a light of red color are also known but the emitting luminance of red color is not sufficient by excitation with a blue visible light. Moreover, they are chemically unstable in some compositions and thus their durability is problematic.

[Non-Patent Literature 1]

H. A. Hoppe, and other four persons, “Journal of Physics and Chemistry of Solids” 2000, vol. 61, pages 2001-2006

[Non-Patent Literature 2]

“On new rare-earth doped M-Si—Al—O—N materials” written by J. W. H. van Krevel, TU Eindhoven 2000, ISBN, 90-386-2711-4

[Patent Literature 1]

JP-A-2002-363554

[Patent Literature 2]

U.S. Pat. No. 6,682,663

[Patent Literature 3]

JP-A-2003-206481

[Patent Literature 4]

JP-A-2002-322474

[Patent Literature 5]

JP-A-2003-321675

[Patent Literature 6]

JP-A-2003-277746

[Patent Literature 7]

JP-A-2004-10786

As conventional art of lighting apparatus, a white light-emitting diode wherein a blue light-emitting diode element and a blue light-absorbing yellow light-emitting phosphor are combined is known and has been practically used in various lighting applications. Representative examples thereof include “a light-emitting diode” of Japanese Patent No. 2900928 (Patent Literature 8), “a light-emitting diode” of Japanese Patent No. 2927279 (Patent Literature 9), “a wavelength-converting molding material and a process for producing the same, and a light-emitting element” of Japanese Patent No. 3364229 (Patent Literature 10), and the like. Phosphors most frequently used in these light-emitting diode are yttrium.aluminum.garnet-based phosphors activated with cerium represented by the general formula:

(Y,Gd) 3 (Al,Ga) 5 O 12 :Ce 3+ .

However, there is a problem that the white light-emitting diode comprising a blue light-emitting diode element and the yttrium.aluminum.garnet-based phosphor has a characteristic of emitting a bluish-white light because of an insufficient red component and hence deflection is found in color-rendering properties.

Based on such a background, there has been investigated a white light-emitting diode wherein a red component which is short in the yttrium.aluminum.garnet-based phosphor is supplemented with another red phosphor by mixing and dispersing two kinds of phosphors. As such light-emitting diodes, “a white light-emitting diode” of JP-A-10-163535 (Patent Literature 11), “a nitride phosphor and a process for producing the same” of JP-A-2003-321675 (Patent Literature 5), and the like can be exemplified. However, a problem to be improved regarding color-rendering properties still remains also in these inventions, and hence it is desired to develop a light-emitting diode where the problem is solved. The red phosphor described in JP-A-10-163535 (Patent Literature 11) contains cadmium and thus there is a problem of environmental pollution. Although red light emitting phosphors including Ca 1.97 Si 5 N 8 :Eu 0.03 described in JP-A-2003-321675 (Patent Literature 5) as a representative example do not contain cadmium but further improvement of their emission intensities has been desired since luminance of the phosphor is low.

[Patent Literature 8]

Japanese Patent No. 2900928

[Patent Literature 9]

Japanese Patent No. 2927279

[Patent Literature 10]

Japanese Patent No. 3364229

[Patent Literature 11]

JP-A-10-163535

The invention intends to reply such demands and an object thereof is to provide an inorganic phosphor which emits an orange or red light having a longer wavelength than that of conventional sialon phosphors activated with a rare earth, has a high luminance, and is chemically stable. Furthermore, another object of the invention is to provide a lighting equipment excellent in color-rendering properties, an image display unit excellent in durability, a pigment, and an ultraviolet absorbent using such a phosphor.

Under such circumstances, the present inventors have conducted precise studies on phosphors using as a host an inorganic multi-element nitride crystal phase containing trivalent E Element such as Al in addition to divalent A Element such as Ca and tetravalent D Element such as Si as main metal elements and have found that a phosphor using an inorganic crystal phase having a specific composition or a specific crystal structure as a host emits an orange or red light having a longer wavelength than that of conventional sialon phosphors activated with a rare earth and also exhibits a higher luminance than that of the red phosphors hitherto reported containing a nitride or oxynitride as a host crystal.

Namely, as a result of extensive studies on inorganic compounds mainly composed of nitrides or oxynitrides containing M Element which becomes a light-emitting ion (wherein M Element is one or two or more elements selected from Mn, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb) and divalent A Element (wherein A Element is one or two or more elements selected from Mg, Ca, Sr, and Ba), tetravalent D Element (wherein D Element is one or two or more elements selected from Si, Ge, Sn, Ti, Zr, and Hf), trivalent E Element (wherein E Element is one or two or more elements selected from B, Al, Ga, In, Sc, Y, La, Gd and Lu), and X Element (wherein X Element is one or two or more elements selected from O, N, and F), they have found that those having a specific composition region range and a specific crystal phase form phosphors emitting an orange light having a wavelength of 570 nm or longer or a red light having a wavelength of 600 nm or longer.

Furthermore, they have found that, among the above compositions, a solid solution crystal phase containing an inorganic compound having the same crystal structure as that of the CaAlSiN 3 crystal phase as a host crystal and incorporated with an optically active element M, particularly Eu as an emission center forms a phosphor emitting an orange or red light having an especially high luminance. Furthermore, they have found that a white light-emitting diode which has a high emission efficiency, is rich in a red component, and exhibits good color-rendering properties can be obtained by using the phosphor.

The host crystal of the phosphor of the invention achieves red-light emission exhibiting an unprecedented luminance by using the multi-element nitride wherein a trivalent element including Al as a representative is used as a main constitutive metal element, quite unlike the ternary nitrides containing divalent and tetravalent elements hitherto reported including L x M y N (2/3x+4/3y) as a representative. Moreover, the invention is a novel phosphor using a crystal phase having a composition and crystal structure quite different from the sialons such as M 13 Si 18 Al 12 O 18 N 36 , MSi 5 Al 2 ON 9 , and M 3 Si 5 AlON 10 (wherein M represents Ca, Ba, Sr, or the like) hitherto reported in Patent Literature 3 and the like and Ca 1.47 Eu 0.03 Si 9 Al 3 N 16 described in Chapter 11 of Non-Patent Literature 2 as a host. Furthermore, unlike the crystal phase containing Al in an amount of about several hundreds of ppm described in Patent Literature 5, it is a phosphor using as a host a crystal phase wherein a trivalent element including Al as a representative is a main constitutive element of the host crystal.

In general, a phosphor wherein an inorganic host crystal is activated with Mn or a rare earth metal as an emission center element M changes an emitting color and luminance depending on an electron state around M Element. For example, in a phosphor containing divalent Eu as the emission center, light emission of blue color, green color, yellow color, or red color has been reported by changing the host crystal. Namely, even in the case that the composition is resemble, when the crystal structure of the host or the atom position in the crystal structure to which M is incorporated is changed, the emitting color and luminance become quite different and thus the resulting phosphor is regarded as a different one. In the invention, a multi-element nitride containing divalent-trivalent-tetravalent elements different from conventional ternary nitrides containing divalent and tetravalent elements is used as a host crystal and furthermore, a crystal phase having a crystal structure quite different from that of the sialon composition hitherto reported is used as a host. Thus, the phosphor having such a crystal phase as a host has not hitherto been reported. In addition, the phosphor containing the composition and crystal structure of the invention as a host exhibits a red light emission having luminance higher than that of those containing a conventional crystal structure as a host.

The above CaAlSiN 3 crystal phase itself is a nitride whose formation in the process of baking an Si 3 N 4 —AlN—CaO based raw material is confirmed by ZHEN-KUN-HUANG et al. for the purpose of aiming at a heat-resistant material. A process of the formation and a mechanism of the formation are precisely reported in an academic literature (c.f. Non-Patent Literature 3), which has been published prior to the present application.

[Non-Patent Literature 3]

ZHEN-KUN-HUANG and other two persons, “Journal of Materials Science Letters” 1985, vol. 4, pages 255-259

As mentioned above, the CaAlSiN 3 crystal phase itself is confirmed in the progress of the study of sialons. Also, from the circumstances, the content of the report described in the above literature only mentions heat-resistant properties and the literature does not describe any matter that an optically active element may be dissolved in the crystal phase and the dissolved crystal phase may be used as a phosphor. Moreover, over the period from that time to the present invention, there is no investigation to use it as a phosphor. Namely, the important findings that a substance obtained by dissolving an optically active element in CaAlSiN 3 crystal phase is a novel substance and it is usable as a phosphor capable of being excited with an ultraviolet ray and a visible light and exhibiting an orange or red light emission having a high luminance have been first found by the present inventors. As a result of further extensive studies based on the findings, the inventors have succeeded in providing a phosphor showing an emission phenomenon with a high luminance in a specific wavelength region by the constitutions described in the following (1) to (24). Moreover, they have also succeeded in providing a lighting equipment and an image display unit having excellent characteristics by the constitutions described in the following (25) to (37) by using the phosphor. Furthermore, by applying the inorganic compound as the phosphor to the constitutions described in the following (38) to (39), they have also succeeded in providing a pigment and an ultraviolet absorbent. Namely, as a result of a series of experiments and studies based on the above findings, the invention has succeeded in providing a phosphor emitting a light with a high luminance in a long wavelength region as well as a lighting equipment, an image display unit, a pigment, and an ultraviolet absorbent utilizing the phosphor. The constitutions are as described in the following (1) to (39).

(1) A phosphor comprising an inorganic compound which is a composition containing at least M Element, A Element, D Element, E Element, and X Element (wherein M Element is one or two or more elements selected from the group consisting of Mn, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb, A Element is one or two or more elements selected from the group consisting of divalent metal elements other than M Element, D Element is one or two or more elements selected from the group consisting of tetravalent metal elements, E Element is one or two or more elements selected from the group consisting of trivalent metal elements, and X Element is one or two or more elements selected from the group consisting of O, N, and F).

(2) The phosphor according to the above item (1), wherein the inorganic compound has the same crystal structure as that of CaAlSiN 3 .

(3) The phosphor according to the above item (1) or (2), wherein the inorganic compound is represented by the composition formula M a A b D c E d X e (wherein a+b=1 and M Element is one or two or more elements selected from the group consisting of Mn, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb, A Element is one or two or more elements selected from the group consisting of divalent metal elements other than M Element, D Element is one or two or more elements selected from the group consisting of tetravalent metal elements, E Element is one or two or more elements selected from the group consisting of trivalent metal elements, and X Element is one or two or more elements selected from the group consisting of O, N, and F), wherein the parameters a, c, d, and e satisfy all the requirements:

0.00001≦ a≦ 0.1  (i),

0.5≦ c≦ 4  (ii),

0.5≦ d≦ 8  (iii),

0.8×(⅔+ 4/3× c+d )≦ e   (iv), and

e≦ 1.2×(⅔+ 4/3× c+d )  (v).

(4) The phosphor according to the above item (3), wherein the parameters c and d satisfy the requirements of 0.5≦c≦1.8 and 0.5≦d≦1.8.

(5) The phosphor according to the above item (3) or (4), wherein the parameters c, d, and e are c=d=1 and e=3.

(6) The phosphor according to any one of the above items (1) to (5), wherein A Element is one or two or more elements selected from the group consisting of Mg, Ca, Sr, and Ba, D Element is one or two or more elements selected from the group consisting of Si, Ge, Sn, Ti, Zr, and Hf, and E Element is one or two or more elements selected from the group consisting of B, Al, Ga, In, Sc, Y, La, Gd, and Lu.

(7) The phosphor according to any one of the above items (1) to (6), which contains, at least, Eu in M Element, Ca in A Element, Si in D Element, Al in E Element, and N in X Element.

(8) The phosphor according to any one of the above items (1) to (7), wherein the inorganic compound is a CaAlSiN 3 crystal phase or a solid solution of a CaAlSiN 3 crystal phase.

(9) The phosphor according to any one of the above items (1) to (8), wherein M Element is Eu, A Element is Ca, D Element is Si, E Element is Al, and X Element is N or a mixture of N and O.

(10) The phosphor according to any one of the above items (1) to (9), which contains, at least, Sr in A Element.

(11) The phosphor according to the above item (10), wherein numbers of atoms of Ca and Sr contained in the inorganic compound satisfy 0.02≦(number of atoms of Ca)/{(number of atoms of Ca)+(number of atoms of Sr)}<1.

(12) The phosphor according to any one of the above items (1) to (11), which contains, at least, N and O in X.

(13) The phosphor according to the above item (12), wherein numbers of atoms of O and N contained in the inorganic compound satisfy 0.5≦(number of atoms of N)/{(number of atoms of N)+(number of atoms of O)}≦1.

(14) The phosphor according to the above item (12) or (13), wherein the inorganic compound is represented by M a A b D 1-x E 1+x N 3-x O x (wherein a+b=1 and 0<x≦0.5).

(15) The phosphor according to any one of the above items (1) to (14), wherein the inorganic compound is a powder having an average particle size of 0.1 μm to 20 μm and the powder is single crystal particles or an aggregate of single crystals.

(16) The phosphor according to any one of the above items (1) to (15), wherein total of impurity elements of Fe, Co, and Ni contained in the inorganic compound is 500 ppm or less.

(17) A phosphor which is constituted by a mixture of the phosphor comprising the inorganic compound according to anyone of the above items (1) to (16) and other crystal phase or an amorphous phase and wherein the content of the phosphor comprising the inorganic compound according to any one of the above items (1) to (16) is 20% by weight or more.

(18) The phosphor according to the above item (17), wherein the other crystal phase or amorphous phase is an inorganic substance having electroconductivity.

(19) The phosphor according to the above item (18), wherein the inorganic substance having electroconductivity is an oxide, oxynitride, or nitride containing one or two or more elements selected from the group consisting of Zn, Al, Ga, In, and Sn, or a mixture thereof.

(20) The phosphor according to the above item (17), wherein the other crystal phase or amorphous phase is an inorganic phosphor different from the phosphor according to any one of the above items (1) to (16).

(21) The phosphor according to any one of the above items (1) to (20), which emits a fluorescent light having a peak in the range of a wavelength of 570 nm to 700 nm by irradiation with an excitation source.

(22) The phosphor according to the above item (21), wherein the excitation source is an ultraviolet ray or a visible light having a wavelength of 100 nm to 600 nm.

(23) The phosphor according to the above item (21), wherein the inorganic compound is a CaAlSiN 3 crystal phase and Eu is dissolved in the crystal phase, and which emits a fluorescent light having a wavelength of 600 nm to 700 nm when irradiated with a light of 100 nm to 600 nm.

(24) The phosphor according to the above item (21), wherein the excitation source is an electron beam or an X-ray.

(25) The phosphor according to any one of the above items (21) to (24), wherein a color emitted at the irradiation with an excitation source satisfies a requirement:

0.45≦ x≦ 0.7

as a value of (x, y) on the CIE chromaticity coordinates.

(26) A lighting equipment constituted by a light-emitting source and a phosphor, wherein at least the phosphor according to any one of the above items (1) to (25) is used.

(27) The lighting equipment according to the above item (26), wherein the light-emitting source is an LED emitting a light having a wavelength of 330 nm to 500 nm.

(28) The lighting equipment according to the above item (26) or (27), wherein the light-emitting source is an LED emitting a light having a wavelength of 330 nm to 420 nm and which emits a white light with mixing red, green, and blue lights by using the phosphor according to any one of the above items (1) to (25), a blue phosphor having an emission peak at a wavelength of 420 nm to 500 nm with an excitation light of 330 nm to 420 nm, and a green phosphor having an emission peak at a wavelength of 500 nm to 570 nm with an excitation light of 330 nm to 420 nm.

(29) The lighting equipment according to the above item (26) or (27), wherein the light-emitting source is an LED emitting a light having a wavelength of 420 nm to 500 nm and which emits a white light by using the phosphor according to any one of the above items (1) to (25) and a green phosphor having an emission peak at a wavelength of 500 nm to 570 nm with an excitation light of 420 nm to 500 nm.

(30) The lighting equipment according to the above item (26) or (27), wherein the emitting source is an LED emitting a light having a wavelength of 420 nm to 500 nm and which emits a white light by using a phosphor according to any one of the above items (1) to (25) and a yellow phosphor having an emission peak at a wavelength of 550 nm to 600 nm with an excitation light of 420 nm to 500 nm.

(31) The lighting equipment according to the above item (30), wherein the yellow phosphor is a Ca-αsialon in which Eu is dissolved.

(32) An image display unit constituted by an excitation source and a phosphor, wherein at least the phosphor according to any one of the above items (1) to (25) is used.

(33) The image display unit according to the above item (32), wherein the excitation source is an LED emitting a light having a wavelength of 330 nm to 500 nm.

(34) The image display unit according to the above item (32) or (33), wherein the excitation source is an LED emitting a light having a wavelength of 330 nm to 420 nm and which emits a white light with mixing red, green, and blue lights by using the phosphor according to any one of the above items (1) to (25), a blue phosphor having an emission peak at a wavelength of 420 nm to 500 nm with an excitation light of 330 nm to 420 nm, and a green phosphor having an emission peak at a wavelength of 500 nm to 570 nm with an excitation light of 330 nm to 420 nm.

(35) The image display unit according to the above item (32) or (33), wherein the emitting source is an LED emitting a light having a wavelength of 420 nm to 500 nm and which emits a white light by using the phosphor according to any one of the above items (1) to (25) and a green phosphor having an emission peak at a wavelength of 500 nm to 570 nm with an excitation light of 420 nm to 500 nm.

(36) The image display unit according to the above item (32) or (33), wherein the emitting source is an LED emitting a light having a wavelength of 420 nm to 500 nm and which emits a white light by using the phosphor according to any one of the above items (1) to (25) and a yellow phosphor having an emission peak at a wavelength of 550 nm to 600 nm with an excitation light of 420 nm to 500 nm.

(37) The image display unit according to the above item (36), wherein the yellow phosphor is a Ca-αsialon in which Eu is dissolved.

(38) The image display unit according to the above items (32) to (37), wherein the image display unit is any of a vacuum fluorescent display (VFD), a field emission display (FED), a plasma display panel (PDP), and a cathode-ray tube (CRT).

(39) A pigment comprising the inorganic compound according to any one of the above items (1) to (25).

(40) An ultraviolet absorbent comprising the inorganic compound according to any one of the above items (1) to (25).

The phosphor of the invention contains a multi-element nitride containing a divalent element, a trivalent element, and a tetravalent element, particularly a crystal phase represented by CaAlSiN 3 , another crystal phase having the same crystal structure as it, or a solid solution of these crystal phases as a main component and thereby exhibits light emission at a longer wavelength than that in the cases of conventional sialon and oxynitride phosphors, so that the phosphor of the invention is excellent as an orange or red phosphor. Even when exposed to an excitation source, the phosphor does not exhibit decrease of luminance and thus provides a useful phosphor which is suitably employed in VFD, FED, PDP, CRT, white LED, and the like. Moreover, among the phosphors, since the host of a specific inorganic compound has a red color and the compound absorbs an ultraviolet ray, it is suitable as a red pigment and an ultraviolet absorbent.

FIG. 1-1 is an X-ray diffraction chart of CaAlSiN 3 .

FIG. 1-2 is an X-ray diffraction chart of CaAlSiN 3 activated with Eu (Example 1).

FIG. 2 is a drawing illustrating a crystal structure model of CaAlSiN 3 .

FIG. 3 is a drawing illustrating a crystal structure model of Si 2 N 2 O having a similar structure to the CaAlSiN 3 crystal phase.

FIG. 4 is a drawing illustrating emission spectra of phosphors (Examples 1 to 7).

FIG. 5 is a drawing illustrating excitation spectra of phosphors (Examples 1 to 7).

FIG. 6 is a drawing illustrating emission spectra of phosphors (Examples 8 to 11).

FIG. 7 is a drawing illustrating excitation spectra of phosphors (Examples 8 to 11).

FIG. 8 is a drawing illustrating emission spectra of phosphors (Examples 12 to 15).

FIG. 9 is a drawing illustrating excitation spectra of phosphors (Examples 12 to 15).

FIG. 10 is a drawing illustrating emission spectra of phosphors (Examples 16 to 25).

FIG. 11 is a drawing illustrating excitation spectra of phosphors (Examples 16 to 25).

FIG. 12 is a drawing illustrating emission spectra of phosphors (Examples 26 to 30).

FIG. 13 is a drawing illustrating excitation spectra of phosphors (Examples 26 to 30).

FIG. 14 is a schematic drawing of the lighting equipment (LED lighting equipment) according to the invention.

FIG. 15 is a schematic drawing of the image display unit (plasma display panel) according to the invention.

In this connection, with regard to the symbols in the figures, 1 represents a mixture of a red phosphor of the invention and a yellow phosphor or a mixture of a red phosphor of the invention, a blue phosphor, and a green phosphor, 2 represents an LED chip, 3 and 4 represent electroconductive terminals, 5 represents a wire bond, 6 represents a resin layer, 7 represents a container, 8 represents a red phosphor of the invention, 9 represents a green phosphor, 10 represents a blue phosphor, 11 , 12 , and 13 represent ultraviolet ray-emitting cells, 14 , 15 , 16 , and 17 represent electrodes, 18 and 19 represent dielectric layers, 20 represents a protective layer, and 21 and 22 represent glass substrates.

The following will describe the present invention in detail with reference to Examples of the invention.

The phosphor of the invention comprises an inorganic compound which is (1) a composition containing at least M Element, A Element, D Element, E Element, and X Element (wherein M Element is one or two or more elements selected from the group consisting of Mn, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb, A Element is one or two or more elements selected from the group consisting of divalent metal elements other than M Element, D Element is one or two or more elements selected from the group consisting of tetravalent metal elements, E Element is one or two or more elements selected from the group consisting of trivalent metal elements, and X Element is one or two or more elements selected from the group consisting of O, N, and F) and is (2) (a) a crystal phase represented by the chemical formula CaAlSiN 3 , (b) another crystal phase having the same crystal structure as that of the crystal phase, or (c) a solid solution of these crystal phases (hereinafter, these crystal phases are collectively referred to as “a CaAlSiN 3 family crystal phase”). Such a phosphor of the invention shows a particularly high luminance.

M Element is one or two or more elements selected from the group consisting of Mn, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb. M Element is preferably one or two or more elements selected from the group consisting of Mn, Ce, Sm, Eu, Tb, Dy, Er, and Yb. M Element more preferably contains Eu and is still more preferably Eu.

A Element is one or two or more elements selected from the group consisting of divalent metal elements other than M Element. Particularly, A Element is preferably one or two or more elements selected from the group consisting of Mg, Ca, Sr, and Ba and is more preferably Ca.

D Element is one or two or more elements selected from the group consisting of tetravalent metal elements. Particularly, D Element is preferably one or two or more elements selected from the group consisting of Si, Ge, Sn, Ti, Zr, and Hf and is more preferably Si.

E Element is one or two or more elements selected from the group consisting of trivalent metal elements. Particularly, E Element is one or two or more elements selected from the group consisting of B, Al, Ga, In, Sc, Y, La, Gd, and Lu and is more preferably Al.

X Element is one or two or more elements selected from the group consisting of O, N, and F. Particularly, X Element is preferably composed of N or N and O.

The composition is represented by the composition formula M a A b D c E d X e . A composition formula is a ratio of numbers of the atoms constituting the substance and one obtained by multiplying a, b, c, d, and e by an arbitrary number has also the same composition. Therefore, in the invention, the following requirements are determined to the one obtained by recalculation for a, b, c, d, and e so as to be a+b=1.

In the invention, the values of a, c, d, and e are selected from the values satisfying all the following requirements:

0.00001≦ a≦ 0.1  (i)

0.5≦ c≦ 4  (ii)

0.5≦ d≦ 8  (iii)

0.8×(⅔+ 4/3× c+d )≦ e   (iv)

e≦ 1.2×(⅔+ 4/3× c+d )  (v).

a represents an adding amount of M Element which becomes an emission center and the ratio a of numbers of atoms M and (M+A) (wherein a=M/(M+A)) in a phosphor is suitably from 0.00001 to 0.1. When a Value is less than 0.00001, the number of M becoming an emission center is small and hence emission luminance decreases. When a Value is larger than 0.1, concentration quenching occurs owing to interference between M ions, so that luminance decreases.

In particular, in the case that M is Eu, a Value is preferably from 0.002 to 0.03 owing to high emission luminance.

c Value is the content of D Element such as Si and is an amount represented by 0.5≦c≦4. The value is preferably 0.5≦c≦1.8, more preferably c=1. When c Value is less than 0.5 and when the value is larger than 4, emission luminance decreases. In the range of 0.5≦c≦1.8, emission luminance is high and particularly, emission luminance is especially high at c=1. The reason therefor is that the ratio of formation of the CaAlSiN 3 family crystal phase to be described below increases.

d Value is the content of E Element such as Al and is an amount represented by 0.5≦d≦8. The value is preferably 0.5≦d≦1.8, more preferably d=1. When d Value is less than 0.5 and when the value is larger than 8, emission luminance decreases. In the range of 0.5≦d≦1.8, emission luminance is high and particularly, emission luminance is especially high at d=1. The reason therefor is that the ratio of formation of the CaAlSiN 3 family crystal phase to be described below increases.

e Value is the content of X Element such as N and is an amount represented by from 0.8×(⅔+ 4/3×c+d) to 1.2×(⅔+ 4/3×c+d). More preferably, e=3. The reason therefor is that the ratio of formation of the CaAlSiN 3 family crystal phase to be described below increases. When e Value is out of the range, emission luminance decreases.

Among the above compositions, compositions exhibiting a high emission luminance are those which contain, at least, Eu in M Element, Ca in A Element, Si in D Element, Al in E Element, and N in X Element. In particular, the composition are those wherein M Element is Eu, A Element is Ca, D Element is Si, E Element is Al, and X Element is N or a mixture of N and O.

The above CaAlSiN 3 crystal phase is an orthorhombic system and is a substance characterized by a crystal phase having lattice constants of a=9.8007(4) Å, b=5.6497(2) Å, and c=5.0627(2) Å and having indices of crystal plane described in the chart of FIG. 1-1 and Table 4 in X-ray diffraction.

According to the crystal structure analysis of the CaAlSiN 3 crystal phase conducted by the inventors, the present crystal phase belongs to Cmc2 1 (36th space group of International Tables for Crystallography) and occupies an atomic coordinate position shown in Table 5. In this connection, the space group is determined by convergent beam electron diffraction and the atomic coordinate is determined by Rietveld analysis of X-ray diffraction results.

The crystal phase has a structure shown in FIG. 2 and has a similar skeleton to the Si 2 N 2 O crystal phase (mineral name: sinoite) shown in FIG. 3 . Namely, the crystal phase is a crystal phase wherein the position of Si in the Si 2 N 2 O crystal phase is occupied by Si and Al and the positions of N and O are occupied by N, and Ca is incorporated as an interstitial element into a space of the skeleton formed by Si—N—O, and has a structure where the atomic coordinates are changed to the positions shown in Table 5 with the replacement of the elements. Si and Al occupy the Si position in the Si 2 N 2 O crystal phase in an irregularly distributed (disordered) state. Thus, this structure is named as a sinoite-type sialon structure.

The inorganic compound having the same crystal structure as CaAlSiN 3 shown in the invention means the inorganic compound which is a CaAlSiN 3 family crystal phase mentioned above. The inorganic compound having the same crystal structure as CaAlSiN 3 includes those having lattice constants changed by the replacement of the constitutive element(s) with other element(s) in addition to the substances showing the same diffraction as the results of X-ray diffraction of CaAlSiN 3 . For example, a CaAlSiN 3 crystal phase, a solid solution of the CaAlSiN 3 crystal phase, and the like may be mentioned. Herein, one wherein the constitutive element (s) are replaced with other element (s) means a crystal phase wherein, in the case of the CaAlSiN 3 crystal phase, for example, Ca in the crystal phase is replaced with M Element (wherein M Element is one or two or more elements selected from the group consisting of Mn, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb) and/or M Element and one or two or more elements selected from the group consisting of divalent metal elements other than Ca, preferably the group consisting of Mg, Sr, and Ba, Si is replaced with one or two or more elements selected from the group consisting of tetravalent metal elements other than Si, preferably the group consisting of Ge, Sn, Ti, Zr, and Hf, Al is replaced with one or two or more elements selected from the group consisting of trivalent metal elements other than Al, preferably the group consisting of B, Ga, In, Sc, Y, La, Gd, and Lu, and N is replaced with one or two or more elements selected from the group consisting of O and F. In this connection, the CaAlSiN 3 family crystal phase of the invention can be identified by X-ray diffraction or neutron-ray diffraction.

The CaAlSiN 3 family crystal phase is changed in lattice constants by the replacement of Ca, Si, Al, or N as the constitutive components with other element(s) or the dissolution of a metal element such as Eu but the atomic position determined by the crystal structure, the site occupied by the atom, and its coordinate is changed to not so large extent that the chemical bond between skeletal atoms is cleaved. In the invention, in the case that the lengths of chemical bonds of Al—N and Si—N (distance between adjacent atoms) calculated from the lattice constants and atomic coordinates determined by Rietveld analysis of the results of X-ray diffraction and neutron-ray diffraction with the space group of Cmc2 1 are within ±15% as compared with the length of the chemical bond calculated from the lattice constants and atomic coordinates of CaAlSiN 3 shown in Table 5, it is defined that the crystal phase has the same crystal structure. In this manner, a crystal phase is judged whether it is a CaAlSiN 3 family crystal phase or not. This judging standard is based on the fact that, when the length of the chemical bond changes beyond ±15%, the chemical bond is cleaved and another crystal phase is formed.

Furthermore, when the dissolved amount is small, the following method may be a convenient judging method of a CaAlSiN 3 family crystal phase. When the lattice constants calculated from the results of X-ray diffraction measured on a new substance and the peak position (2θ) of diffraction calculated using the indices of crystal plane in Table 4 are coincident with regard to main peaks, the crystal structures can be identified to be the same. As the main peaks, it is appropriate to conduct the judgment on about ten peaks exhibiting strong diffraction intensity. In that sense, Table 4 is a standard for identifying the CaAlSiN 3 family crystal phase and thus is of importance. Moreover, with regard to the crystal structure of the CaAlSiN 3 crystal phase, an approximate structure can be defined also using another crystal system such as a monoclinic system or a hexagonal system. In that case, the expression may be one using different space group, lattice constants, and indices of crystal plane but the results of X-ray diffraction are not changed and the identification method and identification results using the same are identical thereto. Therefore, in the invention, X-ray diffraction is analyzed as an orthorhombic system. The identification method of substances based on Table 4 will be specifically described in Example 1 to be described below and only a schematic explanation is conducted here.

A phosphor is obtained by activating a CaAlSiN 3 family crystal phase with M Element (wherein M Element is one or two or more elements selected from the group consisting of Mn, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb). The phosphor having a particularly high luminance among the CaAlSiN 3 family crystal phases is a phosphor containing as a host a CaAlSiN 3 crystal phase using a combination that A is Ca, D is Si, E is Al, and X is N.

A phosphor using Ca x Sr 1-x AlSiN 3 (wherein 0.02≦x<1) crystal phase which is a crystal phase obtained by replacing part of Ca with Sr or its solid solution as host crystals, i.e., a phosphor wherein numbers of atoms of Ca and Sr contained in the inorganic compound satisfy 0.02≦(number of atoms of Ca)/{(number of atoms of Ca)+(number of atoms of Sr)}<1, becomes a phosphor exhibiting a shorter wavelength than that of the phosphor using as a host a CaAlSiN 3 crystal phase having a composition of the range.

The phosphor using as a host an inorganic compound containing nitrogen and oxygen is excellent in durability in a high-temperature air. In this case, durability at a high temperature is particularly excellent at the composition where numbers of atoms of O and N contained in the inorganic compound satisfy 0.5≦(number of atoms of N)/{(number of atoms of N)+(number of atoms of O)}≦1.

In the case that the inorganic compound containing nitrogen and oxygen is used as a host, since the ratio of formation of the CaAlSiN 3 family crystal phase increases at the composition represented by M a A b D 1-x E 1+x N 3-x O x (wherein a+b=1 and 0<x≦0.5), emission luminance is high. This is because trivalent N is replaced with divalent O by the number of the atom the same as the number of the tetravalent D Element replaced with trivalent E Element in the composition and hence charge neutrality is maintained, so that a stable CaAlSiN 3 family crystal phase is formed.

In the case that the phosphor comprising the inorganic compound having the same crystal structure as CaAlSiN 3 of the invention is used as a powder, the average particle size of the inorganic compound is preferably from 0.1 μm to 20 μm in view of dispersibility into the resin and fluidity of the powder. Moreover, the powder is single crystal particles or an aggregate of single crystals but emission luminance is further improved by using single crystal particles having an average particle size of 0.1 μm to 20 μm.

In order to obtain a phosphor exhibiting a high emission luminance, the amount of impurities contained in the inorganic compound is preferably as small as possible. In particular, since the contamination of a large amount of Fe, Co, and Ni impurity elements inhibits light emission, it is suitable that raw powders are selected and the synthetic steps are controlled so that the total of these elements becomes not more than 500 ppm.

In the invention, from the viewpoint of fluorescence emission, it is desirable that the nitride contain the CaAlSiN 3 family crystal phase as a constitutive component of the nitride in high purity and as much as possible, and is possibly composed of a single phase, but it may be composed of a mixture thereof with the other crystal phases or an amorphous phase within the range where the characteristics do not decrease. In this case, it is desirable that the content of the CaAlSiN 3 family crystal phase is 50% by weight or more in order to obtain a high luminance. Further preferably, when the content is 20% by weight or more, luminance is remarkably improved. In the invention, the range as a main component is a content of the CaAlSiN 3 family crystal phase of at least 20% by weight or more. The ratio of content of the CaAlSiN 3 family crystal phase can be determined from the ratio of the intensity of the strongest peaks in respective phases of the CaAlSiN 3 family crystal phase and the other crystal phases through the measurement of X-ray diffraction.

In the case that the phosphor of the invention is used for applications excited with an electron beam, electroconductivity can be imparted to the phosphor by mixing it with an inorganic substance having electroconductivity. As the inorganic substance having electroconductivity, there may be mentioned oxides, oxynitrides, or nitrides containing one or two or more elements selected from the group consisting of Zn, Al, Ga, In, and Sn, or mixtures thereof.

The phosphor of the invention can emit a red light by the combination of a specific host crystal and an activating element but, in the case that mixing with the other colors such as yellow color, green color, and blue color is necessary, it is possible to mix inorganic phosphors emitting lights of these colors according to necessity.

The phosphors of the invention exhibit different excitation spectra and fluorescent spectra depending on the composition and hence can be set at those having various emission spectra by suitably selecting and combining them. The embodiment may be appropriately set at a required spectrum based on the application. Particularly, one wherein Eu is added to the CaAlSiN 3 crystal phase in a composition of 0.0001≦(number of atoms of Eu)/{(number of atoms of Eu)+(number of atoms of Ca)}≦0.1 exhibits emission of a light having a peak in the range of a wavelength of 600 nm to 700 nm when excited with a light having a wavelength in the range of 100 nm to 600 nm, preferably 200 nm to 600 nm, and exhibits excellent emission characteristics as red fluorescence.

The phosphors of the invention obtained as above are characterized in that they have a wide excitation range of from an electron beam or an X-ray and an ultraviolet ray to a visible light, i.e., ultraviolet rays or visible lights having wavelengths from 100 nm to 600 nm, emit an orange to red light of 570 nm or longer, and particularly exhibit red color of 600 nm to 700 nm at a specific composition, and they exhibit a red light ranging 0.45≦x≦0.7 in terms of the value of (x, y) on CIE chromaticity coordinates, as compared with conventional oxide phosphors and existing sialon phophors. Owing to the above emission characteristics, they are suitable for a lighting equipment, an image display unit, a pigment, and an ultraviolet absorbent. In addition, since they are not degraded even when exposed to a high temperature, they are excellent in heat resistance and also excellent in long-term stability under an oxidizing atmosphere and under a moist environment.

The phosphors of the invention do not limit the production process but a phosphor exhibiting a high luminance can be produced by the following process.

A high-luminance phosphor is obtained by baking a raw material mixture, which is a mixture of metal compounds and may constitute a composition represented by M, A, D, E, and X by baking the mixture, at a temperature range of 1200° C. to 2200° C. in an inert atmosphere containing nitrogen.

In the case of synthesizing CaAlSiN 3 activated with Eu, it is suitable to use a powder mixture of europium nitride or europium oxide, calcium nitride, silicon nitride, and aluminum nitride as a starting material.

Moreover, in the case of synthesizing a composition containing strontium, incorporation of strontium nitride in addition to the above affords a stable (Ca,Sr)AlSiN 3 crystal phase wherein part of the calcium atoms in the crystal phase is replaced with strontium, whereby a high-luminance phosphor is obtained.

In the case of synthesizing a phosphor using as a host CaAlSi(O,N) 3 and activated with Eu, wherein part of the nitrogen atom in the crystal phase is replaced with oxygen, a starting material of a mixture of europium nitride, calcium nitride, silicon nitride, and aluminum nitride is preferable in the composition of a small oxygen content since the material has a high reactivity and the synthesis in high yields is possible. In this case, as oxygen, oxygen impurity contained in the raw material powders of europium nitride, calcium nitride, silicon nitride, and aluminum nitride is used.

In the case of synthesizing a phosphor of a large oxygen content using CaAlSi(O,N) 3 activated with Eu as a host, when a mixture of either of europium nitride or europium oxide or a mixture thereof, anyone of calcium nitride, calcium oxide, or calcium carbonate or a mixture thereof, silicon nitride, and aluminum nitride or a mixture of aluminum nitride and aluminum oxide is used as a starting material, the material has a high reactivity and the synthesis in high yields is possible.

It is appropriate that the above mixed powder of the metal compounds is baked in a state that a volume filling rate is maintained to 40% or less. In this connection, the volume filling rate can be determined according to (bulk density of mixed powder)/(theoretical density of mixed powder)×100 [%]. As a vessel, a boron nitride sintered article is suitable because of low reactivity with the metal compounds.

The reason why the powder is baked in a state that a volume filling rate is maintained to 40% or less is that baking in the state that a free space is present around the starting powder enables synthesis of a crystal phase having little surface defect since the CaAlSiN 3 family crystal phase as a reaction product grows in a free space and hence the contact of the crystal phases themselves decreases.

Next, a phosphor is synthesized by baking the resulting mixture of the metal compounds in a temperature range of 1200° C. to 2200° C. in an inert atmosphere containing nitrogen. Since the baking is conducted at a high temperature and the baking atmosphere is an inert atmosphere containing nitrogen, the furnace for use in the baking is a metal-resistor resistive heating type one or a graphite resistive heating type one and an electric furnace using carbon as a material for a high-temperature part of the furnace is suitable. As the method of the baking, a sintering method of applying no mechanical pressure externally, such as an atmospheric sintering method or a gas pressure sintering method is preferred since baking is conducted while the volume filling rate is maintained at 40% or less.

In the case that the powder aggregate obtained by the baking is strongly adhered, it is pulverized by means of a pulverizing machine usually used industrially, such as a ball mill or a jet mill and the like. The pulverization is conducted until the average particle size reaches 20 μm or less. Particularly preferred is an average particle size of 0.1 μm to 5 μm. When the average particle size exceeds 20 μm, fluidity of the powder and dispersibility thereof into resins become worse and emission intensity becomes uneven from part to part at the time when an emission apparatus is formed in combination with a light-emitting element. When the size becomes 0.1 μm or less, the amount of defects on the surface of a phosphor powder becomes large and hence emission intensity decreases in some phosphor compositions.

Of the phosphors of the invention, the phosphors using the inorganic compound containing nitrogen and oxygen as a host can be also produced by the following process.

It is a process wherein oxygen is allowed to exist in the raw material to be baked so that the ratio (percentage) of mol number of oxygen to total mol number of nitrogen and oxygen in the raw material to be baked (hereinafter referred to as an “oxygen existing ratio in a raw material”) becomes from 1% to 20% in a state of a bulk density of 0.05 g/cm 3 to 1 g/cm 3 at a baking temperature of 1200° C. to 1750° C. at the time when a starting mixed powder containing an elementary substance and/or compound of M Element, a nitride of A Element, a nitride of D Element, and a nitride of E Element is baked.

The oxygen existing ratio in a raw material means a ratio (percentage) of mol number of oxygen to total mol number of nitrogen and oxygen in the raw material to be baked at baking and the nitrogen in the raw material to be baked is nitrogen derived from the raw powder, while the oxygen includes oxygen to be incorporated from the baking atmosphere into the material to be baked at baking in addition to the oxygen contained in the raw powder beforehand. The oxygen existing ratio in a raw material can be determined by the measurement using an oxygen nitrogen analyzer. The oxygen existing ratio in a raw material is preferably from 2% to 15%.

The method of allowing oxygen to exist in such an oxygen existing ratio in a raw material at baking includes:

(1) a method of using raw nitrides containing a desired concentration of oxygen as raw materials to be baked,

(2) a method of allowing raw nitrides to contain a desired concentration of oxygen by heating the raw nitrides beforehand under an oxygen-containing atmosphere,

(3) a method of mixing a raw nitride powder with an oxygen-containing compound powder to form a raw material to be baked,

(4) a method of introducing oxygen into the raw material to be baked by contaminating oxygen in the baking atmosphere at baking of raw nitrides and oxidizing the raw nitrides at baking, and the like. In order to produce a high-luminance phosphor industrially stably, preferred is (1) the method of using raw nitrides containing a desired concentration of oxygen as raw materials to be baked or (3) the method of mixing a raw nitride powder with an oxygen-containing compound powder to form a raw material to be baked. In particular, more preferred is a method of using raw nitrides containing a desired concentration of oxygen as raw materials to be baked and also mixing the raw nitride powder with an oxygen-containing compound powder to form a raw material to be used, which is a combination of the above methods (1) and (3).

In this case, the oxygen-containing compound powder is selected from substances which form metal oxides at baking. As these substances, use can be made of oxides, inorganic acid salts such as nitrates, sulfates, and carbonates of respective metals, i.e., metals constituting the raw nitrides, organic acid salts such as oxalates and acetates thereof, oxygen-containing organometallic compounds, and the like, of respective metals, i.e., metals constituting the raw nitrides. However, from the viewpoints that oxygen concentration is easily controlled and association of impurity gases into the baking atmosphere can be suppressed at a low level, it is preferred to use metal oxides.

The oxygen existing ratio in raw material can be easily determined by conducting chemical analysis of all the raw materials. In particular, the ratio of nitrogen to oxygen can be determined by analyzing concentrations of nitrogen and oxygen.

The elementary substance and/or compound of M Element to be used as a raw material may be any substance as far as M Element is incorporated into a host crystal of the phosphor at a high temperature, including metals (elementary substances), oxides, nitrides, sulfides, halides, hydrides of M Element and also inorganic acid salts such as nitrates, sulfates, and carbonates, organic acid salts such as oxalates and acetates, organometallic compounds, and the like, and there is no limitation in its kind. However, from the viewpoint of good reactivity with other nitride materials, metals, oxides, nitrides, and halides of M Element are preferred and oxides are particularly preferred since the raw materials are available at a low cost and the temperature for phosphor synthesis can be lowered.

In the case of using at least Eu as M Element, use can be made of one or two or more of Eu metal containing Eu as a constitutive element, europium oxide such as EuO and Eu 2 O 3 , and various compounds such as EuN, EuH 3 , Eu 2 S 3 , EuF 2 , EuF 3 , EuCl 2 , EuCl 3 , Eu(NO 3 ) 3 , EU 2 (SO 4 ) 3 , EU 2 (CO 3 ) 3 , Eu(C 2 O 4 ) 3 , Eu(O-i-C 3 H 7 ) 3 , but Eu halides such as EuF 2 , EuF 3 , EuCl 2 , and EuCl 3 are preferred since they have an effect of accelerating crystal growth. Moreover, Eu 2 O 3 and Eu metal are also preferred since a phosphor having excellent characteristics can be synthesized from them. Of these, Eu 2 O 3 is particularly preferred, which is cheap in a raw material cost, has little deliquescency, and enables synthesis of a high-luminance phosphor at a relatively low temperature.

As raw materials for elements other than M Element, i.e., raw materials for A, D, and E Elements, nitrides thereof are usually used. Examples of nitrides of A Element include one or two or more of Mg 3 N 2 , Ca 3 N 2 , Sr 3 N 2 , Ba 3 N 2 , Zn 3 N 2 , and the like, examples of nitrides of D Element include one or two or more of Si 3 N 4 , Ge 3 N 4 , Sn 3 N 4 , Ti 3 N 4 , Zr 3 N 4 , Hf 3 N 4 , and the like, and examples of nitrides of E Element include one or two or more of AlN, GaN, InN, ScN, and the like. The use of powders thereof is preferred since a phosphor having excellent emission characteristics can be produced.

In particular, the use, as raw materials of A Element, of a highly active and highly reactive nitride material having mol number of oxygen of 1% to 20% relative to the total mol number of nitrogen and oxygen remarkably accelerates the solid phase reaction between the raw mixed powder of nitrides and, as a result, it becomes possible to lower the baking temperature and atmosphere gas pressure at baking without subjecting the raw mixed powder to compression molding. For the same reason, it is preferred to use, as a raw material of A Element, a nitride material particularly having mol number of oxygen of 2% to 15% relative to the total mol number of nitrogen and oxygen.

When the bulk density of the raw mixed powder is too small, the solid phase reaction is difficult to proceed owing to small contact area between the powdery raw materials and hence an impurity phase which cannot lead to synthesis of a preferred phosphor may remain in a large amount. On the other hand, when the bulk density is too large, the resulting phosphor may become a hard sintered one, which not only requires a long-term pulverization step after baking but also tends to lower luminance of the phosphor. Therefore, the bulk density is preferably from 0.15 g/cm 3 to 0.8 g/cm 3 .

When the baking temperature of the raw mixed powder is too low, the solid phase reaction is difficult to proceed and the aimed phosphor cannot be synthesized. On the other hand, when it is too high, not only unproductive baking energy is consumed but also evaporation of nitrogen from the starting material and the produced substance increases and hence there is a tendency that the aimed phosphor cannot be produced unless the pressure of nitrogen which constitutes part of atmosphere gas is increased to a very high pressure. Therefore, the baking temperature is preferably from 1300° C. to 1700° C. The baking atmosphere of the raw mixed powder is in principle an inert atmosphere or a reductive atmosphere but the use of an atmosphere containing a minute amount of oxygen wherein the oxygen concentration is in the range of 0.1 to 10 ppm is preferred since it becomes possible to synthesize a phosphor at a relatively low temperature.

Moreover, the pressure of atmosphere gas at baking is usually 20 atm (2 MPa) or lower. A high-temperature baking equipment comprising a strong heat-resistant vessel is required for a pressure exceeding 20 atm and hence the cost necessary for baking becomes high, so that the pressure of the atmosphere gas is preferably 10 atm (1 MPa) or lower. In order to prevent contamination of oxygen in the air, the pressure is preferably slight higher than 1 atm (0.1 MPa). In the case that air-tightness of the baking furnace is wrong, when the pressure is 1 atm (0.1 MPa) or lower, a lot of oxygen contaminates the atmosphere gas and hence it is difficult to obtain a phosphor having excellent characteristics.

Furthermore, the holding time at the maximum temperature at baking is usually from 1 minute to 100 hours. When the holding time is too short, the solid phase reaction between raw mixed powders does not sufficiently proceed and an aimed phosphor cannot be obtained. When the holding time is too long, not only unproductive baking energy is consumed but also nitrogen is eliminated from the surface of the phosphor and the fluorescence characteristics deteriorate. For the same reasons, the holding time is preferably from 10 minutes to 24 hours.

As explained in the above, the CaAlSiN 3 family crystal phase phosphor of the invention exhibits a higher luminance than that of conventional sialon phosphors and, since decrease in luminance of the phosphor is small when it is exposed to an excitation source, it is a phosphor suitable for VFD, FED, PDP, CRT, white LED, and the like.

The lighting equipment of the invention is constituted by the use of at least a light-emitting source and the phosphor of the invention. As the lighting equipment, there may be mentioned an LED lighting equipment, a fluorescent lamp, and the like. The LED lighting equipment can be produced by known methods as described in JP-A-5-152609, JP-A-7-99345, Japanese Patent No. 2927279, and so forth with the phosphor of the invention. In this case, the light-emitting source is desirably one emitting a light having a wavelength of 330 to 500 nm, and particularly preferred is an ultraviolet (or violet) LED light-emitting element of 330 to 420 nm or a blue LED light-emitting element of 420 to 500 nm.

As these light-emitting elements, there exist an element comprising a nitride semiconductor such as GaN or InGaN and the like and, by adjusting the composition, it may be employed as a light-emitting source which emits a light having a predetermined wavelength.

In the lighting equipment, in addition to the method of using the phosphor of the invention solely, by the combined use thereof with a phosphor having other emission characteristics, a lighting equipment emitting a desired color can be constituted. As one example, there is a combination of an ultraviolet LED light-emitting element of 330 to 420 nm with a blue phosphor excited at the wavelength and having an emission peak at a wavelength of 420 nm to 500 nm, a green phosphor excited at the wavelength of 330 to 420 nm and having an emission peak at a wavelength of 500 nm to 570 nm, and the phosphor of the invention. There may be mentioned BaMgAl 10 O 17 :Eu as the blue phosphor and BaMgAl 10 O 17 :Eu,Mn as the green phosphor. In this constitution, when the phosphors are irradiated with an ultraviolet ray emitted by the LED, red, green, and blue lights are emitted and a white lighting equipment is formed by mixing the lights.

As an alternative method, there is a combination of a blue LED light-emitting element of 420 to 500 nm with a yellow phosphor excited at the wavelength and having an emission peak at a wavelength of 550 nm to 600 nm and the phosphor of the invention. As such a yellow phosphor, there may be mentioned (Y, Gd) 2 (Al, Ga) 5 O 12 :Ce described in Japanese Patent No. 2927279 and α-sialon:Eu described in JP-A-2002-363554. Of these, a Ca-α-sialon in which Eu is dissolved is preferred owing to high emission luminance. In this constitution, when the phosphors are irradiated with a blue light emitted by the LED, two lights having red and yellow colors are emitted and the lights are mixed with the blue light of LED itself to form a lighting equipment exhibiting a white color or a reddish lamp color.

As another method, there is a combination of a blue LED light-emitting element of 420 to 500 nm with a green phosphor excited at the wavelength and having an emission peak at a wavelength of 500 nm to 570 nm and the phosphor of the invention. As such a green phosphor, there may be mentioned Y 2 Al 5 O 12 :Ce. In this constitution, when the phosphors are irradiated with a blue light emitted by the LED, two lights having red and green colors are emitted and the lights are mixed with the blue light of LED itself to form a white lighting equipment.

The image display unit of the invention is constituted by at least an excitation source and the phosphor of the invention and includes a vacuum fluorescent display (VFD), a field emission display (FED), a plasma display panel (PDP), a cathode ray tube (CRT), and the like. The phosphor of the invention is confirmed to emit a light by excitation with a vacuum ultraviolet ray of 100 to 190 nm, an ultraviolet ray of 190 to 380 nm, an electron beam, or the like. Thus, by the combination of any of these excitation sources and the phosphor of the invention, the image display unit as above can be constituted.

Since the specific inorganic compound of the invention has a red object color, it can be used as a red pigment or a red fluorescent pigment. When the inorganic compound of the invention is irradiated with illumination of sunlight, fluorescent lamp, or the like, a red object color is observed and the compound is suitable as an inorganic pigment owing to good coloring and no deterioration over a long period of time. Therefore, there is an advantage that the coloring does not decrease over a long period of time when it is used in coatings, inks, colors, glazes, colorants added to plastic products or the like. The nitride of the invention absorbs ultraviolet rays and hence is suitable as an ultraviolet absorbent. Therefore, when the nitride is used as a coating or applied on the surface of plastic products or kneaded into the products, the effect of shielding ultraviolet rays is high and thus the effect of protecting the products from ultraviolet degradation is high.

The following will describe the invention further in detail with reference to the following Examples but they are disclosed only for the purpose of easy understanding of the invention and the invention is not limited to these Examples.

The nitride phosphor of the invention exhibits emission at a longer wavelength as compared with conventional sialon and oxynitride phosphors and is excellent as a red phosphor. Furthermore, since luminance decrease of the phosphor is small when it is exposed to an excitation source, it is a nitride phosphor suitably used for VFD, FED, PDP, CRT, white LED, and the like. Hereafter, it is expected that the phosphor is widely utilized in material design in various display units and thus contributes development of industry.