Silicate-based phosphor and manufacturing method of silicate-based phosphor

The present invention relates to a silicate-based phosphor and a manufacturing method of the silicate-based phosphor and, more specifically, to a silicate-based phosphor using a gas phase reaction of SiO x (0.5≦x≦1.9) and a manufacturing method of the silicate-based phosphor.

At present, various illumination light sources such as an incandescent lamp, a fluorescent lamp and so on are used around us. Recently, a white LED, having a combination of characteristics such as low power consumption, long life, safety and so on, gets a lot of attention as an alternative illumination to the incandescent lamp or the fluorescent lamp. Further, a phosphor used in the white LED is also required to have higher performance regarding the emission efficiency and durability.

White LEDs are roughly classified into two types in terms of a method for producing a white color, and among them, the two-wavelength white LED that is the mainstream at present obtains a pseudo white color by using both an GaInN-based blue LED and a yellow phosphor YAG:Ce 3+ (Y 3 Al 5 O 12 :Ce 3+ ) but is not excellent in color rendering property, and thus cannot emit white light close to the natural light (see Non-Patent Document 1).

On the other hand, there exists a three-wavelength white LED excitable with near-ultraviolet light or blue light and emitting white light closer to the natural light. For example, many silicate-based phosphors excite with near-ultraviolet light or blue light and emit visible light and are thus regarded as promising three-wavelength white LED phosphors, but none of them has a high luminance at a practical level (see Non-Patent Documents 2, 3).

Non-Patent Document

Non-Patent Document 1: Satoshi Watanabe “Present Status and Application of InGaN-based high-power LED” Applied Physics, Vol. 74, No. 11, 2005

Non-Patent Document 2: “Phosphor Handbook” edited under the auspices of Phosphor Research Society, Ohmsha, Ltd., 1991

Non-Patent Document 3: T. L. Barry, J. Electrochem. Soc., 115, (1968)

Problems to be Solved by the Invention

Hence, in consideration of the above-mentioned circumstances, an object of the present invention is to provide a silicate-based phosphor excellent in emission intensity and a manufacturing method of the silicate-based phosphor.

Conventionally, as a general manufacturing method of the silicate-based phosphor, a method for obtaining a phosphor by mixing predetermined amounts of a compound containing elements constituting the phosphor host and a compound containing an activator element, both compounds in a solid state such as powder or the like, and firing the mixture at a predetermined temperature is widely used (see Non-Patent Document 2). This synthesis method is realized by the solid-solid phase reaction and is thus called a solid phase method.

However, it is difficult for the solid-solid phase method to manufacture the phosphor purely having a composition according to stoichiometry and to obtain a highly-pure phosphor according to stoichiometry because excessive nonreactive impurities or complex oxide produced by the reaction remains as a result of the solid-solid phase reaction. Consequently, problems such as the aforementioned decrease in luminance of the phosphor and so on are pointed out.

The present inventors found that the phosphor may be synthesized using SiO x in the gas phase which is not usually used in the phosphor manufacturing field (a method for causing volatilized SiO x to react with other solid phase materials to synthesize the phosphor, also called a “gas-solid phase method”), and that the phosphor obtained using the gas-solid phase method may have better emission characteristics than those of the phosphor obtained by the conventional solid phase method, and reached completion of the present invention.

Means for Solving the Problems

More specifically, the present invention includes the following compositions and characteristics.

[1] A manufacturing method of a silicate-based phosphor, including: introducing in a vessel raw material powders having a compound containing light-emitting ions selected from at least one of Eu, Ce, Mn, and Tb; and firing the raw material powders while supplying SiO x (0.5≦x≦1.9) in a gas phase. [2] The manufacturing method of a silicate-based phosphor according to [1] wherein the raw material powders are a mixture further containing at least one of an alkali metal compound, an alkaline-earth metal compound, a magnesium compound, and a rare-earth compound. [3] The manufacturing method of a silicate-based phosphor according to [2] wherein the silicate-based phosphor is M 2 SiO 4 :Eu 2+ (wherein M is one or more selected from a group consisting of Ca, Sr and Ba). [4] The manufacturing method of a silicate-based phosphor according to any one of [1] to [3] wherein the range for x of the SiO x is 0.8≦x≦1.2. [5] The manufacturing method of a silicate-based phosphor according to any one of [1] to [4] wherein the firing is performed by supplying the SiO x to the raw material powders in a gas atmosphere at a temperature of 1200 to 1700° C. and subjecting the raw material powders to a gas-solid phase reaction at a temperature of 700 to 1700° C. [6] The manufacturing method of a silicate-based phosphor according to [5] wherein the gas atmosphere is a reducing gas atmosphere. [7] A silicate-based phosphor manufactured by the manufacturing method of a silicate-based phosphor according to any one of [1] to [6].

Effect of the Invention

The present invention can provide a phosphor having better fluorescence characteristics than those of the phosphor obtained by the conventional solid phase method because of use of the gas phase synthesis at a part of the phosphor manufacturing processes. For example, in comparison between the example of Ba 2 SiO 4 :Eu 2+ and the comparative example synthesized by the conventional method, the phosphor of the example exhibited the emission intensity of about 2.6 times higher than the emission intensity of the phosphor of the comparative example when they were excited at respective optimal excitation wavelengths and about 3.5 times higher when they were excited by a practical near-ultraviolet LED (405 nm), and therefore exhibited very high intensity as compared to the phosphor manufactured by the conventional method.

[ FIG. 1 ] A flowchart of a preferable manufacturing method of a silicate-based phosphor of the present invention.

[ FIG. 2 ] A view illustrating schematics of manufacturing apparatuses realizing a manufacturing method of a silicate-based phosphor of the present invention.

[ FIG. 3 ] A flowchart of a manufacturing method of Example 1.

[ FIG. 4 ] A graph showing X-ray diffraction (XRD) measurement results of Ba 2 SiO 4 :Eu 2+ manufactured by Example 1.

[ FIG. 5 ] A flowchart of a manufacturing method of Comparative Example 1 (a conventional solid phase method).

[ FIG. 6 ] A graph of comparison between fluorescence characteristics (excitation spectra and emission spectra) of a phosphor of Example 1 and fluorescence characteristics of a phosphor of Comparative Example 1.

[ FIG. 7 ] Photographs showing scanning electron microscope (SEM) images of observation at the same magnification of a phosphor surface of Example 1 and a phosphor surface of Comparative Example 1.

[ FIG. 8 ] A graph showing influence of a firing temperature on fluorescence characteristics of a phosphor of Example 1.

[ FIG. 9 ] A graph of comparison between emission intensity of a sample by a solid phase method and emission intensities of samples manufactured under respective firing temperature conditions in Example 1.

[ FIG. 10 ] A graph showing X-ray diffraction (XRD) measurement results of a phosphor of Example 2.

[ FIG. 11 ] A graph showing fluorescence characteristics of a phosphor of Example 2.

[ FIG. 12 ] A graph showing X-ray diffraction (XRD) measurement results of a phosphor of Example 3.

[ FIG. 13 ] A graph showing fluorescence characteristics of a phosphor of Example 3.

Hereinafter, the present invention will be described based on the following concrete embodiments referring to the accompanying drawings, but the present invention is not limited to the embodiments.

A manufacturing method of a silicate-based phosphor according to the present invention includes: introducing in a vessel raw material powders having a compound containing light-emitting ions selected from at least one of Eu, Ce, Mn, and Tb; and firing the raw material powders while supplying SiO x (0.5≦x≦1.9) in a gas phase. In addition, it is preferable that the raw material powders are a mixture further containing at least one of an alkali metal compound, an alkaline-earth metal compound, a magnesium compound, and a rare-earth compound.

Here, as the compound containing the light-emitting ions, though not particularly limited, a compound containing Eu such as Eu 2 O 3 , Eu 2 (CO 3 ) 3 . 2H 2 O, Eu(NO 3 ) 3 .6H 2 O, Eu 2 (C 2 O 4 ) 3 .10H 2 O or the like, a compound containing Ce such as Ce 2 O 3 , Ce 2 (CO 3 ) 3 .5H 2 O, Ce(NO 3 ) 3 .5H 2 O, Ce 2 (C 2 O 4 ) 3 .9H 2 O, Ce 2 (C 2 O 4 ) 3 .10H 2 O or the like, a compound containing Mn such as MnO, MnCO 3 , Mn(NO 3 ) 2 .6H 2 O, Mn(C 2 O 4 ), Mn(C 2 O 4 ) 3 .2H 2 O or the like, a compound containing Tb such as Tb 2 O 3 , Tb 2 (CO 3 ).nH 2 O, Tb(NO 3 ) 3 .6H 2 O, Tb(C 2 O 4 ) 3 .10H 2 O or the like, and a combination thereof are preferably used. Further, though not included in the compound containing the light-emitting ions in a precise sense, CeO 2 or Tb 4 O 7 exhibiting the physical property similar to that of aforementioned Ce 2 O 3 or Tb 2 O 3 may be used.

Further, as the alkali metal compound, though not particularly limited, Li 2 O, Li 2 CO 3 , LiNO 3 , Li 2 C 2 O 4 , Na 2 O, Na 2 CO 3 , NaNO 3 , Na 2 C 2 O 4 , K 2 O, K 2 CO 3 , KNO 3 , Rb 2 O, Rb 2 CO 3 , RbNO 3 , Cs 2 O, Cs 2 CO 3 , CsNO 3 , Cs 2 C 2 O 4 , and a combination thereof are used, and the compound, which can be decomposed and oxidized into an oxide at a high temperature, is preferably used.

Further, as the alkaline-earth metal compound, though not particularly limited, CaO, CaCO 3 , Ca(NO 3 ) 2 , Ca(NO 3 ) 2 .4H 2 O, SrO, SrCO 3 , Sr(NO 3 ) 2 , Sr(NO 3 ) 2 .4H 2 O, BaO, BaCO 3 , Ba(NO 3 ) 2 , BaC 2 O 4 , and a combination thereof are used, and the compound, which can be decomposed and oxidized into an oxide at a high temperature, is preferably used.

Further, a magnesium compound containing divalent Mg, that is equivalent to the alkaline-earth metal compound, can also be used in place of the alkaline-earth metal compound. Further, as the rare-earth compound, though not particularly limited, Sc 2 O 3 , Y 2 O 3 , La 2 O 3 , and a combination thereof are used, and the compound, which can be decomposed and oxidized into an oxide at a high temperature, is preferably used.

In the present invention, by maintaining a raw material mixture preferably containing at least one of the above-descried alkali metal compound, alkaline-earth metal compound, magnesium compound, and rare-earth compound, for example, in a temperature range of 700° C. to 1700° C. for 1 to 100 hours to fire the raw material mixture, and further supplying thereto SiO x , which has become gaseous in a gas atmosphere at a temperature of 1200° C. to 1700° C. to cause a gas-solid phase reaction of the raw material mixture, a phosphor very excellent in emission characteristics is obtained.

Note that when the above-described metal compound contains hydrate, hydroxide, carbonate, nitrate, oxalate which can be decomposed and/or oxidized into an oxide at a high temperature, it is also possible to make the raw material mixture into an oxide, for example, by previously calcining it at a temperature lower than the firing temperature, or make the raw material mixture into a precursor of the phosphor by removing crystallization water therefrom. Further, it is also possible to grind the raw material mixture after the pre-calcination.

A flowchart of a preferable manufacturing method among the methods for manufacturing a silicate-based phosphor of the present invention is illustrated in FIG. 1 . As starting materials, raw materials for causing a solid phase reaction (solid phase reaction raw materials) and a raw material for causing a gas phase reaction (gas phase reaction raw material) are separately prepared (for example, put on separate dishes in a reaction vessel). Then, through mixing and heating of the solid phase reaction raw materials and heating of the gas phase reaction raw material, a desired silicate-based phosphor is manufactured. Here, the heating temperature (firing temperature) range for the solid phase reaction raw materials is preferably in a range of 700° C. to 1700° C., and the heating temperature range for the gas phase reaction raw material for supplying SiO x is preferably in a range of 1200° C. to 1700° C. Note that from a later-described demonstration result, in the case of using Ba 2 SiO 4 :Eu 2+ as the silicate-based phosphor of the present invention, the firing temperature is more preferably set to 1400° C. to 1600° C.

One of important features of the present invention is that raw material powders (solid phase reaction raw materials) are fired while supplying SiO x (0.5≦x≦1.9) in a gas phase (namely, that a part of the starting materials (gas phase reaction raw material) is heated to cause a gas is phase reaction, and the solid phase reactant is fired while the gas phase reactant is reacted with the solid phase reactant, in other words, that a gas-solid phase reaction is caused), that is greatly different from a general solid phase synthesis (namely, all of the starting materials are solid-phase synthesized) used in conventional phosphor manufacturing methods.

Note that the conventional gas phase synthesis is a synthesis method applied to processes for producing a nanoparticle of about 1 to 100 nm. In contract, for manufacturing a phosphor for the white LED, it is required to obtain large particles grown to about 10 to 100 μm, and therefore the above-described solid phase method has been the suitable and time-proven method. Accordingly, researchers in a field for manufacturing the phosphors, in general, are less likely to understand or reach the way of thinking to employ the gas phase synthesis, suitable for the manufacture of nano-order particles, into the manufacture of phosphors. Furthermore, the gas phase raw material used in the conventional gas phase method is an expensive material such as an organic metal compound, and is not the kind handled in a reducing atmosphere gas in manufacturing phosphors, and therefore there is no example reporting practical characteristics for phosphors, obtained by applying the way of thinking of the gas phase synthesis to the manufacture of phosphor. On the other hand, the manufacturing method of the present invention is characterized by the gas-solid phase synthesis of causing SiO x in a gas phase to react with the other raw material in a solid phase.

In the manufacturing method of the present invention, SiO x (0.5≦x≦1.9) that is a raw material for synthesis in a gas phase is a material inexpensive and safe to handle. Note that the general manufacturing method of SiO x is performed by heating a mixture of a silicon-dioxide-based oxide powder and a substance reducing the powder, for example, silicon metal in an inert gas atmosphere or under a reduced pressure in a temperature range of 1100 to 1600° C., and cooling and collecting the generated SiO x gas. However, unreacted substance (Si, SiO 2 ) or SiO 2 generated by oxidization of SiO sometimes exist as impurities in the SiO x .

The verification by the inventors until now shows that since SiO x when it is closer to SiO more suitably acts, the range for x of SiO x preferably falls within 0.8≦x≦1.2, and more preferably, 0.95≦x≦1.1. Such a suitable high-purity SiO is commercially available from, for example, OSAKA Titanium technologies Co., Ltd. and Sanyo Trading Co., Ltd.

SiO x in the solid state can be volatile and be in the gas phase by being heated in a gas atmosphere at 1200 to 1700° C., preferably, at 1400 to 1700° C. into a gas phase. The SiO x in the gas phase is supplied to the raw material mixture and heated at a desired temperature in the temperature range of 700° C. to 1700° C. to cause gas-solid phase reaction.

Examples of the gas atmosphere include (1) an inert gas atmosphere composed of nitrogen, argon or the like, (2) an oxidized gas atmosphere composed of air, oxygen, oxygen-containing nitrogen, oxygen-containing argon or the like, and (3) a reducing gas atmosphere such as hydrogen-containing nitrogen containing 0.1 to 10 volume % hydrogen, hydrogen-containing argon containing 0.1 to 10 volume % hydrogen or the like. Note that to promote the gas-solid phase reaction of the present invention at a high yield, the carrier gas to supply SiO x and the atmosphere during firing is particularly preferably a reducing atmosphere such as hydrogen-containing nitrogen containing 0.1 to 10 volume % hydrogen, hydrogen-containing argon containing 0.1 to 10 volume % hydrogen or the like.

Though the silicate-based phosphor of the present invention manufactured as described above is not particularly limited as long as it is synthesized by the above-described manufacturing method, M 2 SiO 4 :Eu 2+ , Li 2 MSiO 4 :Eu 2+ , M 3 SiO 5 :Eu 2+ , M 2 (Mg, Zn)Si 2 O 7 :Eu 2+ , M 3 Si 2 O 7 :Eu 2+ , M 3 MgSi 2 O 8 :Eu 2+ , MAl 2 Si 2 O 8 :Eu 2+ , M 3 Sc 2 Si 3 O 12 :Ce 3+ , M 9 Sc 2 Si 6 O 24 :Eu 2+ , and a combination thereof are preferable. Here, M is one or more selected from a group consisting of Ca, Sr and Ba. Note that from the viewpoint of practical use of the phosphor based on various characteristics other than the emission characteristics, M 2 SiO 4 :Eu 2+ is preferable as the silicate-based phosphor of the present invention, and (Ba 1-y Sr y ) 2 SiO 4 :Eu 2+ (0≦y≦1) is more preferable.

Note that the starting materials for manufacturing (Ba 1-y Sr y ) 2 SiO 4 :Eu 2+ (0≦y≦1) and the materials (the starting materials except SiO x , for example, BaCO 3 ) undergoing a solid phase reaction are well solid-phase synthesized in the temperature range (1200 to 1700° C.) suitable for the gas phase synthesis of SiO x , so that by heating the phosphor manufacturing vessel in the aforementioned preferable temperature range, volatilization of SiO x and the solid phase synthesis (namely, firing) can be effectively performed at the same time.

Some examples of phosphor manufacturing apparatuses 1 realizing the manufacturing method of the silicate-based phosphor of the present invention are illustrated in FIG. 2 . The manufacturing apparatus 1 illustrated in FIG. 2( a ) is configured such that a gas permeable (for example, porous) first dish 5 on which raw material powders 3 (namely, the solid phase reaction raw materials) containing a compound containing the light-emitting ions are put is provided inside a vessel 2 , a second dish 6 on which SiO x powders 4 (namely, the gas phase reaction raw materials) are put, is provided below the first dish 5 , and gas supply ports 7 a , through which a carrier gas is supplied, and a gas exhaust port 7 b are provided in side surfaces and an upper surface of the vessel 2 respectively (called a vertical manufacturing apparatus for comparison to later-described FIG. 2( b )). By heating the inside of the vessel 2 at a predetermined temperature, the solid phase reaction raw materials 3 are fired, and a firing reaction proceeds while SiO x in the gas phase (indicated with a numeral 8 in the drawing) volatilized from the SiO x powders 4 in the gas atmosphere (preferably, in a reducing gas atmosphere) is passing through the first dish 5 and entering the raw material powders 3 . Note that examples of the materials of the first dish 5 for containing the solid phase reaction raw material powders include, for example, boron nitride (BN), alumina (Al 2 O 3 ), and silicon carbide (SiC), and however, boron nitride (BN) is preferable, since it is unlikely to cause reaction with the raw material powders during firing. Further, though not illustrated, the vertical manufacturing apparatus may be configured such that the second dish 6 may be introduced in another vessel and SiO x in the gas phase may be supplied together with the carrier gas to the solid phase reaction raw material powders 3 from the gas supply ports 7 a.

Further, as illustrated in FIG. 2( b ), a horizontally configured manufacturing apparatus 1 may be used which is configured such that the first dish 5 , on which the raw material powders 3 are put, and the second dish 6 , on which the SiO x powders 4 are put, are set on the same horizontal plane 2 a in the vessel 2 , and the supply port 7 a and the exhaust port 7 b for the carrier gas are provided in side surfaces of the vessel 2 so that the carrier gas flows from the second dish 6 to the first dish 5 (see arrows in the drawing). Note that in this case, since SiO x (see the numeral 8 ) moves along the flow of the carrier gas from a space above the second dish 6 to a space above the first dish 5 and showers on the raw material powders 3 in the first dish 5 , the first dish 5 does not always need to be made of a gas permeable material.