Phosphor, its preparation method and light emitting devices using the same

This application is a continuation application filed under 35 U.S.C. §111(a), claiming the benefit under 35 U.S.C. §120 and §365(c) of a PCT International Application Number PCT/CN2007/000852, filed Mar. 16, 2007, it being further noted that foreign priority benefit is based upon Chinese Patent Application 200610065812.X, filed Mar. 24, 2006 in the State Intellectual Property Office of P.R. China, the disclosures of which are thereby incorporated by reference.

The present invention relates to a phosphor that can be excited by ultraviolet, purple or blue LEDs, the preparation method thereof, and light emitting devices using the same.

Light emitting diodes (“LEDs”) have attracted much attention due to many advantages, such as small volume, low power consumption, long lifetime, fast-response, environmental friendliness, and high reliability etc. They are used widely in indicating lamps, decorating lamps, signal lamps etc. It can be looked forward to the coming future that LEDs will access into general lighting field with the faster and advanced developments.

Generally, there are two ways to generate white LED: one way is to combine the red, green and blue LEDs to get white light; the other way is to excite phosphors with LED to obtain white light. According to the difference in phosphors, the latter approach includes three routes: matching yellow phosphor with blue LED, matching green and red phosphors with blue LED, or matching red, green and blue phosphors with purple or UV LEDs.

As for current LED techniques, white LEDs are preferred to be generated by incorporating blue LED with YAG (yttrium aluminum garnet) yellow phosphor. In the Chinese patent CN97196762, this phosphor is reported in details. However, due to the characteristics of the phosphor, the luminous efficiency of white LEDs using this YAG phosphor is not yet adequate at present, and it is not applicable in general lighting field by taking into account the energy-saving. Therefore, the studies on novel phosphors with good luminescence performance are focused by many researchers from all over the world.

A silicate-borate phosphor represented by the formula (Y,La) 1-x-y-z Ce x Gd y Tb z (Mg,Zn,Gd) 1-p Mn p B 5-q-s (Al,Ga) q X s O 10 has been reported in the German patent DE19730005. Phosphors comprising silicon, disclosed in British patents GB1334838, GB1326868 and GB1379949, with emission main peaks at 370-430 nm, are employed as cathode ray exciting phosphors. An alkaline-earth silicate phosphor that can be excited by blue light to generate yellow light, with similar performance as that of the YAG phosphor, has been developed by Barry (J. Electrochem. Soc., 1968, 115: 1181-1184), and has been described in white LED in U.S. Patent Publication US20040051111.

One aspect of the present invention is to provide a phosphor that possesses desirable chemical stability, high luminous efficiency and can be excited efficiently by ultraviolet, purple or blue LED's.

Another aspect of the present invention is to provide a preparation method for the phosphor mentioned above.

Still another aspect of the present invention is to provide a light emitting device that incorporates the above mentioned phosphor.

A phosphor according to one aspect of the invention contains, for example, rare earth, silicon, alkaline-earth metal, halogen, and oxygen, as well as aluminum or gallium. Rare earth refers to “rare earth elements” or “rare earth metals,” and hereinafter, the expression “rare earth” will be used. The rare earth is at least one metal element selected from a group consisting of Sc, Y, La, Pr, Nd, Gd, Ho, Yb and Sm, as well as at least one metal element selected from a group consisting of Ce, Eu and Tb. The alkaline-earth metal is at least one metal element selected from a group consisting of Mg, Ca, Sr and Ba. The halogen is at least one element selected from F and Cl. The phosphor according to one aspect of the present invention possesses high conversion efficiency, and can be used to produce white LED with high luminous efficiency.

As one embodiment, the phosphor can be represented by the general formula of

a Ln 2 O 3 .MO. b M′ 2 O 3 .f SiO 2 .c AX e :d R, wherein

Ln is at least one metal element selected from a group consisting of Sc, Y, La, Pr, Nd, Gd, Ho, Yb and Sm;

M is at least one metal element selected from a group consisting of Ca, Sr and Ba;

M′ is at least one metal element selected from Al and Ga;

A is at least one metal element selected from a group consisting of Li, Na, K, Mg, Ca, Sr and Ba;

X is at least one element selected from F and Cl;

R is at least one metal element selected from a group consisting of Ce, Eu, Tb and Mn;

0.01≦a≦2;

0.35≦b≦4;

0.01≦c≦1;

0.01≦d≦0.3;

0.01≦f≦3; and

0.6≦e≦2.4.

The phosphor according to the present invention has excellent luminescent properties such as wide exciting wavelength scope, efficient emitting transition and chemical stability, and can be excited by ultraviolet, purple or blue LED. New light emitting devices can be obtained by incorporating the phosphor into the LED.

A preparation method for the phosphor mentioned above includes the following:

(1) According to the general formula:

a Ln 2 O 3 .MO. b M′ 2 O 3 .f SiO 2 .c AX e :d R, wherein

Ln is at least one metal element selected from a group consisting of Sc, Y, La, Pr, Nd, Gd, Ho, Yb and Sm;

M is at least one metal element selected from a group consisting of Ca, Sr and Ba;

M′ is at least one metal element selected from Al and Ga;

A is at least one metal element selected from a group consisting of Li, Na, K, Mg, Ca, Sr and Ba;

X is at least one element selected from F and Cl;

R is at least one metal element selected from a group consisting of Ce, Eu, Tb and Mn;

0.01≦a≦2;

0.35≦b≦4;

0.01≦c≦1;

0.01≦d≦0.3;

0.01≦f≦3; and

0.6≦e≦2.4;

weighing elementary substance or compounds or salts of Ln, M, M′, halide of A, and compounds or salts of R and Si as raw materials based on the stoichiometric ratio;

adding at the same time, excess quantity of SiO 2 and/or AXe as flux into the above raw materials, then mixing and grinding together to form a mixture.

(2) baking the mixture at high temperature under reducing atmosphere to form a baked product.

(3) Carrying out a post-treatment to the baked product to obtain the phosphor of the present invention.

According to (1) above, the compounds of Ln, M, M′, A, R and Si are selected from oxide, hydroxide etc.; the salts are selected from the corresponding carbonate, nitrate, organic salt etc.

According to (1) above, the amount of the flux is 0.001-20 wt % by weight of the total phosphor.

According to (1) above, the starting materials can be mixed and grinded in alcohol, acetone or water.

According to (2) above, the operation of baking can be carried out once, twice or more.

According to (2) above, the temperature of baking is at 500˜1600° C.

According to (2) above, each baking operation should last for 0.5˜15 h.

According to (3) above, the post-treatment includes grinding, air flow crushing, washing, sifting, drying and grading, etc.

According to (3) above, the washing step in the post-treatment can be done by using acid solution, alkali solution or water.

According to (3) above, the grading step in the post-treatment can be carried out with at least one method selected from a group consisting of sedimentation method, sieving method, hydraulic classification and air flow grading.

It is easily found that the above preparation method of the present phosphor is advantageous for being very simple, involving no pollution and having low cost. Also, this phosphor can be excited by UV, purple or blue light to emit broadband visible light with wavelengths peaking at 500-600 nm and having full width at half maximum (“FWHM”) beyond 30 nm. That is to say, the phosphor of the present invention can match UV, purple or blue LED, and can be implanted directly or along with other phosphors into LEDs to produce white or color light emitting devices.

In accordance with an aspect of the present invention, a light emitting device can be produced by combining the present phosphor with at least a kind of LED, such as UV, purple or blue LED. The phosphor contains rare earth, silicon, alkaline-earth metal, halogen, and oxygen, as well as aluminum or gallium. The rare earth is at least one metal element selected from a group consisting of Sc, Y, La, Pr, Nd, Gd, Ho, Yb and Sm as well as at least one metal element selected from a group consisting of Ce, Eu and Tb The alkaline-earth metal is at least one metal element selected from a group consisting of Mg, Ca, Sr and Ba. The halogen is at least one element selected from F and Cl.

The phosphor can be represented by the general formula of

a Ln 2 O 3 .MO. b M′ 2 O 3 .f SiO 2 .c AX e :d R, wherein

Ln is at least one metal element selected from a group consisting of Sc, Y, La, Pr, Nd, Gd, Ho, Yb and Sm;

M is at least one metal element selected from a group consisting of Ca, Sr and Ba;

M′ is at least one metal element selected from Al and Ga;

A is at least one metal element selected from a group consisting of Li, Na, K, Mg, Ca, Sr and Ba;

X is at least one element selected from F and Cl;

R is at least one metal element selected from a group consisting of Ce, Eu, Tb and Mn;

0.01≦a≦2,

0.35≦b≦4,

0.01≦c≦1,

0.01≦d≦0.3,

0.01≦f≦3, and

0.6≦e≦2.4.

The above-described phosphor of the present invention has excellent luminescent properties and stability with novel composition.

The preparation method for the phosphor is simple, involving no pollution and having lower cost.

A light emitting device is obtained by incorporating the phosphor into an LED, which has long lifetime and high luminous efficiency.

FIG. 1 shows the excitation spectrum of Example 1;

FIG. 2 shows the emission spectrum of the Example 1.

In order to further illustrate the present invention and the advantages thereof, the following specific examples are given, it being understood that the same are intended only as illustrative and in nowise limitative. The scope of protection of this invention will be further embodied in the claims.

The above-described phosphor has broad emitting range, high efficiency, better uniformity and stability. The production method is simple, no pollution and a lower cost. A light emitting device can be obtained by incorporating this phosphor into a UV, purple or blue light emitting device.