Abstract:
The present invention relates to a process for preparing rare earth trichromatic phosphor, comprising the following steps: (1) providing a matrix material doping with both europium (Eu) and terbium (Tb); (2) grinding and mixing the said matrix material; and (3) making the product obtained in step (2) to react at 800-1000° C for 3-5 hours. According to the present process, only one matrix material and two rare earth reactive ions (Eu 3+ , Tb 3+ ) are desired to synthesize rare earth trichromatic phosphor. That is to say, no reducing reagent is needed and thus no pollution is brought.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a process for preparing rare earth trichromatic phosphor.  
         DESCRIPTION OF THE RELATED ART  
         [0002]    In 1974, in the Journal of Electrochemical Society (volume 121, page 1627), J. M. P. J. Verstegen (Phillips Company, Netherlands) reported a process for preparing rare earth trichromatic phosphor. According to this process, three kinds of fluorescent powders, which are (Y, Eu) 2 O 3  giving red light, (Tb, Ce)MgAl 11 O 19  giving green light and (Ba, Eu)Mg 2 Al 16 O 27  giving blue light respectively, were firstly prepared under different conditions and then mixed together in certain ratio to give the required rare earth trichromatic phosphor.  
           [0003]    However, the rare earth ion Eu 2+  giving blue light can only be obtained from Eu 3+  using a special reduce process which is very complicated and needs reducing agent. Unfortunately, up to the present, no process can take the place of such a process. Therefore, a new simple, environment-friendly process is desired. The objective of the present invention is to provide a process for preparing rare earth luminescent materials, which is simple and does not need any reducing agent and so would not bring any environmental pollution.  
         SUMMARY OF INVENTION  
         [0004]    In &lt;Chemistry and Physics of Abnormal Valence Rare Earth Elements&gt; (Ed. Chunshan SHI and Qiang SU, Scientific Press, Beijing, 1994, in Chinese), Shi (Present inventor) repoted that, under certain conditions, electron transfer between a pair of rare earth ions which are electronic configurations conjugate can be achieved, and abnormal valence changes thereof can occur.  
           [0005]    According to the above theory, the present invention provides a new process for preparing the rare earth trichromatic phosphor, comprising the following steps:  
           [0006]    (1) providing a matrix material doping with both europium (Eu) and terbium (Tb);  
           [0007]    (2) grinding and mixing the said matrix material; and  
           [0008]    (3) making the product obtained in step (2) to react at 800-1000° C. for 3-5 hours.  
         DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
         [0009]    As mentioned above, under certain conditions, electron transfer between a pair of rare earth ions which are electronic configurations conjugate can be achieved, and abnormal valence changes thereof can occur. For example, Eu 3+  and Tb 3+  are such a pair of conjugate rare earth ions which, in certain substrate, having the following equilibrium: Eu 3+ +Tb 3+ =Eu 2+ +Tb 4+ . Therefore, in a given substrate, three ions, which are Eu 3+  giving red light, Tb 3+  giving green light and Eu 2+  giving blue light respectively, can coexist and form a trichromatic phosphor, while Tb 4+  is not luminescent. Further, Ce 3+  and Eu 3+  are also a pair of conjugate rare earth ions and the following equilibrium can also exist between them in certain substrate: Eu 3+ +Ce 3+ =Eu 2+ +Ce 4+ . Therefore, in the above trichromatic phosphor, if Ce 3+  is further added, then it can not only sensitize Tb 3+ , but also regulate the concentration of Eu 3+  and Eu 2+ .  
           [0010]    According to the present invention, the following three systems doped with rare earth ions europium (Eu 3+ ) and terbium (Tb 3+ ) can be used to prepare the trichromatic phosphor:  
           [0011]    (1) calcium boron phosphate which can be expressed by a chemical formula of CaBPO 5 : xEu, yTb, and a system which further comprises cerium ion (Ce 3+ ) as a sensitizing agent and can be expressed by CaBPO 5 : xEu, yTb, zCe;  
           [0012]    (2) calcium boron aluminum phosphate which can be expressed by a chemical formula of CaAl r B 1-r PO 5 : xEu, yTb, and a system which further comprises cerium ion(Ce 3+ ) as a sensitizing agent and can be expressed by CaAl r B 1-r PO 5 : xEu, yTb, zCe, wherein r is a mole fraction with r=0.5-0.8; and  
           [0013]    (3) calcium chlorine oxygen boronat which can be expressed by a chemical formula of Ca 2 B 5 O 9 Cl:xEu,yTb, and a system which further comprises cerium ion(Ce 3+ ) as sensitizing system and can be expressed by Ca 2 B 5 O 9 Cl:xEu,yTb,zCe; In all of the above formulas, x, y, z all means mole fractions, and x=0.02-0.05, y=0.001-0.01, z=0.001-0.01 respectively.  
           [0014]    After have been grounded and mixed, the materials reacted for 3-5 hours both in air and at 800-1000° C. The resulting products were cooled and then a white powder is obtained. Finally, the products in the form of white powder were excitated using ultraviolet light of a wavelength of 365 nm or 254 nm to obtain a trichromatic phosphor in which three wavelengths of 611 or 614 nm, 544 or 545 nm, 402 or 430 nm respectively can coexist.  
           [0015]    According to the present invention, only one, but not three, kind of matrix compound is needed to produce the present rare earth trichromatic phosphor; and only two, but not three, kinds of rare earth reactive ions are doped:Eu 3+  and Tb 3+ . Moreover, the Eu 2+  giving blue light is obtained through the electron transfer between Eu 3+  and Tb 3+ , in which, no reducing agent is needed. In addition, it can be synthesized in air. Thus this process is simple, and will not cause any environmental pollution. If Ce 3+  is used, a better sensitization effect can be obtained. 
       
    
    
     EXAMPLES  
     Example 1  
     The Synthesis of CaBPO 5 :xEu,yTb System  
       [0016]    Eu 2 O 3 , Tb 4 O 7 , both with purity of 99.99% (Shanghai Yuelong), CaCO 3 , B 2 O 3 , (NH 4 ) 2 HPO 4 , all with analytical purity (Beijing Chemical Plant), were weighed in a stoichiometric way. Eu 3+  was added with a mole fraction of 0.05, Tb 3+  with a mole fraction of 0.01. (NH 4 ) 2 HPO 4  is in excess of 10%. They were grounded and mixed in agate mortar and put in a Si-C tube furnace, heated at 300° C. for 20 minutes and then heated at 850° C. for 5 hours, cooled to room temperature. The product is a white powder. Its crystalline structure was determined by x-ray diffraction analysis. The powder was excited at 365 nm and 254 nm respectively, the emission peaks for Eu 3+ , Tb 3+ , and Eu 2+  are at 611 nm, 544 nm and 402 nm respectively. The emission intensity at 365 nm is stronger than that at 254 nm.  
       Example 2  
     The Synthesis of CaBPO 5 : xEu, yTb, zCe System  
       [0017]    CeO 2 , Eu 2 O 3 , Tb 4 O 7 , all with purity of  99 . 99 % (Shanghai Yuelong), CaCO 3 , B 2 O 3 , (NH 4 ) 2 HPO 4 , all with analytical purity (Beijing Chemical Plant), were weighed in a stoichiometric way. Eu 3+  was added with a mole fraction of 0.05, Tb 3+  with a mole fraction of 0.01, Ce 3+  with a mole fraction of 0.01. (NH 4 ) 2 HPO 4 is in excess of 10%. They were grounded and mixed in agate mortar and put in a Si-C tube furnace, heated at 300° C. for 30 minutes and then heated at 900° C. for 4 hours, cooled to room temperature. The product is a white powder. Its crystalline structure was determined by x-ray diffraction analysis. The powder was excited at 365 nm and 254 nm respectively, the emission peaks for Eu 3+ , Tb 3+ , and Eu 2+  are at 611 nm, 544 nm and 402 nm respectively. As compared with example 1, the emission intensities of Tb 3+  and Eu 2+  are stronger.  
       Example 3  
     The Synthesis of CaAl 0.8 B 0.2 PO 5 : xEu, yTb System  
       [0018]    Eu 2 O 3 , Tb 4 O 7 , all with purity of 99.99% (Shanghai Yuelong), CaCO 3 , Al 2 O 3 , B 2 O 3 , (NH 4 ) 2 HPO 4 , all with analytical purity (Beijing Chemical Plant), were weighed in a stoichiometric way. Eu 3+  was added with a mole fraction of 0.02, Tb 3+  with a mole fraction of 0.005. (NH 4 ) 2 HPO 4  is in excess of 10%. They were grounded and mixed in agate mortar and put in a Si-C tube furnace, heated at 360° C. for 20 minutes and then heated at 950° C. for 5 hours, cooled to room temperature. The product is a white powder. Its crystalline structure was determined by x-ray diffraction analysis. The powder was excited at 365 nm and 254 nm, the emission peaks for Eu 3+ , Tb 3+ , and Eu 2+  are at 611 nm, 544 nm and 430 nm respectively. The emission intensity at 365 nm is stronger.  
       Example 4  
     The Synthesis of CaAl 0.8 B 0.2 PO 5 : xEu, yTb, zCe System  
       [0019]    CeO 2 , Eu 2 O 3 , Tb 4 O 7 , all with purity of 99.99% (Shanghai Yuelong), CaCO 3 , Al 2 O 3 , B 2 O 3 , (NH 4 ) 2 HPO 4 , all with analytical purity (Beijing Chemical Plant), were weighed in a stoichiometric way. Eu 3+  was added with a mole fraction of 0.02, Tb 3+  with a mole fraction of 0.005, Ce 3+  with a mole fraction of 0.001. (NH 4 ) 2 HPO 4  is in excess of 10%. They were grounded and mixed in agate mortar and put in a Si-C tube furnace, heated at 360° C. for 20 minutes and then heated at 950° C. for 5 hours, cooled to room temperature. The product is a white powder. Its crystalline structure was determined by x-ray diffraction analysis. The powder was excited at 365 nm and 254 nm, the emission peaks for Eu 3+ , Tb 3+ , and Eu 2+  are at 611 nm, 544 nm and 430 nm respectively. Compared to example 3, the emission intensities of Tb 3+  and Eu 2+  are stronger.  
       Example 5  
     The Synthesis of Ca 2 B 5 O 9 Cl: xEu, yTb System  
       [0020]    Eu 2 O 3 , Tb 4 O 7 , all with purity of 99.99% (Shanghai Yuelong), CaCO 3 , H 3 BO 3 , CaCl 2 . 2 H 2 O all with analytical purity (Beijing Chemical Plant), were weighed in a stoichiometric way. Eu 3+  was added with a mole fraction of 0.04, Tb 3+  with a mole fraction of 0.01. They were grounded and mixed in agate mortar and put in a Si-C tube furnace, heated at 300° C. for 20 minutes and then heated at 850° C. for 3 hours, cooled to room temperature. The product is a white powder. Its crystalline structure was determined by x-ray diffraction analysis. The powder was excited 365nm and 254 nm, the emission peaks for Eu 3+ , Tb 3+ , and Eu 2+  are at 614 nm, 545nm and 430 nm respectively. The emission intensity at 365 nm is stronger.  
       Example 6  
     The Synthesis of Ca 2 B 5 O 9 Cl: xEu, yTb, zCe System  
       [0021]    CeO 2 , Eu 2 O 3 , Tb 4 O 7 , all with purity of 99.99% (Shanghai Yuelong), CaCO 3 , H 3 BO 3 , CaCl 2 . 2 H 2 O all with analytical purity (Beijing Chemical Plant), were weighed in a stoichiometric way. Eu 3+  was added with a mole fraction of 0.04, Tb 3 +with a mole fraction of 0.01, Ce 3+  with a mole fraction of 0.005. They were mixed in agate mortar and put in a Si-C tube furnace, heated at 300° C. for 20 minutes and then heated at 850° C. for 3 hours, cooled to room temperature. The product is a white powder. Its crystalline structure was determined by x-ray diffraction analysis. The powder was excited at 365 nm and 254 nm, the emission peaks for Eu 3+ , Tb 3+ , and Eu 2+  are at 614 nm, 545 nm and 430 nm respectively. Compared to example 5, the emission intensities of Tb 3+  and Eu 2+  are stronger.