Study Of YAG:Ce Yellow Phosphors For White-LEDs Application Prepared By Wet-Chemical Method And Luminescent Properties

Yttrium aluminum garnet (Y3Al5O12,YAG), activated with trivalent cerium Y3-xAl5O12:Cex (YAG:Ce), is a yellow phosphor which is studied earliest and most completely. YAG:Ce phosphors have wide application prospect and the important value of research in white phosphor-based LED commercial market. In this thesis, based on development of different synthesis methods of YAG:Ce3+phosphors, we study that the effect of synthesis methods on their propertie of YAG:Ce yellow phosphors. We adopted co-precipitation method, solvothermal method and the combination of co-precipitation and solvothermal method to prepare pure phase YAG and further analyzed their properties. The mian results of study are as follows:1. Single phase YAG could be prepared after solvothermal processing at160℃for24h and sequent sintering treatment at900℃for3h in air atmosphere. The emission spectra of YAG:Ce phosphors indicated that the emission intensity of phosphors increased with increasing calcination temperature and reached the maximum value when x (Y3-xAl5O12:Cex) was0.03. In the process of precipitation, pH of the precursor solution changes with varying the dosage of triethylene tetramine(TETA). The heterogeneous distribution of Al3+and Y3+will occur in the precursor when the value of pH is below8. Then the volume of TETA is above1.2mL to ensure the photoluminescent property of YAG:Ce phosphor.2. Pure YAG phase has been obtained by co-precipitation method sintered at800℃for3h. The formation temperature of pure YAG phase is lower than those prepared by co-precipitation method using ammonia water (1000℃) and ammonium hydrogen carbonate (900℃) as precipitants. The results show that the emission intensity of phosphors increased monotonically with increasing sintering temperature, and the optimal cerium doping concentration is lmol%. When pure ethanol was used as the solvent to dissolve the mother salt solution, the highly efficient YAG:Ce phosphors can be prepared. In the process of precipitation, the pH value of the precursor solution fluctuates with varying the dosage of TETA. When the volume of TETA is above1mL, Y3+and Al3+would undergo precipitation with the ratio of3:5.3. Ce-doped YAG ultra-fine particles were successfully synthesized by solvothermal method, which were induced in an autoclave where TETA solution was firstly used as solvent at250℃for4h. Due to the Ostwald ripening process, larger particles forms at the expense of smaller ones. The particle shape is more regular spherical and the crystallinity of particles increase with increasing the holding time and the dosage of TETA,. With the prolongation of holding time and increase in filling factor, the PL emission intensity of YAG:Ce phosphors increase due to the gradual increase in the substituted Ce3+content and the growth of particles with single crystalline. This synthesis process was relatively simple and could be easily controlled.