Study On Synthesis And Surface Coating Of Yellow Phosphor For White-LEDs

Because phosphor is the critical material of white LED producing, its performance directly affects the brightness, color coordinates, color temperature and color rendering of white LEDs. Chemical coprecipitation is a widely applicable method for preparing YAG:Ce luminous materials which can precisely control the doping amount and has high reacting activity. At the same time, due to the environmental and materia itself factors, the physical-chemical properties of YAG:Ce without processing is instability that force to find a way to improve the stability of YAG:Ce. It is a kind of effective method for coating phosphor.In this paper, Y_3-xAl₅O₁₂:Ce_x yellow phophors were synthesized by coprecipitation method and the Al2O3 coating key technology is studied. The performance indexes of color temperature, color coordinates and colour index for white LEDs have been obtained. The main contents are as follows:â‘ Stuty the influences of different fluxes NaF, AlF3, BaF2, LiF, H₃BO₃, H2SiO3 on phisical-chemical properties of YAG:Ce yellow phospor. It is shown that the optimal photoluminescence intensity of the YAG:Ce phosphor were obtained on the condition of containing 6% NaF. The synthsis temperature has reduced 300℃and the emission peak is blue shift. The particles are spherical-like shapes, narrow size distributions with mean size mostly at 11μm. H₃BO₃ flux is the second. And addition of the AlF₃, H₂SiO₃, BaF₂ and LiF, the emission intensity can increase only little. In the fluxing process, H₂SiO₃ is into YAG grad which cause wavelength redshift. The effect of mixing H₃BO₃ with NaF is better than a single flux.â‘¡Study the effects of firing contidions on phosphor photoluminescence property in the method of chemical precipitation. The results show that at the condition of reducing atmosphere, The YAG:Ce yellow phosphor has the maximum luminous intensity for 468nm excitation wavelength and 520nm emission wavelength at 1300℃.â‘¢Using NaAc-HAc conjugate system prepare phosphor coated Al2O3. The mass ratio of Al₃O₂ and phosphor is 7:100 and the concentration of aluminun-salt water solution is 0.56M. Drop into the solution of 0.5M conjugate system that YAG:Ce yellow phosphor immers in NaAc/Hac for 12h. It has the best effect of phosphor coated Al₂O₃ at 250℃.â‘£The optical properties of phosphor coated Al2O3 have shown that the maximum excitation wavelength of phosphor after coating is 468nm and the maximum emission wavelength is 532nm, color coordintes is (x=0.4519, y=0.5294), colour tempreture is 3569K, colour developing index Ra is 39.8, and the resistant light attenuation capability has increased 20% at high tempreture. The white LED is packaged by good performance phosphor with blue LED chip. The color tempreture Tc is 6690K, light efficient is 30.34lm/W, colour developing index Ra is 79.9, color coordinates is (x=0.3097, y=0.3266). It can meet the basic requirement of white LEDs.