Preparation And Properties Of Rare Earth Doped YAG Phosphor Powders And Transparent Films

The films of Ce-doped yttrium aluminum garnet(Ce:YAG) have high light uniformity, thermal stability, high transparency, good luminous efficiency etc., It have shown excellent application prospects as new type packaging materials for white LED. The traditional process is that we mixed Ce:YAG phosphors and epoxy resin to encapsulate on the blue chip. But the powder particles will settle in the colloid, it resulted that the lighting is uneven. If we use Ce:YAG thin film instead of phosphors doped organic epoxy resin, we can avoid the problem that the light is not uniform, improve the thermal conductivity, and solve the problem of heat dissipation.In this paper, we use ultrasonic co-precipitation mixed molten salt method to prepare Ce:YAG nanopowders, the target is sintered in N2, then we used PLD(Pulsed Laser Deposition) method to prepare Ce:YAG films. We have done systematic studies on the influence of powders' synthesis process, the effect of targets' pressing process, the effect of PLD deposition and annealing process on the structure and optical properties of the thin films, and we also studied the optical properties on the Gd/Pr single or co-doped Ce-YAG thin films.Compared with the traditional co-precipitation method, We used ultrasonic co-precipitation mixed molten salt method to prepare rare earth doped YAG powders, it can reduce the calcined temperature from 1100 ? to 1000 ? and shorten the time from 5 h to 3 h, and the phosphors have high crystallinity, the particle size is concentrated in 450-580 nm. Studies found that we prepared the precursor by 45 KHz ultrasonic for 3 h, and the precursor is presintered to 700 ? for 1 h, the weight of mixed molten salt(KI:KCl=1:2) is 3/2 times that of presintering body, the phosphors have high crystallinity, uniform particle size,and best fluorescence. Then, we studied the preparation process of phosphors target, we can use 30 MPa pressure and 1550 ? temperature to obtain the target, and the density reached to 4.65 g/cm3, the atomic ratio reached to 1.63(theoretical value is 1.7). Finally, through the improvement of PLD technique we produced Ce:YAG films with excellent optical performance successfully, the study found that, when the substrate temperature is heated to 350 ?, the target-substrate distance is 4cm, single pulse power is 200 mJ, the films are coated 6h in N2, then annealed to 1100? for 5h in N2, the samples have best structure and properties. The visible light transmittance of films reach to 70%, the fluorescence emission peak matched with the commercial phosphors, thin films are dense, have smooth surface, the mean square roughness is lowest.On the basis of the study of Ce:YAG thin films, through Gd/Pr single or co-doped, the emission peak of Ce:YAG thin films will occur red shift and appear other emission peak at red band, it improved red light emission component of the Ce:YAG thin films, the color temperature was reduced, the color tone becomed warming. The experimental results show that, through Gd/Pr co-doped, the emission peak of 5d?4f transition of Ce3+ occurred that the peak shifted 25 nm to red region, and appeared new peak at 606 nm, the films have high warming component, the result above is meaningful for the application of YAG phosphor films in white-LED.