Preparation And Spectrum Tuning Of Yttrium Aluminum Garnet Phosphors For White Light-emitting Diode

White light-emitting diodes (WLED) are poised for another revolutionizing the luminescence lighting industry after semiconductor technology leading to micro-electronics revolution and have the potential of replacing the conventional incandescent, fluorescent and discharge-column-type fluorescent lamps for small volume, endurable vibration, long lifetime, non-pollution etc. Nowadays the blue LED chip combined with yellow cerium doped yttrium aluminum garnet phosphors (YAG:Ce) is the most common pattern to produce white light. However as a important component of producing LED, the capabilities of YAG:Ce phosphors still need improved.This work is to aim at the yttrium aluminum garnet luminous powder which activates by the cerium (YAG:Ce) by using a novel and a traditional preparation method respectively and by changing doping strategy. The more attentions are paid to adjustment of microstructure and morphology and improvement of the luminescence performance. The expected findings have the vital significance to this material for large scale production and the further optimization of properties.We have drawn some creative conclusions as follows:1. A novel preparation method----sol-spray pyrolysis method was investigated experimentally in detail. By using a special kind of nano-sized pseudo-boehmite power as starting material, after peptizing, a stable composite hydrosol was obtained, then this sol was sprayed to xerosol and sintered to YAG:Ce fluorescent materials without any further ball-milling treatment. The bottleneck of selecting metal alkoxides in the traditional sol-gel was broken and the problems which controlling pure phrase,large grain size and high energy consumption met in traditional solid state method were overcome. At 1000℃, YAG phrase can be obtained, the near sphere grain's average crystal size is around 3μm and the grain-size distribution of phosphor particle is obviously narrow.2. To investigate the mechanisms of luminescence properties and to optimize the luminous parameters, we examine a series of doping effects. Taking YAG as host, through doping method----co-doping different irons with cerium (Gd³⁺,Ga³⁺,Pr³⁺,Eu³⁺,Ho³⁺,Mg2+), changing partial substitutions positive ion and anion groups of the host, how the changed host effects on the luminescence to Ce³⁺ was studied. The energy transfer among different rare earth ions and Ce³⁺ is analyzed and how to adjust the phosphor's emitting wavelength was also approached. Furthermore, the influence of the flux(Li2CO3) on the luminescence intensity of phosphor was examined. The results indicate the doping of Mg2+ ion leads to red shift of the emitting wavelength, so it helps to improve colour character of LED. The optimized amount of flux Li2CO3 is ca. 0.006mol, the luminescence intensity with flux is 6 times higher than that without flux. 3. The spherical granulation mechanism has been analyzed theoretically. Based on the theoretical results, the experimental process parameters to obtain sphere-like YAG:Ce phosphors are obtained. The additives of tetraethoxysilane (TEOS),polyethylene glycol (PEG) and cetyltrimethyl ammonium bromide (CTAB) were tested. It is found that by adding TEOS, Al2Y4O9 phase with AlYO3 phase could be effectively suppressed, while spherical morphology could be received at around 900℃,1100℃and 1200℃respectively. Consequently, the luminous intensity is 3 times to that without using TEOS under the same sintering condition. On the contrary, the spherical morphology was not achieved by using PEG and CTAB respectively.4. The comparative test among solid state method, traditional sol-gel and this sol-spray pyrolysis was evaluated experimentally. We found that the sol-gel and spray pyrolysis method with nano pseudo-boehmite particulates as aluminium source could produce YAG phrase relatively easily at lower temperature(ca. 1000℃)and obtain pure YAG phrase at 1400℃. Moreover, the new spray pyrolysis method is much easier to receive pure phase without necessity of ball-milling treatment. Hence, the new preparation method of sol-aided spray pyroloysis has the remarkable merits in the resources, environment, price and value, enlargement production. The drawbacks of lowering brightness upon tradition milling treatment in traditional sol-gel method can be overcome by this novel route.