Synthesis And Characterization Of YAG: Ce Phosphor By Spray Pyrolysis

Semiconductor light-emitting diode (LED) with several merits such as energy savings, long life-times, rapid response, high reliability, recyclable, unpolluted, flexible distribution of light, simplified and flexible design, ease of miniaturization due to the small size of the light source, is deemed to the most valuable new light sources in 21st century. At present, white LED can be generated by mixing primary light from a blue LED with light created by using the blue LED to excite cerium doped yttrium aluminum garnet (YAG:Ce) yellow phosphor, and the products have already got application commercially. YAG:Ce phosphors are prepared conventionally by solid-state reactions. This process involves heat treatments at high temperatures, and the phosphors prepared have irregular morphologies and large size. At the same time loss in luminescent output due to mechanical grinding influences the performance of application seriously.Spray pyrolysis is a method of turning the water solution prepared by placing the metallic salt to deionized water into the solid state particle directly. The phosphor particles prepared by spray pyrolysis, show spherical morphology with relatively uniform size and homogenous composition. Furthermore, spray pyrolysis have advantages of large-scale production and simple equipment. Therefore, spray pyrolysis becomes a focus on the luminescent materials in recent years.In this paper, phosphor was synthesized by a two-step spray pyrolysis process, and factors on morphology and luminescence were also investigated. Luminescence mechanism of phosphor and effect mechanism of flux were studied initially. The main points of the thesis are as following:(1) The luminescence mechanism, realization methods and key materials of white LED are overviewed. Characteristics of various phosphors synthetic technologies for white LED are discussed.(2) The effects on the phosphor performance were studied. Spherical phosphor particles with narrow size distribution and strong emission intensity were prepared by optimizing the concentration of solution, the flow rate of carrier gas and the annealing temperature and so on;(3) Substitution by Gd³⁺, Tb³⁺ ions in the Y³⁺ sites will red shift the emission light of the phosphor while substitution by B³⁺ ions in the Al³⁺ sites will blue shift the emission light. The emission maximum could be obtained when Y was substituted by 60% Gd or 80% Tb, and the emission wavelength was 538nm;(4) Adding proper flux would increase raw material reaction activity and reduce garnet forming temperature. Deviation from cubic symmetry is the primary factor resulting in the spectral shifts observed in cerium-doped garnets. Compression of the Ce³⁺ tetragonally distorted cubic site results in a lowering of the first excited 5d state (hence the luminescence) to even lower energies (longer wavelengths). Substituting Tb, Gd for Y results in an even larger splitting; the visible emission band shifts to the red with increasing Tb, Gd content. On the other hand, replacing Al with B causes a smaller splitting, shifting emission to the blue, as in the case of Li.(5) The phosphors prepared can be used to achieve white light when excited by blue light of the LED. The achieved color temperature is 6165K, with a color rendering index of 79.9 and a color point near the coordinate x=0.3184 and y=0.3419. It could satisfy light source requirements.