Preparation And Characterization Of Cerium-doped Yttrium Aluminum Garnet Phosphor By Co-precipitation Method

Phosphor is the key material for the preparation of white LED,so the progress of phosphor preparation technology has a very important role in the development of white LED.The solid phase method is used to produce YAG:Ce³⁺ phosphor in the industry,but there are many disadvantages,such as large particle size and non-uniform,high calcination temperature,low luminous efficiency and low color temperature.Therefore,it can not meet the requirements of white LED,and further improve the luminous efficiency,reduce the particle size and improve the color temperature.Chemical co-precipitation method is helpful to control the doping amount accurately,improve the reactivity of the powder,reduce the synthesis temperature,and easily prepare the phosphor with excellent performance.Therefore,the preparation of cerium doped yttrium aluminum garnet(YAG:Ce³⁺)phosphor by co-precipitation method was chosen to meet the requirements of white LED.In the first part of the experiment,the effect of various factors on the luminescent properties of phosphors were studied,such as the titration method,the ratio of the mixed precipitant,the concentration of the metal solution,the surface active agent,the reaction temperature,the calcination temperature and the flux.A precursor was prepared at room temperature?25°C?using PEG-6000 as a surfactant and using ammonia water?3mol/L?and ammonium bicarbonate?1mol/L?as a mixed precipitate?1:1 by volume?.Then,the luminous intensity and luminous efficiency of the phosphor obtained after calcination at 1550 ° C were the highest,and the quantum yield reached 85%.When sodium fluoride was added as flux,the particle size reached 2.47 ?m at a calcination temperature of 1400°C,the dispersion of powder was very good and the luminescent intensity was the highest.When barium fluoride was added as flux,the particle size reached 2.64?m at a calcination temperature of 1550°C.The phosphor has good crystal morphology and the highest luminescence intensity.And the existence of a large number of the barium aluminate crystals with a needl-like form seriously affects the luminescent properties of the phosphor powder at low temperature.When boric acid was added as a flux,the phosphor luminescent performance is the best after calcined at a high temperature of 1400°C.When the calcination temperature is too high,the agglomeration of the powder is very serious and is not easy to break,so that the powder luminescence performance is seriously reduced.When adding barium fluoride and boric acid as mixed flux,the phosphor luminescent performance is the best after calcined at a high temperature of 1550°C.The particle size reached 4.55?m,and the absolute quantum yield reached 91%.The second part of the experiment mainly discusses the luminescent properties of phosphors prepared by semi-liquid phase and solid phase method.When using the semi-liquid phase method to prepare the phosphor,the luminescent properties of the phosphors prepared by using nano-alumina as aluminum source are better than that of using aluminum hydroxide.When nano-alumina and aluminum hydroxide are used as aluminum sources,the luminescent properties of the phosphor prepared by calcination at 1450°C are the best.When the phosphor was prepared by solid phase method,the luminescent properties of the phosphor were gradually increased with the increase of calcination temperature,and reached the highest at 1550°C.The absolute quantum yield of the phosphor prepared by the co-precipitation method is up to 85% and the solid phase is 73%.The absolute quantum yield of the phosphor prepared by the semi-liquid phase is 81%.In the third part of the experiment,the effect of doping rare earth ions(Ce³⁺?La³⁺?Pr³⁺)on the luminescent properties of phosphors was discussed.The results show that the luminous performance of the phosphor is the best when the Ce³⁺ ion doping concentration is 4%.The addition of La³⁺ ions did not significantly improve the luminescence of phosphors in the red light region,which resulted in the decrease of luminescence properties of phosphors.The addition of Pr³⁺ ions allowed the phosphor to add two emission peaks in the red light region.The emission peaks located at 608 nm and 638 nm belong to the electronic transition of Pr³⁺ ions from 1D2 to 3H4 and 3P0 to 3H5.Therefore,the addition of Pr³⁺ ions can obviously improve the luminescence of phosphor in red light region.