Preparation And Luminescent Properties Of Yttrium Aluminum Garnet For Laser Illumination

LED industry is developing rapidly.In the field of lighting and display,new luminescent materials are constantly studied.It has become a common goal to develop luminescent materials with higher luminous efficiency and better color rendering effect.However,with the increase of driving power density,blue LED chips will have the problem of"efficiency sudden drop"of rapid attenuation of luminous efficiency,which limits the wide application of WLED in high-power and high brightness lighting and display.In contrast,the efficiency threshold of laser diode is much higher.By increasing the input current density,it is easy to realize high-power and high brightness laser illumination.As an important component of laser illumination and display,the optical properties of new phosphor materials have an important impact on the indexes of LD.Based on the wide spectrum,high luminous efficiency and high stability of Y₃Al₅O₁₂（Yttrium Aluminum Garnet,referred to as YAG）phosphor materials,different types of phosphor conversion materials were prepared,and their luminescence properties were regulated.The specific research contents and conclusions are as follows:1.The Phosphor-in-Glass（Pi G）composite of Y₃（Ga,Al）₅O₁₂:Ce³⁺(YAG:Ce³⁺)phosphor powders and（Y,Gd）₃Al₅O₁₂:Ce³⁺(Gd YAG:Ce³⁺)phosphor powders was prepared by low temperature co sintering.Due to the single spectral color of Y₃Al₅O₁₂:Ce³⁺(YAG:Ce³⁺)Pi G and the lack of red and green light components,its color rendering performance in high-power laser lighting and display is poor,which can not meet the needs of high-quality laser lighting and display applications.Based on the characteristics of wide spectrum,high luminous efficiency and high stability of yttrium aluminum garnet structured phosphor materials,green-emitting YAGG:Ce³⁺and orange-emitting Gd YAG:Ce³⁺phosphor powders materials were selected as phosphor components in Pi G,and Pi G materials with high color rendering properties were obtained.The effects of preparation temperature,the ratio of Phosphor-to-Glass（Pt G）powder,the ratio of YAGG:Ce³⁺and Gd YAG:Ce³⁺phosphors powders and sample thickness on their properties were studied in detail.By adjusting the experimental conditions,under the excitation of 1.63 W/mm²blue laser,the color rendering index（RA）of YAGG:Ce³⁺/Gd YAG:Ce³⁺Pi G can reach 79.7,which is significantly improved compared with YAG:Ce³⁺Pi G,about 13.7%,and a high luminous efficiency of 163.14 lm/W is obtained.These results show that the Pi G in this study is suitable for the field of high-power laser illumination and has great potential.2.Sandwich Structured Pi G film（SS-Pi G film for short）was prepared by low temperature co sintering method using green-emitting YAGG:Ce³⁺phosphor powders and orange-emitting Gd YAG:Ce³⁺phosphor powders.In order to improve the heat dissipation performance,two types of Pi G films were synthesized on two surfaces of sapphire substrate.The effects of synthesis temperature,the ratio of Pt G powder and film thickness on the luminescence and transmittance of the samples were studied in detail.By adjusting the thickness of Pi G film,under blue laser excitation,the color rendering index of SS-Pi G film（81.4）is significantly higher than that of single YAG:Ce³⁺Pi G film（～24.3%）.In addition,due to the sandwich structure,the heat dissipation effect is improved,and the SS-Pi G film can be excited with a higher blue laser density.When excited with a 7.69 W/mm²blue laser,the high luminous flux density of 1362 lm/mm²and 177 lm/W high luminous efficiency can be obtained,which is 178.5%higher than that of the traditional multilayer Pi G film.These results show that SS-Pi G film has a good application prospect in high-power laser illumination and display.3.YAGG:Ce-YAG composite phosphor ceramics were prepared by high temperature vacuum sintering.In order to suppress the evaporation of gallium in high temperature reduction atmosphere,high performance YAGG:Ce phosphors powders were synthesized at low temperature by the improved sol-gel method.Then the YAGG:Ce phosphors powders were evenly dispersed into the high thermal conductivity YAG ceramic matrix by ceramic synthesis technology.The micro morphology and luminescent properties of composite phosphor ceramics were systematically studied.For achieved YAGG:Ce-YAG ceramic,the similar refractive index and structure of two phases can benefit the ceramic product to achieve high transparency,while the high performance of phosphor powders will favor the luminescence efficiency.To evaluate the applicability for laser lighting,we also studied the high-temperature thermal conductivity and the heat dissipation property of final ceramic products.And due to outstanding thermal properties,the YAGG:Ce-YAG phosphor ceramic can achieved as high as 700 lm/mm²under the excitation of 8.2 W/mm²blue laser light.It shows that it has a good application prospect as a green conversion material for high-power laser illumination and display.