Preparation And Luminescence Properties Of Mg-α-Sialon:Eu²⁺ Phosphor Ceramics For Laser Illumination

Laser diodes(LD)are becoming a new lighting choice due to the sudden drop in LED efficiency.Especially after laser lighting was applied to automobile headlamp lighting,there are more and more researches on LD lighting.At present,YAG:Ce3+composite phosphor transparent ceramic package LD with excellent luminescence saturation characteristics has become the mainstream.However,the color temperature of the LD encapsulated by the phosphor ceramic is incompatible with the thermal quenching property of YAG:Ce3+ceramics because the crystal structure rigidity of YAG matrix itself is not high enough.And the difference of thermal expansion coefficient between different materials in YAG:Ce3+composite phosphor transparent ceramics may lead to material failure in advance in the high thermal stress generated by LD.Therefore,it is necessary to explore new phosphor transparent ceramics for LD lighting while continuing in-depth research on YAG:Ce3+composite phosphor transparent ceramics.In this paper,Mg-α-Sialon:Eu2+phosphor ceramics were prepared by hot pressing sintering.The main research contents and results are as follows:Firstly,the effects of different components and sintering temperatures on the microstructure of samples were studied.The results show that the α-Sialon lattice expands obviously with the increase of m,and the solution contents of Eu2+and Mg2+increase,and the microstructure of the sample sintered at 1850℃ gradually changes from columnar and equiaxed crystals to equiaxed crystals.In the sample m=2n=1.2,x=0.04,the average grain size is about 1μm.With the increase of m,densification becomes more and more difficult,because the formation of AlN polymorphs containing Mg and Eu consumes a large amount of liquid phase.In addition,it is found that the densification of the samples with high Eu2+ion content is relatively easier,but the grain growth is inhibited,and the amount of Eu containing glass phase increases significantly,because the relatively large radius of Eu2+ion is difficult to be dissolved into the α-Sialon lattice.Then,the effects of microstructure on mechanical properties,transmittance and luminescence properties of sample were investigated.For the sample composed of m=2n and sintered at 1850℃,the hardness of the sample increases with the transformation from long columnar grains to equiaxed grains.At m=2n=1.2,the visible linear transmittance is almost 0 in 3 80-700nm band under the influence of AIN polytype and its refractive index,and gradually increases in the visible transmittance(500-780nm).In the sample M84,the glass phase was the least at the sintering temperature of 1900℃,and the linear transmittance was as high as 27%.With the increase of m and temperature,the rigidity of α-Sialon crystal decreases with lattice expansion,resulting in red shift of emission peak.Then,the densification and transmittance of Mg-α-Sialon:Eu2+phosphor ceramics composed of m=0.8 and n=1.0 were investigated by adding additional 1wt%lanthanum oxide.The sample M08E4 was treated by planetary grinding to improve the sintering activity and the solid solubility of Eu2+and Mg2+in α-Sialon crystal lattice.Finally,the photochromic properties of Mg-α-Sialon:Eu2+were investigated.The emission intensity of most samples reaches its maximum at the power density of 2.5W/mm2,and light saturation occurs.As m increases,the color temperature decreases.The luminescence saturation of sample M08E4 occurs at the power density of 1W/mm2 at 1.5h of planetary grinding.