| As a new type of lighting/display technology that replaces traditional light sources,laser lighting/display has the advantages of compact structure,long service life,high brightness,good directionality and wide color gamut coverage.Laser remote excitation of fluorescence conversion materials is currently the mainstream solution for obtaining phosphor light sources for laser lighting/display.Phosphor ceramics have the advantages of good thermal stability,high luminous efficiency and easy realization of structural component design,which has become a fluorescence conversion for laser lighting/display.The material of choice.Ce:Lu AG/Ce:YAG phosphor ceramics have high quantum efficiency and low thermal quenching,which are very suitable for high-power laser illumination/display conversion materials.In order to meet the application requirements of laser lighting/display,the structure design and optimization of phosphor ceramics are required to achieve high luminous efficiency while having high luminous uniformity and stable color.Based on the above research background,Ce:Lu AG transparent phosphor ceramics were prepared by solid-phase reaction combined with vacuum sintering technology,and the influence of doping concentration and ceramic thickness on the photoelectric and color performance was studied.And through the microstructure design,porous Ce:Lu AG/Ce:YAG ceramics with different porosity and micropore size were prepared,and their microstructure and luminescence properties were characterized.The main work of this paper is as follows:(1)The 0.05,0.1,0.2,0.3,0.4 at.%Ce:Lu AG transparent ceramics were prepared by solid-phase reaction vacuum sintering,and the effect of doping concentration on the luminescence of Ce:Lu AG ceramic COB packaged LED devices was systematically studied.The luminescence saturation performance of ceramics of different thicknesses excited by LD is explored.0.2 at.%Ce:Lu AG has the highest PL emission intensity and excellent thermal quenching performance(only 7%reduction at 225°C).The absorption and emission characteristics of Ce:Lu AG ceramics with different concentrations under excitation of 454 nm blue LEDs indicate that the increase of doping concentration can enhance the absorption of blue light and obtain an adjustable CCT(5653 K-7433 K),0.1 at.%Ce:Lu AG ceramics have the highest luminous efficiency of 179 lm/W.Under the excitation of 450 nm LD with a power density of 24.6 W/mm~2,the luminous flux of 0.1 at.%Ce:Lu AG ceramics with 1 mm thickness reaches 3646 lm without reaching luminescence saturation.(2)To improve the high CCT and color drift problems of phosphor ceramics under high-power excitation in laser projection systems,the microstructures of Ce:Lu AG ceramics were designed by introducing pores as scattering centers.0,5,10,15,20 vol.%porous 0.3 at.%Ce:Lu AG phosphor ceramics with different porosities were prepared.The microstructures of ceramics show that the pores in the porous ceramics are irregular polygons with uniform distribution in the ceramics.The connected pores appear in the ceramics with high porosities of 15,20 vol.%.The luminescence performance of the LED transmission mode was studied by using 0.3 at.%Ce:Lu AG ceramics with different thicknesses and porosities.The results show that the porous ceramics with a thickness of 0.3 mm and a PMMA addition of 0 vol.%have higher light extraction efficiency,demonstrating that the scattering and absorption effect of blue light are better,and the luminous efficiency is 210 lm/W.The effect of the porosity in the 0.3mm thick porous Ce:Lu AG phosphor ceramics on the luminescence saturation performance,luminescence uniformity and luminescence color stability under the excitation of blue LD were further studied.Using 450 nm LD to excite the phosphor ceramics with different porosities in the reflection mode,the luminescence saturation did not occur under 15 W laser excitation.The Ce:Lu AG ceramics with the porosity of 5 vol.%obtained a high luminous flux of 4290 lm.Moreover,as the incident power increases,the ceramics have a stable CCT(7190 K-7288 K)and luminous color(color coordinates moving from(0.2688,0.4693)to(0.2711,0.4453)).The CCT obtained by the light uniformity test at different angles of 10°-170°is stable at about 6600 K.The results show that the porous Ce:Lu AG ceramic can be used as a promising color converter for laser projection display with high luminous efficiency and luminous color stability.(3)In order to solve the"yellow ring effect"and other luminous uniformity problems of Ce:YAG phosphor ceramics in laser lighting applications,and to improve the directionality of the emitted light.Porous Ce:YAG ceramics with the porosities of0,2.5,5,10,15,20 vol.%were prepared.When the porosity is 10 vol.%,the maximum luminous flux of Ce:YAG ceramics reaches 3430 lm.The luminescence saturation of Ce:YAG ceramics with 15 and 20 vol.%porosity occurs,which is due to the sharp decrease of thermal conductivity of high porosity.The CCT of Ce:YAG ceramics with the porosity of 10 vol.%is stable in the range of 6636 K-6901 K as the incident power increases to 15 W,and the color coordinates move from(0.3025,0.3788)to(0.2995,0.3607),the CCT measured at different angles from 10°to 90°changes slightly in the range of 4272 K-4448 K.The facula limiting ability ability of porous Ce:YAG ceramics with different porosities was further evaluated,and the results showed that Ce:YAG ceramics with the porosity of 10 vol.%have a relatively small light spot emission area,and the center brightness reached 1669592 cd/m~2.The luminescence properties of porous Ce:YAG ceramics with the porosity of 10 vol.%and different pore sizes(1.8?m,3?m,5?m,10?m,15?m)were further studied.The highest luminous flux of porous Ce:YAG ceramics with a pore size of 5?m is up to 4020 lm,with stable power-dependent CCT(7028 K-7315 K)and color stability(color coordinates shift from(0.2962,0.3635)to(0.2938,0.3479)).The results show that porous Ce:YAG phosphor ceramics have both high luminous saturation threshold and color stability,and have excellent luminescence uniformity and light collection performance,which are very suitable for high-quality laser lighting color converters. |
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