Optical Properties Of Phosphor-in-Glass Films For Laser Lighting And Display

As a new generation advanced lighting or display technology,laser lighting and laser display has attracted great attentions owing to their ultra-high brightness,high luminous efficacy,energy saving,brilliant images and/or large sizes.It’s well known that the blue LED chips have the "efficiency droop" problem,which problem makes LED chips unsuitable for super-high-power or brightness solid state lighting applications.These general color converters materials applied in white LED applications such as Phosphors,Phosphor ceramics,and Phosphor-in-Glass(PiG)are not suitable for laser excitation,due to the low thermal conductivity of these materials hinders their applications in high-power blue-laser-driven solid state lighting.To solve this problem,we have designed a single-layer PiG film for laser lighting and a laminated PiG film for laser display.With regard to the laser lighting,the Y3Al5O12:Ce(YAG)-based PiG films was obtained via co-fired with a thermally conductive sapphire substrate.By varying the firing temperature,phosphor-to-glass(PtG)ratio,film thickness and the incident power of the blue laser,the microstructure and optical properties of the YAG PiG films were investigated thoroughly.It shows that the porosity of the PiG film is controlled by the firing temperature,PtG ratio and thickness,which in turn has a great impact on the luminance saturation of the YAG PiG film.When the PtG ratio or the thickness of the PiG film increases,the luminance saturation becomes worse and both of the luminous flux and luminous efficacy decrease.The white laser light can be realized by controlling the PtG ratio or the thickness of the PiG film.For the PiG film with a PtG ratio of 1:1 and a thickness of 50μm,the threshold maximum for luminance saturation,luminous flux and luminous efficacy are 10.1 W(i.e.,12.9 Wmm-2),10481m and 137 lmW-1,respectively.When an additional sapphire substrate coated by one-dimensional photonic crystals is attached to the PiG film,the film shows an improvement in luminous flux and efficacy,and produces the white light with a luminous flux of 1709 lm,a luminous efficacy of 211 lmW-1,color rending index of 65 and a correlated color temperature of 6602 K under the maximum 8.09 W(i.e.,10.3 Wmm-2)blue laser light excitation.For the laser display,we propose to develop laminated phosphor-in-glass(PiG)films as laserdriven color converters for wide-color-gamut and high brightness laser displays.βSialon:Eu and Calson:Ce phosphors were respectively chosen as the green and orange emitters,and were co-fired with glass frits on a sapphire substrate coated by onedimensional photonic crystals to form PiG films directly.The phosphor content and film thickness impacted an influence in the micro structure,luminance saturation and optical properties of β-Sialon and Calson PiG films under blue laser irradiations,bothβ-Sialon and Calson PiG films reached a maximum luminance saturation of 6.09 Wmm-2 when their micro structures were optimized.The lamination architecture of PiG films had a great impact on the optical properties of laser-driven white light,and the maximum ones were achieved as the green-emitting PiG film was positioned on the orange-emitting film adhered to the sapphire substrate.Under 4.8 Wmm-2 blue laser excitation,the laminated double-layer PiG films enabled to create white light with a wide color gamut of 107%NTSC,luminous efficacy of 74.44 lm W-1,luminous flux of 282.13 lm and a color temperature of 7902 K.It indicates that the YAG-based PiG film could be applied in high power laser-driven solid state lighting when its micorstructure is carefully tailored,and that the laminated PiG films are promising color converters for use in high-power and wide color gamut laser displays or projectors.