Performance improvement of reflective phosphor film via adjusting the thickness realizing bright and efficient laser lighting

Phosphor-in-glass-film (PiG-F) has been extensively investigated, showing great potential for use in laser lighting technique. Thickness is apparently a key parameter for PiG-F, affecting the heat dissipation, absorption, and reabsorption, thus determining the luminous efficacy and luminescence saturation threshold (LST). Conventional studies suggest that thinner films often have lower thermal load than that of the thicker ones. Unexpectedly, we found that the Lu₃Al₅O₁₂:Ce (LuAG:Ce)-based PiG-F with a moderate thickness (78 μm) yielded the optimal LST of 31.9 W (14.2 W·mm^-2, rather than 28.0 W (12.3 W·mm^-2) for the thinnest one (56 μm). This unexpected result was further verified by thermal simulations. With the high saturation threshold together with a high luminous efficacy (∼296 lm·W^-1), an ultrahigh luminous flux of 7178 lm with a luminous exitance of 2930 lm·mm^-2 was thus attained. We believe the new, to the best of our knowledge, findings in this study will substantially impact the design principles of phosphors for laser lighting.