Enhanced luminous exitance and saturation threshold of Y₃Al₅O₁₂:Ce phosphor-in-glass films via incorporation of highly thermally conductive boron nitride particles

Phosphor-in-glass film (PiG-film) displays great potential for high performance laser-driven white lighting, benefiting from its facile fabrication and high efficiency. However, the low thermal conductivity of the glass matrix may lead to thermal quenching of phosphors and limit the maximum luminous flux of the light source. Here, boron nitride (BN) with high thermal conductivity and low absorption coefficient was embedded into Y₃Al₅O₁₂:Ce PiG-film to facilitate the heat-transfer process, and to regulate the propagation of both laser and fluorescence. The influences of BN particle size and doping concentration on surface morphology (pore formation), luminescence saturation threshold (LST), luminous flux, and the spatial distribution of correlated color temperature (CCT) were investigated and correlated. Moreover, the luminescence spot confinement was analyzed and luminous exitance was obtained. Benefiting from the formation of effective BN heat-transfer network, the luminous efficacy of both YAG-45-2 % and YAG-45-1 % films surpass the non-doped one as laser power density >19.00 W/mm². A LST higher than 27.04 W/mm² was observed in YAG-45-2 % film, more than 42 % higher than the non-doped one. Though the extra reflection of blue laser by BN particles downgrades the CCT spatial distribution uniformity, the particles strongly scatter the fluorescence and restrict the fluorescence-emitting spot (diameter) expansion from 307 to 174 μm, and a high luminous exitance of 1614 lm/mm² was achieved in YAG-45-2 % film. These results firmly demonstrate that incorporation of particles with high thermal conductivity and low absorption coefficient in PiG-film is a feasible strategy for achieving high-brightness laser lighting.