Low-temperature blade-coated CaAlSiN₃:Eu²⁺ phosphor-in-glass films on sapphire for thermally stable amber optoelectronic conversion

A low-temperature, vacuum-free blade-coating process was developed to fabricate CaAlSiN₃:Eu²⁺ phosphor-in-glass (PiG) films directly on sapphire substrates for thermally stable amber emission. The 600 °C process enables uniform film formation, controllable thickness, partial consolidation, and a continuous PiG/sapphire interface without observable delamination while preserving the crystalline phase and emission characteristics of the nitride phosphor. Among phosphor loadings from 51 to 63 wt%, the 60 wt% PiG film exhibited the best overall performance, with amber emission centered at approximately 600 nm, CIE coordinates of (0.5508, 0.4028), a correlated color temperature of 1719 K, a luminous efficacy of radiation of 106.2 lm/W, an internal quantum efficiency of 60.9%, and an external quantum efficiency of 42.5%. Temperature-dependent photoluminescence measurements showed that the optimized PiG film retained approximately 92% of its 25 °C emission intensity at 150 °C. A fused-silica substrate control showed similar intrinsic thermal-quenching behavior at the same measured PiG-layer temperature, whereas the sapphire-supported film maintained a lower operating temperature and higher PL output under identical optical loading because of improved heat spreading. These results indicate that low-temperature blade-coated CaAlSiN₃:Eu²⁺ PiG films on sapphire provide a scalable and thermally robust color-conversion platform for automotive amber lighting and high-power light-emitting diode (LED) modules.