Cold-sintered phosphor film@Cu converter for ultrahigh-brightness laser illumination

Phosphor ceramics have been regarded as promising color converters for high-quality laser illumination, but they often suffer from optothermal performance degradation during high-temperature sintering processes. Herein, an optothermal-enhanced cold-sintered phosphor film@Cu (PF@Cu) converter is developed. A low-temperature (150 °C) cold sintering process (CSP) was introduced, and tunable composite pastes were prepared with geopolymer, alkali activator, and phosphor materials. High-performance yellow-emitting PF@Cu (Y-PF@Cu) and yellow/red-emitting PF@Cu (Y/R-PF@Cu) converters were prepared with densified PFs that were tightly integrated with the Cu substrate while effectively preserving the intrinsic luminescent properties of the phosphors. The optimized Y-PF@Cu converter achieves a record luminous flux (LF) of 9624.7 lm@35 W/mm², a correlated color temperature (CCT) of 5931 K, and a color rendering index (CRI) of 60.7. The further optimized Y/R–PF@Cu converter delivers excellent comprehensive performance, including a high thermal conductivity of 50.6 W/(m·K), an LF of 2652.2 lm@17.5 W/mm², a CCT of 2604 K, and a significantly improved CRI of 91.2. This work demonstrates the feasibility of CSP for fabricating color converters and provides an efficient strategy for synergistic optothermal optimization in ultrahigh-brightness laser illumination applications.