Abstract The development of advanced high-power-density laser-driven light source requires durable and color-tunable inorganic phosphor-in-glass film composites as color converter. One challenge remains for the phosphor-in-glass film is the thermal erosion and degradation of phosphor, as harsh condition or long duration time is required to densify the film for conventional sintering. Here we develop a rapid thermal annealing technique that achieves high film densification (porosity 10 kW) infrared irradiation. As demonstrated by high-resolution electron microscopy observation, a trivial interfacial reaction occurs, leading to almost intact phosphor particles and thus restrained luminous loss. For instance, the red-emitting Sr0.8Ca0.2AlSiN3:Eu2+ exhibits a record internal quantum efficiency of 91.2% in the processed film and achieves a luminous flux of 2379 lm and efficacy of 140 lm W−1 after fabricating a phosphor wheel. This method reduces energy consumption, enables high-throughput screening, and offers material universality and design flexibility, paving the way for new opto-functional materials and applications.