Achieving high brightness and thermally stable far-red luminescence via ultrathin phosphor–glass composite engineering

Far-red (FR) emission (>700 nm) with high efficiency and excellent thermal stability is in great demand for solid-state lighting applications in health illumination. However, currently used FR materials often face challenges such as complex synthesis, low efficiency, and thermal instability. In this study, we present a highly efficient and thermally stable far-red phosphor, Mn⁴⁺-activated La_1−xCa_xAlO_3−yF_y, with a dominant emission wavelength of 731 nm. Based on this, an ultrathin phosphor–glass composite (PGC), with a FR luminescence quantum yield of 68.2%, is prepared using a tape-casting process combined with a low-temperature cofiring technique. The impact of ionic substitution on the crystal structure and luminescence properties is examined to establish the optimal doping conditions. Interestingly, we observed that the prepared PGC exhibits temperature-dependent luminescence distinct from that of FR phosphor. The luminescence lifetime for the PGC is measured to be nearly 3.576 ms, representing a 28.4% decrease compared to that of the pure phosphor. Ultimately, light-emitting diodes (LEDs) are fabricated by combining the PGC with a violet chip, and their electroluminescence (EL) properties are strongly dependent on the configuration of the PGC composite. This research offers a straightforward and versatile method for producing ultrathin far-red PGCs that hold promise for diverse photonic applications.