Thermal-Pressure Induced Phase Transition for Enhanced K2SiF6:Mn4+ Luminescence toward Efficient LEDs

Modulating phase transitions in fluoride phosphors is essential for developing high-performance luminescent materials, but conventional extreme-condition methods often cause structural damage and efficiency degradation. This study proposes a thermal-pressure coupling strategy to achieve reversible Fm-3m to P6 3 mc phase transformation in K 2 SiF 6 :Mn 4+ under mild conditions. The distorted [MnF 6 ] 2- octahedra in the P6 3 mc enhance d-orbital hybridization, significantly reinforcing the zero-phonon line (ZPL). Consequently, luminescence intensity increases by 1.54-fold, external quantum efficiency (EQE) improves by 29.5%, and 90% intensity is retained at 200 °C. LED devices employing P6 3 mc phosphor sheets achieve a color rendering index (Ra) of 84.4 and luminous efficacy of 138.2   lm/W while maintaining stable Ra and correlated color temperature (CCT) across 20 - 300   mA driving currents. Notably, device temperature at 200   mA operation is reduced by 30% compared to conventional methods. This work establishes an effective approach for optimizing fluoride phosphors and advancing high-performance lighting technologies.