Surface Vibration‐Mediated and Multiphonon Relaxation‐Assisted Antithermal‐Quenching Shortwave Infrared Emission in Ho‐Based Double Perovskite With Long Lifetime

Abstract Thermal quenching generally predominates in Er 3+ 1540 nm luminescence quenching at elevated temperatures, due to intensified lattice vibration and efficient overtone vibrational relaxation by O─H stretch. This issue impedes practical device applications of shortwave infrared Er‐doped phosphors. Herein, with the mediation of surface vibrational phonons, anti‐thermal quenching of Er 3+ 1540 nm emission is reported in (220)‐dominated Er 3+ ‐doped Cs 2 NaHoCl 6 double perovskite. The downshifting emissions can be boosted with rising temperatures from 303 to 543 K, reaching 225%@483 K of the initial intensity at 303 K, accompanied with a long lifetime of 33.02 ms at 483 K. By combining temperature‐dependent in situ Raman and Fourier transform infrared spectroscopies with the excited‐state dynamics results, the coordination role of water molecules is verified, serving as promoters instead of quenchers on the (220) facet at high temperatures. Furthermore, efficient energy transfer from Ho 3+ to Er 3+ enables intense 1540 nm emission with a photoluminescence quantum yield of 78.1% under 450 nm excitation. Finally, a compact thermally stable phosphor‐converted light‐emitting diode (LED) is designed as a narrowband shortwave infrared light source with a blue LED chip. This work pushes the improved understanding of achieving thermal‐enhanced Er 3+ luminescence for potential broad applications.