The prominent thermal quenching (TQ) effect of organic-inorganic metal halides limits their applications for lighting and imaging. Herein, we report an organo-metal halide scintillator (TTPhP)(2)MnCl4 (TTPhP+ = tetraphenylphosphonium cation), which exhibits a weak TQ effect up to 200 degrees C under ultraviolet-visible light (efficiency loss of 5.5%) and X-ray radiation (efficiency loss of 37%). The light yield of the (TTPhP)(2)MnCl4 scintillator (37 000 photons MeV-1 at 200 degrees C) under X-ray radiation is >2 times that of the commercial scintillator LuAG:Ce (15 000 photons MeV-1 at 200 degrees C). The microscopic mechanism of the weak TQ effect is demonstrated to be the scintillator having the ability to compensate for the emission losses from trapped charges and the large Mn-Mn distance (10.233 angstrom) suppressing nonradiative recombination at high temperatures. We further demonstrate the applications of (TTPhP)(2)MnCl4 as high-power white-light-emitting diodes operated at currents of