Thermochromic Phosphors Based on One‐Dimensional Ionic Copper‐Iodine Chains Showing Solid‐State Photoluminescence Efficiency Exceeding 99 %

Abstract Thermochromic phosphors are intriguing materials for realizing thermochromic behaviors of light‐emitting diodes. Here a highly luminescent and stable thermochromic phosphor based on one‐dimensional Cu 4 I 6 (4‐dimethylamino‐1‐ethylpyridinium) 2 is reported. This unique ionic copper‐iodine chain‐based hybrid exhibits near‐unity photoluminescence efficiency owing to the through‐space charge‐transfer character of relevant electronic transitions. More importantly, an alternative mechanism of thermochromic phosphorescence was unraveled, supported by a first principles simulation of concerted copper atom migration in the copper‐iodine chain. Furthermore, we successfully fabricate a bright thermochromic light‐emitting diode using this Cu 4 I 6 (4‐dimethylamino‐1‐ethylpyridinium) 2 thermochromic phosphor. Our reported flexible ionic copper‐iodine chain‐based thermochromic luminescent material represents a new type of cost‐effective functional phosphor.