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

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 Cu₄ I₆ (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 Cu₄ I₆ (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.