2D Cuprous Halide Scintillator with Dual Excitation‐Dependent and Thermochromic Luminescence toward Multifunctional Optoelectronic Applications

Excitation- and temperature-dependent multicolor luminescent materials are valuable in advanced optoelectronic devices while they haven't been realized in 2D metal halides owing to the restrictions of Kasha's rule. Herein, we reported a novel 2D lead-free halide of (AMP)₂Cu₂Br₄ (AMP = N-aminomorpholine) through structural engineering, in which the [Cu₂Br₄]^2- layer is composed of corner- and edge-shared [CuBr₄] tetrahedron. The non-centrosymmetric structure enables (AMP)₂Cu₂Br₄ to exhibit an impressive second-harmonic generation signal of ≈0.8 times that of KH₂PO₄ (KDP). Remarkably, (AMP)₂Cu₂Br₄ possesses two independent self-trapped exciton-emitting states under different excitation energies, which display multicolor luminescence outputs from blue, white, to orange with near-unity photoluminescence quantum yields (PLQYs). Additionally, the luminescence can be regulated in a wide temperature range of 300-400 K due to reversible energy transfer between two emitting bands, acting as a luminescence ratio thermometer with a ultrahigh relative thermal sensitivity of 56.755% K^-1. High PLQY and large Stokes shift further endow (AMP)₂Cu₂Br₄ strong radioluminescence with an ultrahigh light yield of 92,400 photons·MeV^-1, low detection limit of 121 nGy_air·s^-1 and a short afterglow of 0.41 ms. The abundant photophysical properties highlight the multiple optoelectronic applications of 2D cuprous halide in white light-emitting, laser technology, flexible temperature sensors, and X-ray imaging.