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

Abstract 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) ₂ Cu ₂ Br ₄ (AMP = N‐aminomorpholine) through structural engineering, in which the [Cu ₂ Br ₄ ] ²⁻ layer is composed of corner‐ and edge‐shared [CuBr ₄ ] tetrahedron. The non‐centrosymmetric structure enables (AMP) ₂ Cu ₂ Br ₄ to exhibit an impressive second‐harmonic generation signal of ≈0.8 times that of KH ₂ PO ₄ (KDP). Remarkably, (AMP) ₂ Cu ₂ Br ₄ 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) ₂ Cu ₂ Br ₄ strong radioluminescence with an ultrahigh light yield of 92,400 photons·MeV ⁻¹ , low detection limit of 121 n Gy _air ·s ⁻¹ and a short afterglow of 0.41 m s. 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.