Hot‐Pressing of Single Crystals Enables High‐Performance White‐Light Emitting Copper Halide Scintillators Toward Underwater X‐Ray Imaging

ABSTRACT Lead‐free copper halide scintillators have emerged as promising candidates for underwater x‐ray imaging; however, their performance is constrained by insufficient crystallinity when fabricated via conventional hot pressing techniques. Herein, we introduce a novel single‐crystal hot‐pressing scintillator (SCHPS) strategy to synthesize highly crystalline and phase‐pure (C 12 H 28 N) 2 CuI 3 scintillators. In sharp contrast to the conventional precursor hot‐pressing scintillators (PHPS) approach, the SCHPS exhibits ultra‐broadband emission (FWHM > 280 nm) originating from dual self‐trapped excitons (STEs). Benefiting from the substantially suppressed nonradiative recombination, a near‐unity photoluminescence quantum yield of 98.42% is achieved, markedly surpassing that of its PHPS counterpart (88.59%). As a result, the SCHPS demonstrates an outstanding scintillation performance, including a high light yield of 43115 ph MeV −1 , a superior spatial resolution of 13.8 lp mm −1 , and an ultralow detection limit of 42 nGy air s −1 , which outperforms not only those PHPS counterparts (11267 ph MeV −1 , 7.5 lp mm −1 , 682 nGy air s −1 ) but also most reported lead‐free scintillators. Moreover, the SCHPS shows excellent environmental, thermal, and radiation stability, ensuring reliable operation under harsh conditions. This work provides a scalable and effective route toward a high‐performance, eco‐friendly scintillator, paving the way for low‐dose, high‐resolution underwater x‐ray imaging applications.