Dual-Band Emission from Intrinsic and Extrinsic Self-Trapped Excitons in a Zero-Dimensional Copper Halide Cs<sub>3</sub>Cu<sub>2</sub>Br<sub>5</sub>
Zengshan Xing, Memoona Qammar, Aleksandr A. Sergeev, Zhicong Zhou, Pai Geng, Christopher C. S. Chan, Jonathan E. Halpert, Kam Sing Wong
Abstract
Zero-dimensional Cs 3 Cu 2 X 5 (X=Cl, Br, or I), the intensively studied light-emitting materials, generally exhibit single-band emissions from intrinsic self-trapped excitons (STEs), while defect-induced (extrinsic) STEs were considered nonemissive. Herein, we observed a dual-band emission from intrinsic and extrinsic STEs for Cs 3 Cu 2 Br 5 at low temperature, and their emission mechanisms are elucidated. The intrinsic and extrinsic STEs are trapped from different initial states, with remarkably large trapping depths (>900 meV) evaluated at 50 K, indicating their negligible detrapping rates. In addition, the stronger electron–phonon coupling for extrinsic STE could shift the extrinsic STE band to intersect with the ground state in the configuration coordinate diagram, acting as a nonradiative pathway. This explains the vanishment of extrinsic STE emission at room temperature and the reported low photoluminescence quantum yields (<50%). With growing efforts to obtain multiple-band emitters, our insights into the emission mechanisms of intrinsic and extrinsic STEs provide valuable bases for further material engineering.