Prospect of Hexagonal CsMg(I_1–xBr_x)₃ Alloys for Deep-Ultraviolet Light Emission

Abstract Materials for deep-ultraviolet (DUV) light emission are extremely rare, significantly limiting the development of efficient DUV light-emitting diodes. Here we report CsMg(I 1− x Br x ) 3 alloys as potential DUV light emitters. Based on rigorous first-principles hybrid functional calculations, we find that CsMgI 3 has an indirect bandgap, while CsMgBr 3 has a direct bandgap. Further, we employ a band unfolding technique for alloy supercell calculations to investigate the critical Br concentration in CsMg(I 1− x Br x ) 3 associated with the crossover from an indirect to a direct bandgap, which is found to be ∼ 0.36. Thus, CsMg(I 1− x Br x ) 3 alloys with 0.36 ⩽ x ⩽ 1 cover a wide range of direct bandgap (4.38–5.37 eV; 284–231 nm), falling well into the DUV regime. Our study will guide the development of efficient DUV light emitters.