Prospect of Hexagonal CsMg(I1-x Br 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. In this Letter, 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.