Low-dimensional metal halides are promising luminescent materials with efficient self-trapped exciton (STE) emission at room temperature; however, the understanding of optical behaviors and trends is still limited due to the complex excited-state energy landscape. In this Letter, first-principles calculations reveal multiple STEs in 1D CsCu₂X₃ (X = Cl, Br, I), which are bright visible-light-emitting materials. Three types of STEs with distinct structures are identified, and their relative stabilities are halogen-dependent despite the same crystal structure shared by all three halides. The emission energy of each type of STE is found to be blue-shifted from CsCu₂Cl₃ to CsCu₂Br₃ to CsCu₂I₃; the experimentally observed red shift of the emission peak is not due to the electronegativity trend of halogen atoms but originates from the emissions from three different types of STEs. The emitting STE is the lowest-energy STE in CsCu₂Br₃ and CsCu₂I₃ but a metastable one in CsCu₂Cl₃.

中文翻译：

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发光一维卤化物中多个自陷激子的发射趋势

低维金属卤化物是有前途的发光材料，在室温下具有有效的自陷激子（STE）发射。然而，由于复杂的激发态能量格局，对光学行为和趋势的理解仍然受到限制。在这封信中，第一性原理计算揭示了1D CsCu ₂ X ₃（X = Cl，Br，I）中的多个STE ，它们是明亮的可见光发射材料。鉴定出三种具有不同结构的STE，尽管三个卤化物具有相同的晶体结构，但它们的相对稳定性仍取决于卤素。发现每种类型的STE的发射能量都从CsCu ₂ Cl ₃蓝移到CsCu ₂ Br ₃到CsCu ₂ I ₃ ; 实验观察到的发射峰红移不是由于卤素原子的电负性趋势，而是源于三种不同类型STE的发射。发射的STE是CsCu ₂ Br ₃和CsCu ₂ I _3中能量最低的STE，但在CsCu ₂ Cl _3中是亚稳态的。