Unraveling the Photoluminescent Properties of Sb-Doped Cd-Based Inorganic Halides: A First-Principles Study

Sb-doped Cd-based inorganic halides, with varying connections of CdCl₆ octahedra ranging from 0D to 3D, exhibit a variety of photoluminescent properties. Single-band emission is observed in Sb-doped Rb₄CdCl₆ (0D) and Cs₂CdCl₄ (2D), while dual-band emission is seen in Sb-doped RbCdCl₃ (1D) and CsCdCl₃ (3D). Density-functional-based first-principles calculations were conducted. The results reveal that cation vacancies, acting as charge compensators, influence the luminescence properties of dopant centers. In CsCdCl₃, the local cation vacancy V_Cd^″ for Sb³⁺ at the Cd²⁺ site ([Sb□Cl₉]^6-) significantly modifies the photoluminescence property, accounting for the observed dual-band emission alongside the nonlocal compensation case. This effect is insignificant in Sb-doped Rb₄CdCl₆, RbCdCl₃, and Cs₂CdCl₄, due to the large distances or high formation energies of Cd vacancies in these hosts. However, in Sb-doped RbCdCl₃, two different potential energy minima, one that involves typical structure relaxation and the other that is off-center, lead to the observed dual-band emission. Furthermore, the shift of the charge transition level illustrates the different temperature dependences of the dual-band emission caused by the charge-compensating point defects. These insights not only enhance our understanding of luminescent materials based on halides containing ns² dopants but also provide valuable guidance for the design and optimization of luminescent materials.