Defects, (Sb, Er) Dopant Interactions, and Band Gap Engineering in Cs₂AgInCl₆ Double Perovskites

In this work, the double perovskite Cs₂AgInCl₆ and its Sb³⁺- and Er³⁺-doped powders have been studied to understand how defects and dopants influence optical characteristics. Incomplete AgCl incorporation creates V_k and F centers, as well as defect-related In⁺ and Ag^- states, leading to photoluminescence (PL) bands at approximately 440, 610, and 630 nm, with the dominant peak at 630 nm. Cs₂AgInCl₆ exhibits a direct band gap of 4.29 eV, which is reduced by chlorine vacancies. Sb³⁺ doping results in weak PL, whereas Er³⁺ introduces visible-near-infrared (Vis-NIR) emission (525-1520 nm). Density functional theory (DFT) supports these observations, predicting a direct 4.42 eV gap for Cs₂AgInCl₆, narrowed by chlorine cation defects (3.3-3.9 eV), Sb³⁺ (3.41 eV), and Er³⁺ (3.97 eV) incorporation. Overall, the findings suggest that emission efficiency is limited by complex defect-dopant interactions; however, band gap tuning through doping indicates potential applications for wide-range photodetection.