Enhancing Luminescence in Hue-Tunable White-Light Emitting K4CdCl6:Sb3+,Mn2+ All-Inorganic Halide Perovskites: Insights from Defect Engineering and Energy Transfer

All-inorganic halide perovskites (AIHPs) have emerged as highly promising optoelectronic materials owing to their remarkable properties, such as high-optical absorption coefficients, photoluminescence efficiencies, and dopant tolerance. Here, we investigate the AIHPs K4CdCl6:Sb3+,Mn2+ that demonstrate hue-tunable white-light emission with an exceptional photoluminescence quantum yield of up to 97%. Through a detailed investigation, we reveal that efficient energy transfer from Sb3+ to Mn2+ plays a dominant role in the photoluminescence of Mn2+, instead of the conventional 4T1g → 6A1g transition of Mn2+. Thermodynamic analysis highlights the crucial role of a Cl-rich environment in obtaining the K4CdCl6 phase, while transformation from K4CdCl6 to KCdCl3 can be achieved under Cl-poor and K-poor conditions. The theoretical analysis reveals that defect Cli is more readily formed compared to defect VK, corroborating experimental findings that the K4CdCl6:Sb3+ phase is exclusively obtained when the solution contains HCl concentrations higher than 4 mol L-1. Our work provides valuable insights into the photoluminescence mechanism of Sb3+, defect engineering through heterovalent doping, and efficient energy transfer between Sb3+ and Mn2+ in K-Cd-Cl-based perovskites, which offers a new perspective for the design and development of novel AIHPs with superior optoelectronic performance.