Enhanced Optical Performance of Lead- Free Cs₂AgInCl₆ Perovskites via Potassium Substitution for White LEDs

As an alternative to toxic lead halide perovskites, inorganic halide double perovskites (DPs) of the form Cs₂AgInCl₆ have emerged as a robust luminescent material for greener lighting technologies. The direct bandgap nature and superior long-term stability compared to their lead counterparts further attract their commercial implications. However, their light emission efficiency is still lower than lead-based perovskites. Herein, the addition of K⁺ at the Ag⁺ site of Cs₂AgInCl₆ crystals imparts enhancement in photoluminescence (PL) properties that agree with the theoretical calculations. As prepared samples exhibit a broadband PL emission profile (405–820 nm at λ_max ~ 629 nm) with a wide bandgap (~ 3.3 eV) and a large Stokes shift.  Notably,  the photoluminescence quantum yield of Cs₂AgInCl₆ increases by almost eight folds on increasing the content of K+ to 20 mol% and retains its luminesce intensity by ~ 85% over 180 days, confirming its excellent moisture stability, owing to the better passivation of the non-radiative trap states. The combination of blue-emitting CsPbBr₃ and broadband DPs as color conversion layers results in a characteristic warm white with a correlated color temperature of 3878 K, color rendering index of 85, and CIE coordinates of (0.387, 0.385).