Spectral Modulation of Lead-Free Cs ₂ NaInCl ₆ Double Perovskites via Sb ³⁺ /Mn ²⁺ Codoping and Bromide Ion Substitution for Multifunctional Applications

The toxicity, ambient instability, ultraviolet (UV) light-induced degradation, and poor thermal stability of lead-based halide perovskites (LHPs) limit their technological applications. Double halide perovskites (DPs) have emerged as a viable alternative to LHPs because of their exceptional stability and low toxicity. We have studied the effect of Sb3+/Mn2+ and Br– ions substitution on the optical properties of Cs2NaInCl6 DPs. The Sb3+ doping produces intense blue emission under long-wavelength UV light excitation by relaxing the parity-forbidden transition in Cs2NaInCl6. Additional codoping of Mn2+ generates a red emission peak at 615 nm, caused by the 4T1 → 6A1 transition. The Br– ion substitution shifts the blue emission peak from 445 to 472 nm due to enhanced crystal field around Sb3+ ions. Thus, exhibiting a pure white light emission with CIE coordinates (0.3658, 0.3339) through a single luminophore, along with a photoluminescence quantum yield (PLQY) of 62.3%, and a high color rendering index of 87. The as-synthesized DPs show excellent thermal, structural, UV, and storage stability. The synthesized material was employed on a UV-LED to demonstrate a stable single-component white light-emitting diode. Furthermore, since the synthesized DP exhibits a change in emission color with excitation wavelengths, it was successfully employed for demonstrating application in multistimuli luminescence anticounterfeiting.