Rational design of a lead-free Cs2Na0.4Ag0.6In0.9Bi0.1Cl6:0.15Mn2+ double perovskite for enhancing the colour rendition index of UV-pumped W-LEDs

Abstract

Compared with lead halide perovskites, double perovskites (DPs) have drawn much attention because of their intriguing optoelectronic qualities, environmental stability, and non-toxicity. Herein, we systematically designed a Cs₂Na_0.4Ag_0.6In_0.9Bi_0.1Cl₆:_0.15Mn²⁺ double perovskite by alloying Ag⁺ and Bi³⁺ at the Na⁺ and In³⁺ sites in the host lattice. Ag⁺ broke the parity forbidden transition of Cs₂NaInCl₆, and Bi³⁺ significantly broadened the emission spectra from 450–700 nm. Doping of Mn²⁺ further reduced the defect density and enhanced the radiative recombination. Broad emission owing to the ⁴T₁ → ⁶A₁ transition of Mn²⁺ ions was observed at 665 nm. Upon doping, the sample exhibited a PLQY of 44.9%. Temperature-dependent emission characteristics of the synthesized double perovskite were also studied. Even at a high temperature of 100 °C, the emission intensity was reduced only by 53%, and the material possessed a high activation energy of 0.46 eV. The optimised sample was physically blended with blue emitting BaMgAl₁₀O₁₇:Eu²⁺ to obtain complete spectral color coverage in visible light when excited with a 365 nm UV light source. CIE coordinates of (0.37, 0.39), CCT of 4457.53 K and CRI of 87.4 were obtained for the optimised sample. Cs₂Na_0.4Ag_0.6In_0.9Bi_0.1Cl₆:0.15Mn²⁺ was found to be a promising luminescent material for enhancing the color rendition index of UV-pumped white LEDs. The as-prepared double perovskite is a multifunctional material that can be used for WLEDs, photodetectors and display screens.