Rational design of a lead-free CsNaAgInBiCl:Mn double perovskite for enhancing the colour rendition index of UV-pumped W-LEDs.

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 CsNaAgInBiCl:Mn double perovskite by alloying Ag and Bi at the Na and In sites in the host lattice. Ag broke the parity forbidden transition of CsNaInCl, and Bi significantly broadened the emission spectra from 450-700 nm. Doping of Mn further reduced the defect density and enhanced the radiative recombination. Broad emission owing to the T → A transition of Mn 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 BaMgAlO:Eu 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. CsNaAgInBiCl:0.15Mn 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.