Energy Upconversion in Rare‐Earth‐Doped Tin‐Based Double Halo Perovskites, A2SnCl6 (A = K, Rb, and Cs)

A wet chemical methodology has been developed to synthesize the undoped and rare‐earth‐doped A 2 SnCl 6 samples (A = K, Rb, and Cs) in cubic symmetry. The double perovskite (K 2 PtCl 6 ) structure of these samples was confirmed from their PXRD, SAED, FTIR, and Raman spectra. The crystallites showed octahedral morphology in the FESEM and HRTEM images. The optical band gap of undoped A 2 SnCl 6 increased with an increase in the size of the alkali metal ion. Eu 3+ and Tb 3+ (5 mol‐%) doped A 2 SnCl 6 showed intense red‐orange and green emission when excited at 380 nm. The various radiative properties of the emission bands were analyzed using the Judd‐Ofelt theory. Yb 3+ /Er 3+ co‐doped A 2 SnCl 6 showed multicolor upconversion under 980 nm excitation, and the emission region varied with the alkali metal. These samples show bright emission with optimum CCT and CIE coordinates, indicating that the rare‐earth‐doped A 2 SnCl 6 samples are suitable in applications involving Near‐UV and Near‐IR excitations.