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 A2SnCl6 samples (A = K, Rb, and Cs) in cubic symmetry. The double perovskite (K2PtCl6) 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 A2SnCl6 increased with an increase in the size of the alkali metal ion. Eu3+ and Tb3+ (5 mol‐%) doped A2SnCl6 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. Yb3+/Er3+ co‐doped A2SnCl6 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 A2SnCl6 samples are suitable in applications involving Near‐UV and Near‐IR excitations. Rare‐earth doped air‐stable tin‐based double perovskites were prepared by a simple wet chemical method. The samples were demonstrated as excellent red, green, and upconversion luminescent materials.