Influence of Mn2+ doping on the optical properties of Cs2AgBiCl6 double perovskite luminescent phosphors

Lead free double perovskites have emerged as a highly stable alternatives to organic–inorganic halide perovskites in recent years. In this work, we have successfully endowed weakly luminescent Cs2AgBiCl6 double perovskite with strong red luminescence by incorporating Mn2+ in their lattices. It was also observed that the intensity of red emission increased with increase in Mn2+ concentration. Electron paramagnetic resonance (EPR) and energy dispersive X ray spectroscopy manifest the presence of isolated Mn2+ ions in Cs2AgBiCl6. The obtained hyperfine coupling constant of 90 Gauss from EPR spectra also confirms the octahedral coordination of Mn2+ ions. Scanning electron micrographs of pure and Mn2+ doped Cs2AgBiCl6 exhibit octahedral particles. X-ray diffraction patterns of different concentration of Mn2+ in Cs2AgBiCl6 reveals that all samples crystallize in face centred cubic structure with Fm3-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\stackrel{-}{3}$$\end{document}m symmetry. The crystallite size and lattice strain were found to increase with increase in Mn2+ concentration. Detailed changes in structural parameters of Cs2AgBiCl6 upon Mn2+ doping evaluated using rietveld refinement of XRD spectra indicates a linear decrease in unit cell volume. Raman spectra measurements which divulges a decrease in Ag–Cl and Bi–Cl octahedral volume on introducing smaller size Mn2+ ion which leads to the overall decrease of unit cell volume. Thermal gravimetric analysis discloses that the Mn2+:Cs2AgBiCl6 double perovskites are stable upto 520 °C. This work demonstrates an easy way of tuning the photophysical properties of Cs2AgBiCl6 by transition metal doping and can widen their application prospects in optoelectronics.