Deep trap state emission in vacancy-ordered double perovskite Cs₂SnCl₆ microcrystals

Appropriately doped lead-free double perovskites (LFDPs) or vacancy-ordered double perovskites (VODPs) exhibit efficient and stable white-light emission via self-trapped excitons (STEs), and therefore hold significant potential for applications in lighting and display technologies. However, the intrinsic luminescence of the host is often disregarded when studying the doped materials because most LFDPs or VODPs possess indirect bandgaps or parity-forbidden transitions from conduction band to valence band. Here, we report a weak warm white light emission from pure Cs₂SnCl₆ microcrystals, and attribute this emission to the deep trap state according to the observations of absorption and photoluminescence (PL) spectra. The bandgap and structural characteristics of Cs₂SnCl₆ were further illustrated by analyzing the absorption, PL, Raman spectra and PL dynamics under variable pressure and temperature conditions. The emission mechanism of the deep trap levels in Cs₂SnCl₆ microcrystals and their potential impact on the STEs emission were discussed based on the spectroscopic observations.