An Er3+-Doped Cs2NaScCl6 Lead-Free Double Perovskite with Efficient Broadband Visible to Near-Infrared Emission and Multimodal Upconversion Luminescence

Lanthanide ions are widely used as dopants for halide perovskites for their broad energy level coverage from the visible to near-infrared (NIR) range. In this work, Cs2NaScCl6:Er3+ was synthesized by an improved solid-state reaction method, which showed effective NIR emission under ultraviolet excitation. Through calculations based on density functional theory and Bader charge analysis, it is shown that [ErCl6]3- octahedra show a strong localization effect in the Cs2NaScCl6:Er3+ lattice, which is conducive to the charge transfer process of Cl-Er3+, and charge transfer sensitization is responsible for the efficient visible to NIR luminescence of Er3+, where the NIR emission around λem = 1540 nm originated from the Er3+:4I13/2 → 4I15/2 transition with an ultrahigh photoluminescence quantum yield that reached ∼28.3%. Notably, Cs2NaScCl6:Er3+ also exhibited bright upconversion luminescence of green light (at 540 nm) under excitation by a variety of NIR laser diodes (808, 980, and 1550 nm) via self-sensitization processes.