Efficient and Stable 1550 nm Near-Infrared Emission in Er³⁺-Bi³⁺ Codoped Cs₂SnCl₆ Microcrystals

Although all-inorganic lead-free metal halides exhibit considerable potential for optoelectronic applications, achieving high-performance 1540 nm near-infrared (NIR) emission in these systems is a significant challenge. Herein, we demonstrate a codoping strategy utilizing Bi³⁺ and Er³⁺ ions to enable enhanced 1540 nm NIR luminescence in vacancy-ordered Cs₂SnCl₆ double perovskite phosphors compatible with commercial near-ultraviolet LED excitation sources. By leveraging the spin-orbit permitted ¹S₀ → ³P₁ transition of Bi³⁺ as an effective sensitization pathway, we successfully activated the NIR emission band corresponding to the Er^{3+ 4}I_13/2-⁴I_15/2 electronic transition. The optimized phosphor achieved a notable quantum efficiency of 10.3% for the Er³⁺-derived NIR emission. Moreover, the Er³⁺ 1540 nm emission exhibits excellent stability over six months, retaining 92.5% of their initial PL intensity. Finally, we fabricated NIR phosphor-converted LEDs based on Bi³⁺- and Er³⁺-codoped Cs₂SnCl₆ and successfully applied them to night imaging. This work expands the application potential of the Cs₂SnCl₆ matrix, paving the way for its development as a near-infrared phosphor for advanced optoelectronic applications.