Enabling efficient near-infrared emission in lead-free double perovskite via a codoping strategy

Abstract

Metal halides show great promise as a new generation of near-infrared (NIR) light-emitting materials. Compared with other light-emitting materials, double perovskites possess structures with different dimensionalities, which can support multiple emission centers, leading to varied photoluminescence. Among various doping centers, ytterbium(III) (Yb³⁺) has attracted attention because of its unique two-energy-level structure (²F_5/2 and ²F_7/2). However, the NIR emission of Yb³⁺ remains unsatisfactory because of poor resonance energy transfer between Yb³⁺ and sensitizers. Here, effective NIR-emitting lead-free perovskites are developed by co-doping antimony(III) (Sb³⁺) and lanthanide(III) ions into Cs₂NaInCl₆. Under excitation at 318 nm, Cs₂NaInCl₆:Sb³⁺/Yb³⁺ showed a broadband NIR emission peak at 1001 nm, whereas Cs₂NaInCl₆:Sb³⁺/Nd³⁺ exhibited three NIR emission peaks at 896, 1077, and 1358 nm. The exciton dynamics of the materials were investigated. Experiments and density functional theory calculations revealed that the NIR emission of Yb³⁺ originated from a charge-transfer state (CTS) and energy transfer, whereas that of Nd³⁺ arose from resonance energy transfer. Profiting from the high-energy self-trapped exciton (STE) emission and CTS with Yb³⁺, a high photoluminescence quantum yield of 48.95% was realized. The excellent NIR luminescence performance combined with high environmental stability demonstrates the potential of these metal halides for use in night-vision technologies.