All‐Inorganic Rare‐Earth‐Based Double Perovskite Nanocrystals with Near‐Infrared Emission

Abstract Lead‐free halide perovskite nanocrystals (NCs) with the unique optical properties are of interest for broad applications. There are a few studies on near‐infrared (NIR) emission in perovskite NCs. Here, all‐inorganic rare‐earth‐based Cs 2 NaEr 1− x B x Cl 6 (B: In, Sb, or Bi; x = 0, 0.13, and 0.5) double perovskite (DP) NCs have been successfully sythesized. The Cs 2 NaErCl 6 NCs show good air stability and emit a sharp NIR photoluminescence (PL) at telecommunication wavelength of 1543 nm, originating from 4 I 13/2 → 4 I 15/2 transition of the Er 3+ , and its average lifetime is 35.7 µs. Especially for Cs 2 NaEr 0.5 Sb 0.5 Cl 6 NCs, NIR PL can be enhanced 23‐fold with the lifetime being 119.1 µs. Moreover, femtosecond transient absorption measurements prove that a long‐lifetime trap state promotes NIR emitting in the mixed Sb/Er DP NCs.