Synthesis and Near-Infrared Emission of Yb-Doped Cs₂AgInCl₆ Double Perovskite Microcrystals and Nanocrystals

Cs₂AgInCl₆ double perovskite (DP) is a direct band gap, stable, and environmentally benign material with a three-dimensional perovskite structure. However, the band gap (?3.3 eV) is too wide for optoelectronic applications in the near-infrared (NIR) region. To achieve optical functionality in the NIR window, we have doped Yb³⁺ in both microcrystals and colloidal nanocrystals of Cs₂AgInCl₆ DPs. Our Yb-doped Cs₂AgInCl₆ DP microcrystals and nanocrystals show NIR emission at ?994 nm (1.24 eV), whereas the band gap of the hosts is in the UV region. Therefore, the Yb-emission does not suffer from self-absorption. The microcrystals exhibit a single-exponential decay with 2.7 ms long lifetime corresponding to ²F_5/2 → ²F_7/2 transition of Yb³⁺ f electrons. The nanocrystals show biexponential decay (3 ms and 749 μs), probably because of the proximity of Yb to the surface of nanocrystals. Interestingly, NIR emission and perovskite structure of samples are stable for >3 months in ambient conditions for future optoelectronic applications.