Boosting Near-Infrared Luminescence of Lanthanide in Cs AgBiCl Double Perovskites via Breakdown of the Local Site Symmetry.

Currently, lanthanide (Ln )-doped near-infrared (NIR)-emitting double perovskites (DPs) suffer from low photoluminescence quantum yield (PLQY). Herein, we develop a new class of NIR-emitting DPs based on Ln -doped Cs (Na/Ag)BiCl . Benefiting from the Na -induced breakdown of local site symmetry in the Cs AgBiCl DPs, effective NIR emissions of Ln are realized through Bi sensitization. Specifically, 7.3-fold and 362.9-fold enhanced NIR emissions of Yb and Er are achieved in Cs Ag Na BiCl DPs relative to those in Na-free Cs AgBiCl counterparts, respectively. The optimal absolute NIR PLQYs for Yb and Er in Cs Ag Na BiCl DPs are determined to be 19.0 % and 4.3 %, respectively. Raman spectroscopy and first-principles density functional theory calculations verify the sublattice distortion in Cs (Na/Ag)BiCl DPs via Na doping. These findings provide fundamental insights into the design of efficient NIR-emitting Ln -doped DPs for versatile optoelectronic applications.