Unity photoluminescence quantum yield and superior stability achieved in lanthanide-doped lead-free Cs2NaInCl6 double perovskites for highly efficient light emitting diodes

Achieving highly fluorescent and stable perovskite materials has remained a significant challenge in recent years. While several works have reported high photoluminescence and moderate stability in various perovskite systems, this study reports for the first time a photoluminescence quantum yield of 100% with exceptional stability through lanthanide doping of the Cs₂Na_0.9Ag_0.1In_0.95Bi_0.05Cl₆ double perovskite. The lanthanide doping process resulted in a strong and efficient broadband self-trapped exciton (STE) emission. Remarkably, the Yb³⁺-doped Cs₂Na_0.9Ag_0.1In_0.95Bi_0.05Cl₆, and Er³⁺-doped Cs₂Na_0.9Ag_0.1In_0.95Bi_0.05Cl₆ sample exhibited a warm-white light emission with near-unity PLQY of 99.8% and 100%, respectively, while the pristine sample delivered a 2.3% PLQY only. Structural characterization confirmed the high purity of the samples with near-stoichiometric composition of the materials, with no detectable evidence for secondary phases. The samples maintained their superior emission properties over extended periods of testing. When assembled into a white-light-emitting diode (WLED), the materials generated a strong broadband luminescence (EL) with an excellent color rendering index (CRI) of 91.3 and a correlated color temperature (CCT) of 2826 K, achieving a highly efficient and stable performance. This study highlights that lead-free double perovskites can be reliable and highly efficient materials for commercial LED devices, paving the way for a more sustainable and efficient lighting solution.