Tuning the optical properties of Cs2SnCl6:Bi and Cs2SnCl6:Sb lead-free perovskites via post-annealing for white LEDs

Lead halide perovskites show outstanding optoelectronic properties, however, they are toxic, and their stability is poor. Therefore, this paper focuses on how to tune the visible emission of Cs2SnCl6:Bi and Cs2SnCl6:Sb lead-free perovskites phosphors by post-annealing treatment. The photoluminescence peaks Cs2SnCl6:Bi show obvious red shift from 455 to 483 nm by 300 °C post-annealing, could lead to the increase in the concentration of chlorine vacancies, and the PLQY holding up to 50.8%. Cs2SnCl6:Sb are reported still as orange-red emissive phosphors by 300 °C post-annealing, showed a peak around 630 nm, the PLQY increased from 19.8% to 41.6%, compared with as-synthesized. Because of their inorganic nature, our phosphors also showed excellent thermal stability and can withstand exposure to water. White LEDs are constructed using Cs2SnCl6:Sb (orange-red-emitting) and Cs2SnCl6:Bi (cyan-emitting) active materials in combination with commercial UV LED chips. The resulting emission color can be described by Commission Internationale de I’Eclairage (CIE) coordinates expressed as (0.347, 0.345). These two compounds contain the same anion, which helps to eliminate cross-contamination and ion-exchange during their preparation and processing. Results obtained in this wok provide foundation for using post-annealing technique for optimization of lead-free perovskite emitters.