Blue-light-excited narrowing red photoluminescence in lead-free double perovskite Cs2−xKxAg0.6Na0.4In0.8Bi0.2Cl6−xBrx with cryogenic effects

With the addition of Na+ and Bi3+ to the lead-free double perovskite Cs2AgInCl6, high photoluminescence quantum yields (PLQYs) can be achieved, making Cs2AgInCl6 more promising; however, it is still difficult to achieve blue-light-excited narrowing emission. In this study, Cs2−xKxAg0.6Na0.4In0.8Bi0.2Cl6−xBrx was developed with K+ and Br−, realizing blue-light-excited narrowing red photoluminescence under cryogenic temperatures. The transitional non-localized donor energy level was formed by KBr addition, changing the exciton excitation and transition process. With the increase in the x value, Cs2−xKxAg0.6Na0.4In0.8Bi0.2Cl6−xBrx can be excited by blue light at 150 K and emit a narrowing red light. When 1 : 1 KBr was added, the full width at half maximum (FWHM) of Cs2−xKxAg0.6Na0.4In0.8Bi0.2Cl6−xBrx red light emission was further narrowed to only 73 nm, when excited by 467 nm blue light at 10 K. This study will stimulate further research on lead-free double perovskites in the field of display technologies.