Understanding the Limitations of Chloride Double Perovskites as Hosts for Stable Cr³⁺ Luminescence

Chloride double perovskite, a promising frontier for cutting-edge light-conversion research worldwide, is harnessed by incorporating transition-metal ions and advanced crystal engineering. Despite the significant progress in transition-metal-ion-doped chloride double perovskite, challenges such as insufficient thermal stability remain substantial barriers to their practical applications. Additionally, the quenching mechanisms in these materials are not fully understood. This study presents a proof of concept by synthesizing Cr-doped Cs₂AgInCl₆ using a sintering-free ball-mill mechanochemistry method. The resulting Cs₂AgIn_1-<i>x</i>Cr_<i>x</i>Cl₆ exhibits an emission spectrum ranging from 850 to 1350 nm, bridging the gap between near-infrared and shortwave infrared regions. We thoroughly investigate the changes in the absorption coefficient, thermal quenching, and thermal-activated energy transfer using temperature-dependent photoluminescence and time-resolved spectra. Moreover, we utilize the photocurrent excitation (PCE) spectra to elucidate the quenching process and the associated energy states. Our findings reveal an unexpected luminescence quenching in the materials in the room temperature region, which is attributed to interactions between the Cr-excited states and self-trapped exciton (STE) states. This study explores how PCE can provide insights into the relationship between band structure and quenching dynamics, offering a perspective on the challenges of achieving efficient and thermally stable Cr³⁺ luminescence in chloride double perovskites.