Near-infrared emission, energy transfer, and mechanisms of Mn2+ and Cr3+ Co-doped lead-free Cs2AgInCl6 double perovskites

Doping metal ions into lead halide perovskites is a promising method to regulate their structural stability and optical properties. In this work, Mn2+/Cr3+ codoped Cs2AgInCl6 double perovskite single crystals (DPSCs) were synthesized using a programmed cooling hydrothermal method. Upon light excitation at 350 nm, the co-doped CAIC:Mn2+,Cr3+ DPSC samples exhibit two photoluminescence (PL) bands with a wide emission switch ranging from orange to NIR. The photoluminescence quantum yield (PLQY) of the NIR emission can be increased to 49.30% by varying the concentration of dopant ions. The high PLQY is attributed to the energy transfer (ET) from selftrapped excitons (STEs) to Mn2+ and Cr3+ dopant ions. The presence of ET was confirmed by analyzing time-resolved photoluminescence (TRPL) and temperature-dependent PL. Moreover, we determine the ET pathway from STE to Mn2+ ions at low temperatures using temperature-dependent PL spectra. The emission colors of CAIC:Mn2+,Cr3+ DPSCs can be continuously tuned from yellow to orange by controlling temperature. This ET-induced dual emission seems to be governed by thermal activation. A model is proposed to explain the efficient ET processes from the host DPSCs to Mn2+ and Cr3+ dopants, as well as possible ET processes from Mn2+ to Cr3+ ion centers.