Conversion of the non-luminous lead-free inorganic halide perovskite variant CsNiCl3 nanocrystals into photoluminescent materials by Cu+ and In3+ doping

All-inorganic CsPbX3 (X = Cl, Br, I) perovskite nanocrystals (NCs) as promising optoelectronic materials have attracted tremendous research interest because of their intense photoluminescence, broad absorption, and tunable bandgap. Even with these fascinating characteristics, their practical applications are still suffering from the presence of toxic lead and inadequate stability. Herein, we successfully synthesize CsNiCl3 NCs in a comparatively low-temperature route for the first time. By Cu+ and In3+ doping, CsNiCl3 NCs can be converted from non-luminous into photoluminescent materials. The broad green fluorescence emission at 530 nm of CsNiCl3 NCs with high luminescence intensity and quantum yield (42.2%) is achieved. Broad band emission with a large Stokes shift can be attributed to the recombination process of self-trapped excitons (STEs). The transient fluorescence spectra of the doped CsNiCl3 NCs show two ultra-long lifetimes of about 50 and 120 µs, which are assigned to the STE recombination, indicating that the nonradiative recombination process is suppressed after doping. Our research provides an innovative method for developing environmentally friendly lead-free metal halide NCs.