Individual Particle-Level Picture of Charge Carrier Recombination in Bi-Doped CsPbBr < inf > 3 < /inf > Nanocrystals

Abstract

Doping is an important strategy for both introducing new properties and modifying the intrinsic properties of a semiconductor. In this work, we investigate Bi-doped CsPbBr3 nanocrystals (NCs), which are less toxic and weakly luminescent compared to the parent system, employing ultrafast pump-probe and fluorescence upconversion techniques and single-particle-based fluorescence correlation spectroscopy technique to obtain individual particle-level understanding of the charge carrier recombination pathways and dynamics in these systems. The results reveal the heterogeneity of the system in terms of photoluminescence (PL) brightness/efficiency of the individual NCs. Three different types of NCs (bright, dim, and dark) have been identified in doped samples that arise from the difference in the extent of doping and consequent variation in the density of Bi-induced states; the latter act as traps for the electrons and assist in nonradiative recombination of charge carriers. An ultrafast trapping process (∼2 to 6 ps), which renders a majority of the Bi-doped NCs into dark ones, is found to be the primary cause of weak PL of the doped systems. The individual particle-level information obtained in this work using a combination of techniques provides new insight into the low PL of Bi-doped CsPbBr3 perovskite NCs.