Compositional Tuning of Carrier Dynamics in CsNa Ag BiCl Double-Perovskite Nanocrystals.

We devised a hot-injection synthesis to prepare colloidal double-perovskite CsNaBiCl nanocrystals (NCs). We also examined the effects of replacing Na with Ag cations by preparing and characterizing CsNa Ag BiCl alloy NCs with ranging from 0 to 1. Whereas CsNaBiCl NCs were not emissive, CsNa Ag BiCl NCs featured a broad photoluminescence band at ∼690 nm, Stokes-shifted from the respective absorption by ≥1.5 eV. The emission efficiency was maximized for low Ag amounts, reaching ∼3% for the CsNaAgBiCl composition. Density functional theory calculations coupled with spectroscopic investigations revealed that CsNa Ag BiCl NCs are characterized by a complex photophysics stemming from the interplay of (i) radiative recombination via trapped excitons localized in spatially connected AgCl-BiCl octahedra; (ii) surface traps, located on undercoordinated surface Bi centers, behaving as phonon-assisted nonradiative decay channels; and (iii) a thermal equilibrium between trapping and detrapping processes. These results offer insights into developing double-perovskite NCs with enhanced optoelectronic efficiency.