An anion-driven Sn2+ exchange reaction in CsPbBr3 nanocrystals towards tunable and high photoluminescence

Fast and efficient ion-exchange reactions endow CsPbX3 nanocrystals (NCs) with superior photoluminescence (PL) properties. In this study, SnX2 (X = I, Cl) was used as a Sn precursor to conduct the cation exchange reaction, which was promoted by anion exchange between the parent CsPbBr3 NCs and the guest X in SnX2. The anion-driven cation exchange reaction occurred efficiently (10 min). CsSnI3 NCs were created by ion-exchange reactions between CsPbBr3 NCs and the SnI2 precursor. The CsSnI3 NCs retained the initial morphology of CsPbBr3 NCs and revealed a high PL efficiency (59%) and prolonged PL lifetime. In contrast, the exchange reaction of Sn2+ ions in CsPbBr3 NCs did not occur in a short time using SnBr2 as a precursor. After the cation exchange reaction, the 4f peaks of Pb ions in X-ray photoelectron spectroscopy spectra shifted to low binding energies as compared to those of the parent CsPbX3 NCs. This is ascribed to the increase in the number of Pb-oleate (Pb-OA) species. Contrary to the hot-injection method used to synthesize CsSnI3 NCs, the kinetically controlled ion exchange reactions lead to the synthesis of CsSnI3 NCs with a high structural stability. Thus, an anion-exchange-promoted cation exchange reaction is a particularly efficient versatile tool to dope Sn2+ into CsPbX3 NCs.