Unraveling the Structure-Dependent Radiative and Nonradiative Decays in (CdSe)₁₃ Clusters through First-Principles Calculations

Abstract

Although several physical models have been proposed to interpret the photoluminescence intermittency that hinders the applications of single semiconductor quantum dots, the structure dependence of radiative and nonradiative recombination of excitons remains unclear. In order to address the structure–property correlation of II–VI quantum dots, the variations of radiative and nonradiative decay rate constants, kr and knr, of (CdSe)13 clusters with structural descriptors are studied using first-principles calculations together with the semiclassical two-state model. Attributed to their small size and diverse structures, the four isomers of (CdSe)13 exhibit distinct optical absorption and emission properties. Their kr and knr values vary in a wide range, though they have the same cluster size. While a previously suggested correlation between kr and electron–hole spatial overlap is verified, dependence of knr on reorganization energy, Huang–Rhys factor, transition energy, etc. is explored. Correlation of knr with Huang–Rhys factor is further analyzed in terms of vibrational modes and cluster shapes. In addition, a descriptor based on chemical softness, Δs = s+ – s–, is proposed, and a good correlation between knr and Δs is revealed. The revealed structure-dependent radiative and nonradiative electron–hole recombination behaviors would be helpful for understanding and suppressing the photoluminescence intermittency in semiconductor quantum dots.