Radiative and non-radiative exciton recombination rate constants in ZnSe clusters

Abstract

Understanding the origin of photoluminescence intermittency and its correlation with microstructure is crucial for the design and preparation of quantum dots (QDs) with high fluorescence quantum yield. ZnSe clusters provide a typical model for studying the effect of their size, geometrical and electronic structures on their radiative and non-radiative process of II-VI QDs. The rate constants of radiative and non-radiative processes, kr and knr, of the (ZnSe)n clusters were computed by using first-principles calculations, Einstein spontaneous radiation theory and Fermi’s golden rule. The kr and knr variations with cluster size were analyzed in term of a number of quantities. Emission energy and reorganization energy were identified to play dominant roles in the determination of kr and knr for the studied clusters. Furthermore, a correlation between these two quantities and the geometric rigidity of the ZnSe clusters was revealed. The clusters with greater geometric rigidity tend to possess larger emission energy, and smaller reorganization energy. While radiative and non-radiative electron–hole recombination rates of the ZnSe clusters vary in a complicated way because of their diverse structures and prominent quantum size effect, our study highlights the correlation between recombination rate and cluster structure, which would be helpful for the design of QD materials with high fluorescence quantum yields.