Radiative and non-radiative decay kinetics of (CdSe)N (N = 3 and 4) clusters

Photoluminescence intermittency in semiconductor quantum dots (QDs) has limited their applications in single QD process. Understanding the origin of intermittency and its correlation with microstructure is crucial for the design and preparation of QDs with high fluorescence quantum yield. The small-sized (CdSe)3 and (CdSe)4 clusters provide a typical model for studying the effect of size, structure, surface defect, etc., on the radiative and nonradiative rates of II–VI QDs. The rate constants of radiative and nonradiative processes, kr and knr, are computed for the model systems using first-principles calculations, Marcus theory, and Fermi’s golden rule. Although kr and knr vary in a complicated way from cluster to cluster, their correlation with the geometrical and electronic properties of ground- and excited-state structures are revealed. Structure distortion in excitation, spatial overlap between the Kohn-Sham orbitals occupied by excited electron, reorganization energy, Huang-Rhys factor of dominant vibrational modes, as well as the unsaturation of surface atoms exert influences on kr and knr. Moreover, these quantities correlate with each other and their roles may change in the radiative/nonradiative process. While some quantities, such as reorganization energy and atomic unsaturation, have been used solely to estimate the photoluminescence yield, a combination of these factors is suggested to give reliable predictions. In addition, our calculations indicate that kr and knr can be tuned by designing the QDs with specific geometrical and electronic structures.Photoluminescence intermittency in semiconductor quantum dots (QDs) has limited their applications in single QD process. Understanding the origin of intermittency and its correlation with microstructure is crucial for the design and preparation of QDs with high fluorescence quantum yield. The small-sized (CdSe)3 and (CdSe)4 clusters provide a typical model for studying the effect of size, structure, surface defect, etc., on the radiative and nonradiative rates of II–VI QDs. The rate constants of radiative and nonradiative processes, kr and knr, are computed for the model systems using first-principles calculations, Marcus theory, and Fermi’s golden rule. Although kr and knr vary in a complicated way from cluster to cluster, their correlation with the geometrical and electronic properties of ground- and excited-state structures are revealed. Structure distortion in excitation, spatial overlap between the Kohn-Sham orbitals occupied by excited electron, reorganization energy, Huang-Rhys factor of dominant v...