Ligand-Mediated Photobrightening and Photodarkening of CdSe/ZnS Quantum Dot Ensembles

Abstract

Variation of the steady-state optical properties of quantum dots (QDs) caused by photoinduced charge transfer is a widely known phenomenon which hinders QD applications requiring long-term stability of the optical signal, for example, bioimaging, single-photon sources, molecular tracking, and lasing. Intense light irradiation may provoke QD photodarkening, when their photoluminescence (PL) quantum yield (QY) is reduced, or photobrightening, when the QY increases and QD PL becomes brighter. In order to understand the nature of these processes and to determine the optimal operating conditions for QDs with different core sizes and shell thicknesses, we have systematically studied the photodarkening and photobrightening phenomena for different wavelengths and intensities of irradiation. The results have shown that changes in the core size only slightly alter the effect of light irradiation on the QD optical properties, whereas the irradiation wavelength and shell thickness are the major factors that determine...