Determination of the Dark Fraction of Semiconductor Quantum Dots in Solution Based on Their Non-Exponential Luminescence Decays Measured in Different Dielectric Environments

Abstract A significant fraction of colloidal semiconductor quantum dots in solution can be non-emissive, or dark. As a result, the ensemble photoluminescence quantum yield is lower than the intrinsic quantum yield of the emissive, or bright, subpopulation. Here, we introduce a straightforward method for determining the dark fraction of semiconductor quantum dots in solution based on their non-exponential photoluminescence decays measured in dielectric environments with different refractive indices. Applied to gradient-alloyed thick-shell semiconductor quantum dots, the method shows that the intrinsic emission quantum yield of the bright subpopulation ranges from 0.679 to 0.763, depending on the solvent refractive index. Comparison with independently determined ensemble photoluminescence quantum yield gives a bright fraction of 0.607 ± 0.058, which corresponds to a substantial dark fraction of 0.393 ± 0.058. In general, this work provides a simple experimental route for quantifying hidden non-emissive populations in colloidal quantum dot ensembles.