Abstract
<jats:p>Alloying, i.e., mixing different cation or anion species to form compositionally graded or homogeneous semiconductor nanocrystals, has recently become a popular strategy to tune the optical properties of colloidal quantum dots, yet its impact on excitonic fine structure remains poorly understood. Using atomistic empirical pseudopotential calculations with screened configuration interaction, we investigate the fine-structure splitting in spherical zinc-blende CdxZn1-xSe quantum dots (3.2–8.0 nm). Pure dots show the expected degenerate dark and bright multiplets, but alloying lowers the symmetry, inducing valence band splittings, lifting excitonic degeneracies, and redistributing oscillator strengths. We find strong dot-to-dot variations of the fine structure at fixed size/composition; disorder effects exceed those of shape anisotropy. Our results explain multiexponential photoluminescence decay and polarization changes in CdxZn1-xSe nanocrystals, establishing alloy fluctuations as the dominant mechanism controlling excitonic fine structure in cation-exchanged emitters.</jats:p>