Auger Suppression in n-Type HgSe Colloidal Quantum Dots

Transient infrared photoluminescence upconversion is used to study the exciton dynamics in small-gap HgSe colloidal quantum dots in the 2000-6500 cm^-1 (0.25-0.80 eV) range. The intraband mid-infrared photoluminescence decays show absent or greatly reduced Auger relaxation of biexcitons, proposed as a generic feature of weakly n-type quantum dots due to the sparse density of states in the conduction band. The nonradiative relaxation of the intraband carriers is instead consistent with near-field energy transfer to molecular vibrations of the surface ligands. In contrast, the interband near-infrared photoluminescence decays exhibit the typical distinct exciton and biexciton lifetimes with Auger coefficients comparable to other similarly sized quantum dots. Also observed are spectral and dynamical evidence of fine structure in the intraband transitions consistent with spin-orbit splitting of the electron P levels, and the emergence of plasmonic resonances in large particles.