Observation of optical referigeration on CdSe/CdS quantum dots

Optical refrigeration on CdSe/CdS (core/shell) quantum dots (QDs) was observed for the first time. From the observed temperature drop and the experimental conditions, the effective cooling power in our experiment was estimated to be ~10^-14 W per dot. Experiments were done with samples (colloidal QDs suspension) synthesized in our lab following the method recently developed at Peng's group (DOI: 10.1021/jacs.6b02909), which can effectively eliminate the excitonic non-radiative decay path inside the QDs. The cooling effect comes from the significant up-conversion of the mean emission energy (typical up-conversion of the mean emission energy is >25 meV) observed in the photoluminescence spectra of our samples under sub-band excitation (excitation energy is much lower than the energy band gap of the QDs). Details of the experiments and the observation will be discussed in the presentation.