Optical refrigeration on cadmium selenide/cadmium sulfide quantum dots

Critical progress in perfecting semiconducting quantum dots' photoluminescence quantum yield has been made in the past few years. The production of quantum dots with nearly unitary quantum yield has significantly expanded their possible applications, as it is the case of optical refrigeration. We report for the first time optical refrigeration achieved in cadmium selenide/cadmium sulfide (core/shell) structure nanocrystals. Experiments were carried out in colloidal quantum dots suspension, where the excitonic non-radiative decay paths of the quantum dots are effectively suppressed by applying sub-band excitation, eliminating the possible states for energy down-conversion. The cooling effect comes from the significant energy up-conversion observed in the photoluminescence spectra of the samples under sub-band excitation. These results highlight the possibility of realizing temperature control on semiconducting quantum dots through optical approaches, which could provide power cooling mechanism for nano devices and cryogenic systems.