Upconversion luminescence of colloidal CdS and ZnCdS semiconductor quantum dots

Upconversion luminescence is observed from colloidal US and CdZnS quantum dots dispersed in hexanes. These binary and ternary nanocrystals were synthesized via noninjection approaches and at relatively low temperature and exhibit cubic crystal structures and narrow size distributions. The upconversion luminescence of these nanocrystal ensembles is similar to their corresponding photoluminescence emission, regarding peak shape, position, and dynamics. The upconversion luminescence yield exhibits a near-quadratic laser power dependence. Accordingly, our study indicates that the upconversion luminescence is due to two-photon excitation.