PNNL

Abstract

Strong upconversion luminescence is observed from colloidal CdS and CdZnS quantum dots dispersed in hexanes. The nanocrystals were synthesized via non-hot-injection approaches at relatively low temperature, exhibiting cubic crystal structures and narrow size distribution. The upconversion luminescence emission spectra of these binary and ternary nanocrystal ensembles studied are similar in both peak shape and position compared to their corresponding photoluminescence emission spectra. The upconversion luminescence exhibits a near quadratic laser power dependence. Furthermore, the upconversion and photoluminescence show similar decay dynamics. Accordingly, our study indicates that the upconversion luminescence is due to two-photon excitation.