The third-order optical nonlinearity and upconversion luminescence of CdTe quantum dots under femtosecond laser excitation

Abstract

The aqueous CdTe quantum dots (QDs) were synthesized by the electrostatic reaction method. The optical properties of CdTe QDs were investigated by femtosecond Z-scan and time-resolved luminescence technique in nonresonant spectral region. The nonlinear absorption and refraction are ascribed to two-photon absorption, and time-resolved upconversion photoluminescence produces biexponential decay pattern at infrared femtosecond laser excitation. Upconversion luminescence is composed of a band-edge excitonic state and a photoinduced trapping state. The short-lived band-edge excitonic emission is independent of the detection wavelengths, and long-lived species becomes even longer with the increase of detection wavelengths, which indicates the size dependence of surface excitonic emission.