Photodynamics of Nonlinear Effects of Picosecond Laser Action on CdSe/ZnS QDs Colloidal Solutions

Abstract

The intensity of incident radiation on photodynamics of nonlinear processes in colloidal solutions of CdSe/ZnS quantum dots is investigated. The difference between nonlinear processes that occur during and after the action of a laser pulse is established and studied experimentally. Analysis of luminescence kinetics during the laser action showed that an increase in intensity leads not only to the effect of optical limiting but also to the appearance of superradiance for quantum dots of different diameters. The pump−probe experiments revealed the effect of a “dynamic valve” caused by an interference of two processes, relaxation via dimensionally quantized levels and phononless relaxation via surface or dark states, at the stage following laser excitation. Mathematical model of deactivation of the highly excited states formulated in the form of Riccati equations showed good agreement with the experiment of Picosecond Laser Action on CdSe/ZnS QDs Colloidal Solutions.