Descriptions of Edge Exciton Decay Dynamics in CdSe Quantum Dots Dissolved in Cyclohexane and Water Based on a Stochastic Model of Biexciton Recombination

The relaxation dynamics of “hot” (excitation at 490 nm/2.53 eV) and edge (excitation at 590 nm/2.1 eV) excitons in CdSe quantum dots dissolved in cyclohexane and water has been studied using femtosecond laser pump–probe spectroscopy as a function of the initial concentration of excitons (pump pulse energy). It has been shown that the relaxation rate of the hot excitons and the population rate of the edge excitons depend weakly on the initial concentration of the hot excitons. The edge-exciton relaxation rate depends significantly on the initial concentration of excitons, which is reflected in the dependence of the relaxation rate on the pump pulse energy. It has been shown that the edge-exciton relaxation kinetics is described in terms of the stochastic model with only two constants, the Auger recombination constant $$k_{i}^{{{\text{Auger}}}}$$ and the relaxation constant of the first-order excitons $$k_{i}^{1} = {i \mathord{\left/ {\vphantom {i {{{\tau }_{1}}}}} \right. \kern-0em} {{{\tau }_{1}}}}$$ . The values of both constants depend weakly on the pump pulse wavelength and on the solvent water or cyclohexane.