Relaxation of Multiple Excitons in ZnCdS and ZnCdS/ZnS Alloy Quantum Dots

The relaxation dynamics of “hot” and band-edge excitons in ZnCdS (2.8 eV edge exciton) and ZnCdS/ZnS (2.7 eV) quantum dot alloys was studied using femtosecond pump (360 nm, 3.44 eV, 25 fs)— probe (380–700 nm) laser spectroscopy. Transients were studied as a function of the pump pulse energy, which changes the number of excitons. The relaxation of the “hot” exciton is controlled by the Auger mechanism. The decay time of a “hot” exciton depends very weakly on the pump energy and is in the range of 140–190 fs. The decay of a band-edge exciton depends significantly on the pump energy, which suggests an Auger recombination mechanism. The multiexponential transient decay is well described within the stochastic model with only two constants \(k_{i}^{{Auger}}\) and \(k_{i}^{1} = {i \mathord{\left/ {\vphantom {i {{{\tau }_{1}}}}} \right. \kern-0em} {{{\tau }_{1}}}}\) .