Nonlinear optical approach to multiexciton relaxation dynamics in quantum dots

Unlike the majority of molecular systems quantum dots can accommodate multiple excitations, which is a particularly important attribute for potential lasing applications. We demonstrate in this work the concept of using nth order nonlinear spectroscopies in the transient grating configuration as a means of selectively exciting (n-1) 2 excitons in a semiconductor and probing the subsequent relaxation dynamics. We report a direct observation of multiparticle dynamics on ultrashort time scales through comparison of third and fifth order experiments for CdSe colloidal quantum dots. Time constants associated with multiexciton recombination and depopulation dynamics are reported. Deviation from a Poisson model for the distribution of photoexcited excitons, biexcitons, and triexcitons is also discussed.