Effect of nanocrystal growth conditions on exciton decay and spin dephasing in an ensemble of CdSe nanocrystals grown in glass

The dynamics of exciton decay and spin dephasing in an ensemble of CdSe quantum dots grown in a glass matrix has been investigated by studying the polarized time-integrated four-wave mixing signal at 10 K. Quantum dots of equal size, but with different growth conditions, have been found to exhibit similar decay times but significantly (orders of magnitude) different spin depolarization times. We connect this effect to the difference in the quantum dot anisotropy. The anisotropy results in the splitting of bright J=1 exciton states that causes the oscillation of circularly excited excitons between the two linearly polarized split states. In a quantum dot ensemble with a random distribution in the exciton level splitting, that results in the depolarization of the four-wave mixing signal observed in the scattering of sigma(-) and sigma(+) polarized light on the population grating created by two sigma(+) pulses. The dependence of the quantum dot anisotropy on the growth conditions is discussed in terms of thermophysics of nanoparticle growth in glass.