Relaxation and dynamics of intra-center excitations in semi-magnetic Zn0.8Mn0.2Te multiquantum wells

Intra-center luminescence dynamics was investigated under low excitation density in Zn0.8Mn0.2Te/Zn0.59Mg0.41Te multiquantum wells both experimentally and by Monte Carlo simulation. A model developed earlier for bulk Cd1−xMnxTe is applied to the nanostructures with wells׳ width equal to 7 and 26 monolayers. Low temperature experimental transients showed build-up part. Besides time-resolved luminescence spectra of Mn2+-ions׳ band indicate that energy of the band maximum shifts in two time scale. The Monte Carlo simulation showed that fast shift derives from transition between the lowest intra-center states 4T2→4T1 within the same Mn2+-ion. The explanation is supported by calculations applied to bulk Cd0.4Mn0.6Te under similar excitation conditions. Mean relaxation rate of the 4T2→4T1-transition is estimated to be 5 µs−1. The slow relaxation is determined by energy transfer between Mn2+-ions, its rate being four orders of magnitude less than that of the transition. Calculations showed weak correlation between energies of the 4T1- and 4T2-states which causes the transition energy fluctuations. This results in the transition rate dispersion, which is taken into account by exponential dependence on the transition energy. Loss of the correlation is shown to be mainly originated from symmetry breakdown. Noticeable non-exponential decay in Mn2+-luminescence transients is described by stochasticity in decay rates.