On the dominant mechanism of the nonradiative excitation of manganese ions in II–VI diluted magnetic semiconductors

Doping II–VI semiconductors and low-dimensional structures based on them by manganese leads to the effective quenching of electroluminescence and photoluminescence under the condition that the electron excitation energy of the crystal exceeds the energy of the intracenter transition of the Mn$^{2+}$ ion $E_{\mathrm{Mn}}\approx$ 2.1 eV. Quenching implies effective energy transfer from a photoexcited crystal to Mn$^{2+}$ ions. Three mechanisms of such nonradiative energy transfer are possible, notably, the dipole–dipole mechanism, the exchange mechanism, and a mechanism related to the latter, which is associated with $sp$–$d$ mixing. Although it is thought that the dipole–dipole mechanism is not particularly efficient because of the forbidden intracenter transition for Mn$^{2+}$, while the dominant mechanism is the spin-dependent exchange mechanism, not all experimental facts accumulated to date confirm this conclusion. Two experimental approaches that make it possible to reveal the dominant energy-transfer mechanism to Mn$^{2+}$ ions and evaluate the partial contributions of various mechanisms are considered in the article. One of these approaches is associated with optically detected magnetic resonance at single semimagnetic quantum dots, and the second one is associated with plasmon enhancement of the energy transfer to Mn$^{2+}$ ions by means of the dipole–dipole interaction.