Introducing single ${\text{Mn}}^{2+}$ ions into spontaneously coupled quantum dot pairs

We present the photoluminescence excitation study of the self-assembled CdTe/ZnTe quantum dots doped with manganese ions. We demonstrate the identification method of spontaneously coupled quantum dots pairs containing single ${\text{Mn}}^{2+}$ ions. As the result of the coupling, the resonant absorption of the photon in one quantum dot is followed by the exciton transfer into a neighboring dot. It is shown that the ${\text{Mn}}^{2+}$ ion might be present in the absorbing, emitting, or both quantum dots. The magnetic properties of the ${\text{Mn}}^{2+}$ spin are revealed by a characteristic sixfold splitting of the excitonic line. The statistics of the value of this splitting is analyzed for the large number of the dots and gives the information on the maximum density of the neutral exciton wave function.

Figure 1

(a) An exemplary photoluminescence (PL) spectrum of a neutral exciton confined in a single QD containing one ${\text{Mn}}^{2+}$ ion. (b) The statistical distribution of the value of the splitting induced by $X$-Mn exchange interaction as a function of emission energy for single or coupled QDs with a ${\text{Mn}}^{2+}$ ion in the emitting dot or absorption energy for coupled QDs with a ${\text{Mn}}^{2+}$ ion in the absorbing dot. The black line shows the results of calculations in the box model of a QD which reproduces the maximum of the wave function density for a given neutral exciton energy.

Figure 2

The macrophotoluminescene (PL) spectrum of the CdTe QDs ensemble. In the PLE measurements the excitation energy range is set around the maximum of the PL band. At the detection window energetic density of QDs is low enough to distinguish lines from single QDs in a micro PL experiment. The drawing in the top-right part of the figure presents the exciton transfer mechanism between two coupled QDs.

Figure 3

PLE maps reveal spontaneous coupling between (a) nonmagnetic QDs, QDs with ${\text{Mn}}^{2+}$ ion in (d) absorbing, (e) emitting and (b) both QDs. Figures (c) and (f) show cross sections taken at resonant energies (2044.8 and 2145.1 meV, respectively), which correspond to the absorption and emission spectrum of a QD with a single ${\text{Mn}}^{2+}$ ion.

Figure 4

(a) PLE and (b) emission spectrum of two different QDs with a single ${\text{Mn}}^{2+}$ ion compared to the numerical simulation results, which reproduce the oscillator strengths of excitonic transitions.