Confined excitons in CdSe/CdMnS and CdSe/ZnMnS nanoplatelets

We have used absorption and PL spectroscopies to study the magneto-optical properties of colloidal CdSe/CdMnS and CdSe/ZnMnS core-shell nanoplatelets. We observe three absorption features tentatively attributed to the e₁h₁, e₁l₁, and e₂h₂ confined excitons. In the presence of a magnetic field B applied normal to the substrate surface, the PL from e₁h₁ becomes circularly polarized as σ₊, indicating the presence of exchange interaction between the carrier spins and the spins of the Mn²⁺ ions. The circular polarization initially increases with B and saturates at 4T. At a fixed B the circular polarization decreases with increasing temperature and vanishes around 50K. The circular polarization peak, unlike previously studied samples [1], coincides with the e₁h₁ exciton. This is attributed to the smaller thickness (2ML) of the CdSe core compared to the previously studied samples (5ML).
We also measured the e₁h₁ exciton magnetic splitting from the magneto-transmission spectra. Saturation splittings up to 5 meV have been observed.
1- J.R. Murphy et. al., Applied Physics Letters 108,242406 (2016).