2, Bilkent University, Ankara, , Turkey
3, Nanyang Technological University, Singapore, , Singapore
The current study invastigates the magneto-optical properties of CdSe/CdMnS core/shell colloidal nanoplatelets (NPs). Replacing a single or a few cations of the host semiconductor nanocrystal with magnetic dopants introduces new physical properties (e.g., giant magnetization and g-factor), which are of potential value for a spin-based applications. The studied NPs consisted of a CdSe core, covered by four monolayers of CdMnS shell, creating a quasi-type-II electronic nanostructure. The material's design enabled the alignment of the dopant ground and first excited states nearly in resonance with the band-edge levels of the host semiconductor,thus, inducing a strong sp-d spin exchange interaction. The magneto-optical properties were investigated by probing the single exciton recombination emission, using a micro-photoluminescence in the presence of an external magentic field (B0), as well as continous-wave and time-resolved optically detected magnetic resonance (ODMR) spectroscopy. The ODMR spectrum was characterized by a sextet manifold, revealing the existence of a single Mn+2 dopant in the vicinity of a single photo-generated exciton.
The ODMR observations were supported by a theoretical model, based on the effective mass approximation of the NPs electronic states, perturbed by the relevant exchange interactions: electron-Mn+2, hole- Mn+2 and electron-hole, with a dependence on the core/shell heterostructure design. The simulation revealed the physical constants, such as the g-factor of the electron and hole, ge,xx= ge,yy= 1.94, ge,zz=2.1, and gh,xx= gh,yy= -0.88, gh,zz=-1.0, respectively. The host-guest exchange energies are also extracted, being Js-d = 1.8975 meV and Jp-d = -1.8942 meV. To the best of our knowledge the ODMR method was never been applied before for the study of magnetically doped colloidal nanostructures, while the information about selective coupling of specific carrier with magnetic spins is of a paramount importance in the engineering the magneto-optical properties.