Magneto-photoluminescence and optically detected magnetic resonance studies of magnetically doped colloidal core/shell nanocrystals
Yahel Barak a, Joanna Dehnel a, Rotem Strassberg a, Savas Delikanli b c
a Schulich Faculty of Chemistry, Solid State Institute, Russell Berrie Nanotechnology Institute, Technion – Israel Institute of Technology, Haifa, Israel
b Nanyang Technological University, LUMINOUS - Centre of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, Singapore, Nanyang Avenue, 50, Singapore, Singapore
c Bilkent University, Turkey, Ankara, Turkey
nanoGe Fall Meeting
Proceedings of nanoGe Fall Meeting19 (NGFM19)
#NCFun19. Fundamental Processes in Semiconductor Nanocrystals
Berlin, Germany, 2019 November 3rd - 8th
Organizers: Ivan Infante and Jonathan Owen
Poster, Yahel Barak, 421
Publication date: 18th July 2019

Colloidal nanostructures are known for their tunable photo-physical properties by variation of size, shape, and composition, while magnetically doped nanostructures endow them with an additional degree of freedom. The confined structures enhance the so-called sp-d spin-exchange interaction between photo-generated carriers (electron and hole) and spins of the magnetic impurities, hence, encouraging unique properties, like giant magnetization and giant g-factor of the carriers. The degree of magnetization depends on the shape, size, type of impurity, and its position concerning the host-carrier distribution function. The current study focused on the magneto-optical properties of Mn+2 ions embedded in CdSe/CdS nanoplatelets (NPLs) and nanorods (NRs), positioning a single or a few Mn+2 ions in the shell regime. The pristine CdSe/CdS structures mainly show a quasi-type-II band-edge energy alignment between the core and the shell constituents, allowing electron distribution over the entire structure. So, selective positioning of magnetic impurities in the shell regime permits selective monitoring of the electron-Mn+2 spin-exchange interaction. The magneto-optical properties are a fingerprint for those spin-exchange interactions. The first fingerprint was observed in the photoluminescence (PL) spectra recorded at various temperatures and under the influence of various magnetic fields.

The carrier-impurity interaction was further investigated using an optically detected magnetic resonance (ODMR) spectroscopy. An ODMR spectrum refers to a plot of a change in luminescence intensity due to a magnetic resonance perturbation at the excited state. Modulation dependence ODMR can revile the spin dynamics in the NCs. The experimental results showed a major band, with sextet split fine structure in the NPLs and a two-band with a different character in the NRs. Theoretical model, using spin Hamiltonian containing Zeeman interaction, carrier-impurity spin-exchange, and electron-hole exchange interactions, assisted in simulating the ODMR spectrum. This model suggests the occurrence of an electron spin-flip which is coupled by exchange interaction to the Mn+2 nuclear spin projections (IMn= ±5/2), thus leading to the sextet manifold. The simulation revealed the physical constants, such as the g-factor of the electron and the host-guest exchange energy.  To the best of our knowledge, the ODMR method was never being applied before for the study of magnetically doped nanostructures, while the information about the selective coupling of a specific carrier with guest spins reflect the possibility of engineering magneto-optical properties. The discussed materials of special interest for various future applications.   

© Fundació Scito
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