Browsing by Author "Yakovlev, Dmitri R."

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    Bright-dark exciton interplay evidenced by spin polarization in cdse/cdmns nanoplatelets for spin-optronics
    (American Chemical Society, 2025-01-08) Shornikova, Elena V.; Yakovlev, Dmitri R.; Tolmachev, Danil O.; Prosnikov, Mikhail A.; Christianen, Peter C. M.; Shendre, Sushant; Işık, Furkan; Delikanlı, Savaş; Demir, Hilmi Volkan; Bayer, Manfred
    Diluted magnetic semiconductor (DMS) colloidal nanocrystals demonstrate remarkable magneto-optical properties. The ability to control their magnetization and, consequently, the circular polarization of exciton emission holds significant potential for spintronic applications. However, the interplay between bright and dark exciton recombination and its impact on the polarization of emission are not yet fully understood. We measure the magneto-optical properties of colloidal CdSe/CdMnS nanoplatelets at cryogenic temperatures in high magnetic fields up to 30 T. The degree of circular polarization of photoluminescence demonstrates nonmonotonous behavior in a magnetic field. In low magnetic fields, the polarization degree is positive due to an exchange interaction of excitons with localized spins of magnetic Mn2+ ions. After reaching a maximum, the polarization degree starts to decrease and reverses the sign to negative in high magnetic fields, which is unusual in DMSs. The critical magnetic field, in which the sign is reversed, increases when the temperature is elevated. We develop a model that explains this behavior by an interplay of bright and dark exciton recombination. In high magnetic fields, the dark exciton radiative recombination rate accelerates due to mixing with the bright state, and the intrinsic Zeeman splitting of dark exciton overcomes the exchange with Mn2+ ions. As a result, the lowest |-2 > exciton energy level dominates in emission, providing negatively polarized photoluminescence.
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    High-frequency EPR and ENDOR spectroscopy of Mn2+ ions in CdSe/CdMnS nanoplatelets
    (American Chemical Society, 2023-02-20) Babunts, Roman A.; Uspenskaya, Yulia A.; Romanov, Nikolai G.; Orlinskii, Sergei B.; Mamin, Georgy V.; Shornikova, Elena V.; Yakovlev, Dmitri R.; Bayer, M.; Işık, Furkan; Shendre, S.; Delikanlı, Savaş; Demir, Hilmi Volkan
    Semiconductor colloidal nanoplatelets based of CdSe have excellent optical properties. Their magneto-optical and spin-dependent properties can be greatly modified by implementing magnetic Mn2+ ions, using concepts well established for diluted magnetic semiconductors. A variety of magnetic resonance techniques based on high-frequency (94 GHz) electron paramagnetic resonance in continuous wave and pulsed mode were used to get detailed information on the spin structure and spin dynamics of Mn2+ ions in core/shell CdSe/(Cd,Mn)S nanoplatelets. We observed two sets of resonances assigned to the Mn2+ ions inside the shell and at the nanoplatelet surface. The surface Mn demonstrates a considerably longer spin dynamics than the inner Mn due to lower amount of surrounding Mn2+ ions. The interaction between surface Mn2+ ions and 1H nuclei belonging to oleic acid ligands is measured by means of electron nuclear double resonance. This allowed us to estimate the distances between the Mn2+ ions and 1H nuclei, which equal to 0.31 ± 0.04, 0.44 ± 0.09, and more than 0.53 nm. This study shows that the Mn2+ ions can serve as atomic-size probes for studying the ligand attachment to the nanoplatelet surface.