Browsing by Subject "Diluted magnetic semiconductors"

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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.
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    Magneto-optical studies of CdSe/CdMnS/CdS core/multi-shell colloidal nanoplatelets
    (SPIE, 2016) Petrou, A.; Scrace, T. A.; Murphy, J. R.; Zhang, P.; Norden, T.; Zhang, T.; Thomay, T.; Cartwright, A. N.; Delikanlı, Savaş; Akgül, Mehmet Zafer; Demir, Hilmi Volkan
    We studied the photoluminescence (PL)) from CdSe/CdMnS/CdS core/multi-shell colloidal nanoplatelets, a versatile platform to study the interplay of optical properties and nanomagnetism. The photoluminescence (PL) exhibits σ+ polarization in the applied magnetic field. Our measurement detects the presence of even a single magnetic monolayer shell. The PLL consists of a higher and a lower energy component; the latter exhibits a circular polarization peak. The time-resolved PL (trPL) shows a red shift as function of time delay. At early (later) times the trPL spectra coincide with the high (low) energy PL component. A model is proposed to interpret these results.
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    Magneto-optics of excitons interacting with magnetic ions in CdSe/CdMnS colloidal nanoplatelets
    (American Chemical Society, 2020-06) Shornikova, E. V.; Yakovlev, D. R.; Tolmachev, D. O.; Ivanov, V. Y.; Kalitukha, I. V.; Sapega, V. F.; Kudlacik, D.; Kusrayev, Y. G.; Golovatenko, A. A.; Shendre, S.; Delikanlı, Savaş; Demir, Hilmi Volkan; Bayer, M.
    Excitons in diluted magnetic semiconductors represent excellent probes for studying the magnetic properties of these materials. Various magneto-optical effects, which depend sensitively on the exchange interaction of the excitons with the localized spins of the magnetic ions can be used for probing. Here, we study core/shell CdSe/(Cd,Mn)S colloidal nanoplatelets hosting diluted magnetic semiconductor layers. The inclusion of the magnetic Mn2+ ions is evidenced by three magneto-optical techniques using high magnetic fields up to 15 T: polarized photoluminescence, optically detected magnetic resonance, and spin-flip Raman scattering. We show that the holes in the excitons play the dominant role in exchange interaction with magnetic ions. We suggest and test an approach for evaluation of the Mn2+ concentration based on the spin− lattice relaxation dynamics of the Mn2+ spin system.
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    Mn2+-doped CdSe/CdS core/multishell colloidal quantum wells enabling tunable carrier-dopant exchange interactions
    (American Chemical Society, 2015) Delikanlı, S.; Akgül, M. Z.; Murphy, J. R.; Barman, B.; Tsai, Y.; Scrace, T.; Zhang, P.; Bozok, B.; Hernández-Martínez, P.L.; Christodoulides, J.; Cartwright, A. N.; Petrou, A.; Demir, Hilmi Volkan
    In this work, we report the manifestations of carrier-dopant exchange interactions in colloidal Mn2+-doped CdSe/CdS core/multishell quantum wells. The carrier-magnetic ion exchange interaction effects are tunable through wave function engineering. In our quantum well heterostructures, manganese was incorporated by growing a Cd0.985Mn0.015S monolayer shell on undoped CdSe nanoplatelets using the colloidal atomic layer deposition technique. Unlike previously synthesized Mn2+-doped colloidal nanostructures, the location of the Mn ions was controlled with atomic layer precision in our heterostructures. This is realized by controlling the spatial overlap between the carrier wave functions with the manganese ions by adjusting the location, composition, and number of the CdSe, Cd1-xMnxS, and CdS layers. The photoluminescence quantum yield of our magnetic heterostructures was found to be as high as 20% at room temperature with a narrow photoluminescence bandwidth of ∼22 nm. Our colloidal quantum wells, which exhibit magneto-optical properties analogous to those of epitaxially grown quantum wells, offer new opportunities for solution-processed spin-based semiconductor devices. © 2015 American Chemical Society.