2. Articole
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Item Luminescent properties of low-dimensional ZnO: Ag powders obtained by chemical deposition from aqueous solution [Articol](2023) Goglidze, Tatiana; Goncearenco, Evghenii; Dementiev, Igor; Nedeoglo, Natalia; Iurieva, Tatiana; Nedeoglo, DumitruPhotoluminescence (PL) spectra of ZnO:Ag highly dispersed powders obtained by chemical deposition from aqueous solution are investigated in the wavelength range between 360 and 750 nm at room temperature under excitation between 250 and 350 nm. Before starting the synthesis, the Ag dopant was introduced into the initial solution in the form of AgNO3 silver nitrate in the amount of 12, 102, and 252 mg. The PL spectra consist of an ultraviolet emission (380 nm) attributed to AgZn acceptor-bound exciton, a short-wavelength violet emission (400 –450 nm) and a wide long-wavelength yellow-orange emission (560 – 600 nm). With decreasing excitation energy, the violet emission decreases in intensity, while the yellow-orange emission increases. This is caused by the phenomenon of self-absorption of the short-wavelength emission and energy transmission to the centers of the long-wavelength emission. A rapid decrease in intensity of all the PL bands is found for the sample with maximum Ag concentration. This fact is due to the appearance of the second phase in the form of silver oxide and, consequently, a decrease in the concentration of AgZn point defects responsible for the bands.Item High performance ZnSe-based ultraviolet photodetectors with Cr/Au, Ni/Au and hybrid Ag-nanowire contacts [Articol](2024) Sirkeli, Vadim; Nedeoglo, Natalia; Nedeoglo, Dmitrii; Yilmazoglu, Oktay; Hajo, Ahid; Preu, Sascha; Küppers, Franko; Hartnagel, HansItem Luminescent properties on ZnO:Cr nanocrystals and thin layers [Articol](Springer Nature, 2020) Goglidze, Tatiana; Dementiev, Igor; Goncearenco, Evghenii; Iurieva, Tatiana; Nedeoglo, Dumitru; Nedeoglo, NataliaBoth undoped and chromium doped zinc oxide nanocrystal powders are obtained by chemical deposition and hydrothermal methods. ZnO and ZnO:Cr thin layers on the surface of ZnSe and ZnSe:Cr samples, respectively, are obtained by isovalent substitution of selenium by oxygen in the process of thermal treatment of the samples in air. Photoluminescence spectra of the ZnO and ZnO:Cr nanopowders and thin layers obtained by various techniques are investigated at room temperature. Cr doped ZnO powders obtained by chemical deposition and hydrothermal methods improves the powder quality, as evidenced exciton emission is more intensive. New emission bands are found in visible (615 nm, 625 nm) and infrared (925 nm, ~2000 nm) spectral ranges for ZnO:Cr nanopowders and thin films. The contribution of Cr impurity to the formation of emission bands is discussed.Item Luminescent properties of Sb-doped ZnSe single crystals [Articol](2019) Sushkevich, Konstantin; Goncearenco, Evghenii; Nedeoglo, Natalia; Nedeoglo, DmitriiPhotoluminescence (PL) spectra of ZnSe:0.1at%Sb single crystals are studied between 90 and 300 K. The samples are grown by the chemical vapor transport (CVT) method with iodine as a transport agent and doped with Sb impurity during the growth. A yellow PL band with a maximum at 2.16 eV (575 nm) at room temperature is observed for the first time. A model of a (SbSeISe) acceptor center with the energy level located at 0.52 eV above the valence band edge is proposed, and the mechanism of the formation of this yellow PL band under direct and indirect excitation is discussed.Item Purification of ZnSe crystals from electrically active background impurities by ytterbium doping [Articol](John Wiley & Sons, 2014) Radevici, Ivan; Sushkevich, Konstantin; Sirkeli, Vadim; Nedeoglo, Dmitrii; Nedeoglo, Natalia; Huhtinen, Hannu; Paturi, PetriinaHall coefficient, electrical conductivity, and electron mobility are investigated for n-ZnSe:Yb single crystals with high concentration of electrically active background impuritiesItem Obtaining of II-VI compound substrates with controlled electrical parameters and prospects of their application for nanoporous structures [Articol](John Wiley & Sons, 2014) Colibaba, Gleb; Goncearenco, Evghenii; Nedeoglo, Dmitrii; Nedeoglo, Natalia; Monaico, Eduard; Tiginyanu, IonItem The structure of high-temperature blue luminescence centers in zinc selenide and mechanisms of this luminescence [Articol](Springer Nature, 1998) Ivanova, G.N.; Kasiyan, V.A.; Nedeoglo, Dmitrii; Nedeoglo, Natalia; Simashkevich, A.V.The characteristic features of temperature quenching of the intensity of the edge luminescence bands of n-ZnSe crystals annealed in different media (vacuum, Zn, Se) are investigated a wide temperature range. A change in the mechanisms of high-temperature exciton luminescence in the short-wavelength region of the spectrum (443 nm) with increase in temperature of the crystal is observed. It is shown that the nature of temperature quenching of the long-wavelength edge luminescence band (458 nm) is evidence of dissociation of associative luminescence centers with increase in the sample temperature.Item Magnetic and luminescent properties of nickel-doped ZnSe crystals [Articol](Elsevier, 2015) Sirkeli, Vadim; Radevici, Ivan; Sushkevich, Konstantin; Nedeoglo, Natalia; Nedeoglo, DmitriiMagnetic and photoluminescent properties of nickel-doped ZnSe crystals with impurity concentrations varied by changing the Ni amount in the source material from 0.001 to 0.50 at.% are studied in 5–300 K temperature range. Investigation of magnetic properties shows that Ni impurity in ZnSe forms isolated paramagnetic centers and probability of Ni–Ni pairs formation is negligible due to low Ni concentration in the samples. The contribution of Ni impurity to edge emission and its influence on infra-red emission are discussed. It is found that complete concentration quenching of luminescence within all studied spectral range is observed starting with Ni concentration of 0.50 at.%.Item A comparative analysis of infrared luminescence spectra of ZnSe:Yb, ZnSe:Gd, and ZnSe:Cr crystals [Articol](Wiley, 2014) Colibaba, Gleb; Goncearenco, Evghenii; Nedeoglo, Dmitrii; Nedeoglo, NataliaPhotoluminescent and optical properties of ZnSe crystals doped with Yb and Gd rare-earth elements (REEs) and Cr impurity are investigated in infrared (IR) spectral range. The influence of stoichiometric deviation on photoluminescence (PL) spectra of the crystals is investigated and the structure of complex IR PL bands is analysed. The good coincidence between the IR PL spectra of the samples doped with Yb, Gd, and Cr is shown. Correlation between the component parts of the bands at 1 and 2 µm is found and possibility to control the composition of IR PL spectra by enrichment of the samples with Zn or Se is discussed. The model that explains the formation of associative centres based on the REEs and background Cu impurity fixed in the nodes of crystal lattice with tetrahedral symmetry, which are responsible for IR PL bands, is proposed. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)Item Infrared photoluminescence of ZnSe:Gd crystals [Articol](Elsevier, 2015) Colibaba, Gleb; Goncearenco, Evghenii; Nedeoglo, Dmitrii; Nedeoglo, NataliaPhotoluminescent and optical properties of ZnSe crystals doped with Gd impurity are investigated in infrared (IR) spectral range. The influence of crystal growth temperature, impurity concentration, stoichiometric deviation and post-annealing cooling rate, concentration of Cr and Cu background impurities, temperature and excitation level on photoluminescent and optical properties of the samples is studied. Based on these investigations, the structure of complex IR photoluminescence (PL) bands is analyzed. Correlation between the component parts of the bands at 1 and 2 µm is found and possibility to control the IR PL spectra by enrichment of the samples with Zn or Se is discussed. Coincidence of the IR PL spectra structure is shown for the samples doped with Gd, Yb, and Cr impurities. The model that explains the formation of complexes based on rare-earth elements (REEs) and Cr and Cu background impurities fixed in the nodes of crystal lattice with tetrahedral symmetry, responsible for IR PL bands, is proposed.