Facultatea de Fizică şi Inginerie / Faculty of Physics and Engineering
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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 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 ZnO powders synthesized by isovalent method [Articol](2016) Goglidze, Tatiana; Dementiev, Igor; Koval, Andrei; Nedeoglo, Natalia; Nedeoglo, DmitriiZinc oxide powders have been prepared by the isovalent substitution method by means of high - temperature annealing of a zinc sulfide powder synthesized by a chemical method. Investigation of photoluminescence (PL) spectra in dependence on annealing temperat ure varied from 870 to 1050 С has made it possible to find the temperature range of 920 – 950 С for the most active isovalent substitution of oxygen atoms for sulfur atoms and the formation of a ZnO S phase. X - ray diffraction analysis has revealed that the p owder with crystal lattice parameters а о = 0.3249 nm and с о = 0.5206 nm and the ratio of с о / а о = 1.60, which are characteristic of zinc oxide crystals, is synthesized at the maximum annealing temperature. It has been found that the maximum of a structurel ess PL band in the spectrum for the ZnO powder at room temperature is localized at 500 nm. It has been supposed that the band is caused by ―free electron – acceptor‖ radiative transitions, where the acceptor level is 0.95 eV above the valence band edge.