2. Articole

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End date: 2021Subject: search.filters.subject.photoluminescence

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    CRYSTALLINE STRUCTURE, SURFACE MORPHOLOGY AND OPTICAL PROPERTIES OF NANOLAMELLAR COMPOSITES OBTAINED BY INTERCALATION OF InSe WITH Cd
    (2015) Untila, Dumitru; Caraman, Iuliana; Evtodiev, Igor; Canțer, Valeriu; Spalatu, Nicolae; Leontie, Liviu; Dmitroglo, Liliana; Luchian, Efimia
    A material composed of InSe and CdSe crystallites was obtained by heat treatment at 753K of InSe single crystalline plates in Cd vapour for 3÷24 hours. The average diameters of CdSe and InSe crystallites determined from diffraction lines analysis are respectively equal to 20 nm and 22 nm. The photoluminescence spectra at 300K and 80K of composite decompose well into two Gaussian curves, one is in good correlation with the photoluminescence of CdSe crystals and the other is shifted to higher energies than the width of the band gap of CdSe crystals.
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    FOTOLUMINESCENŢA STRATURILOR NANOLAMELARE DE GaSe OBŢINUTE PRIN INTERCALAREA CU Cd
    (2012) Dmitroglo, Liliana; Evtodiev, Igor; Caraman, Iuliana; Nedeff, Valentin; Dafinei, Adrian
    S-au analizat spectrele de emisie fotoluminescentă a lamelor monocristaline p-GaSe cu concentraţia golurilor3•1014 cm-3 şi a lamelor intercalate cu Cd în fază de vapori la temperatura 500 °C. Durata tratamentului termic a fost de 20 şi 24 ore. Spectrul de emisie al cristalelor de GaSe conţine liniile excitonilor direcţi localizaţi cu energia de legătură ~6 meV, prima repetare fononică a acestora (ħωf =20 meV) şi banda de emisie a excitonilor indirecţi cu emisia fononilor cu energia 15 meV. Spectrul de emisie a compozitelor obţinute prin intercalarea lamelor de GaSe cu Cd se obţine în rezultatul suprapunerii benzilor de emisie a compusului CdSe şi banda impuritară a monoseleniurii de galiu. Structura spectrului FL depinde de durata tratamentului termic. La majorarea timpului de tratament se amplifică subbanda corespunzătoare compusului CdSe.
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    PREPARATION AND CHARACTERIZATION OF Ga 2O 3 AND GaN NANOPARTICLES
    (SPIE, 2015) Rusu, Emil; Ursachi, Veaceslav; Raevschi, Simion; Vlazan, Paulina
    In this communication, we present results on preparation of GaN nanoparticles by conversion of Ga 2O 3 nanocrystals in a flow of NH 3 and H 2. The monoclinic Ga2O 3 nanoparticles have been prepared by hydrothermal method with gallium nitrate and sodium hydroxide as precursors. Ga2O 3 nanowires are produced with increasing the duration of the hydrothermal process up to 24 hours. The production of β-phase Ga2O 3 has been confirmed by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. According to XRD, Raman and FTIR spectra, wurtzite type GaN nanocrystals with an average size of 28.6 nm are obtained by nitridation of Ga2O3 nanoparticles. Doping of Ga2O 3 nanomaterial with Eu 3+ ions in the hydrothermal process is demonstrated, and the emission spectra of this Eu-doped nanomaterial are compared with those of Eu-doped nanoparticles prepared previously by solid state reactions.
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    PHOTOELECTRIC AND PHOTOLUMINESCENCE PROPERTIES OF CdTe–GaTe COMPOSITE
    (2016) Caraman, Iuliana; Spalatu, Nicolae; Evtodiev, Igor; Untila, Dumitru; Leontie, Liviu; Caraman, Mihail
    A GaTe–CdTe composite was obtained by thermal treatment at 1020 K of GaTe single crystals in Cd vapor atmosphere. The composite photoluminescence, photoconductivity, and com- position are studied in this work. The photosensitivity and photoluminescence band structure are determined for both the primary crystals and the composite. The CdTe crystallites create, in the GaTe bandgap, recombination and trapping levels, which determine the structure of the photoluminescence spectra and the spectral range of composite photosensitivity. The photoluminescence spectrum of the composite at 80 K contains characteristic bands of both composite components, GaTe and CdTe. From the analysis of thermally stimulated luminescence curves, the energies of the electron trapping levels in the composite are determined.
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    OPTICAL PROPERTIES OF GaTe-ZnTe NANOLAMELLAE COMPOSITE
    (2015) Spalatu, Nicolae; Evtodiev, Igor; Caraman, Iuliana; Evtodiev, Silvia; Rotaru, Irina; Caraman, Mihail; Untilă, Dumitru
    A material composed of GaTe and ZnTe crystallites with average diameter of ~ 37 nm and 68 nm respectively was obtained by heat treatment at the temperature of 1000K and 1073K of GaTe plates in Zn vapour for 24 hours. The absorbance spectra of composite material obtained at 1073K and that calculated from diffuse reflection using the Kubelka-Munk formula contains the bands characteristic for light absorption in ZnTe and GaTe crystallites. The photoluminescence spectrum of composite material at the temperature of 80K is composed to the excitonic band in GaTe and impurity bands of ZnTe crystallites.
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    LUMINESCENT PROPERTIES ON ZnO:Cr NANOCRYSTALS AND THIN LAYERS
    (Springer Nature, 2020) Goglidze, Tatiana; Dementiev, Igor; Goncearenco, Evghenii; Iurieva, Tatiana; Nedeoglo, Dumitru; Nedeoglo, Natalia
    Both 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.
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    LUMINESCENT PROPERTIES OF Sb-DOPED ZnSe SINGLE CRYSTALS
    (2019) Sushkevich, Konstantin; Goncearenco, Evghenii; Nedeoglo, Natalia; Nedeoglo, Dmitrii
    Photoluminescence (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.
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    SYNTHESIS AND OPTICAL PROPERTIES OF Ga2O3 NANOWIRES GROWN ON GaS SUBSTRATE
    (Elsevier, 2019) Leontie, L.; Sprincean, Veaceslav; Spaltu, N.; Cojocaru, A.; Susu, Ana; Lupan, Oleg; Vatavu, Elmira; Carlescu, Aurelian; Untila, Dumitru; Caraman, Iuliana; Evtodiev, Igor; Tiginyanu, Ion; Caraman, Mihail
    Gallium oxide (β-Ga2O3) nanowires were synthesized by heat treatment of single crystal β-GaS plates in air. Crystal structure and composition of synthesized materials were studied by X-ray diffraction, energy dispersive X-ray spectroscopy and Raman spectroscopy. Thermal treatment of β-GaS plates at 1023 K leads to the formation of a Ga2O3 (native oxide) layer on β-GaS (0001) surface of plates. Layer thickness and size of Ga2O3 wires contained were found to depend on temperature and duration of applied heat treatment. For 1023 K and 6 h, the length of Ga2O3 wires laid in the range from units to tens of nanometers, while for 1123 K and 30 min, between 30 and 40 μm.
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    INFRARED PHOTOLUMINESCENCE OF ZnSe:GD CRYSTALS
    (Elsevier, 2015) Colibaba, Gleb; Goncearenco, Evghenii; Nedeoglo, Dmitrii; Nedeoglo, Natalia
    Photoluminescent 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.
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    PHOTOLUMINESCENCE OF ZnSe SAMPLES DOPED WITH ANTIMONY AND IODINE
    (Elsevier, 2021) Sushkevich, Konstantin; Goncearenco, Evghenii; Nedeoglo, Natalia; Nedeoglo, Dmitrii
    Photoluminescence (PL) spectra of ZnSe samples grown by Chemical Vapour Transport (CVT), Physical Vapour Transport (PVT), and from melt have been studied in the temperature range from 100 to 300 K. Impurity-defect composition of the studied samples was varied by doping with antimony (Sb) or iodine (I), as well as co-doping with Sb and I, both during the crystal growth and crystal annealing in the respective melts. It is established that the PL band with maximum at (570–580) nm is present only in the spectra for ZnSe samples co-doped with Sb and I, independent of growth technique mand doping method. The (SbSe–ISe) radiative centre, with the energy level placed 0.5 eV above the valence band top, is proposed to be responsible for this PL band.