Facultatea de Fizică şi Inginerie / Faculty of Physics and Engineering

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    Composition and surface optical properties of GaSe: Eu crystals before and after heat treatment [Articol]
    (2024) Sprincean, Veaceslav; Haoyi, Qiu; Tjardts, Tim; Lupan, Oleg; Untila, Dumitru; Aktas, Oral Cenk; Adelung, Rainer; Leontie, Liviu; Cârlescu, Aurelian; Gurlui, Silviu; Caraman, Mihail
    This work studies the technological preparation conditions, morphology, structural char- acteristics and elemental composition, and optical and photoluminescent properties of GaSe single crystals and Eu-doped β–Ga2O3 nanoformations on ε–GaSe:Eu single crystal substrate, obtained by heat treatment at 750–900 ◦C, with a duration from 30 min to 12 h, in water vapor-enriched atmosphere, of GaSe plates doped with 0.02–3.00 at. % Eu. The defects on the (0001) surface of GaSe:Eu plates serve as nucleation centers of β–Ga2O3:Eu crystallites. For 0.02 at. % Eu doping, the fundamental absorption edge of GaSe:Eu crystals at room temperature is formed by n = 1 direct excitons, while at 3.00 at. % doping, Eu completely shields the electron–hole bonds. The band gap of nanostructured β–Ga2O3:Eu layer, determined from diffuse reflectance spectra, depends on the dopant concentration and ranges from 4.64 eV to 4.87 eV, for 3.00 and 0.05 at. % doping, respectively. At 0.02 at. % doping level, the PL spectrum of ε–GaSe:Eu single crystals consists of the n = 1 exciton band, together with the impurity band with a maximum intensity at 800 nm. Fabry–Perrot cavities with a width of 9.3 μm are formed in these single crystals, which determine the interference structure of the impurity PL band. At 1.00–3.00 at. % Eu concentrations, the PL spectra of GaSe:Eu single crystals and β–Ga2O3:Eu nanowire/nanolamellae layers are determined by electronic transitions of Eu2+ and Eu3+ ions.
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    Synthesis and optical properties of Ga2O3 nanowires grown on GaS substrate [Articol]
    (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.