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Item COMPOSITION AND SURFACE OPTICAL PROPERTIES OF GASE:EU CRYSTALS BEFORE AND AFTER HEAT TREATMENT(2024) Sprincean, Veaceslav; Haoyi, Qiu; Tjardts, Tim; Lupan, Oleg; Untila, Dumitru; Aktas, Oral Cenk; Adelung, Rainer; Leontie, Liviu; Cârlescu, Aurelian; Gurlui, Silviu; Caraman, MihailThis 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.Item PHOTOELECTRIC AND PHOTOLUMINESCENCE PROPERTIES OF CdTe–GaTe COMPOSITE(2016) Caraman, Iuliana; Spalatu, Nicolae; Evtodiev, Igor; Untila, Dumitru; Leontie, Liviu; Caraman, MihailA 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.Item PREPARATION, CHEMICAL COMPOSITION, AND OPTICAL PROPERTIES OF (β–Ga2O3 COMPOSITE THIN FILMS)/(GaSxSe1−x LAMELLAR SOLID SOLUTIONS) NANOSTRUCTURES(2023) Sprincean, Veaceslav; Leontie, Liviu; Caraman, Iuliana; Lupan, Oleg; Adeling, Rainer; Gurlui, Silviu; Cârlescu, Aurelian; Doroftei, Corneliu; Caraman, MihailGaSxSe1−x solid solutions are layered semiconductors with a band gap between 2.0 and 2.6 eV. Their single crystals are formed by planar packings of S/Se-Ga-Ga-S/Se type, with weak polarization bonds between them, which allows obtaining, by splitting, plan-parallel lamellae with atomically smooth surfaces. By heat treatment in a normal or water vapor-enriched atmosphere, their plates are covered with a layer consisting of β–Ga2O3 nanowires/nanoribbons. In this work, the elemental and chemical composition, surface morphology, as well as optical, photoluminescent, and photoelectric properties of β–Ga2O3 layer formed on GaSxSe1−x (0 ≤ x ≤ 1) solid solutions (as substrate) are studied. The correlation is made between the composition (x) of the primary material, technological preparation conditions of the oxide-semiconducting layer, and the optical, photoelectric, and photoluminescent properties of β–Ga2O3 (nanosized layers)/GaSxSe1−x structures. From the analysis of the fundamental absorption edge, photoluminescence, and photoconductivity, the character of the optical transitions and the optical band gap in the range of 4.5–4.8 eV were determined, as well as the mechanisms behind blue-green photoluminescence and photoconduc- tivity in the fundamental absorption band region. The photoluminescence bands in the blue-green region are characteristic of β–Ga2O3 nanowires/nanolamellae structures. The photoconductivity of β–Ga2O3 structures on GaSxSe1−x solid solution substrate is determined by their strong fundamental absorption. As synthesized structures hold promise for potential applications in UV receivers, UV-C sources, gas sensors, as well as photocatalytic decomposition of water and organic pollutants.Item OPTICAL PROPERTIES OF GaTe-ZnTe NANOLAMELLAE COMPOSITE(2015) Spalatu, Nicolae; Evtodiev, Igor; Caraman, Iuliana; Evtodiev, Silvia; Rotaru, Irina; Caraman, Mihail; Untilă, DumitruA 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.Item 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, MihailGallium 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.Item STRUCTURA CRISTALINĂ ŞI PROPRIETĂŢILE OPTICE ALE MATERIALELOR COMPOZITE OBŢINUTE PRIN INTERCALARE CU Cd A MONOCRISTALELOR DE GaSe ŞI GaTe(CEP USM, 2019) Vatavu, Elmira; Dmitroglo, Liliana; Untilă, Dumitru; Sprincean, Veaceslav; Caraman, MihailFormarea prin tratament termic a monocristalelor de GaSe şi GaTe în vapori de Cd a materialului compus din cristalite de GaSe şi CdSe şi, respectiv, de GaTe şi CdTe cu dimensiuni nanometrice a fost confirmată prin analiza diagramelor XRD, imaginilor SEM şi a difuziei combinate Raman. Nanocompozitele GaSe-CdSe şi GaTe-CdTe sunt materiale fotoluminescente (FL) în regiunea oranj-roşu a spectrului. Benzile de FL a compozitelor sunt formate prin suprapunerea benzilor de FL impuritară a cristalitelor componente ale nanocompozitelor GaSe-CdSe şi GaTe-CdTe.