2. Articole

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Start date: 2010Subject: 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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    LUMINESCENT PROPERTIES OF LOW-DIMENSIONAL ZnO:Ag POWDERS OBTAINED BY CHEMICAL DEPOSITION FROM AQUEOUS SOLUTION
    (2023) Goglidze, Tatiana; Goncearenco, Evghenii; Dementiev, Igor; Nedeoglo, Natalia; Iurieva, Tatiana; Nedeoglo, Dumitru
    Photoluminescence (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.
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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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    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, 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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    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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    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, Mihail
    GaSxSe1−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.
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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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    PHOTOLUMINISCENCE METHOD AS A TOOL FOR INVESTIGATION OPTICAL PROPERTIES OF COORDINATION COMPOUNDS WITH Eu (III)
    (CEP UPSC, 2023) Ghenea, Vladislav
    Fotoluminescența (PL) reprezintă un instrument eficient pentru investigarea proprietăților de emisie ale compușilor coordinativi ai Eu(III). Este prezentat principiul de funcționare și instrumentarea de bază a tehnicii de fotoluminescență. Configurația este descrisă și este prezentat un exemplu de date experimentale privind compusul de coordonare [Eu(μ2-OC2H5)(btfa)(NO3)(phen)]2·phen. Sunt descrise avantajele și dezavantajele de bază, precum și domeniile de aplicație.
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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.