2. Articole

Permanent URI for this collectionhttps://msuir.usm.md/handle/123456789/47

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Author: search.filters.author.Evtodiev, IgorSubject: search.filters.subject.photoluminescence

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Now showing 1 - 7 of 7
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    Crystalline structure, surface morphology and optical properties of nanolamellar composites obtained by intercalation of InSe with Cd [Articol]
    (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 [Articol]
    (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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    Photoelectric and photoluminescence properties of CdTe–GaTe composite [Articol]
    (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 [Articol]
    (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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    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.
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    Anisotropy of the Exciton Processes in GaSe Crystals with Low S and Te Concentrations [Articol]
    (American Scientific Publishers, 2009) Evtodiev, Igor
    The anisotropy of the excitonical processes in the GaSe crystals and GaSe with small quantities of GaS(GaSe0.99S0.01) crystals has been studied through the optical specters (SO) and through the photoluminescence (PL) from the perpendicular surface on the symmetry axis C6 (E⊥C polarization) and from the flat surface parallel with the C6axis (E∥C and E⊥C polarization). The edge of the fundamental band of the GaSe crystals as well as of the GaSe0.99S0.01 and GaSe0.99Te0.01 crystals is formed at T = 78 K of the direct excitons' band. The width of the free excitons' band is determined by the processes of interaction between the excitons and optical and acoustic phonons. Phonons with energy of 17 meV and 27 meV participate to the formation of the edge towards small energies of the excitonic band in the GaSe crystals. The average energy of the phonons that participate to the formation of the excitonic absorbtion band in the GaSe crystals with small concentrations of S and Te equals 17 meV. Due to the mechanism of interaction of the excitons and phonons the integral absorption coefficient for the studied crystals (polarized E⊥C) is in small increase once with the temperature whilst the integral absorption coefficient in the maximum of the direct excitons' band. The n = 1 state is in diminution. For example, for the GaSe0.99Te0.01 crystals, α increases from 2700 at T = 78 K to 2025 cm−1 at 220 K. The edge towards small energies of the free excitons' band in the GaSe crystals and GaSe crystals with small quantities of S and Te is in a great concordance with Toyozowa's theory. The constant of interaction between the free excitons with phonons with an average energy of 135 cm−1 equals 0.9. Using the spectral characteristic of the reflection coefficient from the surface parallel to the C6 axis, there has been determined the refraction index placed in the center of the excitons n = 1 which equals 2.62 for GaSe and 2.58 and 2.55 respectively for the GaSe0.99S0.01 and GaSe0.99Te0.01 crystals. The shifting of the reflection specters towards big energies like ∼10 meV in a E⊥C polarization comparing to E∥C is determined by the difference of the oscillators' strength in these polarizations. The PL at T = 78 K specters from the surface parallel with the C6 axis (polarized E∥C) confirm the difference between the forces of the excitons' oscillators in the E∥C and E⊥C polarization. The intensity of PL bands, at the (001) surface as well as at the (100) surface depends on the excitation intensity by a function of a I = Ln force towards the emission bands of the direct and indirect free excitons the force factor is overlinear, and for the impurity nature bands it represents ∼0.5. The parameters that determine the width of the bands of excitonic PL is determined, considering the strong concentration of the structural faults at the (100) surface of the GaSe and GaSe0.99Te0.01 and GaSe0.99S0.01 GaSe crystals. Out of the spectral analysis I(L) the nature of the impurity bands has been determined, and from the PL specter structure there has been determined the energy of the accepting level which equals 93 meV from the maximum of the valence band of the GaSe crystals. Out of the analysis of the PL specter in a E∥C and E⊥C polarization (the (100) surface) it was stated that the process of emissional annihilation of the indirect excitons in the E∥C polarization takes place once with the emission of the phonons of a 38 meV energy whilst at the E⊥C polarization there are emitted phonons with an energy of 17 meV. GaSe with small concentrations of GaS and GaTe leads to the forming of a considerable concentration of localizing centers of the direct excitons and at the same time to the shifting towards small and big energies of the excitonic emission band (state n = 1) comparing to the GaSe crystals with a stoikiometric composition.
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    Optical properties of ZnO thin films obtained by heat treatment of Zn thin films on amorphous SiO2 substrates and single crystalline GaSe lamellas [Articol]
    (Elsevier, 2016) Dmitroglo, Liliana; Evtodiev, Igor; Untila, Dumitru
    Optical absorption and photoluminescence of polycrystalline ZnO films obtained by thermal oxidation of Zn thin films deposited on amorphous SiO 2 (quartz) and (0001) surface of single crystalline GaSe lamellas have been investigated. The absorption edge of submicrometric ZnO films on quartz is determined by direct transitions corresponding to an optical band gap of 3.88 eV, at 300 K. For ZnO films with thickness between 1.5 and 10 μm, the absorption threshold is of excitonic nature. Photoluminescence of polycrystalline ZnO films on amorphous quartz reaches its maximum in the orange spectral range, while that of ZnO films on oriented single crystalline GaSe substrate covers the entire visible range. [ABSTRACT FROM AUTHOR]