Facultatea de Fizică şi Inginerie / Faculty of Physics and Engineering
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Item 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, EfimiaA 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.Item Fotoluminescenţa straturilor nanolamelare de GaSe obţinute prin intercalarea cu Cd [Articol](2012) Dmitroglo, Liliana; Evtodiev, Igor; Caraman, Iuliana; Nedeff, Valentin; Dafinei, AdrianS-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.Item Nanolamellar structures of Oxide-AIIIBVI: Cd semiconductors type for use as detectors of radiation in the UV spectral region [Articol](Technical University of Moldova, 2011-07-07) Dmitroglo, Liliana; Untila, Dumitru; Chetruș, Petru; Evtodiev, Igor; Caraman, Iuliana; Lazăr, Gabriel; Nedeff, ValentinIn the paper, optical and photoelectrical properties of GaSe and InSe single crystal films of 10-5÷10-7 m submicron thickness and of semiconductor-native oxide structures obtained by annealing at (450÷700)°C in a normal atmosphere, are studied. The absorption spectrum of InSe lamella as well as of GaSe lamella in the energetic range from the red threshold up to 4,5 eV contains three bands with a rapid increase of the absorption coefficient which varies in the limits of (100÷106) cm-1 At the energies higher than 1,25 eV and 2,01 eV for InSe and GaSe respectively the light absorption are determined by the direct optical transitions in the centre of the Brillouin zone and at the energies higher than. At the absorption coefficients of (100÷102)cm-1 the indirect optic transitions are present. 3,0 eV also by the direct optical transitions in the points of the bands high symmetry. The resistive photosensitivity bands cover the spectral range Eg≤ hν ≤ 4,5 eV for lamellar photoresistors in which electric field EC6. The resistive photosensitivity band width could be controlled by the lamella thickness for d ≥1μm. The open circuit voltage spectral distribution is analysed from which results that at the oxidation temperature of 700°C in GaSe layer at the heterojunction interface the defects are formed on which the charge carriers, collected in the junction, are dissipated. The noneequilibrium charge carrier free path is of 0,8 μm.Item Photoluminescence of Nanocomposites Obtained by Heat Treatment of GaS, GaSe, GaTe and InSe Single Crystals in Cd and Zn Vapor [Articol](2016) Evtodiev, Igor; Caraman, Iuliana; Kantser, Valeriu; Untila, Dumitru; Rotaru, Irina; Dmitroglo, Liliana; Evtodiev, Silvia; Caraman, MihailThe photoluminescence (PL) spectra of GaS, GaSe, GaTe and InSe semiconductors used as the basis materials to obtain nanocomposite by heat treatment in Zn and Cd vapor were studied. The PL spectra of ZnS–GaS, CdSe– GaSe, CdSe–InSe, ZnSe–InSe composites consist of wide bands covering a wide range of wavelengths in the antistokes region for CdSe, ZnSe and GaS crystallites from composites. The antistokes branches of spectra are interpreted as the shift of PL bands to high energies for nanosized crystallites.Item Optical properties of p -GaSe single crystals doped with Te [Articol](2009) Evtodiev, Igor; Leontie, Liviu; Caraman, Mihail; Stamate, Marius D.; Aramă, EfimOptical absorption in the region of fundamental absorption edge and photoluminescence at 78 and 293 K of p-GaSe crystals doped with Te 0.05, 0.10, and 0.05 at. % have been studied. At low concentrations 0.05 at. %, Te atoms liquidate structural defects in GaSe single crystals and modify their excitonic absorption and photoluminescence. For increased concentrations of 0.10 and 0.50 at. %, Te creates impurity states responsible for the red shift of the fundamental absorption edge of GaSe and appearance of new photoluminescence bands, B at 2.000 eV and C at 1.700 eV. The activation energies of the thermal quenching of Te-related PL bands B and C was found to be 28 and 32 meV for T 150 K and 84 and 62 meV for T 150 K, respectively.Item Photoluminescence properties of lamellar nano-composites obtained by Cd intercalation of GaSe and GaSe: Eu single crystals [Articol](2015) Untila, Dumitru; Cantser, Valeriu; Caraman, Mihail; Evtodiev, Igor; Leontie, Liviu; Dmitroglo, LilianaIn this work surface morphology, composition and photo- luminescence at 293 K and 78 K, of composite obtained by intercalation of GaSe and GaSe:Eu (0.49 at.% and 1.00 at.%) single crystal lamellas with Cd from vapor phase at 753 K and 830 K are investigated. As-obtained composite consists of CdSe and microstructured GaSe single crystallites. Photoluminescence spectrum of GaSe:Eu single crystal lamellas is composed of Eu3+ emission band 5 7 5 7 0 1 0 2( ,D F D FÆ Æ , and 5 7 1 3D FÆ transitions) and indirect exciton line in GaSe crystallites. Emission spectrum of single crystalline GaSe−CdSe composite, at 78 K and 293 K, consists of donor-acceptor band in GaSe microcrystallites and emission band of CdSe crystallites. Composite derived from the intercala- tion of GaSe:Eu (0.49 at.%) single crystals with Cd ex- hibits strong visible luminescence. Its quasi-continuous photoluminescence spectrum is produced by superposi- tion of luminescent emissions of CdSe nano- and mi- croparticles, and microstructured GaSe.Item Optical properties of bismuth oxide thin films prepared by reactive d.c. magnetron sputtering onto p-GaSe (Cu) [Articol](2008) Leontie, Liviu; Caraman, Mihail; Evtodiev, Igor; Cuculescu, Elmira; Mija, AnaBismuth oxide (Bi2O3) thin films with thickness in the range 20 – 160 nm have been deposited by d.c. reactive magnetron sputtering of Bi in an atmosphere Ar : O2 (1 : 1), onto single crystalline p-GaSe (Cu) substrates. The optical constants, n and k, of oxide films have been determined from the analysis of the polarization ellipse of the reflected radiation from outer surface of Bi2O3/p-GaSe structures. In the wavelength range 400 – 800 nm the refractive index of nanometric Bi2O3 films onto GaSe(Cu) decreases from 2.10 to 1.78 and it seen to in- crease at decreasing sample thickness. In order to determine the interaction mechanism between semiconducting oxide film and GaSe surface, the spectral characteristics of photocurrent through Bi2O3/p-GaSe junc- tion and optical absorption in the range 400 – 800 nm have been examined. As resulted from respective analyses, Bi2O3 film generates new valence bonds, which contribute to the in- crease in the density of localized states at Bi2O3/p-GaSe (Cu) junction interface.Item Photoelectric and photoluminescence properties of CdTe–GaTe composite [Articol](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 Optical properties of GaTe-ZnTe nanolamellae composite [Articol](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 Laborator de ştiinţe integrate Didact Vega pentru învăţământul preuniversitar [Articol](Tipografia "CentroGrafic" ,Cahul, 2015) Evtodiev, Silvia; Luchian, Efimia; Evtodiev, Igor; Untilă, Dumitru; Caraman, MihailExperimental investigations are a set of analysis techniques and methods, very important for today's society and in particularly for undergraduate and graduate education. To achieve the objectives and purpose in the most efficient way, in this paper were chosen solutions offered by the PASCO company (Didact Vega), whose equipments offers a wide range of procedures for conducting investigations. SPARKscience includes reading, data analysis and real time processing software, SPARKvue and capstone. Data acquisition system includes over a thousand PASPORT sensors for physics, chemistry, biology and environmental engineering. The SPARK mobile system can be used for experimental investigations both in laboratory and in the field. Integrated Science Laboratory contains a broad and well-structured base of labs (SPARKlab) offers to pupil/student/teacher the posibility to increase the level, volume and quality of experimental investigations in the field of Integrated Sciences .