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Zahner S.,University of Bayreuth | Kador L.,University of Bayreuth | Allakhverdiev K.R.,TUBITAK - Marmara Research Center | Allakhverdiev K.R.,Azerbaijan National Academy of Aviation | And 2 more authors.
Journal of Applied Physics

Crystals of the layered chalcogenide semiconductor gallium selenide (GaSe) were studied with fluorescence lifetime imaging microscopy in the frequency domain, the excitation source being a cw frequency-doubled Nd:YAG laser modulated between 25 and 50 MHz. The non-zero photoluminescence (PL) lifetime leads to a change of the relative modulation amplitude (m) and a phase lag (φ) of the luminescence with respect to the excitation. The data were analyzed with the polar-plot (or phasor) approach by plotting m sin φ versus mcos φ. Data points of different spots on the sample show strong inhomogeneities and form looping structures in the polar plot. Moreover, they extend distinctly outside the characteristic semi-circle. The latter point is due to the nearly quadratic variation of the PL signal with excitation intensity, whereas the looping structures indicate the presence of energy transfer processes between (at least) two different emitting states. The analysis of the data shows that the same exciton state(s) are involved in both absorption and PL emission of GaSe. © 2014 AIP Publishing LLC. Source

Angermann Ch.,University of Bayreuth | Karich P.,University of Bayreuth | Kador L.,University of Bayreuth | Allakhverdiev K.R.,Materials Institute | And 3 more authors.
Quantum Electronics

Maker fringe experiments on the layered chalcogenide semiconductor gallium selenide (GaSe) with weak cw diode lasers are presented. It is demonstrated that nonlinear photoluminescence emitted by this material and by the similar compound GaSe 0.9S 0.1 under illumination with a 632.8-nm He-Ne laser shows very strong resonance enhancement upon heating when the absorption edge and exciton levels are shifted towards the laser line. The photoluminescence appears to be strongest when the energy level of the direct exciton, which emits it, is resonant with the photon energy of the laser. The previously observed enhancement of the photoluminescence by electric fields is interpreted in this context. © 2012 Kvantovaya Elektronika and Turpion Ltd. Source

Guliyev E.,State Agency on Nuclear and Radiological Activity Regulation | Kuliev A.A.,Sakarya University | Kuliev A.A.,Azerbaijan National Academy of Aviation | Ertugral F.,Sakarya University | Ertugral F.,University of Liverpool
Nuclear Physics A

Low-energy magnetic and electric dipole excitations in the even-even isotopes 176-180Hf have been systematically studied within the rotational, translational and Galilean invariant Quasiparticle Random Phase Approximation (QRPA). The results of the calculations show that most of the states predicted to have magnetic character and the computed M1 strength in these nuclei is less strongly fragmented than in mid-shell isotopes. The results of the calculations are in good agreement with experimental data. The results of the calculations indicate the presence of a few prominent negative parity dipole K=1 states in the energy investigated region. The comparison of the calculations with the available experimental data makes possible the interpretation of the states where parity could not be assigned experimentally. © 2013 Elsevier B.V. Source

Huseyinoglu M.F.,TUBITAK - Marmara Research Center | Salaeva Z.,TUBITAK - Marmara Research Center | Secgin A.,TUBITAK - Marmara Research Center | Allakhverdiev K.R.,TUBITAK - Marmara Research Center | Allakhverdiev K.R.,Azerbaijan National Academy of Aviation
Proceedings of SPIE - The International Society for Optical Engineering

Aerosols affect the radiation budget of the Earth by scattering and absorbing the incoming solar radiation, and by acting as cloud condensation nuclei (CCN) to form clouds and/or change their properties. Because of their high spatio-temporal variability and remote nature, investigations of aerosols physical properties have been rather limited until the last few decades. Lately, multiwavelength Raman lidars became an important tool for the measurements of aerosol physical parameters. Such lidars allow to get three aerosol backscattering and two extinction coefficients (so called 3β+2α) and from these optical data the particle microphysical parameters such as number, surface area and volume concentrations, effective radius, particle size distribution, particle and volume polarizations and complex refractive index can be retrieved through inversion with regularization, principle component analysis and linear estimation techniques. During 2009-2011, using a homemade multiwavelength Raman lidar with a Quantel BrilliantB Nd:YAG laser generating also the 2nd and the 3rd optical harmonics, the spatial and temporal distribution of aerosols and their microphysical properties have been measured and evaluated in various seasons, meteorological conditions and with different horizontal measurement angles. Reliability of our results have been confirmed with the synergistic measurements done with lidars located in Greece, the EUFAR aircraft (European Facility for Airborne Research, FAAM-Bae146 aircraft), ACEMED campaign (Evaluation of CALIPSO's (Cloud-aerosol Lidar and Infrared Pathfinder Satellite Observation) aerosol classificatiomn scheme over Eastern Mediterranean) and GOSAT (Global Greenhouse Gas Observation by Satellite project). In early 2012, the addition of the scanning module mounted on the top of the telescope, allowed to obtain information about the aerosol distribution within fixed and regular time intervals in a given time frame and from various measurement angles, and thus it made possible to cover a large spatial area and to evaluate the changes in the aerosol microphysical properties in space and time. It uses Newport ESP301 Motion Controller allowing to make measurements in 340° azimuthal and ± 15° vertical scanning angles by a 300 x 600 mm plane mirror. In this paper, the description of the new multiwavelength aerosol lidar scanning system installed in the Scientific and Technological Research Council of Turkey (TUBITAK) Marmara Research Center (MRC), KA09 Laser and Lidar Laboratory is explained, and the first results obtained from the data acquired during Spring and Summer 2012 are presented by integrating the results with a geographical map of Gebze Area. © 2013 SPIE. Source

Garibov A.,Azerbaijan Academy of Sciences | Madatov R.,Azerbaijan Academy of Sciences | Madatov R.,Azerbaijan National Academy of Aviation | Mustafayev Y.,Azerbaijan Academy of Sciences | And 3 more authors.
Journal of Electronic Materials

Using Raman light scattering and Rutherford backscattering, we studied the structural disorder of layered GaS crystals before and after hydrogen (H2+) implantation with energy of 140 keV. Initially, the elemental components of GaS were distributed uniformly in depth, and this distribution remained stable up to a dose of 5 × 1015 at./cm2. Doses up to 1 × 1015 at./cm2 increased the photoresponse (from 0.66 to 5.3 times) over a wide wavelength range from 490 nm to 900 nm. Additionally, the irradiated samples displayed new photoresponse peaks with maximums at λ = 668 nm and λ = 739 nm, corresponding to new energy levels of 0.59 eV and 0.77 eV, respectively. However, further dose increase up to 5 × 1015 at./cm2 dramatically reduced the photoresponse due to structural disorder (amorphization). The experimental value of the critical dose for initial amorphization was greater than 1 × 1015 at./cm2, which agrees with the calculated value. Raman scattering confirmed the photoresponse results. © 2015, The Minerals, Metals & Materials Society. Source

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