Browsing by Author "Mușinschi, Valeriu"

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Absorption and photoconductivity of PbMoO4 crystals [Articol]
(2011) Mușinschi, Valeriu; Caraman, Mihail; Mușinschi, Camelia
Spectral characteristics of the fundamental absorption coefficient and photoconductivity of PbMoO4 crystals with two polarizations in a temperature range of 77 to 300 K are investigated. The measurements of light transmitted in the polarized radiation for both orientations ( E|| C4 and E ┴ C4, C4 is the [001] crystallographic direction corresponding to the optical axis) of crystals are carried out. Spectral dependence of the absorption coefficient at the edge absorption (λ ≈ 0.3-0.5 μm) shows that the edge absorption is determined by indirect assisted by phonons transitions. The measured spectral dependence of the absorption coefficient at two orientations of polarization of light and the known theoretical dependence were combined and compared for determination the types of optical transitions in the fundamental absorption of PbMoO4 crystals. Limited energies Egind and Egdir for E|| C4 and E ┴ C4 were found. A detailed investigation of the fundamental absorption of PbMoO4 crystals is presented. A simple model of band structure of crystals is proposed. The photoconductivity of PbMoO4 single crystals is investigated on E|| C4 and E ┴ C4 at 300 K in the fundamental absorption spectral region of 2.8 to 5.0 eV. The spectral dependence of the photoconductivity is studied and discussed in conjunction with reported optical data. The monopolar character of the photoconductivity was confirmed by investigation time-of-flight motion of carriers. The present study reveals only the intrinsic photoconductivity in PbMoO4 pure single crystals. Spectral responses of the photocurrent through PbMoO4 crystals showed one spectral band in a range of 3.1 to 5.0 eV with maximums at 3.45 and 3.73 eV for E|| C4 and E ┴ C4, respectively. A good correlation of the photoconductivity bands at E|| C4 and E ┴ C4 with absorption bands at also polarizations has been demonstrated. The unipolar time-of flight motion of carriers was analyzed, and drift mobility of electrons and its temperature dependence were determined.
Optical properties of significant acousto-optic crystals [Articol]
(2009) Mușinschi, Valeriu; Syrbu, Nicolae; Mușinschi, Camelia; Caraman, Mihail
Results of the investigation of spectra in the energy ranges of fundamental absorption of PbMoO4 crystals in two radiation polarizations (E║C4) and (E ⊥ C4) of incident light in the 77-300 K temperature range are presented. Possibilities of the interpretation of particularity of absorption spectra on the basis of the proposed band structure are examined. Analysis of measurement results for reflection spectra of paratellurite TeO2 and wulfenite (PbMoO4) crys- tals within the interval 50-1000 cm-1 is presented. The Kramers–Kronig method is used to interpret the peculiarities of reflection spectra. The calculus of reflection spectra is made by the multioscillation model. The interest in the study of the optical properties of TeO2 and PbMoO4 crystals is de- termined not only by the fundamental physical mechanisms present in these materials but also by a wide spectrum of possible applications in high-speed acousto-optic devices that perform spatial, temporal, and spectral modulation of optical beams. A description of experimental results of studying the optical properties of tetragonal TeO2 (class 422) and PbMoO4 (class 4/m) crystals is given. The phenomena usually studied to obtain information on the optical properties of crystals are absorption and reflection in a large wavelength range.