Absorption and photoconductivity of PbMoO4 crystals [Articol]

Abstract

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.