Some features of absorption and photoluminescence of wulfenite (PbMoO4) crystals

Abstract

A description of experimental results of studying the optical absorption and photoluminescence (PL) of tetragonal (class 4/m ) PbMoO4 crystals is given. The light transmitted and reflected in the polarized radiation for both orientation (E || C4 and E ┴ C4,) at 300 and 77 K is measured. The spectral dependence of the absorption coefficient at the edge absorption (λ ≈ 0.30.5 μm) shows that the edge absorption is determined by phonon-assisted indirect transitions. Spectral characteristics of the absorption coefficient of crystals with two radiation polarizations in the temperature range from 77 to 300 K are investigated. The measured spectral dependence of the absorption coefficient at two orientation of polarization of light and the known theoretical dependence were combined and compared for determination the types of optical transitions in fundamental absorption of PbMoO4 crystals. Limited energies Eg ind and Eg dir for E|| C4 and E ┴ C4 were found. A detailed investigation of the fundamental absorption of PbMoO4 crystals is given. The direct optical edge Eg at T = 300 K is 3.28 eV and 3.36 eV for E || C4 and E ┴ C4, respectively. Pure lead molybdate single crystals grown by the Czochralski method were investigated by optical absorption and PL methods. The radiative recombination mainly for interbands transitions in PbMoO4 crystals excited with a 365-nm wavelength was observed and analyzed. All PL spectra undergo a Stokes shift and can be characterized by a large half-width. The absorption spectra were compared with both PL and calculated emission intensity for a degenerate electron gas of the conduction band and nondegenerate hole gas in the valence band for direct transitions [1]