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Oxyhalides of bismuth BiOX (X-halogen) are very interestind materials which find various applications as X-ray luminescent screens, as anti-Stoces (frequency upshift) converters, usualluminophors, and photoconducting analyzer of linear polarized radiation in spectral region 0.24-1.2 µ. Bismuth oxyhalides provides a very convenient matrix for activation by various rare earth and 3d elements: by doping this matrix with different,is possible to obtain a wide variety of optical, luminescent and photoconducting properties.Moreover,these crystals are of essential interest in connection with the research and development work on laser materials.
The present paper gives results of the study of the anisotropy of the BiOCl, BiOBr and BiOJ singlecrystals by investigating their photoconducting spectra obtained with polarization of the E-vector of the electromagnetic wave parallel and perpendicular to each of the two axes ([100] or [010]) of the unit cell. We report so the results of the study of the chemical bonding and electronic structure of BiOX singlecrystals.
The compounds BiOX are broad band (1.80-3.50 eV) photosemiconductors.The maxima of their photoconductivity are in the interval of 0.24-1.2 µ and theirs photosensitivities are S=Iphoto/Idark = 104-106 at the temperature T = 77 K.The anisotropy of photoconducting spectra is believed to be the results of the mathlocyt type (PbFCl) crystal structure of all BiOX compounds.The crystals BiOCl, BiOBr and BiOJ have a layered structure and crystallized in tetragonal symmetry (space group P4/nmm - D74h and were prepared by the method of chemical gass transport reactions in the closed volume.The typical size of the crystals is 15x15x3 mm3 and the ab-plane of the crystals is oriented parallel to (001) crystalline plate while the c-axis is perpendicular to it.
The direction of the E-vector can be varied either by rotating the sample.The anisotropy of 3-5 was observed for the photosensitivies value S.The cange of value of polarization an the 90° (relativ of [100] or [010] crystallographic axis) caused for the cange of photoconductivity of BiOX monocrystalls a 50-100 unit.
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