Optical absorption properties of PB5GEO4(VO4)2 single crystals

Thermal and pulling conditions have been optimized in a laboratory Czochralski apparatus to yield optically homogeneous crystals of hexagonal Pb5GeO4(VO4)2. The wavelength dependence of absorption coefficient was calculated from transmission and reflection measurements in the visible region. A hypothesis regarding the zone structure in connection to the fundamental absorption edge was raised and the bandgap width corresponding to indirect transition at room temperature was determined from the α12-hv curve.