IR AND OPTICAL-PROPERTIES OF PBO GLASS CONTAINING A SMALL AMOUNT OF SILICA

The IR spectrum of a PbO base glass, containing a small amount of SiO2, formed by melt quenching revealed an intense band at 844 cm(-1) besides two other weak bands which have been attributed to the vibrational modes in the silicate group. The analysis indicates that the glass contains about 4 mol% of SiO2 in the form of silicate tetrahedra isolated and disconnected in the network. The results suggest that the PbO plays the role of the glass former. The optical band gap (2.56 eV) of PbO glass was determined from the observed sharp fundamental absorption edge and the Urbach energy Delta E was found to be 16.5 x 10(-3) eV, almost equal to the energy of phonons corresponding to the internal vibrations of Pb-O. The results confirm that the thermal vibrations constitute the physical origin for the tail of the optical absorption edge.