ULTRAVIOLET-ABSORPTION EDGE STUDIES OF HEAVY-METAL OXIDE GLASSES

Ultraviolet absorption edges of many heavy metal oxide glasses includi ng systems BaO-Bi2O3 (In2O3,PbO)-R(n)O(m), BaO-TeO2-R(n)O(m) and Ta2O5 -K2O-R(n)O(m) (R(n)O(m): B2O3, SiO2, P2O5, Al2O3 and Ga2O3 etc) have b een surveyed during development of materials with high density, transp arency and scintillating efficiency. Relations between positions and s hapes of the absorption edges and glass compositions and structures ha ve been discussed. Peaks and/or shoulders at edges of absorption spect ra of many of those glasses have been reported for the first time and attributed to structural change caused by addition of some conventiona l glass formers (R(n)O(m) indicated above). Optical gaps are all found to have energies which decrease with the contents of heavy metal oxid e in the glasses. The absorption edges consist of a long Urbach tail g oing to long wavelengths and a short wavelength portion in which the a ssumption of a parabolic relation between density of states and energy gives a good fit to the Tauc equation. The optical spectra of these g lasses show typical features of electronic energy level structures sim ilar to those of semiconductors.