The effect of gamma-rays on the optical properties of bismuth phosphate glasses

Abstract

The study of the optical absorption spectra in solids provides essential information about the band structure and energy gap in both crystalline and noncrystalline materials. The lower-energy part of the absorption spectrum gives information about the atomic vibrations and the higher-energy part of the spectrum gives a knowledge about electronic states in the normal material. From many amorphous materials an exponential dependence of absorption coefficient on photon energy hro was deduced in general form by Davis and Mott [1] 5(0)) = B(~o)- Eopt)n/hfO (1) where B is a constant and n is an index determined by the nature of the electronic transitions during the absorption process. It has been found [2] that a reasonable fit of Equation 1 with n = 2, particularly at the higher absorption values of the edge, for many amorphous materials is achieved. High-energy radiation such as gamma-rays changes the physical properties of the materials that it passes through. The changes are strongly dependent on the internal structure of the absorbed substances (such as glasses). It may be expected that gamma-rays can cause ionization (or excitation) of the orbital electrons, and possibly displacement of atoms from their sites in the glass lattice. The photoconduction electrons produced will go back and forth and then become freely or loosely bound to trapping centres somewhere in the glass matrix. These new electronic configurations would cause a change in the optical properties of glasses. In this work we studied the optical properties of unirradiated and irradiated Bi203-P205 glasses. Our results are discussed in the light of the approaches mentioned above. Bismuth phosphate glasses were prepared from laboratory reagent grades of Analar phosphorus pentoxide (P205) and Analar bismuth oxide (Bi203) using open alumina crucibles. Details of the preparation technique and chemical analysis of these glasses were given in [3]. The absorption measurements for our glass samples were made using a UV-160 Shimadzu spectrophotometer in the wavelength range 200-1100 nm. The optical density (absorbance) data were obtained directly from this instrument during measurements. The glass specimens were exposed in air to different 7-doses using a 6°Co gamma cell 220 as a source of gamma-radiation. An exposure rate of 1.59 × 104 Gyh -1 was used at room temperature.