Structural and Optical Correlation of Gamma-Irradiated 3d Transition Metals-Doped Lithium Disilicate Glasses

Undoped lithium disilicate glasses together with glasses of the same nominal composition containing 0.2 % of one of the 3d transition metal oxides (TMO) were prepared. Combined optical and FT infrared absorption spectral analysis were carried out for the prepared glasses before and after gamma irradiation with a dose of 8 Mrad. The optical spectrum of undoped glass reveals strong UV absorption which is related to the presence of unavoidable trace iron impurities (mainly Fe3+ ions). UV/Visible absorption spectra of 3d TM ions show additional characteristic absorption bands due to each respective TM ion. The TM ions mostly exhibit the higher valance or tetrahedral coordination states. Gamma irradiation of the undoped glass produces some variations in the optical spectra. The UV spectra reveal a slight increase in intensity while the visible spectra exhibit an induced defect at about 420 nm due to a silicon oxygen hole center or a nonbridging oxygen hole center. Some TM ions are assumed to share or compete for generated electrons and positive holes during the irradiation process. Infrared absorption spectra of the glasses reveal repetitive characteristic vibrational bands due to bending, symmetric stretching and antisymmetric stretching of the Si-O-Si or O-Si-O modes in the silicate network. The introduction of TM ions within the doping level (0.2 %) causes no effect on the IR spectra. The minor effects of irradiation on the IR spectra are related to some changes in the bond angles and/or bond lengths of some structural building units.