CRYSTALLIZATION AND OPTICAL MEMORY EFFECT OF OXIDE GLASSES

Crystallization of IR-transmitting glasses caused by the light (laser) irradiation will be utilized for the ''optical memory'' effect in the field of optoelectronics, and the change of transmittance (T) and/or reflectance will be recorded. Therefore, characterization of the crystalline phase is important for the development of an ''optical memory'' device. Isothermal annealing of iron tellurite, calcium gallate and calcium aluminate glasses resulted in a drastic decrease of T in the IR region due to the crystallization. In the calcium gallate glass, formation of calcium gallate and calcium ferrite (CaFe2O4) was confirmed by XRD. Fe-57-Mossbauer spectra showed the formation of calcium ferrite phase having the Fe3+(Oh)/Fe3+ (Td) ratio of unity. Crystallization of iron tellurite glass resulted in the formation of paratellurite (alpha-TeO2) and iron tellurite, and the latter had a larger DELTA (0.86 mm s 1) than the original glass (DELTA = 0.76 mm s-1). Mayenite (12CaO.7Al2O3) phase having large DELTA (1.67 mm s-1) was precipitated in the matrix of calcium aluminate glass, together with a small amount of iron-containing crystalline phase which had smaller DELTA (0.66 mm s-1). These results suggest that the Mossbauer effect is very effective for studying the relationship between the crystallization and ''optical memory'' effect of glasses, in which the Fe3+ is originally present at the substitutional site of NWF, i.e. Ga3+, Al3+ and Te4+.