Formation of Color Centers in Glasses Exposed to Gamma Radiation

Abstract

Glasses exposed to gamma radiation develop a visible absorption band similar to the F-band developed in alkali halide crystals. The function of cerium in preventing coloration of glass was studied in detail in an ultraviolet-transmitting phosphate base glass in which its characteristic absorption could be measured. When visible absorption was thus prevented, radiation still caused a strong absorption in the ultraviolet which was associated With the electronic structure of cerium. On this basis, transition 'ions of similar electronic structure were introduced. It was found that iron, manganese, cobalt, nickel, vanadium, copper, and, under certain conditions, some other elements do suppress the formation of the visible absorption band formed in the base glass by radiation while forming more or less prominent bands in other spectral regions. Thus the colorless iron phosphate glass remained colorless under radiation and could be considered to be ''protected." Conversely, with cobalt the new band which reached into the visible was relatively intense and stable, suggesting its use to indicate radiation dose.

Synthesis and properties of cerium aluminosilicophosphate glasses

“…These cerium centers provide shallow energy 'traps' that minimize the formation of other more permanent defect centers and enable bleaching of the defects at ambient temperature, thereby limiting visible darkening due to irradiation [2]. Another proposed mechanism, based on the lack of observed changes in the Ce 3+ /Ce 4+ ratio after radiation exposure, suggests that cerium ions provide a pathway for displaced electrons to recombine with holes without permanently changing oxidation state [4,10].…”

“…In general, trapped electrons and holes are generated by the radiation and create new optical absorption bands, in some cases severely darkening the glass [4,9,10]. The presence of multi-valent cerium in the glass provides mechanisms for altering and/or bleaching the charge traps responsible for the darkening.…”

“…In any cerium-containing glass, an internal oxidationreduction (redox) equilibrium is reached between Ce 3+ and Ce 4+ [1][2][3][4][5]. Thus, cerium cations will form redox couples with other polyvalent cations, often resulting in decolorization; e.g., ceric ions (Ce 4+ ) oxidize the ferrous ion impurities (Fe 2+ ) responsible for bluegreen discoloration in silicate glasses [1,6].…”

The ESA radglass activity: a radiation study of non rad-hard glasses

“…Optical glass can be stabilized against transmittance loss caused by ionizing radiation by adding cerium (Ce) or other types of dopants to the composition [2], [3]. While doping with cerium can add a slight yellowish coloration to the glass and also shift the UV transmission edge towards longer wavelengths, it has been shown to provide good stabilization to ionizing radiation and it is the main method used nowadays to produce radiation hard (rad-hard) glasses.…”

“…As far as dioptric optical systems are concerned, it is well known that high energy radiation can cause alteration of the glasses transmission properties through ionization and displacement and the creation of coloration centers [1], [2]. Typically, reduction in the transmission is observed both in the visible and ultraviolet regions.…”