Electron and hole capture processes in Cu-doped glass exhibiting radiophotoluminescence.

Radiophotoluminescence (RPL) is a radiation effect, and materials exhibiting RPL can be used in dosimeters. In this study, we observed remarkable RPL in Cu-doped aluminoborosilicate and silica glasses upon their exposure to60Coγ-rays. The RPL intensity increased proportionally with the irradiation dose up to several hundreds of grays and then saturated beyond a certain dose level. An equation was derived theoretically to express the relationship between the RPL intensity and irradiation dose based on the RPL mechanism, in which copper ions, Cu2+and Cu+, capture electrons and holes, generated by the irradiation, respectively, resulting in a change in the valence. The equation fitted well with the experimental results, providing two parameters for the equation. These parameters are associated with the saturation dose level and sensitivity, which are important for the application of materials to dosimeters. These parameters were discussed based on electron and hole capture processes in the RPL mechanism.

Formation of color centers in a soda-lime silicate glass by excimer laser irradiation.

We have investigated defect generation in soda-lime silicate and iron-doped soda-lime silicate glasses by excimer laser irradiation in order to apply coloration due to radiation-induced defects as a coloring technique for practical glass products. The laser irradiation generated various kinds of defects, i.e., non-bridging oxygen hole centers (NBOHCs), E' centers, and trapped electron centers, as does x-ray and γ-ray irradiation. The amounts of generated NBOHCs, monitored by the absorption intensity, increased at first with the irradiation time for both the ArF and XeF lasers, and eventually became saturated. The saturated values for the ArF laser irradiation were almost the same regardless of the laser intensity, whereas those for the XeF laser irradiation were dependent on the intensity; a higher intensity generated a larger amount of NBOHCs. From the comparison of the energies of the photon and the absorption edge of the soda-lime silicate glasses, the defect generation reactions were expected to be one-photon and two-photon processes for the ArF and XeF lasers, respectively. In order to explain the defect generation behavior, we used a simple kinetic model in which the NBOHCs are reversibly generated and annihilated through the photo-reaction. The model includes a stretched exponential function, which is often observed for reactions occurring in amorphous materials. The dependences of the amounts of the generated NBOHCs on the irradiation time and intensity of the laser pulses derived from the model were consistent with the experimental results.

Fading behavior of X-ray induced color centers in soda-lime silicate glass.

The X-ray induced color centers in soda-lime silicate glass were unstable at room temperature. There was a rapid fading at short-term stage and a slow fading at long-term stage. In the short-term stage, both first-order and second-order fading kinetics played roles in the fading process, while only the first-order fading controlled the long-term stage fading.

X-ray irradiation on the soda-lime container glass.

X-ray irradiation induced defects in the commercial soda-lime container glass were studied by means of optical spectrophotometer and ESR. The induced color might be applied to producing recyclable glasses. The nonbridging oxygen hole centers (NBOHCs) were mainly responsible for the irradiation induced absorptions at 431 and 627 nm of glass. The absorption at 305 nm was attributed to the trapped electron. The induced deep color can be kept for longer than 7 months, but can be almost bleached at 300 degrees C for 20 min.

Preparation of Water-Repellent Glass by Sol-Gel Process Using Perfluoroalkylsilane and Tetraethoxysilane.

Coating films on glass substrate were prepared by sol-gel process using alkoxide solutions containing perfluoroalkylsilane (PFAS) and tetraethoxysilane (TEOS). The physical properties of the coating films were characterized by SEM, FT-IR, and XRD. And their surface properties were investigated by measuring contact angles and atomic compositions. Transparent coating films with smooth surface and uniform thickness could be obtained. The contact angles of the coating films for water and methylene iodide are extremely high, at 118 degrees and 97 degrees, respectively, and their surface free energies are about 9.7 dyn/cm. It was found that the water-repellent glass prepared is very hydrophobic and exhibits excellent water-repellency. Hydrophobic perfluoroalkyl groups are preferentially enriched to the outermost layer at the coating film-air interface, and two layers probably exist in the coating film. The upper layer oriented toward the air is composed of mainly perfluoroalkyl groups originating from PFAS, and the lower layer is composed of mainly -OSiO- groups originating from TEOS. The heat treatment after drying step cannot influence the surface enrichment of the perfluoroalkyl group. The hydrolysis reaction should be more completely done before the dip coating step to obtain lower surface free energy. The burning temperature should be less than 300 degrees C because the perfluoroalkyl group begins to decompose from this temperature. Copyright 2001 Academic Press.