Ni-Ion and \gamma -Ray Irradiated Silica-Based Glasses Characterized by Luminescence and Raman Spectroscopies

An experimental investigation of Ni-ion (energy 3.6 MeV/nucleon) and \gamma -ray irradiation effects on three different types of silica-based glasses: N-BK7 and two pure-silica (Herasil and Suprasil) samples has been conducted. Confocal micro-Raman (CMR) and confocal microluminescence experiments (CML) allowed investigating the glass structural and emission modifications caused by both radiation types. Raman data recorded in the ion-irradiated samples provide evidence for increased concentration of the three membered rings in the pure-silica samples and of the boron nonbridging oxygens in BK7 in the first 15~\mu \text{m} from the surface. The principal CML results, obtained under 325-nm excitation, concern the dose dependences of green light emissions detected at ~530 nm in pure silica and 550 nm in BK7. The related emitting centers are located in the first micrometer under the surface exposed to Ni ions. When exciting these samples at 633 nm, the signature of the Nonbridging Oxygen Hole Center (NBOHC) is detected in the irradiated silica materials. NBOHCs feature the expected dose dependences in the \gamma -ray irradiated samples. Considering the Ni-irradiated materials, their CML profiles have similar shape, suggesting that their concentration is almost constant up to 15- \mu \text{m} depth and then decreases quickly. The CML spectra of the BK7 pristine sample are dominated by a 780-nm emission, whereas after irradiation, a signal peaking at 750 nm becomes preponderant. Such activity follows a sublinear (Dose 0.5 ) growth under \gamma rays; this result if confirmed at lower doses suggests a generation from matrix site rather than a precursor site. The CML profile in the Ni-irradiated specimen suggests that most of the radiation-induced defects are located in the first 15~\mu \text{m} under the surface. The CMR and CML data of the Ni-irradiated materials qualitatively agree with the energy loss simulation performed using the SRIM software.