Evolution of Yb³⁺ environment and luminescence properties under ionizing irradiation in aluminoborosilicate glasses

Yb-doped aluminoborosilicate glasses were irradiated with 2.3 MeV electron and gamma rays at different doses ranging between 10⁴ and 2.6 × 10⁹ Gy and the local structure around the Yb³⁺ ions has been studied using a combination of NMR, EPR and photoluminescence spectroscopic techniques. The spectroscopic results indicate the presence of two distinct Yb³⁺ sites in these glasses and their relative fractions depend on both the Yb concentration and the irradiation dose. These two sites can be attributed to Yb³⁺ ions with and without Yb next-nearest neighbors. The evolution of the shape of the ⁷F_5/2 → ⁷F_7/2 infrared emission band under irradiation is explained by a preferential reduction of the Yb³⁺ ions with Yb next-nearest neighbors at high integrated doses (> 10⁸ Gy). This interpretation is supported by a strong decrease of the visible cooperative luminescence under irradiation due to the reduction into the Yb pairs. In other terms, it shows an interesting effect of ionizing irradiation on the Yb clusters. A low intensity emission band appears in irradiated samples at 390 nm that can be attributed to Yb²⁺. Finally, the decrease of the Yb ³⁺ fluorescence lifetime observed under irradiation appears to be primarily due to electronic interaction of these ions with Non-Bridging Oxygen Hole Centre defects created by the ionizing radiation.