Origin of Radiation-Induced Darkening in Yb³⁺/Al³⁺/P⁵⁺-Doped Silica Glasses: Effect of the P/Al Ratio

Abstract

Yb/Al/P-co-doped silica glasses with different P/Al ratios were prepared using the sol-gel method combined with high-temperature sintering. The evolution of composition-dependent color centers caused by X-ray irradiation in these glasses was correlated with their structural changes, which are controlled by the P/Al ratio. Nuclear magnetic resonance (NMR) and Raman spectra have been used to characterize the glass network structure, and advanced pulse electron paramagnetic resonance (EPR) has been employed to study the local coordination atomic structures of Yb ions in pristine glasses as a function of the P/Al ratio. Si- (Si-E'), Al- (Al-E', Al-ODC, AlOHC), P- (P, P, POHC), and Yb-related (Yb) color centers in irradiated glasses have been observed and explained by optical absorption and continuous wave-EPR spectroscopies. The formation mechanisms of these centers, the structural models of glasses, and the relationship between them were proposed. Direct evidence confirms that the formation of Yb ions induced by radiation is highly dependent on the coordination environment of Yb ions in glasses. In addition, the glass network structure significantly affects the generation of oxygen hole color centers (AlOHCs/POHCs) caused by radiation. These results are useful in understanding the microstructural origin and the suppression mechanism of the radiodarkening effect by phosphorus co-doping in Yb-doped silica fibers.

Effect of Li2O substitution on structures and properties of Nd3+‐doped Al(PO3)3‐Li2O glasses

“…As previously reported, X‐ray absorption fine structure (XAFS) indicates that oxygen atoms fully occupy the first coordination shell of Yb 3+ ions in Yb 3+ /Al 3+ co‐doped silica glass . The absence of oxygen signals in APLx glasses is due to their extremely low natural abundance (∼0.038%) …”

Systematic investigation of composition effects on the radiation-induced attenuation mechanisms of aluminosilicate, Yb-doped silicate, Yb- and Yb,Ce-doped aluminosilicate fiber preforms [Invited]

“…1). Clear evidences were given for the formation of Yb 2+ ions in Yb-doped silica under ionizing irradiation [6,11,40,42]. In this case however, free electron-hole pairs are generated across the bandgap and Yb 2+ ions are no longer created by CT.…”

“…electrons). Since then, this simple idea has remained popular [12,42,44]. Yet the results below lead to envision further important mechanisms brought by Ce.…”

“…The destruction of Ce 3+ ions can result from their oxidation by hole trapping to form Ce 3++ or, alternatively, from their reduction into Ce 2+ ions by electron trapping. Whereas the first destruction route has been largely emphasized from the 60s [8,9,12,42,44], the second one has never been mentioned so far. The reason is probably that Ce 2+ ions are thought to be unstable in glasses, their ground level being close to the conduction band [41].…”

“…The reason is probably that Ce 2+ ions are thought to be unstable in glasses, their ground level being close to the conduction band [41]. Nevertheless, reduction of trivalent into divalent rare-earth ions increasingly appears to be a rather usual feature under irradiation or pumping: it has already been demonstrated for Yb [6,11,40,42] but also for erbium [21] and thulium [48]. There is no obvious reason to rule out this possibility about cerium, even if a trend cannot serve as proof.…”