Ge-codoping effect on X-ray-induced photodarkening in Al-doped and Dy-Al-doped silica glass

Abstract

X-ray induced photodarkening and its suppression by Ge-codoping were investigated in Al-doped, Dy-doped, and Dy-Al-doped silica glasses. Absorption bands of 4f-4f5d transition of Dy2+ were determined in Dy-Al-doped silica glass fabricated by Si nano-powders as a reducing agent, and it was found that pair generation of Dy2+ and Al-OHC was occurred in X-ray irradiated Dy-Al-doped silica glass. Ge-codoping suppresses the above-mentioned pair generation and instead forms the pair of GEC and GLPC+. Similar suppression effect of Ge-codoping was observed in Al-Ge-doped silica glass, where pair generation of Al-OHC and Al-E’ center was suppressed. To investigate the stability of defects, annihilation processes during thermal annealing was measured. Al-OHC and Dy2 + are destabilized by Ge-codoping in Al-doped and Dy-Al-doped silica glasses, while GEC is stabilized in Al-Ge-doped and Dy-Al-Ge-doped silica glasses. Based on these results, local structure models around Al, Ge, and Dy ions and possible mechanisms of photodarkening were proposed

Effect of P/Al ratio on the X‐ray induced darkening in Dy‐doped silica glasses at visible wavelengths

“…The Si related defects of NBOHC and Si–E′ were observed at 4.75 and 5.8 eV with FWHM of 1.02 and 0.8 eV respectively, showing absorption at UV region. The Dy 2+ can be generated during UV irradiation 32,33 by reaction of Dy 3+ + e ‒ + hν → Dy 2+ with absorption peaks of 3.60 and 4.72 eV and FWHM of 1.12 and 1.02 eV, respectively 18 . The oxygen deficiency centers (ODC, ≡Si··M≡, M is Si or Al) are generated from Si‐E′ and M‐E′, showing absorption at 5.08 eV with FWHM of 0.81 eV.…”

Difference between X-ray-induced and 451 nm LD-induced photodarkening in DyAlGe-doped silica glasses

“…By Ge-codoping, GEC and GLPC + are easily generated, and Dy 2+ and Al-OHC are hard to be generated, since the trap levels of GEC and GLPC + are deeper than those of Dy 2+ and Al-OHC. 8) On the other hand, in the case of LD-PD, the defects are caused via excitation of Dy 3+ by 450 nm LD. This can be confirmed from the fact that PD does not occur in F (0).…”

“…In order to investigate PD in Dy-doped silica glass in detail, defect formation induced by X-ray was investigated in the preforms. 7,8) Al-OHC [Al Oxygen Hole Center: ≡Al-O ̇-Si≡ (≡ denotes triple-fold coordination with O, and・denotes a paramagnetic electron)] 9,10) and Dy 2+ are pair-generated. 8) Figure 1(a) shows our proposed model of local structure before and after X-ray-induced-PD (X-PD).…”

“…7,8) Al-OHC [Al Oxygen Hole Center: ≡Al-O ̇-Si≡ (≡ denotes triple-fold coordination with O, and・denotes a paramagnetic electron)] 9,10) and Dy 2+ are pair-generated. 8) Figure 1(a) shows our proposed model of local structure before and after X-ray-induced-PD (X-PD). Since the absorption of Al-OHC and Dy 2+ is large both at the excitation and oscillation wavelengths (451 nm and 582 nm) of the Dydoped fiber laser, as shown in Fig.…”

“…However, when the Ge concentration was higher than ∼2.5 wt%, the suppression effect turned to decrease. 7,8) It is unclear why the suppression effects of Ge-codoping were different for X-PD and LD-PD. In this study, we investigated Ge co-doping effect on LD-PD, and clarified the difference from the effect on X-PD.…”