Influence de l'environnement des ions Yb3+ et Er3+ sur l'évolution de leurs propriétés de luminescence dans des verres d'oxydes sous l'irradiation ionisante

We have investigated the effects of ionizing irradiation (e¯- and γ-) on the Yb3+ and Er3+ luminescent properties in aluminosilicate (AS) and phosphate glasses by trying to understand the impact of initial Yb3+ environment and mostly the role of Yb cluster. For that, AS and phosphate glasses containing different amount of Yb clusters were irradiated in 104-2∙109 Gy dose range. At first, we have shown that the point defect fading is slow down by a clustering effect in the glass. We have obtained a 2-step dependence of point defects quantity versus lg(dose). The cluster presence limits the defect production in the high dose range, whatever the glass composition (AS or phosphate). Consequently, we observed the same two-regions trends for the 2F5/2 lifetime as a function of the lg(dose). But for high content of cluster, the lifetimes value decreases linearly within lg(dose). This result does not depend on the glass type nor on the rare earth element (Er3+), implying a more general mechanism that implying one type of defect in particular. Secondly, we have interpreted the strong variation of the complex EPR signal in phosphate glasses within glass composition, dose and time with the formation of at least 8 point defects. In addition, the origin of the luminescent diamagnetic defect is discussed.Nous avons étudié les effets de l'irradiation ionisante (e¯- et γ-) sur les propriétés luminescentes des ions Yb3+ et Er3+ dans des verres aluminosilicates (AS) et phosphates en essayant de comprendre l'impact de l'environnement initial de Yb3+ et surtout le rôle des clusters d'Yb. Pour cela, des verres AS et phosphates contenant les quantités différentes de clusters d'Yb ont été irradiés à des doses comprises entre 104 et 2∙109 Gy. Nous avons montré que la relaxation des défauts ponctuels est ralentie en présence de clusters d'Yb dans le verre. La quantité de défauts ponctuels en fonction du lg(dose) est stable aux faibles doses puis décrit une courbe en cloche. La présence des clusters d'Yb limite la production de défauts aux doses élevées, quelle que soit la composition du verre (AS ou phosphate).En conséquence, la variation de la durée de vie de l'état excité 2F5/2 en fonction du log de la dose décrit deux régions. Pour un fort contenu de cluster d'Yb, la durée de vie diminue linéairement avec le log de la dose. Ce résultat ne dépend pas du type de verre, ni de la nature de l'élément terre rare (Er3+). Ceci signifie qu'il existe un mécanisme plus général n'impliquant pas un 'un type de défaut particulier. De plus, la complexité du signal RPE dû aux défauts ponctuels dans les verres phosphates a été interprétée grâce à la forte évolution de celui-ci en fonction de la composition du verre, de la dose et du temps. Au moins 8 défauts ponctuels paramagnétiques ont été identifiés ainsi qu'un défaut diamagnétique luminescent dont l'origine est discutée

Point defect stability in gamma irradiated aluminoborosilicate glasses: Influence of Yb3+ doping ions

International audienceYb-doped aluminoborosilicate were irradiated with gamma rays at 10(4), 10(5), 10(6) and 10(7) Gy. The thermal stability as well as the recovery at room temperature of paramagnetic point defects such as Boron Oxygen Hole Center (BOHC), peroxy radicals and E' center were studied. At first, doping with Yb induced a saturation of the E' defect production and more importantly, the E' center recovering temperature was decreased by 50 degrees C. E' and BOHC defects both showed a limited stability at room temperature. By doping with Yb the glasses, the fading time of defects and in particular the BOHC defect recovery was modified. The BOHC defect showed moreover a larger sensitivity to photobleaching compared to the E' centers. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved

New insights on P-related paramagnetic point defects in irradiated phosphate glasses: Impact of glass network type and irradiation dose

International audienceP-related paramagnetic point defects were studied in irradiated Yb-doped phosphate glasses by electron paramagnetic resonance spectroscopy (X and Q-bands). A strong impact of the glass network type on the defect nature is shown. In all glasses, r-POHC defects formation is in strong correlation with Q(2) tetrahedra amount supporting the structure of r-POHC. Ultra-phosphate glasses contain the larger defect type: Peroxy radicals, P-1, P-2, and P-4 defects whose formation is linked to Q(3) tetrahedra presence. In meta-phosphate and poly-phosphate glasses, peroxy radicals appear with r-POHC thermal recovery. In meta-phosphate glasses, a combination of P-1 and P-3 defects was evidenced for the first time, whereas in poly-phosphate glasses, only P-3 defects were identified. Dose effect as well as defect recovery were analyzed. (C) 2014 AIP Publishing LLC

Study of formation and sequential relaxation of paramagnetic point defects in electron-irradiated Na-aluminosilicate glasses: Influence of Yb

International audienceParamagnetic defects in electron irradiated Yb-doped Na-aluminosilicate glasses were studied. In particular, we paid more attention to characterize the defects with Electron Paramagnetic Resonance in links with the glass structure which was analyzed by Raman spectroscopy and Magic Angle Spinning Nuclear Magnetic Resonance. Under e(-)-irradiation hole centers on non-bridging oxygens bonded to Si with close presence of Na+, peroxy radicals, hole centers on oxygens bonded to Al (Al-OHC) and E' centers were detected. Doping glasses with Yb gives rise to more Al-OHC defects. Formations of hole centers and Al-OHC defects as well as their sequential relaxation are linearly anticorrelated. After the end of irradiation, the total amount of paramagnetic defects decreases in 2 months and then remains stable. The relaxation curve presents 2 regions with different rates of defect recovery. We showed in particular that the presence of Yb-clusters in the glasses acts on the relaxation of paramagnetic point defects by decreasing significantly the recovery of defects. (C) 2013 Elsevier B.V. All rights reserved

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

International audienceYb-doped aluminoborosilicate glasses were irradiated with 2.3 MeV electron and gamma rays at different doses ranging between 10(4) and 2.6 x 10(9) 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 F-7(5/2) -> F-7(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 (>10(8) 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 Yb3+ 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. (C) 2010 Elsevier B.V. All rights reserved