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Influence of Yb3+ and Er3+ environment on its’ luminescent properties in oxide glasses under irradiation
Vera Pukhkaya
Vendredi 29/11/2013, 14:00-17:00
Amphi. Becquerel, École Polytechnique, Palaiseau, Institut Polytechnique de Paris (IPP), Palaiseau

Irradiated aluminosilicate glasses are used in various optical applications. Irradiated phosphate glasses are applied in nuclear waste storage and dosimetry. Irradiation with strong doses (> 109 Gy) used in nuclear waste storage leads to glass network modifications. It is important thus to understand the evolution of glass structure under irradiation.

Yb- and Er-doping allows producing of high power IR-lasers with 1.07 μm and 1.54 μm emissions, respectively. Irradiation impacts the spectroscopic properties of RE-doped glasses. Such influence is essential to understand while producing fiber lasers and amplifiers because they can be used in satellite communication and therefore exposed to the irradiation in space.

The main credit in changes of spectroscopic properties is due to radiation-induced point defects. However, the tendency of Yb3+ ions to form clusters can play its role in defect evolution. Moreover, Yb cluster influences Yb3+ luminescence. In this Ph.D. the central question is around the role of cluster in the glass evolution under irradiation. It is thus essential to understand the way of charge trapping by well-diluted Yb3+ ions and those in clusters and their interactions with point defects, to predict the response of Yb3+ luminescent properties under ionizing irradiation treatment.

In present dissertation, the characterization of the effect of Yb3+ environment under irradiation in oxide glass matrices on the evolution of luminescent properties was aimed. In order to compare role of glass chemical composition, 4 different aluminosilicate (AS) and 4 phosphate glasses were chosen. In AS glasses increasing of Al content (decreasing of non-bridging oxygens number) leads to more Yb cluster formation whereas in phosphate glasses there is less Yb cluster due to structural difference between PO4 and SiO4 tetrahedra. In phosphate PO4 group on oxygen is always non-bridging leading to better dissolution of RE3+ ions in phosphate matrices.

The purpose was to compare these glasses in terms of irradiation effects. To follow that, irradiation with electrons of 2.5 MeV (SIRIUS facility, LSI) was carried out in vast achieved dose variation (105-2∙109 Gy). Investigation of radiation-induced point defects in glasses, their evolution within time and temperature and their correlations with luminescent properties of Yb3+ ions under the conditions mentioned above was the general approach in this work.

It is shown in this Ph.D. that the cluster presence limits the defect production in the high dose range, whatever the glass composition (AS or phosphate). Moreover, the point defect fading is slow down by a clustering effect in the glass.

Cooperative luminescence of Yb3+ is a powerful Yb cluster probe because it is observed due to Yb3+ - Yb3+ pair interactions. It is known that Yb cooperative emission decreases under irradiation. The role of particular point defects in this decrease is discussed.

The two-regions trends for the 2F5/2 lifetime as a function of the lg(dose) are observed. 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.

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 Yb/Er-codoped aluminosilicate glasses Yb3+ ions can affect Er3+ environment resulting in 1.54 μm emission. In particular, Yb3+ - Er3+ pair formation is suspended. The influence of e¯-irradiation on Er3+ luminescence is discussed as well.

Contact : Nadege OLLIER


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