Ionoluminescence as a sensor of the defects creation and damage kinetics: application to fused silica

(1) Centre de Sciences Nucléaires et de Sciences de la Matière, Université Paris-Sud, CNRS/IN2P3, Bât 108, 91405 Orsay, France.
(2) Centro de Micro-Análisis de Materiales, Universidad Autónoma de Madrid, C/Faraday 3, Madrid 28049, Spain.
(3) Laboratorio Nacional de Fusión, EURATOM/CIEMAT, CIEMAT, Avda. Complutense 40, Madrid 28040, Spain.

Ion Beam-Induced Luminescence (IBIL) is a very sensitive technique for the analysis of impurities and defect centers, such as those created by irradiation. In situ luminescence during ion beam irradiations can be used to investigate the microscopic processes accompanying the generation of damage and its kinetic evolution with the irradiation fluence. In this contribution we will talk about the advantages of the IBIL technique compared to other analysis techniques. We illustrate the power of ionoluminescence by showing some results obtained in amorphous silica which is a fundamental material in fusion technology [1] for optical viewports, plasma diagnostics, and safety and control systems. Degradation of optical and structural properties of silica due to irradiation is an important issue with a considerable number of features not yet sufficiently understood. We have compared the ionoluminescence in three different types of silica containing a different amount of OH impurities. For all samples, the IBIL spectrum shows two main peaks at 460 and 650 nm which have been associated with different defects in the material: Oxygen-Deficient Centers and Non-Bridging Oxygen Hole Centers, respectively. We have observed that, at the beginning of the irradiation, the red emission is much higher in the samples with high OH-content than in the samples with low OH-content, while the blue emission exhibits an opposite behavior. One of the advantages of the IL is that we can use different ions and energies, i.e. different stopping powers for the analysis. Therefore, we have compared the IBIL produced by ions with different stopping powers (dE/dx), and we observed that the kinetic evolution of the ionoluminescence varies in function of this parameter. For low dE/dx, the yield of both peaks increases monotonically with the dose. However, when we irradiate with high dE/dx, the yield of the two main emissions first increases with the fluence and then it reaches a maximum at a certain dose, where it starts to decrease. We have also studied the dependence of the dose at which this maximum is produced with the stopping power of the incident particle and we have compared our results to those obtained by other spectroscopy techniques used in silica by Awazu et al. [2], observing a good agreement between both results. Many other interesting possibilities can be studied with IBIL: application to other materials, low-temperature irradiations, irradiations at very low and very high energy to separate the electronic and nuclear regimes, irradiating with sequential and simultaneous beams, etc. We are currently investigating many of these possibilities. We conclude that the novel results obtained by comparing the IL behavior under light and heavy ions offer a useful tool to investigate structural damage in materials.

[1] A. Moroño, E.R. Hodgson, J. Nucl. Mater. 258-263 (1998) 1889-1892.
[2] K. Awazu, S. Ishii, K. Shima, S. Roorda, J.L. Brebner, Phys. Rev. B 62 (2009)  3689-3698.