The degrading laser oscillation behaviour in YAG crystals is attributed to the production of colour centres, induced by UV light irradiation. The optical absorption spectrum of UV induced colour centres is investigated using time resolved transient absorption spectroscopy technique. The UV generated spectrum is found to consist of the superposition of three broad absorption bands E1, E2 and E3 peaked near 1.2 × 104, 2.0 × 104, and 2.8 × 104 cm−1, respectively. Various experiments, such as additive coloration, ESR, thermoluminescence, and optical absorption measurement are made. On the basis of experimental results, a model is proposed for the E1, E2 and E3 bands, which are explained by colour centres trapping an electron at an anion vacancy site.
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Katsumi Mori (1977) studied this question.
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