Visible optical spectra of [MATH]-irradiated uranium - doped ZBLAN fibres

Actinides, particularly uranium, are again of interest because these elements provide a broad spectroscopic tunability and open a new field of fibre laser applications. The uranium ion possesses many oxidation states, the most stable being U 4+ and U 6+ , U 3+ is an unusual oxidation state in fluorides. U 3+ is of interest because it can provide an efficient laser emission of between 2 and 2.7 μm. We report visible absorption and fluorescence spectra of pure and γ-irradiated uranium-doped ZBLAN fibres. We show that γ irradiation leads to a high reduction of U 4+ into U 3+ , which is stable over a few years. Strong absorption bands of U 4+ and U 3+ , centered at 650 nm and 860 nm respectively, enable us to estimate the change of the uranium oxidation state