VISIBLE OPTICAL-SPECTRA OF GAMMA-IRRADIATED URANIUM-DOPED ZBLAN FIBERS

Actinides, particularly uranium, are again of interest because these e lements 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 U4+ and U6+. U3+ is an unusual oxidation state in fluorides. U3+ is of interest because it can provide an effi cient laser emission of between 2 and 2.7 mum. We report visible absor ption and fluorescence spectra of pure and gamma-irradiated uranium - doped ZBLAN fibres. We show that gamma irradiation leads to a high red uction of U4+ into U3+, which is stable over a few years. Strong absor ption bands of U4+ and U3+, centered at 650 nm and 860 nm respectively , enable us to estimate the change of the uranium oxidation state.