REDUCTION BY GAMMA-IRRADIATION OF TETRAVALENT URANIUM IN LIYF4-U CRYSTALS FOR LASER APPLICATION

Recently, there has been a considerable interest in obtaining LiYF4 ac tivated with trivalent uranium for IR laser application. It has been s hown from the absorption spectra, that using the Czochralski method, t he uranium ions in LiYF4 are tetravalent. We show that gamma-irradiati on can reduce 100% of U4+ in U3+ in LiYF4, and the conversion efficien cy measured from the absorption spectra of the samples is studied as a function of the time of exposure and the uranium concentration. Final ly the U3+ ions obtained after gamma-irradiation are stable over a few years and a temperature of 450 degrees C is needed to oxidize them.