U3-LASER - SYNTHESIS AND OPTICAL-PROPERTIES( NEW ACTIVATOR ION IN VARIOUS FLUORIDE MATRICES FOR INFRARED)

Recently, there has been considerable interest in infrared diode pumpe d solid state lasers. U3+ in fluoride matrices is a good candidate, ho wever the trivalent state is not the most stable valence state. We sho w that gamma-irradiation can reduce 100% of U4+ in matrices such as Li YF4, LiYbF4 and beta-YF3, but it fails mostly in the fluoride glasses where tetravalent sites are present. A dose rate of about 500 kGy is n ecessary for reducing 1000 ppm of uranium in the single crystals. Then the conversion rate decreases with the increase of uranium concentrat ion. The large crystal-field in LiYF4 and beta-YF3 induces a large gro und multiplet splitting, allowing a four level scheme laser at room te mperature for the I-4(11/2) --> I-4(9/2) transitions terminating at th e highest energy ground multiplet. These transitions occur at 2.5, 2.8 3 and 2.97 mu m for LiYF4 and 2.29, 2.5 and 2.66 mu m in beta-YF3. Mor eover, the emission cross sections for these transitions are at least 10 times larger than the ones for 4f-4f transitions such as the emissi on at 2.7 mu m of Er3+ for example in LiF4. (C) 1997 Elsevier Science B.V.