Spectroscopic behaviour of U(I) containing glasses

Abstract

The aim of our research is to study materials that can have applications as lasers. For this reason, as preliminar work, we prepared in our laboratory some glasses whose composition is xPbO/yNa 2O/ zSiO 2, doped with U(VI) salts (Table I), to understand the PbO influence on the formation of the UO 2+ 2 moiety, especially because the U(VI) coordination in silicate and particular lead silicate glasses is not yet completely clarified [1]. Then we measured the absorption and emission spectra at different % mol SiO 2 PbO Na 2O U (1) 49.50 49.50 - 1.00 UO 2(OAc) 2 (2) 61.50 37.50 - 1.00 UO 2(OAc) 2 (3) 61.50 37.50 - 1.00 UO 3 (4) 61.50 37.50 - 1.00 Na 2UO 4 (5) 61.67 28.67 8.67 1.00 UO 2(NO 3) 2 (6) 61.67 24.67 12.67 1.00 UO 2(NO 3) 2 (7) 61.67 21.67 15.67 1.00 UO 2(NO 3) 2 (8) 61.67 19.67 17.67 1.00 UO 2(NO 3) 2 (9) 59.50 - 39.50 1.00 UO 2(OAc) 2 1 ass. (cm −1) fluor. (cm −1) (1) 19850 (2) 19850 (3) 19850 (4) 19850 (5) 20195, 24100 18740 (6) 20012, 24190 18080, 18740, 19395 (7) 20200, 24230 18080, 18740, 19395 (8) 20350(sh), 24200 18080, 18740, 19395 (9) 20548, 21692(sh), 23873 1 18080, 18740, 19395 1 The spectrum has been measured at 4.2 K. temperatures. Their maxima are reported in T able II. The analysis of the experimental data shows: 1. the absorption spectra of glasses with only PbO as network former are different from those containing also Na 2O, and only these show the presence of the UO 2+ 2 ion. 2. the intensity of the typical uranyl luminescence [2] using same thickness glasses, decreases with the increase of the PbO percentage and in the case of the lead silicate, the fluorescence completely disappears. Therefore, it is possible to deduce: a) the lack or a very low concentration of the UO 2+ 2 moiety in systems containing a high PbO percentage and b) the stabilization of the UO 2+ 2 ion in Na 2O rich systems, i.e. in strongly basic media (and this behaviour is very strange for Weyl [3] claimed the stabilization of U(VI) as UO 2+ 2 in acid glasses). A possible explanation of the above observations could be given on the basis of structural considerations. In fact, in the case of silicate glasses, the structure (no completely defined, indeed) is made by SiO 4 tetrahedra linked in a three-dimensional network. In Such a steric situation, it could be possible for the U(VI) ion to enter an interstitial site and form an UO 2+ 2 molecular ion. On the other hand, when we add PbO that enters as network former and network modifier, the system becomes much more distorted for the strong covalency of the PbO bond (obviously respect to the NaO bond) with consequent formation of bidimensional chains or (Si 2O 5) layers linked by Pb bridges [4]. This steric situation very probably is unfavourable to the formation of the UO 2+ 2 linear ion or to its presence in the interstices. As concluding remarks, we can say that the development of this research in which we tried to understand the spectroscopic and structural behaviour of hexavalent uranium in some lead and sodium silicate glasses in which the ratio Na 2O/PbO is changed, will be the preparation and the study of the systems xPbO/yNa 2O/zSiO 2/UO 2+ 2 /Ln 3+ because, as well known, the energy migration from UO 2+ 2 to Ln 3+ ions is very interesting and conceivably applicable to lasers.