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Spectroscopic Elucidation of Lanthanide Cation Dissolution Mechanism in Borosilicate Glass Hong Li a,1, Zheming Wang b, Liyu Li a, Denis M. Strachan a, Yali. Su a, A.G. Joly b a Pacific Northwest National Laboratory, Richland, Washington 99352, U.S.A. b Environmental Molecular Science Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99352, U.S.A. ABSTRACT Oxides of lanthanide dissolution in a Na2O-Al2O3-B2O3-SiO2 glass using Gd as a probe was studied in detail using Raman, fluorescence, and phonon sideband (PSB) spectroscopic techniques. A mechanism of Gd cation dissolution, via partitioning, in the borate-rich and silicate-rich environments was confirmed by examining characteristics of the Raman band evolution, fluorescence emission and lifetime, and PSBs. The study concluded that i) Gd(III) cations in the borate-rich environment resembles Gd-metaborate local structure, i.e., 1BO4 : 1Gd : 2BO3, ii) Gd cations partitioning in the borate-rich environment at low Gd2O3 concentration, [Gd2O3] - 1/3[B2O3] < 0, and iii) excess Gd(III) cations, [Gd2O3] – 1/3 [B2O3], in the silicate-rich environment at high Gd2O3 concentration, [Gd2O3] – 1/3 [B2O3] > 0. INTRODUCTION Local environments of trivalent lanthanide elements (Ln) such as La(III), Nd(III), Gd(III), and Eu(III) have been widely studied using a range of spectroscopic techniques in amorphous oxide systems such as borate [1], aluminoborate [2-4], silicate [5-7], sodium-borosilicate [8-10], and sodium-aluminoborosilicate [11, 12]. The previous studies suggested that Ln elements dissolved in borate glass forming Ln-metaborate-like local structure [1-3], whereas in the silicate glass, Ln dissolution resulted in formation of nonbridging oxygens, Qn groups (Q = SiO4 unit, n = number of bridging oxyen, Si-O-Si, per SiO4 unit and n = 2 in this case) [5, 6]. Formation of Ln-O-Ln clusters was also reported for both borate [1] and silicate [5-7] systems. Understanding of Ln dissolution is important for designing glass compositions for optical applications, for which formation of Ln-O-Ln clusters in glass should be prevented [13, 14]. For stabilization of nuclear materials by vitrification, significantly higher solubility of trivalent Pu(III) than tetravalent Pu(IV) was discovered from our previous study [15]. The dissolution behaviors of Pu(III) and Pu(IV) closely resemble our earlier discovery on the dissolution behaviors of Ce(III) and Ce(IV) in alkali-aluminoborosilicate glasses [16]. Therefore, trivalent Ln has been extensively used as a surrogate of the trivalent actinide elements such as Am(III), Cm(III), and Pu(III) in the development of glass host matrices for chemical stabilization of radioactive materials. Raman spectroscopy has been widely used to probe glass network evolution as glass composition varies and fluorescence spectroscopy is particularly useful to probe Ln local environment and tendency of Ln-O-Ln cluster formation. Fluorescence phonon side band (PSB) spectroscopy provides a structural probe that is site specific regarding bonding env