Origins of the odd optical observables in plutonium and americium tungstates. Issue 26 (30th May 2019)

• Record Type: Journal Article
• Authors: Cross, Justin N.; Lee, Tsung-Han; Kang, Chang-Jong; Yao, Yong-Xin; Cary, Samantha K.; Stritzinger, Jared T.; Polinski, Matthew J.; McKinley, Carla D.; Albrecht Schmitt, Thomas E.; Lanata, Nicola
• Is Part Of: Chemical science. Volume 10:Issue 26(2019)
• Page Start: 6508
• Page End: 6518
• Publication Date: 2019-05-30
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/c9sc01174a
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : A series of f-block tungstates show atypical coloration for both the Ce(iii ) and Pu(iii ) compounds; whereas the other lanthanide and Am(iii ) compounds possess normal absorption features. The different optical properties are actually derived from the tungstate component rather than from 5f electrons/orbitals. Abstract : A series of trivalent f-block tungstates, MW2 O7 (OH)(H2 O) (M = La, Ce, Pr, Nd, and Pu) and AmWO4 (OH), have been prepared in crystalline form using hydrothermal methods. Both structure types take the form of 3D networks where MW2 O7 (OH)(H2 O) is assembled from infinite chains of distorted tungstate octahedra linked by isolated MO8 bicapped trigonal prisms; whereas AmWO4 (OH) is constructed from edge-sharing AmO8 square antiprisms connected by distorted tungstate trigonal bipyramids. PuW2 O7 (OH)(H2 O) crystallizes as red plates; an atypical color for a Pu(iii ) compound. Optical absorption spectra acquired from single crystals show strong, broadband absorption in the visible region. A similar feature is observed for CeW2 O7 (OH)(H2 O), but not for AmWO4 (OH). Here we demonstrate that these significantly different optical properties do not stem directly from the 5f electrons, as in both systems the valence band has mostly O-2p character and the conduction band has mostly W-5d character. Furthermore, the quasi-particle gap is essentially unaffected by the 5f degrees of freedom. Despite this, our analysis demonstrates that the f-electron covalency effects are quite important and substantially different energetically in PuW2 O7 (OH)(H2 O) and AmWO4 (OH), indicating that the optical gap alone cannot be used to infer conclusions concerning the f electron contribution to the chemical bond in these systems.