Excited-state properties of lamellar solids derived from hydrogen uranyl phosphate and lanthanon ions

Abstract

Hydrogen uranyl phosphate tetrahydrate (HUP) undergoes an essentially complete intercalative ion-exchange reaction with aqueous lanthanon ions to yield a family of hydrated lamellar solids of approximate composition Ln 1 3 UO 2PO 4 (Ln ≡ La, Ce, Pr, Nd, Gd, Tb, Dy and Yb) (LnUP). These compounds have all been characterized by elemental analysis, IR spectroscopy and X-ray powder diffraction; the last technique reveals an expansion of the interlamellar spacing on intercalation. All the solids exhibit visible absorption spectra characteristic of the UO 2 2+ and Ln 3+ chromophores. With the exception of the cerium, praseodymium and neodymium derivatives, which are weakly emissive, the LnUP samples emit efficiently at 295 K when excited with blue or near-UV light. Photoluminescence decay curves are exponential and yield lifetimes for the strongly emissive samples of about 90–210 μs; their radiative quantum yields are typically about 0.1–0.2. These data have been used to calculate unimolecular radiative and non-radiative rate constants for excited-state decay as being about (0.8–1) × 10 3 s −1 and (4–10) × 10 3 s −1 respectively.