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

Abstract

The excited-state properties of the layered compound hydrogen uranyl phosphate (HUP), HU02P04.4H20, and of solids derived therefrom have been examined; the derivatives, prepared by intercalative ion-exchange reactions, have compositions based on stoichiometric proton substitution by NH4+, pyridinium, n-butylammonium, n-octylammonium, K+, and Ag+, 0.5 equiv of Ca2+ and Zn2+, and 0.4 equiv of Cu2+. These compounds have all been characterized by elemental analysis, IR spectroscopy, and X-ray powder diffraction; the last confirms the retention of the lamellar structure upon cationic substitution and reveals that the interlamellar spacing can vary considerably with the choice of cation. All of the samples exhibit electronic absorption spectra characteristic of the UOZ2+ chromophore. Except for the n-octylammonium, Ag+ and Cu2+ salts, the samples all exhibit yellow-green emission characteristic of the UOZ2+ moiety when excited with blue or near-UV light at 295 K. Emission decay curves are exponential for all of the luminescent solids and yield lifetimes, T , ranging from -1 to 450 ps. HUP and its K+, NH4+, pyridinium, and CaZ+ derivatives are all highly emissive with measured radiative quantum efficiencies, @, , approaching unity at 295 K. Values of T and @, have been used to calculate radiative (k,) and nonradiative (k",) rate constants for excited-state decay. Values of k, are nearly constant at -(l-2) X lo3 s-] for the samples, whereas k , values span several orders of magnitude. Possible quenching mechanisms for the weakly emissive and nonemissive solids are described and compared with previously reported solution data.The excited-state properties of inorganic solids are receiving considerable attention as a means of characterizing electronic structure and physical processes occurring within the solid. light-emitting diodes,, as well as the characterization of semiconductor electrodes3 and colloid^.^ Although numerous Useful applications of luminescence, traditionally the basis for such studies, have included the design of phosphors' and (1) L~~~~~~~, H, W, -An ~~~~d~ to ~~~i~~~~~~~~ of Solids"; D~~~~ New York, 1968.

Layered metal uranyl phosphates. Retention of divalent ions by amine intercalates of uranyl phosphates

“…The intercalation chemistry of the inorganic layered compounds is becoming increasingly important; in particular, the ionic exchange and adsorption characteristics and the hostguest relationships of the layered phosphates have been intensively studied in: Zr(HP04)*.H20 (1); Sn(HP04)2.H20 (2); VOP04.2H20 (3), and HU02P04.4H20 (HUP) (4,5).…”

“…Other authors investigated the proton conductivity of HUP and the HUAs (8,9). The photoluminescent of these phosphates are reported in detail by Olken et al (5).…”

Interlayer ammine complexes of metal uranyl phosphates

“…The solids derived from HUP by substituting metallic ions for protons show lower conductivity (I). Other authors have systematically studied the effect that certain chemical substitutions of HUP have on its luminescence (2,3).…”

“…The environments of these cations are compatible with their corresponding hexaaquocations and their electronic spectra show the vibronic transition bands of the U02 moiety in addition to the electronic absorption bands of the metal ions (4). All of the intercalation reactions, ionic exchange, solvation or neutralization, modified the photoluminescent properties (2,3) and the proton conductivities of these solids (1).…”

Ion exchange reactions of n-butylamine intercalates of tin(IV) hydrogen phosphate and hydrogen uranyl phosphate with cobalt(III) complexes

“…O n the other hand, HUP crystallizes in the tetragonal system, with an interlayer distance of 8.8 A. The ion exchange behaviour with alkali metals, alkaline earths, and first row transition metals of these phosphates was investigated (3)(4)(5)(6)(7)(8). However, very little is known about ion exchange with large complexes on these exchangers.…”