Excited-State Properties of Lamellar Solids Derived from Hydrogen Uranyl Phosphate
The excited-state properties of the layered compound hydrogen uranyl phosphate (HUP), HUO2PO4-4H2O, and of solids derived therefrom have been examined; the derivatives, prepared by intercalative ion-exchange reactions, have compositions based on stoichiometric proton substitution by [formula-omitted], 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 [formula-omitted] chromophore. Except for the n-octylammonium, Ag+ and Cu2+ salts, the samples all exhibit yellow-green emission characteristic of the [formula-omitted] 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, τ, ranging from ~ 1 to 450 μS, HUP and its K+, [formula-omitted], pyridinium, and Ca2+ derivatives are all highly emissive with measured radiative quantum efficiencies, φr, approaching unity at 295 K. Values of r and ør have been used to calculate radiative (kr) and nonradiative (knr) rate constants for excited-state decay. Values of kr are nearly constant at ~(1-2) X 103 s-1 for the samples, whereas knr 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.
Olken, Michael M., Richard N. Biagioni, and Arthur B. Ellis. "Excited-state properties of lamellar solids derived from hydrogen uranyl phosphate." Inorganic Chemistry 22, no. 26 (1983): 4128-4134.