Alkali metal oxides: Occupied,unoccupied and excited states

The occupied and unoccupied electronic states of NaO₂ and KO₂ have been investigated by UV photoemission spectroscopy and inverse photoemission spectroscopy, respectively. In addition single electron excitations from occupied into empty levels have been probed by x-ray absorption and electron energy loss spectroscopy. The experimental data are augmented by LCGTO-X model cluster calculations. A detailed assignment of initial and final states is given. The excitation cross sections and an inversion of the ligand field induced3d level splitting in NaO₂ are discussed.     

The development of room temperature phosphorescence into a new technique for chemical determinations : Part 1. Physical Aspects of Room Temperature Phosphorescence

The development and physical aspects of room temperature phosphorescence are reviewed in this first part of a two-part series. Certain fundamental aspects of phosphorescence are presented. The novel phenomenon of room temperature phosphorescence (strong phosphorescence for organic compounds adsorbed on appropriate substrates) is then treated in detail. Specific attention is given to the nature of the support-phosphor interaction and the quenching effects of moisture and oxygen on room temperature phosphorescence. Thorough coverage is also given to the heavy-atom effect. The effects of the sample matrix on certain phosphorescent properties, such as lifetime, intensity and spectral characteristics, are mentioned.     

Quenched disorder and the critical behavior of a partially frustrated system

We report the direct observation of the effects of quenched disorder on the critical behavior of partially frustrated amorphous FeMnZr alloys by the systematic analysis of high-precision ac susceptibility data and dc magnetization data. Interestingly, the analysis reveals that the presence of short-range quenched disorder does not alter the actual critical behavior. However, it does affect quantities such as the Curie temperature, the peak value of effective exponent gamma, width of the peak, and crossover temperatures. The observed temperature dependence of the effective critical exponent can be understood in terms of the field-theoretical renormalization group approach. Also, the present results would help in identifying the main source of the spread in the exponent values reported in the literature.     

An57Fe Mössbauer effect study of the highT c superconductor GdBa2Cu3O7−y

Split source⁵⁷Fe Mössbauer effect spectroscopy has been performed between 4 K and 295 K on the superconducting perovskite GdBa₂Cu₃O_7?y. No evidence is seen for magnetic splitting at low temperatures as reported in some split absorder⁵⁷Fe Mössbauer experiments on this material. There is evidence for phonon mode softening, as observed for¹¹⁹Sn Mössbauer spectra of some other highT _c superconductors.     

Mössbauer studies of57Co-doped layered perovskites

Mössbauer spectra of⁵⁷Co-doped polycrystalline or single-crystal samples of layered perovskites La₂Mo₄ (M=Cu, Co, Ni) and R₂CuO₄ (R=Nd, Eu, Gd) were recorded at room temperature and below. Of the samples studied, only La₂CuO₄ shows a widely separated doublet at room temperature and a single clearly resolved sextet well belowT _N.     

Hyperfine field distributions in ferromagnetic quasicrystals

Recent magnetisation measurements indicated the presence of ferromagnetism in Al−Cu−Mn−Ge quasicrystals with T_c∼535K. In this paper we report the room temperature Mossbauer and X-ray measurements of a series of ferromagnetic AlCuMnFeGe alloys.