S-, X-, Q- und W-Band-Pulver-EPR-Untersuchungen an Tetra-n -butylammonium-bis( 1,2-dicyanoethen-1,2-dithiolato)aurat(II), [(n-C4H9)4N]2[AuII(mnt)2] / S, X, Q and W Band Powder-EPR Investigations on Tetra-n-butylammoniumbis( 1,2-dicyanoethylene-1,2-dithiolato)aurate(II), [(n-C4H9)4N]2 [AuII(mnt)2]

Powder-EPR studies at T = 295 K and T = 12 K on the unstable gold(II) complex [(n- C4H9)4N]2[AuII(mnt)2] diamagnetically diluted by the corresponding NiIIcomplex are reported. Due to (i) the small anisotropy of the g and the 197Au hyperfine tensor AAu, and (ii) the large 197Au quadrupole interaction the powder spectra possess a very complex pattern. Using different EPR frequencies - S band (2.4 GHz), X band (9.5 GHz), Q band (35 GHz) and W band (94 GHz) - the spectra could be analyzed successfully. All spectra were simulated with a computer program which diagonalizes the spin-Hamiltonian matrix exactly.

Isotope effects in ESR spectroscopy

In order to present the relationship between ESR spectroscopy and isotope effects three levels are considered: (i) ESR spectroscopy is described on a general level up to the models for interpretation of the experimental spectra, which go beyond the usually used time and mass independent spin-Hamilton operator, (ii) the main characteristics of the generalized isotope effects are worked out, and finally (iii) the basic, mainly quantum mechanical effects are used to describe the coupling of electron spins with the degrees of freedom, which are accessible under the selected conditions, of the respective paramagnetic object under investigation. The ESR parameters and the respective models are formalized so far, that they include the time and mass depending influences and reflect the specific isotope effects. Relations will be established between the effects in ESR spectra to spin relaxation, to spin exchange, to the magnetic isotope effect, to the Jahn-Teller effects, as well as to the influence of zero-point vibrations. Examples will be presented which demonstrate the influence of isotopes as well as the kind of accessible information. It will be differentiated with respect to isotope effects in paramagnetic centres itself and in the respective matrices up to the technique of ESR imaging. It is shown that the use of isotope effects is indispensable in ESR spectroscopy.

Photoluminescence of atomic gold and silver particles in soda-lime silicate glasses

We report the chemistry and photophysics of atomic gold and silver particles in inorganic glasses. By synchrotron irradiation of gold-doped soda-lime silicate glasses we could create and identify unambiguously the gold dimer as a stable and bright luminescing particle embedded in the glassy matrix. The gold dimer spectra coincide perfectly with rare gas matrix spectra of Au(2). The glass matrix is, however, stable for years, and is hence perfectly suited for various applications. If the irradiated gold-doped sample is annealed at 550 degrees C a bright green luminescence can be recognized. Intense 337 nm excitation induces a decrease of the green luminescence and the reappearance of the 753 nm Au(2) emission, indicating a strong interrelationship between both luminescence centers. Time-dependent density functional theory (TD-DFT) calculations indicate that the green luminescence can be assigned to noble metal dimers bound to silanolate centers. These complexes are recognized as the first stages in the further cluster growth process, which has been investigated with small-angle x-ray scattering (SAXS). In silver-doped glasses, Ag(0) atoms can be identified with electron paramagnetic resonance (EPR) spectroscopy after synchrotron activation. Annealing at 300 degrees C decreases the concentration of Ag(1), but induces an intense white light emission with 337 nm excitation. The white luminescence can be decomposed into bands that are attributed to small silver clusters such as Ag(2), Ag(3) and Ag(4), and an additional band matching the green emission of gold-doped glasses.