Conductivity, luminescence and vibrational studies of the poly(ethylene glycol) 400 electrolyte based on Europium trichloride.

Poly(ethylene glycol) 400/(EuCl3)(x) electrolytic complexes with 0 less than or equal to x less than or equal to 0.327 were prepared. The ionic conductivity of these systems was investigated, and the data were satisfactorily well fitted by the empirical Vogel-Tamman-Fulcher equation. Two different conductivity regions depending on the electrolytic complexes compositions were observed. The conformation of the poly(ethylene glycol) 400 (PEG 400) in the complexes was investigated by FT-IR and Raman spectroscopies. These investigations suggest that the PEG 400 chains in PEG 400/(EuCl3)(x) present a TGT conformation (T = trans, G = gauche). Moreover, by laser luminescence spectroscopy it was also proved that each Eu3+ ion is coordinated by four oxygen atoms of PEG in a distorted C-2v site symmetry

Optical Spectroscopy of Trivalent Lanthanide Ions in Strontium Metaphosphate Glasses

The spectroscopic properties of strontium metaphosphate glass Sr(PO3)2 doped with Sm3+, Dy3+, Ho3+, Er3+ and Tm3+ are reported. From the experimental oscillator strengths of the f\u2192f transitions the phenomenological Judd\u2013Ofelt intensity parameters have been obtained. They appear to be higher than in the similar Pb(PO3)2 host at the beginning of the lanthanide series, whilst they are lower towards the end. Such a behavior is attributed to differences in the local structure around the doping ions in the two hosts. The stimulated emission cross section of the 4I13/2\u21924I15/2 transition of Er3+ is close to the values obtained for laser glasses of technological relevance

Electronic Spectroscopy of Trivalent Lanthanide Ions in Lead Zinc Borate Glasses

New zinc borate glasses of composition 4PbO\ub72ZnO\ub75B2O3\ub7 and 2PbO\ub74ZnO\ub75B2O3 doped with Pr3+, Nd3+, Eu3+, Dy3+, Ho3+ and Er3+ were prepared. Absorption and luminescence spectra were measured and the Judd\u2013Ofelt parameters were calculated. The spectroscopic behaviour appears to be strongly influenced by the presence of the highly polarizable Pb2+ ion. The values of stimulated emission cross sections for selected laser transition appear to be relatively high, suggesting that these materials can be considered as interesting candidates for optical applications

Absorption and Luminescence Spectroscopy of Nd3+ and Er3+ in a Zinc Borate Glass

4ZnO \ub7 3B2O3 glasses doped with Nd3+ and Er3+ were investigated by optical spectroscopy. Emission transition probabilities, radiative life-times and fluorescence branching ratios for several excited states of the Nd3+ and Er3+ ions were estimated from the room temperature absorption spectra. The stimulated emission cross sections \u3c3p for the near infrared laser transitions of Nd3+ and Er3+ were obtained from laser-excited luminescence spectra. The values of \u3c3p are comparable with those shown by glasses used in solid state laser applications

Optical Spectroscopy of Eu3+ Doped Zinc Borate Glasses

Zinc borate binary glasses of composition 4ZnO.3B2O3 undoped and doped with 0.5% mol of Eu3+ were prepared from the melt giving rise to samples of excellent optical quality. In the present work we use the spectroscopic properties of the Eu3+ to obtain information about the structural and dynamic features of our system. Different optical techniques such as site selection, excitation spectroscopy and lifetime measurements as well as Raman spectroscopy were used to study the local environment of the Eu3+ ion in these glasses. No energy transfer is observed at our concentration and moreover non-radiative relaxation from the excited 5D0 state to the 7Fj manifold is not important. A broad distribution of slightly different environments of the Eu3+ ion is reflected in the trend of the Stark splittings of the 7F1 state and in the crystal field parameters for the individual sites as a function of the excitation wavelength. Phonon sidebands are observed in the excitation and luminescence spectra of the Eu3+ impurity. We make an attempt to assign these sidebands to coupling of the vibrational modes of the structural units containing the Eu3+ ion. The strength of the electron-phonon coupling is evaluated and compared with the result obtained for related systems

A Theoretical and Experimental Investigation of the Electronic Structure of Alpha-Fe2O3 Thin Films

Ground and excited states of alpha -Fe2O3 have been investigated by determining the spin-polarized wavefunctions and eigenvalues of an embedded Fe2O912- cluster using the discrete variational Xalpha method. The computed transition energies compare reasonably well with the recorded experimental spectrum of high-purity alpha -Fe2O3 thin films obtained by the sol-gel technique. The theoretical data herein reported predict a very high valence-conduction band gap incompatible with the experimental outcomes, which were routinely interpreted as originated by an interband transition. In contrast to this, the lowest-energy optical transitions have a charge transfer nature, involving excitation of electrons from the occupied O 2p-based spin down levels to the empty Fe atom-like spin down orbitals

Zn4O(O2CNEt2)6 - A Further Molecular-model of ZnO

First-principles local-density molecular-cluster calculations coupled to UV photoelectron and UV electronic spectroscopies have been used to investigate the electronic structure of Zn4O(O2CNEt2)6. The theoretical data are in excellent agreement with experiment and further support the results, discussed, elsewhere on the isostructural Zn4O(acetate)6. We demonstrated that the title compound can be considered as a further molecular model of crystalline ZnO and that the tetrahedral arrangement of the central oxygen plays a leading role in determining the observed optical properties. Furthermore, our results indicate the presence of an extensive pi interaction within the OOCN fragments which is in accord with crystallographic and photoelectron spectroscopy data

An Experimental and Theoretical Study of the Electronic Structure of Zinc Thiophenolate-Capped Clusters

The electronic structure of a series of thiophenolate-capped ionic/neutral clusters ([Zn(SPh)4]2- (1); [Zn4(μ2-SPh)6(SPh)4]2- (2); Zn10(μ3-S)4(μ2-SPh)12 (3); and [Zn10(μ3-S)4(μ2-SPh)12(SPh)4]4- (4), Ph = phenyl), indicated as supertetrahedral fragments and possible molecular models of cubic ZnS, has been investigated by coupling density functional calculations to UV electronic and X-ray photoelectron (XP) spectroscopy. Theoretical outcomes indicate that, on passing from the tetrametallic to the decametallic clusters, there is a modification in the nature of the outermost occupied and lowermost unoccupied molecular orbitals. Actually, both in 1 and in 2 the frontier orbitals are delocalized and mainly composed of the S 3p pairs strongly mixed with the Ph π levels (the HOMOs) and of the linear combinations of Ph π* orbitals, the LUMOs. At variance to that, in 3 and 4 both the HOMO and LUMO are highly localized, the former on μ3-S atoms occupying C3v coordinatively unsaturated tetrahedral positions and the latter on peripheral Zn atoms. The nature of the electronic levels involved in the UV absorption bands is discussed, and the agreement between theory and experiment is satisfactory. Neither experimental nor theoretical electronic excitation energies are influenced by the cluster size. Moreover, XPS data match quite well variations of the Zn and S gross atomic charges along the series. The different Zn−S bonding scheme characterizing terminal, μ2-bridging, and μ3-pyramidal S atoms allows a rationalization of the cluster behavior in solution. Along the investigated series, the only species reasonably mimicking both the structural arrangement and the electronic structure of the solid ZnS is Zn10(μ3-S)4(μ2-SPh)12, which can be considered a molecular model of ZnS nonpolar surfaces