Temperature-dependent studies of the geometrically frustrated pyrochlores Ho2Ti2O7 and Dy2Ti2O7

A temperature-dependent Raman study of Ho2Ti2O7 and Dy2Ti2O7 single crystals was performed in the 5–873 K temperature range. Polarized spectra allowed us to establish the symmetries of the observed bands and revise the mode assignment made in previous works. Our studies revealed also two additional bands near 287 and 300 cm−1 for Dy2Ti2O7, which can be assigned to crystal field transitions in Dy3+ ions. Temperature dependent Raman studies showed large increase of linewidths. These changes have been analyzed in terms of strong third-order phonon-phonon anharmonic interactions. The Raman spectra also showed anomalous softening of the majority of phonon modes upon cooling in the whole temperature range studied. In contrast to this behavior, the F2g 310 cm−1 and Eg 330 cm−1 phonon modes showed hardening upon cooling down to about 100–120 K and then anomalous softening below this temperature. This anomalous behavior of phonon wave numbers has been attributed to the increase in octahedral distortion upon cooling

Synthesis and Characterization of Monodispersed Copper Colloids in Polar Solvents

A chemical reduction method for preparing monodispersed pure-phase copper colloids in water and ethylene glycol has been reported. Owing to the reduction property of ethylene glycol, the reaction rate in ethylene glycol is higher than that in water. In addition, the amount of reducing agent can be reduced largely. Ascorbic acid plays roles as reducing agent and antioxidant of colloidal copper, due to its ability to scavenge free radicals and reactive oxygen molecules. Thermogravimetric results reveal that the as-prepared copper nanoparticles have good stability, and they begin to be oxidized at above 210 °C. Polyvinyl pyrrolidone works both as size controller and polymeric capping agents, because it hinders the nuclei from aggregation through the polar groups, which strongly absorb the copper particles on the surface with coordination bonds

Electron Absorption and Emission Spectra of Eu3+\text{}^{3+} in KEu(WO4\text{}_{4})2\text{}_{2}

Electron absorption and emission spectra of Eu$\text{}^{3+}$ ion in stoichiometric KEu(WO$\text{}_{4}$)$\text{}_{2}$ were measured at the temperature range 15-300 K. The oscillator strengths of f-f transitions and the Judd-Ofelt parameters were evaluated. The assignment of vibronic transitions is given and mechanism of emission decay is discussed

Spectroscopic ProPerties of Eu3+\text{}^{3+} Ion in KEu(MoO4\text{}_{4})2\text{}_{2} Crystal

IR, Raman, electron absorption and emission spectra of KEu(MoO$\text{}_{4}$)$\text{}_{2}$ crystal were measured at the temperature range 8-300 K. The oscillator strengths of f-f transitions were evaluated

Structural and Optical Characterisation of Hydrogenated Soda-Lime Silicate Glasses Doped with Silver and Copper

The results of comparative studies of the effect of hydrogenation upon structural and optical properties of the commercial soda-lime silicate glasses doped either with monovalent silver or copper have been presented. The samples were characterised by means of the scanning and transmission electron microscopy and the UV-VIS-IR absorption spectroscopy. It has been shown that the annealing of suitably ion-exchanged specimens in gaseous hydrogen atmosphere could be considered as an effective procedure for obtaining composite materials of expected properties correlated with the induced changes of the morphology of both the glassy matrix and the dopant

Optical Spectra of Neodymium and Europium Tungstates and Molybdates

Absorption and excitation spectra of lanthanides molybdates and tungstates were measured and analyzed. Probabilities of electronic transitions were analysed on the basis of the Judd-Ofelt theory. The significant differences of intensities were observed. Those differences could result from the symmetry changes, cooperative effects and electron-phonon interaction. The elucidation of intensities given by separate mechanisms needs further investigation