Michael Gaft

Europium probe for estimation of site symmetry in glass films, glasses and crystals

The paper is devoted to the memory of Brian Wybourne the pioneer in theory of symmetry and spectra of trivalent rare earths. We evaluate here the influence of site symmetry of the surrounding molecules in glass matrices on europium ion used as a probe. A method by which systematic classification can be performed on descending site symmetry in a large number of solid hosts is based on the ratios of intensities of electric to magnetic dipole transition. Experimental work involves preparation of a number of glass matrices prepared by a sol–gel method, and incorporating trivalent europium. The fluorescence arising from the quintet D state is used to evaluate the site symmetry of the probe europium ion in the prepared matrices, crystals, conventionally prepared glasses, solutions, and complexes incorporated in sol–gel matrices. From the large amount of tabulated data one can see that for totally symmetric sites the factor I(D0–F2)/I(D0–F1) is lower than one, and increases to 10 for systems with very low symmetry sites. The absolute intensities of the transitions depend also on the amount of covalency of Eu with the surrounding ligands.

Spectroscopic methods applied to zircon

Natural and synthetic (pure and doped) zircon (ZrSiO4) have been studied with a variety of spectroscopic techniques. These techniques are based on different physical phenomena, for instance transitions between spin states of nuclei and electrons, energetic transitions of valence electrons, intra-molecular vibrations, or vibrations of atoms and molecular units in the lattice. All of the diverse spectroscopic techniques, however, have in common that they probe energy differences between a ground and excited states, mostly upon interaction of the mineral with incident radiation. Such interactions are not only determined by the excited elementary particles or molecules themselves but depend greatly on their local environments (i.e. number, type, valence and geometrical arrangement of neighboring atoms). Spectroscopic techniques are thus sensitive to the local structure and provide information on the short-range order. Most research on zircon crystals using spectroscopic techniques was done to study their “real structures,” that is the characterization of deviations from “perfect” zircon. Such features include the incorporation of non-formula elements, structural defects and the presence of inclusions and other impurities. Correspondingly, most of the spectroscopic investigations can be assigned to two major groups. The first group represents studies done to characterize the structural position and local environment of non-formula elements when incorporated in the zircon lattice, and accompanying effects on physical properties. The second group comprises studies subjected to the real structures of “metamict” zircon samples, i.e., changes of the zircon structure caused by the impact of self-irradiation and upon recovery from radiation damage (Ewing et al., this volume). It is most obvious that a spectroscopic bulk or point analysis will first of all yield a spectrum (i.e. a plot of the intensity of the respective physical parameter versus wavelength, frequency or wavenumber), and this is what is used in most studies. In addition, image generation based on …

Nanoparticles of cadmium sulfide with europium and terbium in zirconia films having intensified luminescence

Abstract Semiconductor CdS particles were formed in ZrO 2 films, together with Eu 3+ and Tb 3+ ions. The steady-state, as well as the time-resolved luminescence, revealed that the intensity of emission of the REE is increased significantly in the presence of CdS particles. This phenomenon can be explained by energy transfer resulting from electron–hole recombination in the CdS to the REE. From the lifetime measurements, it is evident that this transfer occurs in the nanosecond scale.

Laser-induced luminescence of rare-earth elements in natural fluor-apatites

Abstract The luminescence spectra of naturally occurring fluor-apatites containing traces of rare-earth elements have been compared with synthetic fluor-apatites to which single rare-earth elements have been intentionally added. Comparison of the laser-induced spectra obtained after different time delays allows identification of the following luminescence centers: Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Tb3+, Dy3+, Er3+, Tm3+, Yb3+ and possibly Yb2+. The technique described here allowed for the first time to detect the luminescence of Pr3+, Eu3+, Er3+, Tm3+ and Yb3+ in natural apatites. Our results were compared with those obtained by ICP and correspondence was observed between the two methods. Our findings allow non-destructive detection by laser light of the different rare-earth elements in apatite minerals.

Spectroscopic properties of cerium in glasses and their comparison with crystals

Abstract Glasses containing Ce were prepared by the sol–gel method at elevated temperatures. Two parallel series one in air and another in nitrogen atmosphere, were obtained. The main constituent of the glasses was silica SiO 2 obtained by hydrolysis of ethoxysilane (TEOS). Parallel series of glasses were prepared with addition of boron and aluminum. Spectroscopic properties of the glasses were mainly studied by absorption spectroscopy, luminescence spectroscopy and life-time measurements. The comparison of the spectral properties of the glasses was made with existing information on spectroscopy of cerium in crystals and conventional glass.

LASER-INDUCED TIME-RESOLVED LUMINESCENCE OF MINERALS

Abstract Laser-induced time-resolved spectroscopy of natural apatite, scheelite, zircon, calcite and fluorite enables the detection of the luminescence centers, which under steady-state conditions cannot be spectroscopically separated. By applying time-resolved spectroscopy we are able to determine rare-earth elements, luminescence of which has been previously hidden by the stronger bands of Eu 2+ , Mn 2+ , (WO 4 ) 4− , (MoO 4 ) 4− and radiation-induced centers. Luminescence of Pr 3+ , Tm 3+ and Er 3+ have been detected for the first time in minerals, also in presence of interfering ions, namely, Sm 3+ , Dy 3+ and Tb 3+ with similar emission spectra.

Eu3+ luminescence in high-symmetry sites of natural apatite

Laser-induced time-delayed spectroscopy permits detection of luminescence of Eu3+ with long decay on the background of the strong emission with short decay in natural fluorapatite and determination of its position in high symmetry Ca(I) site.

Spectroscopic properties of cerium in sol–gel glasses

Abstract Glasses containing Ce were prepared by the sol–gel method at elevated temperatures. Two parallel series, one in air and one in nitrogen atmosphere, were obtained. The main constituent of the glasses was silica SiO2 obtained by hydrolysis of ethoxysilane (TEOS). Spectroscopic properties of the glasses were studied by time-resolved and steady-state luminescence spectroscopy. In the present paper we made an effort to distinguish between the blue luminescence arising from Ce(III) and that obtained from the silica host which is connected with defects in the matrix. While the spectra of both pure silica and Ce activated silica excited at 337 nm or longer wavelength have the similar emission peaking between 400 and 450 nm, the emission of silica is broader and its decay time shorter than that of Ce(III). It seems that Ce quenches the luminescence of the silica centers. When excited at 308 nm by an excimer laser we detect short-lived emission of Ce(III) peaking between 350–380 nm which may be due to excitation to the conductivity band and subsequent recombination of the excited electrons with a hole.

The luminescence of Bi, Ag and Cu in natural and synthetic barite BaSO4

The time-resolved laser-induced luminescence of natural barite BaSO 4 is compared with synthetically prepared BaSO 4 -Bi, BaSO 4 -Ag and BaSO 4 -Cu. It is deduced that in natural barite the narrow orange band with λ max = 625 nm. A = 40 nm and τ = 5 μs is connected with Bi 2+ center. The narrow violet band with λ max = 625 nm, Δ = 35 nm and τ = 1.7 ms is connected with Bi 3+ center. The broad red band with λ max = 635 nm, Δ = 140 nm and τ = 270 μs is connected with Ag + center. The broad red band with λ max = 750 nm, Δ = 110 nm and τ = 350 μs is connected with Cu + center. Such luminescence centers are firstly considered in minerals.

Rare earth ions, their spectroscopy of cryptates and related complexes in sol-gel glasses

The paper is devoted to the memory of my teacher and friend Christian K. Jorgensen who has written the pioneering works on complexes of Rare Earths (RE).