M. Mazzera

Growth of SnO2 nanocrystals controlled by erbium doping in silica

We investigate the effects of erbium doping on SnO(2) nanoclustering in Sn-doped silica. Vibrational spectroscopy data from Raman and infrared absorption measurements show nanostructuring effects on the SnO(2) nanophase. Ultraviolet absorption spectra evidence a gap shift ascribable to size-dependent quantum confinement, also suggesting a role of erbium doping in determining cluster sizes and the amount of localized states on the nanophase boundary. Transmission electron microscopy confirms and details the spectroscopic data. As a result of these measurements, we find that the nanocrystal size distribution becomes narrower, increasing the erbium concentration, while the density of localized states at the nanocrystal surface decreases. The distribution of erbium ions among the possible environments is then examined through simultaneous spectroscopy of luminescence excited by nanocrystal-to-erbium energy transfer and the absorption of nanocrystal luminescence by erbium ions. This analysis shows that erbium behaves as an extrinsic nucleation centre of the SnO(2) nanophase at low doping levels, whereas at high concentrations it modifies the matrix, hindering the growth of SnO(2) crystals and passivating the interface.

Spectroscopic investigation and crystal field modelling of Dy3+ and Er3+ energy levels in yttrium aluminium borate (YAB) single crystals

High resolution (0.04 cm−1) absorption spectra of Dy3+-doped YAl3(BO3)4 (YAB) single crystals were measured by Fourier transform spectroscopy in the spectral (2000–23 000 cm−1) and temperature (9–300 K) ranges. Samples with nominal 1 and 4% Dy/Y molar ratios were studied. Dy3+ transitions from the 6H15/2 ground state to the 6H13/2, 6H11/2, 6H9/2+ 6F11/2, 6H7/2+ 6F9/2, 6H5/2, 6F7/2, 6F5/2, 6F3/2, and 4F9/2 excited states were analysed. A small (~3.3 cm−1) splitting between the first two sublevels of the 6H15/2 ground manifold was detected. The experimentally determined energy levels were fitted with a single-ion Hamiltonian and the crystal-field parameters were obtained. The same procedure was applied to analyse the previously published high resolution spectra of YAB:Er3+, leading to a reliable unified picture for the two dopants.

Evidences of Rare-Earth Nanophases Embedded in Silica Using Vibrational Spectroscopy

Transmission electron microscopy, Raman scattering, Fourier transform infrared spectroscopy, and radio-luminescence are employed to investigate rare-earth (RE) incorporation and aggregate formation in silica glasses prepared by the Sol-Gel method and doped with Ce3+, or Tb3+, Gd3+, Yb3+ with concentrations up to several mol%. The results demonstrate that rare-earth aggregates with a mean diameter extending up to several tens of nanometers occur, further increasing their size after post-densification high temperature treatments. Rare-earth segregation causes a reduction of the OH content of glasses. Nanoclusters are amorphous, possibly close to a (RE)2SiO5 stoichiometry. Room temperature radio-luminescence measurements reveal that the emission spectra are dominated by RE3+ emissions and no bands due to silica matrix defects are detected.

Hyperfine structure of Ho3+ levels and electron-phonon coupling in YPO4 single crystals

High resolution spectroscopy (the finest being 0.01 cm(-1)) was applied in the 75-25,000 cm(-1) and 9-300 K ranges to a 1 mol% holmium doped Y PO(4) single crystal with two purposes: (1) to study the hyperfine splitting of Ho(3+) energy levels of interest for possible quantum manipulation media and (2) to analyze the electron-phonon interaction. The hyperfine structure was clearly revealed for a high number of lines in a wide wavenumber range (up to ~21,500 cm(-1)) and for a large number of multiplets. Several hyperfine patterns were monitored, differing in the number of components (a maximum of 16 could be easily distinguished in a single beautiful pattern), in their separation, and in their relative statistical weight. These features were all understood in terms of a crystal-field model, whose results are in good agreement with experiments and account for the involved level symmetry, the type of transitions (electric and magnetic dipole allowed), and the contribution of a second-order (pseudoquadrupolar) hyperfine coupling between close levels. The electron-phonon interaction, investigated through the thermally induced line shift, was critically discussed in the framework of single phonon coupling and of two phonon Raman scattering models.

Crystal field fine spectroscopy of trivalent terbium in yttrium aluminum borate single crystals

Tb3+ doped single crystals of huntite-type YAl3(BO3)4 (YAB) have been characterized by means of Fourier transform absorption spectroscopy in the wave number range 500-25000 cm−1 and in the temperature range 9-300 K, and by means of 9 K linear dichroism measurements. Crystal-field splitting of the fundamental 7F6 and of the excited 7F5, 7F4, 7F3, 7F2, 7F1, 7F0, and 5D4 manifolds of Tb3+ have been analyzed and fitted within a single ion Hamiltonian model, to obtain free-ion and crystal-field parameters. The electron-phonon interaction has been put into evidence by thermally induced line shift and discussed in the framework of a single phonon coupling model.

Vibrational spectroscopy of silica glasses doped with Eu3+ ions

In the present work the effects produced by Eu3+ incorporation into sol-gel silica (doping level range: 0.001-10 mol%) are monitored by means of Fourier transform vibrational spectroscopy in the wave number range 200-3000 cm−1. Complementary microreflectance, TEM, and Raman spectroscopy measurements are also performed. By increasing the Eu3+ concentration up to 3 mol%, the intrinsic absorption/reflectance bands related to vibrational modes of O–Si–O groups are gradually modified for what concerns the peak position and intensity, and absorption shoulders attributable to the Eu3+ doping appear. At 10 mol% sharp, new, Eu-related peaks grow at the expenses of the intrinsic absorptions. The results can be explained in terms of Eu-rich cluster formation, as also supported by Raman spectra analysis and TEM images. The cluster sizes increase by increasing the Eu3+ concentration. Their structure, in which tetrahedral (SiO4)4- groups are still present, remains amorphous for Eu3+ concentration up to 3 mol%, turning into a nearly ordered arrangement for the higher one. The spectral analysis in the regions of the weaker absorptions due to combination and overtone modes further supports the results and allows to associate the fundamental and overtone frequencies for two modes in Eu3+ 10 mol% doped silica. In the framework of the Morse anharmonic oscillator model, the related anharmonicity parameters and binding energies were calculated and found close to those reported for (SiO4)4- groups.

Plasma Treatment of 3C-SiC Surfaces

Surfaces of cubic silicon carbide (3C-SiC), grown by vapour phase epitaxy with silane and propane as precursors, were treated with plasma to remove residual species deposited during the growth procedure and the sample cooling down, or due to atmospherical contamination. The impurity traces were investigated with optical absorption spectroscopy. No morphology changes due to the plasma exposure were observed.

Rare earth crystal field spectra as a probe of librational motions in BaY2F8 solid state laser crystals

The fine structure (FS) accompanying a few lines, originated by crystal field (CF) transitions of rare earths (RE), as Er3+ and Tm3+, in BaY2F8 single crystals, is analyzed as a function of the RE3+ concentration (0.5÷20 at%) and temperature (9-300 K), by using high resolution (as fine as 0.02 cm−1) Fourier transform spectroscopy and linear dichroism measurements. The 9 K absorption spectra show that FS includes weak, narrow, and closely spaced (0.4÷0.8 cm−1) lines, covering a few cm−1 range on both sides of the narrowest among the CF lines. The FS increases by increasing the RE3+ concentration and vanishes at rather low temperature (40 and 60 K for Er3+ and Tm3+, respectively). The polarized light spectra confirm the association of a given set of FS lines to a specific CF line. The FS is ascribed to the simultaneous excitation of an electronic CF transition and of a local librational (or hindered rotation) mode of the RE3+-F− group. The attribution is supported 1) by specific features of the host matrix and guest rare earths, which allow some mobility of F− ions, and 2) by the spacing of the FS lines, which is in excellent agreement with the calculated RE3+-F− group rotational constant.

Correction to “Evidences of Rare-Earth Nanophases Embedded in Silica Using Vibrational Spectroscopy” [Jun 10 1361-1369]

In the above titled paper (ibid., vol. 57, no. 3, pp. 1361-1369, Jun. 10), the authors recognized some errors in Fig. 3 (Panel A) following the publication of the paper. The correct figure is presented here.