18 research outputs found
FMR Study of the Porous Silicate Glasses with Fe 3
The results of research on new magnetic materials for biomedical applications are discussed. These materials are porous silicate glasses with magnetic fillers. To ensure the smallest number of components for subsequent removal from the body, the magnetic fillers are bare magnetite nanoparticles (Fe3O4). The magnetic properties of these materials have been investigated using the ferromagnetic resonance method (FMR). The FMR analysis has been complemented by scanning electron microscope (SEM) measurements. In order to examine the effect of time degradation on filling the porous glass with bare magnetite nanoparticles the FMR measurement was repeated five months later. For the samples with high degree of pore filling, in contrast to the samples with low degree of pore filling, the FMR signal was still strong. The influence of different pH values of magnetite nanoparticles aqueous suspension on the degree of filling the pores of glasses is also discussed. The experimental results are supported by computer simulations of FMR experiment for a cluster of N magnetic nanoparticles locked in a porous medium based on a stochastic version of the Landau-Lifshitz equation for nanoparticle magnetization
Photoproduction of Long-Lived Holes and Electronic Processes in Intrinsic Electric Fields Seen through Photoinduced Absorption and Dichroism in Ca_3Ga_{2-x}Mn_xGe_3O_{12} Garnets
Long-lived photoinduced absorption and dichroism in the
Ca_3Ga_{2-x}Mn_xGe_3O_{12} garnets with x < 0.06 were examined versus
temperature and pumping intensity. Unusual features of the kinetics of
photoinduced phenomena are indicative of the underlying electronic processes.
The comparison with the case of Ca_3Mn_2Ge_3O_{12}, explored earlier by the
authors, permits one to finally establish the main common mechanisms of
photoinduced absorption and dichroism caused by random electric fields of
photoproduced charges (hole polarons). The rate of their diffusion and
relaxation through recombination is strongly influenced by the same fields,
whose large statistical straggling is responsible for a broad continuous set of
relaxation components (observed in the relaxation time range from 1 to about
1000 min). For Ca_3Ga_{2-x}Mn_xGe_3O_{12}, the time and temperature dependences
of photoinduced absorption and dichroism bear a strong imprint of structure
imperfection increasing with x.Comment: 20 pages, 10 figure
Intrinsic Luminescence of the Undoped Glasses of (CaO-GaO-GeO) System
For the first time the intrinsic luminescence in the undoped (CaO-GaO-GeO) glasses with different composition has been found and investigated in the 80÷300 K temperature range. The new glasses of high chemical purity and optical quality with stoichiometric composition similar to that in calcium-gallium- germanium garnet (CaGaGeO), trigonal Ca-gallogermanate (CaGaGeO), and CaGaO crystals were obtained by the high-temperature synthesis method. The luminescence and photoexcitation spectra analysis, supported by EPR spectroscopy data, yields the following results: (i) the UV-excited non-elementary broad emission band with maxima at roughly 500 nm and 420 nm in the (CaO-GaO-GeO) glasses is due to recombination of ensemble of the transient hole O centres; (ii) the emission bands with maxima at nearly 380 and 710 nm, which were distinctly revealed in glasses with the CaGaGeO and CaGaO compositions, are assigned to the luminescence of UV-induced electron centres of two different types. Possible models of the luminescence centres in (CaO-GaO-GeO) glass network are discussed
EPR spectroscopy of Cu2+ and Mn2+ in borate glasses
Electron paramagnetic resonance (EPR) spectra of the CaB4O7 and LiCaBO3 glasses containing 0.5 and
1.0 mol.% CuO and MnO2 impurity compounds were investigated at room temperature. The glasses with CaB4O7:Cu,
LiCaBO3:Cu, CaB4O7:Mn and LiCaBO3:Mn compositions were produced from the corresponding polycrystalline
compounds using standard glass synthesis and technological conditions developed by the authors. The EPR spectral
parameters of the Cu2+ and Mn2+ centres in both glasses containing 0.5 and 1.0 mol.% CuO and MnO2 doping oxides
were determined. Analysis of EPR spectral parameters shows that Cu impurity is incorporated into the CaB4O7 and
LiCaBO3 glass network as isolated Cu2+ (3d9, 2D5/2) paramagnetic ions. The Cu2+ ions occupy Ca(Li) sites of the borate
glass network coordinated by six O2− anions with geometry of elongated octahedron (D4h symmetry) due to the Jahn-
-Teller effect. The EPR spectra of the Mn-doped CaB4O7 and LiCaBO3 glasses are virtually identical and typical of all
oxide glasses activated with Mn2+ (3d5, 6S5/2) ions. Observed EPR spectra in the Mn-doped glasses were attributed to
isolated Mn2+ (1) centres (geff ≅ 4.3) in octahedral Ca(Li) sites with a strong (fully) rhombic distortion, isolated Mn2+ (2)
centres (geff ≅ 2.0) in octahedral Ca(Li) sites with nearly cubic local symmetry as well as pairs and small clusters of the
Mn2+ ions, coupled by magnetic dipolar and exchange interactions. On the basis of the obtained results and analysis of
referenced data, the local structure of the Cu2+ and Mn2+ centres in the borate glasses have been proposed
EPR Spectroscopy of the Mn^{2+} and Cu^{2+} Centres in Lithium and Potassium-Lithium Tetraborate Glasses
The electron paramagnetic resonance spectra of the glasses with and compositions doped with Mn and Cu were investigated. On the basis of obtained EPR spectra analysis it was shown that the Mn and Cu impurities are incorporated into the glass network as and ions. The EPR spectra in the glasses with and compositions are characterised by the following parameters, measured at T = 300 K: isotropic g-factor ( = 2.00 ± 0.05), isotropic hyperfine constant ( = (8.65 ± 0.05) mT) and peak-to-peak linewidth of hyperfine components = (3.50 ± 0.05) mT. The EPR spectra in the glasses with and compositions, registered at T = 300 K are characterised by the same g-values ( = 2.34 ± 0.05, = 2.06 ± 0.05) and peak-to-peak line width of hyperfine components ( = (5.11 ± 0.05) mT, = (1.80 ± 0.05) mT), whereas anisotropic hyperfine constants show some differences ( = (14.28 ± 0.05) mT, = (2.34 ± 0.05) mT for glass with composition and = (14.21 ± 0.05) mT, = (2.55 ± 0.05) mT for glass with composition). The possible local structure of the and centres in the lithium and potassium-lithium tetraborate glass network has been considered
The MAS NMR study of solid solutions based on the YAG crystal
An 27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) study of nominally pure and Cr-doped yttrium-aluminum garnet (Y3Al5O12 and Y3Al5O12:Cr) crystals is reported. It has been shown that the doping by Cr of the Y3Al5O12 crystals leads to the variation of the occupation by Al atoms both octahedrally and tetrahedrally coordinated sites of the garnet lattice
EPR Spectroscopy of the Mn 2+
The electron paramagnetic resonance spectra of the glasses with and compositions doped with Mn and Cu were investigated. On the basis of obtained EPR spectra analysis it was shown that the Mn and Cu impurities are incorporated into the glass network as and ions. The EPR spectra in the glasses with and compositions are characterised by the following parameters, measured at T = 300 K: isotropic g-factor ( = 2.00 ± 0.05), isotropic hyperfine constant ( = (8.65 ± 0.05) mT) and peak-to-peak linewidth of hyperfine components = (3.50 ± 0.05) mT. The EPR spectra in the glasses with and compositions, registered at T = 300 K are characterised by the same g-values ( = 2.34 ± 0.05, = 2.06 ± 0.05) and peak-to-peak line width of hyperfine components ( = (5.11 ± 0.05) mT, = (1.80 ± 0.05) mT), whereas anisotropic hyperfine constants show some differences ( = (14.28 ± 0.05) mT, = (2.34 ± 0.05) mT for glass with composition and = (14.21 ± 0.05) mT, = (2.55 ± 0.05) mT for glass with composition). The possible local structure of the and centres in the lithium and potassium-lithium tetraborate glass network has been considered
Reversible Mn segregation at the polar surface of lithium tetraborate
We find Mn surface segregation for single crystals of Mn doped Li2B4O7, nominally Li1.95Mn0.05 B4O7(001), but as the temperature increases, evidence of this Mn surface segregation diminishes significantly. At room temperature, the surface photovoltaic charging is significant for this pyroelectric material but is quenched at a temperature well below that seen for the undoped Li2B4O7 samples. The suppression of surface charging in the region of 120°C that accompanies the temperature of Mn dissolution in the bulk of Li2B4O7, i.e., the reversal of Mn surface segregation (215°C), suggests that along the (001) direction, ionic transport must be considered as significant