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1.
We have used spectral hole burning to measure the homogeneous linewidth of the (3)H(6)(1)- (3)F(3)(1) transition of Tm(3+) ions doped into oxyfluoride glass ceramics consisting of nanocrystals of LaF(3) in an aluminosilicate glass matrix. From the magnitude of the hole width in the nanocrystals and its dependence on temperature, we propose that excitation of tunneling modes in the adjacent glassy phase as well as of confined mechanical modes in the nanocrystals is responsible for the broadening.  相似文献   
2.
The evolution of the hyperfine quadrupole interaction in \beta-ZrF4 at Zr sites, is measured between 273 and 740 K via the Perturbed Angular Correlations technique. Two different quadrupole interactions, in a ratio 1:2 of relative fractions, are determined. It is observed that the compound remains stable all over the thermal range. Moisture exposure at room temperature seems not to affect the hyperfine interaction suggesting that \beta-ZrF4 is less sensitive to air water than other varieties of zirconium fluoride. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
3.
In magnetic compounds with Jahn–Teller (JT) ions (such as Mn3+ or Cu2+), the ordering of the electron or hole orbitals is associated with cooperative lattice distortions. There the role of JT effect, although widely recognized, is still elusive in the ground state properties. Here we discovered that, in these materials, there exist excitations whose energy spectrum is described in terms of the total angular momentum eigenstates and is quantized as in quantum rotors found in JT centers. We observed features originating from these excitations in the optical spectra of a model compound LaMnO3 using ellipsometry technique. They appear clearly as narrow sidebands accompanying the electron transition between the JT split orbitals at neighboring Mn3+ ions, displaying anomalous temperature behavior around the Néel temperature TN ≈ 140 K. We present these results together with new experimental data on photoluminescence found in LaMnO3, which lend additional support to the ellipsometry implying the electronic-vibrational origin of the quantum rotor orbital excitations. We note that the discovered orbital excitations of quantum rotors may play an important role in many unusual properties observed in these materials upon doping, such as high-temperature superconductivity and colossal magnetoresistance.  相似文献   
4.
Taylor  M.A.  Martínez  J.A.  López García  A.R.  Dejneka  M. 《Hyperfine Interactions》1999,120(1-8):525-528
By using 181Ta probes, the PAC technique has been used to investigates the behaviour of the hyperfine interaction in 60ZrF4–40BaF2 glass from room temperature (RT) up to the glass temperature Tg (562 K). A first serie of measurements was obtained while heating the as-prepared sample from RT to Tg. A second serie was performed on the as-treated sample after cooling it down to RT and again heated to Tg. In both series the same three components of the quadrupole interaction were observed. Dynamical effects were detected in the main component and activation energies of 0.181 eV and 0.213 eV were obtained. The results are interpreted as dynamical effects associated to the movement in the fluorine ions during polyhedra rearrangements. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
5.
The first results of the study of optical absorption spectra of KTaO3: Er3+ crystals are presented. In the 350–660-nm region, lines are observed deriving from intraconfigurational electronic transitions from the 4 I 15/2 ground state to levels of the 4 F 9/2, 4 S 3/2, 2 H 11/2, 4 F 7/2, 4 F 5/2(4 F 3/2), 2 G 9/2, and 4 G 11/2 excited states of the Er3+ ions. A comprehensive study of transitions to the 4 F 9/2, 4 S 3/2, 2 H 11/2, and 4 F 7/2 levels at 77 K is carried out. The number of lines observed for the above transitions fits the theoretically possible number for ?-? electronic transitions in Er3+ ions in the cubic crystal field. In the case of a differently charged substituted ion, this situation occurs only under nonlocal impurity charge compensation. The energies of the excited state levels for the transitions under study are determined.  相似文献   
6.
Zero-phonon lines of a pair center of Mn4+ ions are observed in the luminescence and luminescence-excitation spectra of SrTiO3:Mn crystal. Based on the experimental data, the energy-level structure of the ground state ∣4 A 2g ,4 A 2g 〉 and excited state ∣4 A 2g ,2 E g 〉 of the Mn4+-Mn4+ pair center is constructed. It is shown that the exchange interaction in the ground state of the Mn4+-Mn4+ pair is antiferromagnetic. Energies of the levels are calculated assuming that the pair is formed by Mn4+ ions occupying neighboring octahedral positions of Ti4+ ions along the [110] axis. Experimental values of the exchange integral in the ground state ∣4 A 2g ,4 A 2g 〉 and energies of spin multiplets in the excited state ∣4 A 2g ,2 E g 〉 agree well with calculation of the exchange interaction carried out within the framework of the channel model with the parameters J ξη = 32 cm4-1 and J ζζ = ?45.5 cm4-1. Experimental data and calculations unambiguously demonstrate that zero-phonon lines in the luminescence and luminescence-excitation spectra have magnetic-dipole nature.  相似文献   
7.
This paper aims to introduce fluoride materials, their conventional processing and how sol-gel processing can be used both to simplify processing and to improve properties. A multistep process incorporating sol-gel synthesis and reactive treatment is used to prepare a monolithic ZBLA fluoride glass. The first step is synthesis of a porous, monolithic, atomically homogeneous hydrous oxide gel containing zirconium, barium, lanthanum, aluminum and possibly sodium as components (ZBLA or ZBLAN). The second step is a relatively low-temperature reactive treatment of the gel with a fluorinating agent to achieve a porous fluoride glass. Subsequently, the gel is viscous sintered to a dense glass. The present status and future challenges in the preparation of optical-quality fluoride glasses via this method will be presented.  相似文献   
8.
A high-frequency (49 and 70 GHz) electron paramagnetic resonance (EPR) study is reported on SrTiO3 single crystals doped with 0.5-at% of manganese. EPR spectra originating from the S=2 ground state of Mn3+ ions are shown to belong to the different types of Jahn–Teller centers that arise as a result of varied ordering of the oxygen vacancies due to the reducing process. The present results indicate the strong covalent reduction of the density of unpaired spins (Fermi term) at the manganese nucleus for the various types of centers.  相似文献   
9.
The photoinduced self-cleaning and super-hydrophilic properties of titania (TiO2) coated glasses are considered to be utilized in many applications. The photocatalytic activity of titania is inherent to the glass composition and to the deposition method. Particularly sodium ions diffused to the titania film from the substrate have tremendous impact on its crystallinity. The deposition method influences surface, structure, and the density of the film. This study aims to provide new findings regarding the mechanism of crystallization of sol?Cgel synthesized titania and its thin films deposited by means of two different methods (dip-coating and spin-coating) onto the glass substrate with a high content of sodium ions (soda-lime glass) and without sodium ions (quartz glass). The main attention is devoted to Raman spectroscopy and Raman point-to-point mapping of the films. The content and the chemical state of the sodium ions were judged using the XPS. It is shown that the dip-coating method led to dense compact material. In this case the crystallization is localized in randomly distributed centers of nucleation. Contrary the spin-coated samples embodied a web-like pattern of cracks, from which the crystallization proceeds throughout the film. Additionally SEM, AFM, XRD, GDS, UV?CVIS methods were performed to support the results.  相似文献   
10.
The unusual behavior of the low-frequency (10 Hz–1 MHz) permittivity in single crystals of ferroelectric multiferroic TbMnO3 has been experimentally and theoretically studied in detail in the region of the narrow temperature peak of the permittivity, associated with the ferroelectric phase transition (TC ~ 27.4 K). It has been found that the εc(ω, T) maximum sharply decreases with increasing measured field frequency, while the temperature position of the maximum is independent of frequency. It has been shown that the observed features of the polarization response can be satisfactorily described within the Landau–Khalatnikov polarization relaxation theory.  相似文献   
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