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1.
TlGaS2 single crystal doped by paramagnetic Fe3+ ions has been studied by electron paramagnetic resonance (EPR) technique. The fine structure of EPR spectra of paramagnetic Fe3+ ions was observed. The spectra reveal a nearly orthorhombic symmetry of the crystal field (CF) on the Fe3+ ions. Two groups each consisting of four equivalent Fe3+ centers were observed in the EPR spectra. The local symmetry of the crystal field on the Fe3+ centers and CF parameters were determined. Experimental results indicate that the Fe ions substitute Ga at the center of the GaS4 tetrahedrons. The rhombic distortion of the sulfur ligand CF is attributed to the effect of Tl ions located in the trigonal cavities between the tetrahedral complexes. The observed twinning of the resonance lines indicates a presence of two non-equivalent positions of Tl ions that confirms their zigzag alignment in the TlGaS2 crystal structure. 相似文献
2.
A single-crystal TlGaSe2 doped by paramagnetic Fe ions has been studied at room temperature by electron paramagnetic resonance (EPR) technique. The fine structure of EPR spectra of paramagnetic Fe3+ ions was observed. The spectra were interpreted to correspond to the transitions among spin multiplet (S=5/2, L=0) of Fe3+ ion, which are splitted by the local ligand crystal field (CF) of orthorhombic symmetry. Four equivalent Fe3+ centers have been observed in the EPR spectra and the local symmetry of crystal field at the Fe3+ site and CF parameters were determined. Experimental results indicate that the Fe ions substitute Ga at the center of GaSe4 tetrahedrons, and the rhombic distortion of the CF is caused by the Tl ions located in the trigonal cavities between the tetrahedral complexes. 相似文献
3.
N. Guskos V. Likodimos S. Glenis J. Typek H. Fuks M. Wabia D.G. Paschalidis D. Tossidis C.L. Lin 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(3):277-282
The magnetic properties of the rare earth molecular compounds with hydrazone ligands containing Nd3+, Gd3+, and Yb3+ have been investigated by electron paramagnetic resonance (EPR) and magnetization measurements. For the Gd-compound, partially
resolved fine structure due to Gd3+ and exchange narrowing effects at low temperatures are observed in the EPR spectra, suggesting, consistent with the EPR and
dc magnetic susceptibility, weak antiferromagnetic exchange interactions. Paramagnetic behavior sustained down to low temperatures
is derived for Yb3+ ions, whereas substantial ferromagnetic exchange coupling is inferred for the lighter Nd3+ ions, indicating significant variations of the exchange integrals along the lanthanide series.
Received 29 April 2002 Published online 31 July 2002 相似文献
4.
The optical absorption spectrum, zero-field splitting (ZFS) and EPR g factor of LiNbO3:Ni2+ are explained uniformly on the basis of complete energy matrix diagonalization procedure (CDP) and Zhao's self-consistent field (SCF) d-orbit of free Ni2+ ions. The agreement between the calculated results and the experimental data shows quantitatively that impurities Ni2+ replace the Nb5+ rather than Li+ sites in LiNbO3:Ni2+. 相似文献
5.
In this paper, we give an alternative suggestion that both the observed optical and electron paramagnetic resonance (EPR) spectra of Yttrium oxide (Y2O3):V3+ are attributed to V3+ ions at the S6 site of Y2O3. This suggestion is different from the opinion in the previous paper that the optical and EPR spectra are attributed to V3+ ions at the C2 and S6 sites, respectively. From the suggestion, the optical band positions and spin-Hamiltonian parameters are calculated by diagonalizing the complete energy matrix for 3d2 ions in trigonal symmetry. The results are in good agreement with the experimental values, suggesting that both the observed optical and EPR spectra in Y2O3:V3+ may be due to V3+ at S6 site of Y2O3 crystal. 相似文献
6.
Two methods for the preparation of LaCoO3 samples were used: thermal decomposition of La-Co citrate precursors obtained by freeze-drying of the corresponding solutions and by a solid state reaction. Microstructural characterization was made by electron paramagnetic resonance spectroscopy (EPR). For assignment of the EPR signals, La1−xSrxCoO3 samples were used as EPR references. The LaCoO3 oxides prepared from citrates and by a solid state reaction were shown to differ in respect of the mean oxidation state of the cobalt ions, the specific surface area and the particle morphology. EPR spectroscopy reveals for ex-citrate LaCoO3 ferromagnetic Co3+ and Co4+ coupled ions. For LaCoO3 samples obtained by a solid state reaction, EPR permits detecting Co3O4 impurities only. 相似文献
7.
C. Ruvalcaba-Cornejo Ma. Elena Zayas R. Palomino-Merino J.E. Espinosa J. Martínez-Juárez S.A. Tomás 《Journal of luminescence》2008,128(2):213-216
ZnO-CdO-TeO2 was employed as a host of Tb3+ and Yb3+ ions. The matrix doped with Tb3+ presents a crystalline/amorphous structure, while the same matrix shows an amorphous structure when it is doped with Yb3+. Optical absorption spectra, measured by using photoacoustic (PA) spectroscopy, allowed to determine the band gap, which is localized in the range 3.47-3.60 eV. Both kinds of ions Tb3+ and Yb3+ in the ZnO-CdO-TeO2 matrix show emissions that are characteristic of such ions. For Tb3+ the signals were allocated in 548, 586, 622 nm, respectively, while for Yb3+ only one signal was registered at 1000 nm. 相似文献
8.
A.D. Prokhorov M.T. Borowiec V.P. Dyakonov V.I. Kamenev P. Aleshkevych H. Szymczak 《Physica B: Condensed Matter》2008,403(18):3174-3178
The electron paramagnetic resonance (EPR) of Nd3+ ion in KY(WO4)2 single crystal was investigated at T=4.2 K using an X-band spectrometer. The observed resonance absorption represents the complex superposition of three spectra corresponding to neodymium isotopes with different nuclear momenta. The EPR spectrum is characterized by a strong g-factor anisotropy. The temperature dependences of the g-factor were caused by strong spin-orbit and orbit-lattice coupling. The resonance lines become broader as temperature increases due to the short spin-lattice relaxation time. 相似文献
9.
Tae Ho Yeom 《Solid State Communications》2003,125(10):547-550
The domain structure of ferroelastic BiVO4 single crystal has been investigated using the electron paramagnetic resonance (EPR) of the Gd3+ ions existing as an impurity in the crystal. Two sets of Gd3+ EPR signals were obtained in the crystallographic ca-plane. These two sets of signals originated not from the two kinds of substitutional sites but from the twin-domain structure in the host crystal. It is found that the BiVO4 crystal investigated with Gd3+ EPR has the prominent (W-plane) domain wall. The domain structure is stable in contrast with a previous report by Baran et al. From the observed W-plane of the domain wall, it is suggested that a ferroelastic transition in BiVO4 is 4/mmm F 2/m instead of 4/m F 2/m. The model of twinning mechanism improved in a previous report by Mn2+ EPR is confirmed by Gd3+ EPR. 相似文献
10.
Intense infrared-to-visible up-conversion (UC) emissions were obtained in hexagonal Yb3+-Tm3+ co-doped NaYF4 nanorods under excitation at 980 nm. Especially, luminescent switching between different UC emission wavelengths at 800, 480 and 450 nm were observed by adjusting excitation powers. Based on power-dependent spectral analyses, it was found that the cooperative energy transfer between Yb3+-Yb3+ pairs and Tm3+ ions play a key role on the luminescent switching besides the saturation effect of Yb3+2F5/2 and Tm3+1G4 excited states. Our results indicate that hexagonal NaYF4 nanostructures have potential applications in miniaturized solid-state laser, optical processing sensors and fluorescent biolabels. 相似文献
11.
In this paper, the formulae of optical spectral levels and electron paramagnetic resonance (EPR) spectra in trigonal symmetry of 3d8 ions are established on the basis of strong field mechanism and a two spin-coupling (SO) parameters model. Unlike the classical crystal-field approach which has only taken the SO coupling of the central metal ions into account, the contribution of the SO coupling of the ligand ions to the optical and EPR spectra has been included in these formulae. When the optical and EPR spectra of the strong covalent crystals are calculated, the reasonable results can be obtained if the two SO parameters model has been put into action. As an application, the optical and EPR spectra of the (NiX6)4− clusters in CsMgX3:Ni2+ (X=Cl, Br, I) crystals have been studied by the complete diagonalization (of energy matrix) method (CDM). The calculated results agree well with experimental findings. From the investigations, a more valid method to calculate the optical and EPR spectra for 3d8 ions clusters is provided. 相似文献
12.
In this paper, the Czochralski growth, absorption spectra, and photoluminescence spectra of Nd:GdVO4 crystals are studied. From its absorption spectra, Nd:GdVO4 is found to exhibit an anisotropic optical absorption effect, and its effective Judd-Ofelt parameters are calculated: Ω2=10.281×10−20 cm2, Ω4=5.426×10−20 cm2 and Ω6=9.943×10−20 cm2. By these parameters, the absorption oscillator strengths, emission oscillator strengths, transition probabilities, fluorescence branch ratios, energy lifetimes, and integrated emission cross-sections are also derived. The photoluminescence spectra of Nd:GdVO4 crystal consist of a wide emission band of host and the characteristic emission bands of Nd3+. Based on the excitation spectrum, both the two evident peaks locating at 345 and 371 nm are ascribed to the characteristic excitation of Nd3+, and an energy transfer from the host to its doping Nd3+ ions is indicated. 相似文献
13.
Effect of allied and alien ions on the EPR spectrum of Mn-containing lithium-manganese spinel oxides
Electron paramagnetic resonance spectroscopy was used for studying the effect of allied and alien ions on the EPR spectrum of Mn4+-containing lithium-manganese spinel oxides. Manganese spinel oxides with paramagnetic Mn4+ and diamagnetic substituents in the 16d spinel sites were studied: Li[Mg0.5Mn1.5]O4, Li[Mg0.5−xCo2xMn1.5−x]O4, 0<x≤0.5, and Li[Li1/3Mn5/3]O4. Ni2+-ions with integer-spin-ground state (S=1) were selected as alien ions: Li[Mg0.5−xNixMn1.5]O4 (0≤x≤0.5), Li[Li(1−2x)/3NixMn(5−x)/3]O4 (0≤x≤0.5), and Li[Ni0.5Mn1.5−yTiy]O4 (0≤y≤1.0). It was shown that in Ni-substituted oxides the low temperature EPR response comes from magnetically correlated Ni-Mn spins, while at high registration temperature Mn4+ ions give rise to the EPR profile. Analysis of the EPR line width allows differentiating between the contributions of the density of paramagnetic species and the strength of the exchange interactions in magnetically concentrated systems. The density of allied and alien paramagnetic species has no effect on the EPR line width in cases when the strengths of antiferro- and ferromagnetic interactions on an atomic site are close. On the contrary, when antiferro- or ferromagnetic interactions on an atomic site are dominant, the EPR line width increases with the density of paramagnetic species. 相似文献
14.
V. G. Babajanyan R. B. Kostanyan P. H. Muzhikyan 《Journal of Contemporary Physics (Armenian Academy of Sciences)》2012,47(1):17-22
The results of investigations of luminescent radiations’ kinetic characteristics for LiNbO3:Yb3+-Er3+, LiNbO3:Er3+, and LiNbO3:Yb3+ crystals under optical excitations at 532 nm and 1064 nm wavelengths are presented. The shapes and times of rise and damping
of luminescent signals at 550 nm, 980 nm and 1555 nm wavelengths under selective excitations in the impurity subsystem of
the investigated materials are determined. Comparison of the temporal characteristics of luminescent responses of LiNbO3 crystals doped separately with Yb3+ and Er3+ ions with those of the LiNbO3:Yb3+-Er3+ crystal allows identifying the contributions from different energy transfer processes of optical excitation taking place
in the impurity subsystem of the material. 相似文献
15.
Neeraj Kumar Giri 《Optics Communications》2008,281(13):3547-3552
Upconversion emission and energy transfer processes in singly, doubly and triply doped tellurite glasses have been studied under 798 and 980 nm laser excitations. Emissions have been observed at 482, 544, 584, 655 nm and at 477, 655, 698, 800 nm corresponding to Tb3+: 5D4 → 7F6, 7F5, 7F4, 7FJ (J = 0, 1, 2, 3) and Tm3+: 1G4 → 3H6, 1G4 → 3F4, 3F3 → 3H6, 3H4 → 3H6 transitions, respectively. Among Tm3+, Yb3+and Tb3+ ions only Tm3+ has a ground state absorption at 798 nm excitation due to 3H4 ← 3H6 transition. For 980 nm excitation only Yb3+ can absorb the incident radiation. However, for both types of excitations, emission from all the three ions Tb, Yb and Tm has been observed. Possible mechanisms are proposed as follows: under 798 nm excitation Tm3+ ions are excited which excite Yb3+ ions through energy transfer. Finally “cooperative energy transfer” from a pair of Yb3+ ions to Tm3+ and Tb3+ ions takes place. Under 980 nm excitation Yb3+ ions absorb the incident energy and excite Tm3+ and Tb3+ ions via cooperative energy transfer. Variation of emission intensity with the ion concentrations of Yb3+, Tm3+ and Tb3+ has been studied. The lifetime of the 1G4 level has also been measured. 相似文献
16.
Yujin Chen 《Solid State Communications》2004,132(8):533-538
Yb3+-doped La2(WO4)3 single crystals were grown by the Czochralski technique. Absorption and fluorescence spectra of the crystal were recorded at the room temperature. The stimulated emission cross-sections of Yb3+ ions were calculated using the reciprocity method and Fuchtbauer-Ladenburg formula, respectively. The fluorescence decay curves of 2F5/2 manifold of Yb3+ ions were recorded at room temperature for both crystal and powder samples. The effect of radiation trapping on the spectroscopic properties is discussed. Comparison with other Yb3+-doped laser crystals is made. The results show that Yb3+:La2(WO4)3 crystal is a promising laser material. 相似文献
17.
The EPR spectrum of first nearest neighbour pairs of Fe3+ ions substituting for Al3+ ions in beryl is reported. The form of the pair spin Hamiltonian is discussed, and operator equivalent factors for fourth-order terms are tabulated. The Fe3+ pair interionic coupling corresponds to isotropic antiferromagnetic exchange with J = + 1.7 cm-1 plus anisotropic dipolar coupling. The pair value of the zero-field splitting parameter D is + 0.0206 cm-1 and shows a substantial shift from the single-ion value. It is proposed that resonance lines previously attributed to Fe3+ ions in Be2+ or Si4+ sites are due to Fe3+ pairs. 相似文献
18.
EPR study of Cr3+-doped tetramethyl cadmium chloride (TMCC) single crystals is carried out at room temperature. The crystal field and spin-Hamiltonian parameters are evaluated from the resonance line positions of different lines observed in the EPR spectra. The g and D parameter values are found to be g=1.9741±0.0002 and D=553±2×10−4 cm−1, respectively. EPR data indicate that the site symmetry of Cr3+ ion in the crystal is distorted octahedron. Cr3+ ions enter the lattice substitutionally replacing Cd2+ sites and bind to the neighboring extra Cd vacancies necessary for charge compensation. The optical absorption spectra are measured in 195–925 nm wavelength range at room temperature. From optical study the energy values of different orbital levels are estimated. Further, the bonding parameters are obtained by correlating optical and EPR data and the nature of bonding in the crystal is discussed. The values of Racah parameters (B and C), crystal field parameter (Dq) and nephelauxetic parameters (h and k) are obtained to be B=722, C=2845, Dq=2043 cm−1, h=1.015 and k=0.21. 相似文献
19.
In this paper, we report the near-infrared luminescence from the Er3+/Yb3+, Tm3+/Yb3+, Er3+/Tm3+ and Nd3+ ions-doped TeO2-ZnO-B2O3-Li2O-Na2O glasses for optical amplification. The X-ray diffraction (XRD) and differential scanning calorimetry (DSC) profiles of the host glass matrix have been carried out. From the DSC thermogram, glass transition (Tg), crystallization (Tc) and melting (Tm) temperatures have been evaluated. The near-infrared spectra of Er3+/Yb3+, Tm3+/Yb3+, Er3+/Tm3+ and Nd3+ ions-doped glasses have shown full-width at half-maxima (FWHM) around 58, 127, 87 and 35 nm, respectively. These glasses with better thermal stability and broad near-infrared emissions should have potential applications in broadly tunable laser sources and broadband optical amplification at low-loss telecommunication windows. 相似文献
20.
The Eu2+ and Dy3+ co-activated Ca-Sr feldspar solid solution compounds, (Ca0.98−xSrx)Al2Si2O8:Eu0.01,Dy0.01 (x=0-0.98), have been prepared by solid-state reaction in weak reductive atmosphere. The fluorescence spectra showed that the emission peaks of these phosphors shifts to shorter wavelength with an increase of Sr2+ solid solution quantity and correspondingly the afterglow color changes from blue to purple. All the changes can be attributed to the various crystal fields around Eu2+ ions. The afterglow with special short wavelength in near ultraviolet region can be obtained by adjusting the host chemical composition. 相似文献