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1.
A study of Gd3+ centers in Ca1?x R x F2+x (R=La, Y) crystals using pulsed EPR spectroscopy is presented. The echo-induced EPR (ESE-EPR) spectrum shows, besides the signal of slightly perturbed cubic Gd3+ centers, a broad signal at g≈2 due to Gd3+ centers at low symmetry sites. To describe the effects of R3+ ions on the EPR Gd3+, a model, including cubic and linear R3+?2F i ? centers, is developed. Its predictions are compared with the experimental results. The composition dependence of the EPR signal due to slightly perturbed cubic Gd3+ centers in mixed Ca1?x R x F2+x crystals is explained taking into account the different clustering tendency in La and Y crystals. Moreover, the formation of mixed clusters involving R3+ and Gd3+ ions is proposed for both series of samples. A greater clustering trend is found in the Y crystals than in the La ones. Gd3+ ions are found to be a “non innocent” paramagnetic probe for structural studies in these mixed crystals. 相似文献
2.
Abstract Solid solutions Ca1 x-yLuxGdy F2+x+y for 10?4 ≤ x ≤ 2 × 10?2 and y=0.0001 have been studied by electron paramagnetic resonance (EPR) and ionic thermal currents (ITC). It has been found that the ITC spectrum from 77 to 420 K is very weak and the main peak is attributed to the relaxation of both Lu3+-F? x and Gd3+F? i nn dipoles. No polarizable clusters are present in the temperature range explored here. The EPR spectra show the presence of Gd3+ tetragonal and cubic centers due to the local and non local compensation, respectively. The continuous decrease in the molar fraction of Gd3+ tetragonal centers together with the low concentration of Lu nn dipoles is an evidence of the existence at these low and intermediate concentrations of large clusters such as the cubo-octahedral hexamer which has been proposed for CaF2 crystals very highly doped with small trivalent cations. 相似文献
3.
V. Trnovcová N. I. Sorokin P. P. Fedorov E. A. Krivandina T. Srámková B. P. Sobolev 《Ionics》2000,6(5-6):351-358
The superionic conductivity and dielectric response of heavily doped fluorite-structured Ba1−xRxF2+x (R=La, Pr, Nd, Gd, Tb, Y, Sc; x=0.005–0.45) crystals are reported. The highest ionic conductivity is found for R=Sc and x=0.1.
Upon ScF3 doping, small Sc3+ ions rearrange their surroundings, create excessive fluoride interstitial ions and bring about a high ionic conductivity.
For each dopant, the concentration dependence of the ionic conductivity is non-linear. A monotonous concentration dependence
of the ionic conductivity is found only for La3+ doping. Upon doping with Nd3+, Gd3+, Tb3+, Y3+ and Sc3+ ions, a conductivity maximum is observed at x=0.1–0.2. Upon Pr3+ doping, this maximum is split. The influence of defect clustering on the concentration dependence of the conductivity is
discussed.
Paper presented at the 6th Euroconference on Solid State Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999. 相似文献
4.
Abstract Solid solutions Ca1-xGdxF2+x for 3 × 10?7≤ x ≤10?1 have been studied by electron paramagnetic resonance (EPR) and ionic thermal currents (ITC). The EPR experiments show the presence of two single-ion sites a cubic and a tetragonal Gd3+ center which co-exist with comparable abundances for intermediate impurity concentrations. The cubic center predominates at very low and high concentrations. Seven different relaxation processes have been identified from the ITC spectra and the variation of their intensity vs. x was measured. The absolute concentrations of the cubic and nn Gd3+ dipoles were calculated. The scavenging of interstitial fluorines by the neutral clusters explains both the abundance of cubic sites at high concentration and the variety of orientable clusters detected by ITC. 相似文献
5.
L. K. Aminov R. Yu. Abdulsabirov M. R. Gafurov S. L. Korableva I. N. Kurkin S. P. Kurzin R. M. Rakhmatullin A. G. Ziganshin 《Applied magnetic resonance》2005,28(1-2):41-53
Electron paramagnetic resonance (EPR) spectra of impurity Yb3+ ions (about 0.1 at.%) in mixed crystals BaF2(1-x) plus LaF3(x) have been investigated for different values of the concentrationx at a frequency of about 9.5 GHz by both continuous-wave (CW) EPR and electron spin echo methods. A spectrum of trigonal symmetry with a complex hyperfine structure is observed in “pure” BaF2:Yb3+ (x=0). Upon admixture of small amounts of LaF3 (x=0.001), additional EPR lines arise with intensities increasing with the increase ofx up to 0.005. These lines are attributed to trigonal centers including two rare-earth ions and two compensating fluorine ions. A further increase ofx results in a decrease of the total EPR spectrum intensity, and atx≥0.05 the CW resonance becomes practically unobservable. This may be due to the formation of rare-earth ion clusters with paramagnetic Yb3+ ions occurring in domains with a disordered structure of surroundings resulting in very broad EPR lines, which cannot be registered by CW EPR. Indeed, very broad (not less than 1 KG) EPR lines were observed by the electron spin echo method for concentrationsx<-0.02. 相似文献
6.
A.V. Mahajan H. Alloul G. Collin J.F. Marucco 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(3):457-475
We present detailed data and analysis of the effects of Zn substitution on the planar Cu site in YBa2Cu3O6+x (YBCO6+x) as evidenced from our 89Y NMR measurements on oriented powders. For x << 1x \ll 1 we find additional NMR lines which are associated with the Zn substitution. From our data on the intensities and temperature dependence of the shift, width, and spin-lattice relaxation rate of these resonances, we conclude that the spinless Zn 3d 10 state induces local moments on the near-neighbour (nn) Cu atoms. Additionally, we conjecture that the local moments actually extend to the farther Cu atoms with the magnetization alternating in sign at subsequent nn sites. We show that this analysis is compatible with ESR data taken on dilute Gd doped (on the Y site) and on neutron scattering data reported recently on Zn substituted YBCO6 + x. For optimally doped compounds 89Y nn resonances are not detected, but a large T-dependent contribution to the 89Y NMR linewidth is evidenced and is also attributed to the occurence of a weak induced local moment near the Zn. These results are compatible with macroscopic magnetic measurements performed on YBCO6 + x samples prepared specifically in order to minimize the content of impurity phases. We find significant differences between the present results on the underdoped YBCO6 + x samples and 27Al NMR data taken on Al3+ substituted on the Cu site in optimally doped La2CuO4. Further experimental work is needed to clarify the detailed evolution of the impurity induced magnetism with hole content in the cuprates. 相似文献
7.
EPR study of Dy
3 +
ions in DyBa
2
Cu
3
O
6 + x 总被引:1,自引:0,他引:1
V. Likodimos N. Guskos J. Typek M. Wabia 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(2):143-147
Concentrated polycrystalline DyBa2Cu3O6+x compounds are studied by X-band EPR spectroscopy. A broad resonance line due to the highly anisotropic EPR spectrum of Dy3+ ions is identified on several specimens at low temperatures. Powder simulation of the EPR spectra complies with the ground
Kramers doublet predicted by crystal field analysis of Dy3+ ions. Calculations of the second and fourth moments of the resonance lines due to the dipole-dipole interactions of Dy3+ indicate the presence of substantial exchange narrowing of the dipolar-broadened EPR linewidth.
Received 3 June 2001 相似文献
8.
Photoluminescence properties of Y0.75-xGdxAl0.10BO3:Eu3+0.10, 0.05R3+ (R= Sc, Bi) (0.00≤x≤0.45)
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Y$_{0.75 -
x}$GdxAl0.10BO$3:Eu$^{3+}0.10, 0.05R3+
($R$=Sc, Bi) ($0.00 ≤ x ≤ 0.45$) powder samples are prepared
by solid-state reaction and their luminescence properties are
investigated. With the replacement of Y3+$ ions by Sc3+$
(or Bi3+)$ and Gd3+$ ions in (Y,Al)BO$3:Eu, the
intensities of emission at 254 and 147~nm are remarkably improved,
because Sc3+$ ions can absorb UV light and transfer the energy
to Eu3+$ ions efficiently. Moreover, Gd3+$ and Bi$^{3 +
}$ ions act as an intermediate ``bridge' between the sensitizer and
the activator (Eu3+)$ in energy transfer to produce light in
the (Y, Gd)BO$3:Bi3+$, Eu3+$ system more effectively.
After doping an appropriate concentration of Gd3+$ into
Y$_{0.50}$Gd$_{0.25}$Al0.10BO$3:Eu3+_{0.01}$,
Bi$^{3+}_{0.05}$, the emission intensity reaches its maximum, which
is nearly 110{\%} compared with the red commercial phosphor
(Y,Gd)BO$3:Eu and better chromaticity coordinates (0.650, 0.350)
are obtained. 相似文献
9.
D. Zayachuk Ye. Polyhach E. Slynko O. Khandozhko C. Rudowicz 《Applied magnetic resonance》2003,24(3-4):369-377
An electron paramagnetic resonance (EPR) experimental study of crystalline and powder p-Pb1?x?y Sn y Gd y Te samples for various matrix compositionx and Gd contenty has been carried out. The study reveals that grinding the crystals into powder as well as their low-temperature annealing turns Gd impurity ions from the EPR-silent Gd2+ state to the EPR-active Gd3+ state, whereas high-temperature annealing in vacuum quenches EPR signals from Gd3+ ions. The experimental results are interpreted in terms of a model assuming that the trivalent charge state of the Gd impurity ions in lead and tin tellurides is a component part of the “substituting Gd impurity-Te vacancy” complex. 相似文献
10.
I. I. Antonova I. N. Nizamutdinov R. Yu. Abdulsabirov S. L. Korableva N. M. Khasanova A. A. Galeev V. G. Stepanov N. M. Nizamutdinov 《Applied magnetic resonance》1997,13(3-4):579-606
In single crystal colquiriite LiCaAlF6 doped with Gd3+ ions two EPR spectra of the Gd3+ ions with the Laue site-symmetry groups Ci and C3i were observed. The spectrum angular dependence for trigonal Gd3+ centre was investigated in detail and corresponding spin Hamiltonian parameters were fitted. From analysis of the spin Hamiltonian tensorsB 4 andB 6 it was established that Gd3+ with the Laue group C3i substitutes at Ca2+ site with the excess charge compensation by an ion located along the threefold axis from this site. The transformation formulas for a sixth-rank irreducible Hermitian tensor under coordinate rotation are tabulated in an explicit form. By using the EPR data for Gd3+ substituted in a variety of host crystals, the fourth-rank and sixth-rank tensors of Gd3+ spin Hamiltonians were tabulated and correlated with structures of the coordination polyhedra at substitution sites. The results suppose a predominance of quadratic crystal field contributions into the spin Hamiltonian tensorB 4 of Gd3+. 相似文献
11.
L. K. Aminov I. N. Kurkin S. P. Kurzin I. A. Gromov G. V. Mamin R. M. Rakhmatullin 《Physics of the Solid State》2007,49(11):2086-2090
The electron paramagnetic resonance (EPR) spectra of mixed crystals (BaF2)1 − x
(LaF3)
x
(x = 0, 0.001, 0.002, 0.005, 0.010, 0.020) doped with Ce3+ ions (0.1%) are investigated at a frequency v ≈ 9.5 GHz in magnetic fields up to 1.45 T at temperatures T = 10 and 15 K. The EPR spectrum of “pure” barium fluoride BaF2 (x = 0) is characterized by a single Ce3+-F− center with tetragonal symmetry (i.e., the O center with g
‖ = 2.601 and g
⊥ = 1.555). For a lanthanum trifluoride concentration x ≠ 0, the spectrum exhibits new lines due to the presence of the clusters containing Ce3+ and La3+ ions. The intensity of EPR signals from the O centers decreases rapidly as the lanthanum trifluoride concentration x increases. The lines attributed to a paramagnetic center with tetragonal symmetry and strongly anisotropic g factors (i.e., the K center with g
‖ = 0.725 and g
⊥ = 2.52) are separated in the complex EPR spectrum with the use of the angular dependence of the EPR signal intensity measured
for the samples with x ≥ 0.002. This center is identified as a cubooctahedral cluster of the La6F37 type in which one of the La3+ ions is replaced by the Ce3+ ion.
Original Russian Text ? L.K. Aminov, I.N. Kurkin, S.P. Kurzin, I.A. Gromov, G.V. Mamin, R.M. Rakhmatullin, 2007, published
in Fizika Tverdogo Tela, 2007, Vol. 49, No. 11, pp. 1990–1993. 相似文献
12.
J. Zhong H. Liang Q. Su J. Zhou Y. Huang Z. Gao Y. Tao J. Wang 《Applied physics. B, Lasers and optics》2010,98(1):139-147
The luminescence properties of polyphosphates NaEu x Gd(1?x)(PO3)4 (x = 0–1.00) and the energy transfer from Gd3+ to Eu3+ were studied. In undoped NaGd(PO3)4 sample, the photon cascade emission of Gd3+ was observed under 8S7/2 → 6GJ excitation (201 nm) in which the emission of a red photon due to 6GJ → 6PJ transition is followed by an ultraviolet photon emission due to 6PJ → 8S7/2 transition. When part of Gd3+ ions in the host NaGd(PO3)4 were substituted by Eu3+ ions, the NaGd(PO3)4:Eu3+ sample showed intensive red emission under 172-nm vacuum-ultraviolet (VUV) excitation which is suitable for mercury-free fluorescent lamps and plasma display panel applications. Based on the VUV–visible spectroscopic characteristics and the luminescence decay properties of NaGd(PO3)4:Eu3+, it was found that the quantum cutting by a two-step energy transfer from Gd3+ to Eu3+ can improve the red emission of Eu3+ ions under VUV excitation but only a part of the excitation energy in the excited 6PJ states within Gd3+ ions can be transferred to Eu3+ ions for its red emission, and the nonradiative energy transfer efficiencies from the excited 6PJ states within Gd3+ to Eu3+ were calculated. 相似文献
13.
《Journal of magnetism and magnetic materials》2002,238(2-3):293-300
A systematic study of the magnetic and transport properties of the system (La1−xGdx)0.67Ca0.33MnO3 (0⩽x⩽1) is presented in this article. Through this series, a great crystallographic distortion is achieved but keeping constant the electronic density. At low Gd3+ content, these ions behaves in a paramagnetic state following a Brillouin function. Low-temperature ferromagnetism remains unchanged. However, for the samples with large Gd3+ content a complex magnetic behavior arises from several competing interaction as super-exchange, double-exchange and also the interaction between Gd and Mn ions. Resistivity and thermopower follow a progressive increase as Gd3+ content does, but the polaron energy in the paramagnetic range remains independent of all these changes. Thermopower infinite value is also determined and analyzed. 相似文献
14.
P. H. Umadikar Milind Vaidya S. R. Joshi S. K. Karadnikar R. Nagarajan V. R. Marathe 《Hyperfine Interactions》1988,41(1):521-524
We report here our57Fe Mössbauer studies on the mixed and substituted iron garnets. Magnetisation studies on substituted SmIG system {Sm3?x Cax} [Snx Fe2?x](Fe3)012 (0.2≤x≤1.8) show that the Tc decreases as x increases. We attribute this to the reduced strength of a-d interaction as a result of dilution of a-site. While the Mössbauer spectra seem to reflect this, an interesting feature is the unresolved hyperfine spectrum seen at 80K for x=1.0, even though the transition temperature (Tc) is 285K. For this concentration, varying the rare earth ion from Sm to Er, results in very similar spectra. We speculate spin glass behaviour for x=1.0. In mixed and substituted garnet system {Gd2.5R0.2Ca0.3} [Sn0.3Fe1.7](Fe3)012 (R=Y, Sm, Eu, Ho and Er), we observe well resolved spectra with no change in the hyperfine field with substitution of rare earth. This is consistant with the dominance of a-d interaction in these systems. 相似文献
15.
The ESR of Nd3+ and Gd3+ in the eight intermetallic compounds AB2 (A = Y, La, Ce, Lu; B = Ir, Rh) is reported. The hyperfine constants and the exchange parameters are extracted. 相似文献
16.
Using inorganic oxides and salts instead of alkoxides as the main starting materials, we prepared nanocrystalline YVxP1-xO4:Eu3+ and RVO4:Eu3+ (0x1; R=Y,La,Gd) thin-film phosphors by the Pechini sol–gel dip-coating process. The resulting films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and photoluminescence excitation and emission spectra as well as luminescence decay. The results of XRD showed that a solid solution formed in the YVxP1-xO4:Eu3+ film series from x=0 to x=1 with zircon structure. The same structure also held for the GdVO4:Eu3+ film, but the LaVO4:Eu3+ film crystallized with a different structure, monazite. AFM and SEM studies revealed that the phosphor films consisted of spherical particles ranging from 90 to 400 nm depending on the film compositions. With the increase of x values in YVxP1-xO4:Eu3+ films, the integrated emission intensity and the red (5D0–7F2)-to-orange (5D0–7F1) intensity ratio of Eu3+ increase due to the increased energy-transfer probability from VO43- to Eu3+ and the increased polarizability of the surrounding oxygen ions, respectively. The x values also have an influence on the decay behavior of Eu3+. The YVO4:Eu3+ and GdVO4:Eu3+ films showed very similar luminescence properties due to their same crystal structures. However, the LaVO4:Eu3+ film exhibited a much different
emission property from those of the YVO4:Eu3+ and GdVO4:Eu3+ films due to the structural effects. PACS 73.63.Bd; 78.55.Hx; 78.66.Nk; 81.15.Lm; 81.20.Fw 相似文献
17.
The purpose of this research is to study the effect of doping Gd into
Pb(Zr0.52Ti0.48)O3 ceramics prepared by solid state reaction.
X-ray diffraction patterns show that all PGZT samples are of tetragonal
structure and the highest doping should be no more than 2 mole % Gd at
which the unreacted oxides start to appear. The electron spin resonance
(ESR) spectra of PGZT's indicate that Gd3+ can enter both A site of the
perovskite structure instead of only A site as widely believed. The ESR
peaks resonance shift towards low fields as the concentration is higher,
which is due to the change in crystal field experienced by Gd3+ ions.
At x =0.001, 0.005 and 0.01 dopings, two sets of powder ESR signals arising
from Gd3+ (4f7, spin 7/2) ions at A site. The first set shows some
fine structure having strong absorption peaks centered at 76.26 mT (g =
8.550). The second is a seven-peak spectrum centered at 206.01 mT (g =
3.165), which belongs to the Gd3+ ions at B sites. Furthermore, the
overlapped ESR strong absorption peaks from 309.17 mT to 314.49 mT (g =
2.2818-2.1087) belong to Gd3+ of unreacted Gd2O3. The local
environments of Gd3+ ions were verified from the calculated ESR spectra
using appropriate spin Hamiltonian parameter, i.e. gyromagnetic tensor
g, zero-field splitting D and hyperfine tensor
A. 相似文献
18.
A series of red phosphors R0.8Eu1.2(MoO4)3 (R=La, Y, and Gd) have been synthesized by sol-gel method. The crystallization processes of the phosphor precursors were characterized by X-ray diffraction (XRD) and thermogravimetry-differential thermal analysis (TG-DTA), and the properties of these resulting phosphors have also been characterized by photoluminescence (PL) spectra and reflectance spectra. Field emission scanning electron microscopy (FE-SEM) was also used to characterize the shape and the size of the samples. The results of TG-DTA and XRD indicated that all of the R0.8Eu1.2(MoO4)3 (R=La, Y, and Gd) phosphors crystallized completely at 650 °C. Y0.8Eu1.2(MoO4)3 and Gd0.8Eu1.2(MoO4)3 have two structures, monoclinic and orthorhombic, while La0.8Eu1.2(MoO4)3 only adopts monoclinic structure. The luminescent properties of phosphors R0.8Eu1.2(MoO4)3 (R=La, Y, and Gd) are dependent on their structures to some extent. The orthorhombic Y0.8Eu1.2(MoO4)3 and Gd0.8Eu1.2(MoO4)3 phosphors show very similar luminescent properties, which differ from those of phosphors with monoclinic structure. For all of R0.8Eu1.2(MoO4)3 (R=La, Y, and Gd) phosphors, intense red emission is obtained by exciting at ∼394 and ∼465 nm which are owing to the sharp 7F0→5L6 and 7F0→5D2 lines of Eu3+. Two strongest lines at 394 and 465 nm in excitation spectra of these phosphors match well with the two popular emissions from near-UV and blue GaN-based LEDs, so they could be used as red components for white light-emitting diodes. 相似文献
19.
Growth and the luminescence properties of a lutetium gadolinium garnet doped with Ce3+ and Pr3+ ions
S. V. Nizhankovsky A. Ya. Dan’ko Yu. V. Zorenko V. V. Baranov L. A. Grin’ V. F. Tkachenko P. V. Mateichenko 《Physics of the Solid State》2011,53(1):127-130
Crystals of lutetium gadolinium garnet solid solutions (Lu1 − x
Gd
x
)Al5O12 (0 ≤ x ≤ 0.6) doped with Ce3+ and Pr3+ ions have been prepared by the horizontal directional crystallization method, and their optical and luminescence properties
have been investigated. It has been established that the introduction of gadolinium into the lutetium garnet lattice leads
to a decrease in the antisite luminescence (LuAl centers) in the UV spectral range and to sensitization of the Ce3+ ion luminescence. By contrast, the presence of gadolinium results in the quenching of the Pr3+ luminescence due to the nonradiative excitation transfer from Pr3+ ions to Gd3+ ions. 相似文献
20.
The EPR of paramagnetic impurities Gd3+ and Mn2+ was studied in nonmagnetic Kondo system La1−x
CexCu6 containing in the 1.6–200 K range. The exchange interaction parameters of gadolinium and manganese ions with conduction electrons,
of cerium ions with conduction electrons and with one another, the Kondo temperature of cerium ions, and the temperature behavior
of cerium-ion spin-fluctuation rate have been determined. A pseudogap in the density of states at the Fermi level has been
detected in the CeCu6 regular system, which is apparently due to s-f hybridization. This pseudogap can be destroyed by introducing an aluminum impurity, which induces strong conduction-electron
scattering. It was also found that RKKY interaction among manganese ions in CeCu6−y
Mny is considerably stronger than it is in LaCu6−y
Mny, which implies enhancement of nonlocal spin susceptibility due to an f band contribution to conduction-electron states.
Fiz. Tverd. Tela (St. Petersburg) 40, 593–599 (April 1998) 相似文献