共查询到20条相似文献,搜索用时 15 毫秒
1.
I. Veltruský 《Czechoslovak Journal of Physics》1978,28(6):675-695
The theory of covalency is applied to the discussion ofg-factors and hyperfine constantsA of a V4+ ion in tetrahedral sites in garnets Ca3X2Ge3O12 with X=Sc, Al, Lu, In, and NaCa2. Mg2V3O12, Ca3Sc2Si3O12, Sr3Sc2Ge3O12. The site symmetry is S4. Coefficients in LCAO-MO wave function and the Fermi contact interaction constantx are determined by an iterative procedure from experimental data. The spin-orbit coupling coefficient
d
and radial average r
–3 are deduced from the condition of solvability of four equations: overlap and charge-transfer integrals are also determined.The author is grateful to Dr. P.Novák for many valuable discussions on the subject and Dr. J.Jokl from the Institute of Macromolecular Chemistry of Czechoslovak Academy of Sciences for optical measurements. 相似文献
2.
Temperature dependence of EPR of the octahedral Fe3+ and Mn2+ ions in four different garnets is studied between 77 K and the room temperature. The observed change of the spin hamiltonian parametersB
2
0
,B
4
0
,B
4
3
is of the order of several %, while theg-factor is temperature independent within the experimental errors. The role of thermal expansion and the effect of phonons on the temperature variation of B
2
0
is analyzed. It is shown that the inhomogeneous thermal expansion may account for theB
2
0
(T) dependence observed.The authors wish to thank Dr. B. V.Mill of Moscow State University (USSR) for supplying the single crystals of Na3Sc2V3O12, Ca3Al2Ge3O12 and Ca3Ga2Ge3O12 garnets. 相似文献
3.
The optical absorption spectra (d-d transition bands) and covalent effect of Ni2+ ions in octahedral sites of Ca3Sc2Ge3O12 crystal have been investigated by the full energy matrix based on the two spin–orbit coupling parameters model. The bond length of octahedral site is Ri?=?2.19 Å, which can be determined by the cubic crystal-field parameter and optical spectral data. The lattice distortion of the Ni2+ center in Ca3Sc2Ge3O12 crystal is also obtained from the calculations. In addition, the result has shown that the covalent effect of Ni2+ ion in the octahedral site of Ga3Sc2Ge3O12 is obvious and cannot be ignored. The calculated d-d transition bands agree well with that of the experimental findings, suggesting that the present methods can explain reasonably the optical spectral data and covalent effect of 3d8 ions in octahedral lattices. 相似文献
4.
采用凝胶-燃烧法合成了Ca3Sc2Si3O12 ∶Ce绿色LED用荧光粉,用X射线粉末衍射(XRD)、扫描电镜(SEM)、荧光光谱仪等对合成产物进行了分析和表征.结果表明:通过添加H3BO3做助熔剂,制得的荧光粉晶相纯正,颗粒形貌均呈现为较规则的类球形,而且所得荧光粉的粒径均小于1 μm.发射光谱呈现为一宽带,发射主峰位于505 nm,该宽峰对应于Ce3+关键词:
白光LED
荧光粉
3Sc2Si3O12 ∶Ce')" href="#">Ca3Sc2Si3O12 ∶Ce
发光 相似文献
5.
A. V. Sobolev I. A. Presnyakov K. V. Pokholok V. S. Rusakov T. V. Gubaidulina A. V. Baranov G. Demazeau 《Bulletin of the Russian Academy of Sciences: Physics》2007,71(9):1314-1321
Anion-deficient substituted ferrites Ca2Fe2 − x
N
x
O5 (N = Sc3+, Al3+) and mixed manganite CaMn7O12 have been investigated by 119Sn and 57Fe probe M?ssbauer spectroscopy. The mechanism of charge compensation for heterovalent impurity Sn4+ ions in the structure of the ferrite Ca2Fe2O5 has been established. The presence of nonequivalent crystallographic positions of manganese cations, caused by their charge
ordering in the structure of the manganite CaMn7O12, is shown. Magnetic ordering of Mn3+ and Mn4+ cations in the octahedral sublattice of CaMn7O12 at T < T
M2 ≈ 90 K is established.
Original Russian Text ? A.V. Sobolev, I.A. Presnyakov, K.V. Pokholok, V.S. Rusakov, T.V. Gubaidulina, A.V. Baranov, G. Demazeau,
2007, published in Izvestiya Rossiiskoi Akademii Nauk Seriya Fizicheskaya, 2007, Vol. 71, No. 9, pp. 1347–1354. 相似文献
6.
K.V. Ivanovskikh A. Meijerink A. Speghini C. Ronda M. Bettinelli 《Journal of luminescence》2010,130(5):893-16384
The silicates Ca3Sc2Si3O12, Ca3Y2Si3O12 and Ca3Lu2Si3O12, both undoped and doped with Pr3+ ions, have been synthesized by solid-state reaction at high temperature. The luminescence spectroscopy and the excited state dynamics of the materials have been studied upon VUV and X-ray excitation using synchrotron radiation. All doped samples have shown efficient 5d-4f emission upon direct VUV excitation of 5d levels, but only Ca3Sc2Si3O12:Pr3+ shows luminescence upon interband VUV or X-ray excitation. The VUV excited emission spectra of Ca3Y2Si3O12:Pr3+ and Ca3Lu2Si3O12:Pr3+ show features attributed to emission from two distinct sites accommodating the Pr3+ dopant. The decay kinetics of the Pr3+ 5d-4f emission in Ca3Sc2Si3O12:Pr3+ upon VUV excitation across the band gap are characterized by decay times in the range 25-28 ns with no significant rise after the excitation pulse. They appear to be faster upon X-ray irradiation than for VUV excitation. Weak afterglow components are attributed to defect luminescence. 相似文献
7.
A. A. Galeev N. M. Khasanova A. V. Bykov G. R. Bulka V. M. Vinokurov N. M. Nizamutdinov 《Applied magnetic resonance》1996,11(1):61-86
Dopant Fe3+ ions in tetrahedral and octahedral positions of Ge4+ in the crystal Li2Ge7O15 were studied using EPR. Fe3+ substitutes for Ge4+ with a local charge compensation. The octahedral site and the tetrahedral sites significantly differ by the value of the invariant sumS(B 4) of theB 4 tensor of the spin Hamiltonian of Fe3+. The irreducible tensor products {V 4 ? V 4}4 and {V 4?V 4}2 theV 4 tensor of the crystal field calculated using the point-charge model for octahedral and tetrahedral complexes provide the predominant contribution of the crystal field to theB 4 andB 2 tensors of the spin Hamiltonian of Fe3+, respectively. A comparison of the fourth-rank tensorsB 4 of the spin Hamiltonian and {V 4?V 4}4 of the crystal field determined at 300 K with those determined at 77 K supports the conclusion that the phase transition is accompanied by combined rotation of the [GeO4] tetrahedra with the [Ge(1)O6] octahedron almost unaltered. The spectrum lines are narrow and the variety of point defects in the vicinity of the paramagnetic impurity ions Fe3+, Cr3+ and Cu2+ is not detected. These facts are inconsistent with the statistically distributed model for the Li(2) atom. In specific cases at 300 K, when the wings of the two spectrum lines of theM→M+1 and theM+2 →M+3 transitions of Fe3+ ions belonging to one system of translationally equivalent positions overlap an extra line appears in the center between these lines. It is suggested that this effect is due to the soft phonon mode above the phase transition temperature. 相似文献
8.
E. V. Bol’shakova A. V. Malov P. A. Ryabochkina S. N. Ushakov K. N. Nishchev 《Optics and Spectroscopy》2011,110(6):910-916
We examine the oscillator strengths and the intensity parameters Ω
t
(t = 2, 4, 6) of yttrium-aluminum, scandium-containing, and gallium garnet crystals doped with Er3+ ions. A comparative analysis of the oscillator strengths and the intensity parameters Ω
t
(t = 2, 4, 6) of garnets with different contents of Al3+ and Sc3+ ions (Gd2.4Er0.5Sc1.8Al3.3O12, Gd2.4Er0.5Sc1.9Al3.2O12, Gd2.4Er0.5Sc2.0Al3.1O12) is performed, as a result of which the oscillator strengths and the intensity parameters Ω
t
(t = 2, 4, 6) of these crystals are shown to have close values. We find that Ca3(NbGa)5O12 crystals doped with Er3+ ions are characterized by highest values of the oscillator strengths for hypersensitive transitions and of the intensity
parameter Ω2 of Er3+ ions compared to the values of these quantities in the examined garnet crystals, which is determined by the fact that the
symmetry of the local environment of Er3+ ions in these crystals is C
1, C
2, or C
2ν. We reveal that, as the concentration of Er3+ ions in these crystals increases from 1 to 39 at %, both the oscillator strength of the hypersensitive transition 4
I
15/2 → 2
H
11/2 of Er3+ ions and their intensity parameter Ω2 tend to decrease, which can be related to an increase in the relative fraction of Er3+ ions with higher symmetry of the local environment. 相似文献
9.
Pavel Novák 《Czechoslovak Journal of Physics》1994,44(6):603-611
Theoretical analysis of the first magnetocrystalline anisotropy constantK
1 of BaFe12O19 is performed. Two contributions toK
1 are considered — single ion anisotropy and dipolar anisotropy. ParameterD which determines the magnitude of the single ion contribution is calculated on the basis of the superposition model. It is argued that the disagreement between calculated and observed values ofK
1 is most likely connected with the contribution of Fe3+ ions on bipyramidal sites, for which the value ofD is uncertain. 相似文献
10.
Mössbauer spectroscopy of a semiconductive phosphate glass (10V2O5 30Fe2O3 60P2O5 at low temperature
T. Oohata K. Shirahata T. Toriyama T. Inamura K. Yoshino H. Iijima 《Hyperfine Interactions》1994,94(1):2131-2136
In order to clarify the difference between the local structures of Fe3+ and those of Fe2+ ions in a semiconductive phosphate (10V2O5-30Fe2O3-60P2O5) glass, the temperature dependencies of the isomer shift (IS), quadrupole splitting (QS) and absorption area (AR) for Fe3+ and Fe2+ ions were measured. Debye temperatures (
D) for Fe3+ and Fe2+ ions were determined to be 318 ± 29 K and 223 ± 18 K, respectively, from the temperature dependence of the absorption area (AR). From the temperature dependence of the quadrupole splitting(QS), B strength parameters for Fe3+ and Fe2+ ions, which are the coefficients for theT
3/2 term, were deduced. It was found that in this phosphate glass, Debye temperatures
D(AR) were consistent with those obtained using the relation of the B parameter to Debye temperature described in the literature. Also from the temperature dependence of the isomer shift, the difference between the thermal effects except the second-order Doppler shift for Fe3+ ions and those for Fe2+ ions was compared. 相似文献
11.
The lattice parameter,a, increases with the increase of Ti4+ substitution while it decreases with the increase of Ge4+ substitution in Cu1+x
A
x
Fe2–2x
O4 compounds [A=Ti4+, Ge4+Sn4+]. On substitution of Sn4+,a does not vary. CuFe2O4 exhibits single domain (SD) behaviour that changes to multi domain (MD) type on Ti4+ substitution. On Ge4+ substitution initially all the compositions exhibit SD behaviour while forx>0.2 they show MD behaviour. All Sn4+ substituted compositions exhibit SD behaviour. The Curie temperature decreases on addition of Ti4+, Sn4+ and Ge4+. The magnetic momentn
B (77 K) initially increases and then decreases with the substitution of Ti4+, Ge4+, and Sn4+. This is explained by cation distribution and reduction of Fe3+ ions.The authors wish to thank Prof. R. N. Patil for encouragment and useful discussion. One of the authors (B.L.P.) is grateful to UGC (New Delhi) for granting Teacher Fellowship for Ph.D. course. 相似文献
12.
Yongfu Liu Xia Zhang Zhendong Hao Yongshi Luo XiaoJun Wang Jiahua Zhang 《Journal of luminescence》2012,132(5):1257-1260
The yellow-emitting phosphor [Ca3?(x+0.06)LuxCe0.06](Sc2?yMgy)Si3O12 obtained from Lu3+ and Mg2+ co-modified green-emitting silicate garnet Ca3Sc2Si3O12:Ce3+ (CSS:Ce3+) exhibits promising applications for white LEDs. In this paper, we discuss the effect of charge balance on the garnet structure formation. The changes of bond length and covalence caused by the replacement of Lu3+ and Mg2+ for Ca2+ and Sc3+ are analyzed. The shift of the Ce3+ emission and excitation can be attributed to the combined results from crystal field splitting effect and centroid shift of Ce3+ 5d levels. Thermal stability is analyzed according to configurational coordinate diagram. 相似文献
13.
A. Agnesi S. Dell’Acqua A. Guandalini G. Reali A. Toncelli M. Tonelli E. Cavalli 《Applied physics. B, Lasers and optics》2000,71(2):153-156
CW diode-pumped laser operation of Nd3+ in Ca3Sc2Ge3O12 (CaSGG) single garnet crystal has been demonstrated for the first time. We measured an 18% slope efficiency and 2.7-nm tunability
with two different laser cavities. A spectroscopic characterization of our sample has also been performed including the absorption
cross section in the 800-nm region and the emission cross section and radiative lifetime of the upper laser level.
Received: 7 December 1999 / Revised version: 6 February 2000 / Published online: 27 April 2000 相似文献
14.
The spectral distributions of the visible absorption and fluorescence emission under electron beam excitation of Eu3+-doped (Y2O3) and (YVO4) powders have been detected and analyzed. (Y2O3: Eu3+) has a cubicC crystal structure with a unit cell dimension a=10·61 Å. Its observed transitions from7
F
0 to many upper states have been recognized; the observed number of Stark components is in agreement with that based on theC
2 site symmetry of the Eu3+ ion in Y2O3. Eu3+-doped yttrium vanadate has a typical zircon tetragonal crystal structure with unit cell dimensions ofc=6·29 Å anda=7·11 Å. The observed transitions in (Eu3+: YVO4) have been identified and assigned in accordance with theD
2d site symmetry of the Eu3+ ion in this lattice.The authors would like to express their deep gratitude to Professor G. F. J.Garlick, University of Hull, England, for offering experimental facilities in his Physics Department. 相似文献
15.
Magnetic phase transitions in disordered crystalline iron germanates of the type Sr2LnFe3Ge3O14 (Ln=La; Nd) were observed at low temperatures by means of57Fe Mössbauer spectroscopy. The hyperfine interaction of Fe3+ magnetic moments ordered in one octahedral and two tetrahedral magnetic sublattices is discussed. A local environment computation on the octahedral sites confirms the assumption that the wide distribution found for the 4.2 K octahedral hyperfine fields is due to the random occupation by Fe3+ and Ge4+ ions of the nearest cation environment of the octahedral iron. The effect of substituting Ln rare earth ions in the Thompson cubes on the magnetic behaviour of these compounds is pointed out. 相似文献
16.
X-ray, electrical conductivity, magnetic hysteresis and IR studies for the system Co2−x
Ge1−x
Fe2x
O4 were carried out. All the compounds, 0⩽x⩽1, showed cubic symmetry. X-ray intensity calculations, magnetic hysteresis measurements and IR studies indicated the presence
of Ge4+ at tetrahedral, Co2+ at octahedral and Fe3+ at both the sites. The activation energy and threshold frequency decreased with increasing value ofx. The compounds withx⩽0.5 arep-type and those withx⩾0.75 aren-type semiconductors. Magnetic hysteresis indicated that all the compounds are ferrimagnetic except forx=0 which is antiferromagnetic. The shapes of χ/χ
i
vsT plots, highH
c values andJ
R/Js ratios showed that all the compounds exceptx=0 exhibit single-domain behaviour. Curie temperature,T
c increased with increasing Fe3+ ions. The probable ionic configuration for the system is suggested as Ge
1−x
4+
Fe
x
3+
[co
2−x
2+
Fe
x
3+
]O
4
2−
. 相似文献
17.
Crystals of two types, namely, Gd3Sc2Al3O12 doped by Ca2+ and Cr3+ ions and Gd3Sc2Ga3O12 doped by Nd3+ and Cr3+, are studied using x-ray diffraction. In order to elucidate how an impurity is embedded in the lattice, its effect on the electron density distribution and microstrains of the crystal lattice is investigated. It is shown that chromium ions can occupy the lattice sites located predominantly in the octahedral environment of the oxygen ligands. 相似文献
18.
B. V. Padlyak 《辐射效应与固体损伤》2013,168(1-6):411-418
The X-band (v ? 9.4 GHz) ESR spectra of the UV-, X-, and γ-irradiated glasses of CaO-Ga2O3-GeO2 system with compositions similar to Ca3Ga2Ge3O12, Ca3Ga2Ge4O14, and Ca3Ga2O6 crystals have been investigated at 300 and 77 K. It was shown that X- and γ-irradiation of the Ge-contained glasses induce simultaneously electron and hole paramagnetic centers, stable at room temperature. The UV-irradiation of Ge-contained glasses leads to the generation of stable centers of electron type, whereas the X- and γ-irradiation of glasses with Ca3Ga2O6 composition induces stable hole centers, exclusively. The electron centers are assigned to E′ (Ge) centers with different local environments. ESR spectrum of hole centers is ascribed to O? centers, localized on non-bridging oxygen of the glass network. The E′ (Ge) and O? centers show high thermal stability in the CaO-Ga2O3-GeO2 glass network. The obtained ESR spectra are described by spin Hamiltonian with g-factor of axial and rhombic symmetry for the E′ (Ge) and O? centers, respectively. The nature, electron structure and some formation peculiarities of the radiation defects in CaO-Ga2O3-GeO2 glasses are discussed in comparison with other glasses as well as Ca3Ga2Ge3O12 and Ca3Ga2Ge4O14 crystals. 相似文献
19.
Ca3Sc2Si3O12 doped with 1 mol% Eu3+ and having a cubic garnet structure was prepared by a solid state reaction. The low temperature luminescence spectrum shows no measurable 5D0→7F0 band, in agreement with the location of the lanthanide dopant in a site of D2 symmetry, i.e. with a Ca2+ substitution. On the other hand, the spectrum is clearly dominated by the 5D0→7F4 band, which is significantly stronger than that for the other transitions originating from the 5D0 level. This unusual behavior is explained on the basis of a model describing the distortion of the EuO8 coordination polyhedron from a cubic geometry to the actual D2 one. 相似文献
20.
The X-band EPR spectra of Cr3+, Mn2+, and Fe3+ impurity ions in glasses of (CaO?Ga2O3?GeO2) system are investigated in the 77÷300 K temperature range. The experimental data analysis yields the following results: (i) Impurity chromium ions are incorporated into the (CaO?Ga2O3?GeO2) glasses network in Cr3+ (3d3,4F3/2) paramagnetic valence state only and occupy the strong distorted oxygen coordinated octahedral sites. (ii) For all activated and non-activated (CaO?Ga2O3?GeO2) glasses the iron impurity is present at concentration roughly 0.01 wt.%. Isotropic EPR signals atg eff=4.29 andg eff=2.00 are assigned to Fe3+ (3d5,6S5/2) ions in the sites with strong rhombic distortion and in the sites with nearly cubic symmetry respectively. (iii) The manganese EPR spectrum in (CaO?Ga2O3?GeO2) glasses is weakly dependent on temperature, doping procedure as well as manganese concentration. EPR spectra of impurity manganese ions in glasses with Ca3Ga2Ge3O12 and Ca3Ga2Ge4O14 compositions are virtually identical and belong to Mn2+ (3d5,6S5/2) ions. Impurity manganese ions are incorporated into the (CaO?Ga2O3?GeO2) glass network as isolated Mn2+ centres and clusters of Mn2+ ions. 相似文献