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1.
The luminescence associated with the Eu3+ ion in LiEuCl4 has been studied at cryogenic temperatures under conditions of high resolution. Emission was observed to originate from both the 5D0 and 5D1 excited states, and transitions to the , and 7F4 ground levels were observed. The fine structure observed within these emission bands was found to be consistent with the existence of an effective D4 site symmetry for the emitting Eu3+ species, even though the europium polyhedron was found to be that of a bisdisphenoid. 相似文献
2.
Intensity parameters of Sm3+ in borate glasses were obtained by fitting the oscillator strengths to the Judd-Ofelt formula and a study of energy transfer from gadolinium to samarium was performed. An increase of samarium fluorescence originating from the level was observed in the presence of gadolinium, in the concentration range of 0.1–3 wt% samarium with gadolinium constant at 3 wt%. The intensity of samarium fluorescence on excitation at 273 nm increased by one order of magnitude in the presence of gadolinium. From the excitation spectrum of the double-doped glasses (Gd + Sm), it was deduced that energy absorbed by gadolinium is transferred from gadolinium levels to the and samarium levels.The mechanism of this energy transfer was obtained by plotting the energy transfer probabilities as a function of samarium concentration. A linear dependence of (η intensity of gadolinium in the presence of samarium) versus square of concentration of Sm + Gd is obtained. From this it is concluded that the transfer is of electric-multipolar type, mainly dipole-dipole. A small increase (about 10%) of fluorescence of samarium in the presence of gadolinium excited at levels where no energy transfer can take place is attributed to the fact that the quenching of samarium occurring by the cross relaxation is suppressed by the presence of gadolinium as seen from concentration dependence of samarium doped glasses compared to double-doped glasses. 相似文献
3.
The luminescence associated with the Eu3+ ion in K2EuCl5 has been studied at cryogenic temperatures under conditions of high resolution. Emission was observed to originate from both the 5D0 and 5D1 excited states, and transitions to the , and 7F4 ground levels were observed. The fine structure observed within these emission bands was found to be consistent with the existence of an effective C4 site symmetry for the emitting Eu(III) species, even though the crystal structure does not indicate the presence of a true or pseudo C4 axis. 相似文献
4.
Growth of terbium aluminate single crystals and investigation of Nd3+ ion spectroscopic properties in them are described. Detailed investigation of absorption and luminescence spectra of Nd3+ ions in TbAlO3 at T = 77 and 300°K permits obtainment of a complete diagram of the Stark components energy. The spectral-structural regularities of Nd3+ ions in orthoaluminate monocrystals are analyzed. The dependence on interionic distance of the position of the center of gravity of the ground terms of Nd3+ ion along with the nephelauxetic shift of term of Nd3+ ion is investigated. 相似文献
5.
Use of Nd3+, Eu3+, and Gd3+ as local structural probes allows the determination of the rare earth positions in the NaxSr3?2xLnx(PO4)2 (Ln = La to Tb) and KCaLn(PO4)2 phases (Ln = rare earth). Moreover, a common feature of both series is a particularly high splitting of the excitation and levels of the Gd3+ ions. 相似文献
6.
D.A. Lemenovskii V.P. Fedin A.V. Aleksandrov Yu.L. Slovohotov Yu.T. Struchkov 《Journal of organometallic chemistry》1980,201(1):257-268
Electron-acceptor properties of bis-niobocenes (η5-C5H4Y)(H)b(H)(η5-C5H4Y) with X Y H and XY SiMe2OSiMe2have been investigated. Bis-niobocenes are shown to readily add two electrons forming stable salts of the corresponding dianions [(η5-C5H4Y)(H)Nb(η5 : η1- C5H3X)2Nb(H)(η5-C5H4Y)]2-. The surplus electrons can be removed to give quantitative regeneration of initial neutral bis-niobocenes. The crystal and molecular structure of the title compound has been determined; R 0.044, interatomic distance are Nb…Nb 3.93, NbH 1.62, average NbC(π) 2.36, NbC(σ) 2.31 Å, other distances correspond to the usually observed values. Unlike the neutral bis-niobocenes, there is no direct metalmetal bond in the dianionic structures. This conclusion is supported by electronic spectra of neutral and dianionic species. 相似文献
7.
W. Laqua 《Journal of solid state chemistry》1975,14(2):133-143
The self-diffusion coefficients of 63Ni2+ and 67Ga3+ have been measured in nickel-gallium spinels of the general formula between 1653 and 1838 K using the restactivity method. Thin radioactive oxide layers are produced on inactive sample surfaces by sedimentation from aqueous solution. The sample composition corresponds to the solubility limit of NiO, respectively, β-Ga2O3 in the spinel lattice.It has been concluded that diffusion of Ni2+-and Ga3+-ions occurs via vacant cation sites.The values obtained for the two cations, which are in the same order of magnitude, are used to calculate the rational reaction constants for NiGa2O4 formation after Schmalzried.There is a satisfying agreement between these reaction constants and those values determined by thickness measurement of spinel reaction layers; the agreement between values of activation energy is very good.It is suggested that NiGa2O4 formation proceeds after the Wagner mechanism of counterdiffusion of cations. 相似文献
8.
The magnetic interaction in the structural units [Fe2O7]8?, built of two corner-sharing FeO4 tetrahedra, in Na8Fe2O7 () has been studied by magnetic susceptibility measurements (4.2–500 K). An exchange integral of ?37 K is obtained by comparison of the experimental values and the calculated ones using a Heisenberg-Dirac-Van Vleck-type Hamiltonian ? = . The hypothesis of magnetically isolated [Fe2O7]8? groups is corroborated by Mössbauer spectroscopy between 1.5 and 77 K. The susceptibility measurements of the solid solutions Na8Fe2?xMxO7 (M = Al, Ga; 0 ≤ x ≤ 0.2 for Al; 0 ≤ x ≤ 2 for Ga) leads to the same conclusion of the existence of isolated Fe3+Fe3+ pairs in Na8Fe2O7. The type of substitution of Fe by Al or Ga is determined; homonuclear Fe3+Fe3+ and M3+M3+ pairs and heteronuclear Fe3+M3+ pairs are formed. 相似文献
9.
E.M. Akulonok V.Ya. Khaimov-Malkov Yu.K. Danileiko A.A. Manenkov V.S. Nechitailo T.P. Lebedeva 《Journal of solid state chemistry》1978,26(1):17-25
A problem of trap diffusion, that is diffusion of point defects in crystals participating in a solid-phase chemical reaction with motionless impurity ions, is solved. Time dependences of the reaction-front displacement, Xf, and its steepness, are determined analytically for N0 ? C0 and numerically for all relations of N0 and C0where C0 and N0 are the initial concentration of impurity and the eqilibrium defect concentration, respectively, D is a diffusion coefficient, and g is a chemical reaction constant. Dependence of Xf vs C0 and t is confirmed for oxygen annealing of corundum crystals doped with titanium which, reacting with the point defects, changes its valency. The data are obtained for dependence of displacement Xf upon partial oxygen pressure and thermotreatment temperature as well as upon the sign of the constant electric field applied to the sample. From these data we conclude that the reaction of titanium impurity, changing from the three-valent to the tetravalent state at the activation energy of 80 ± 8.5 kcal/mole is due to anisotropic diffusion of charged aluminum vacancy and holes in the valence band. The diffusion coefficient for that process at 1500°C is estimated to be larger than 10?5 cm2/sec. Using the trap-diffusion features, the concentration of optical centers of the 0.315-μm absorption band in ruby is also estimated. 相似文献
10.
Takamasa Ishigaki Shigeru Yamauchi Junichiro Mizusaki Kazuo Fueki Hifumi Tamura 《Journal of solid state chemistry》1984,54(1):100-107
The tracer diffusion coefficient, , of oxide ions in LaCoO3 single crystal was determined over the temperature range of 700–1000°C by a gas-solid isotopic exchange technique using 18O tracer. For the determination, two methods, the gas phase analysis and the depth profile measurement, were employed. Under an oxygen pressure of 34 Torr, the temperature dependence of in LaCoO3 was expressed by at 950°C was found to be proportional to P?0.35O2. The diffusion of oxide ions occurs through a vacancy mechanism. The activation energy for the migration of oxide ion vacancies was estimated as 18 kcal · mole?1. 相似文献
11.
Electron spin resonance spectra attributed to four Fe3+ centers designated Oa, Ob, Ta, Tb have been observed in crystals of muscovite and phlogopite. The results are discussed using the spin Hamiltonian with ge ~ 2.002. The angular variation of the resonance lines is used to determine the ESR axes of the four different sites. Two species are octahedrally coordinated (Oa and Ob) and are assigned to two different surroundings of Fe3+ in the octahedral sheet. The remaining two species (Ta and Tb) may be assigned to the tetrahedral FeO4. The Ta sites have a symmetry axis lying along one of the FeO bonds. The symmetry axis is created by an excess of negative charge on the oxygen bound to the neighboring tetrahedral substitution. Rhombic symmetry of the Tb sites is due to the presence of fluorine anions substituting some hydroxyl ions. One of the ESR axes is directed toward the fluorine ion. 相似文献
12.
The 1 1A″, 2 1A″, 3 1A′, 4 1A′, and 5 1A′ potential energy surfaces (PES) relevant to the collision-induced dissociation (CID) process are approximated by three diatomics-in-molecules models differing from each other in the source of diatomic input. The semi-empirical model, the most realistic of the three, shows the CID to depend critically on the position of avoided crossings on the PES and on the magnitude of the non-adiabatic coupling, which is estimated numerically. The 1A″ calculations support a qualitative two-step mechanism recently proposed by Poppe and Whitton. The 1A′ surfaces exhibit a degree of complexity which precludes a simple picture of the CID process. The results suggest that only a quantum scattering treatment or perhaps a very detailed surface-hopping trajectory calculation will be adequate for the interpretation of the experimental observations on this reaction, and the estimation of the cross sections. 相似文献
13.
Results on the rate of polymerization of acrylic acid by S2O2?8 ion in alkaline and acid conditions are presented. Rp depended upon and both in acid and alkaline solutions. The influence of ionic strength, the effect of pH on Rp and the catalytic effect of Ag+ and Cu2+ on the system have been discussed. Suitable mechanisms are proposed. 相似文献
14.
15.
Junichiro Mizusaki Masafumi Yoshihiro Shigeru Yamauchi Kazuo Fueki 《Journal of solid state chemistry》1985,58(2):257-266
In order to elucidate the defect structure of the perovskite-type oxide solid solution La1?xSrxFeO3?δ (x = 0.0, 0.1, 0.25, 0.4, and 0.6), the nonstoichiometry, δ, was measured as a function of oxygen partial pressure, PO2, at temperatures up to 1200°C by means of the thermogravimetric method. Below 200°C and in an atmosphere of PO2 ≥ 0.13 atm, δ in La1?xSrxFeO3?δ was found to be close to 0. With decreasing log PO2, δ increased and asymptotically reached . The value corresponding to was about ?10 at 1000°C. With further decrease in log PO2, δ slightly increased. For LaFeO3?δ, the observed δ values were as small as <0.015. It was found that the relation between δ and log PO2 is interpreted on the basis of the defect equilibrium among Sr′La (or V?La for the case of LaFeO3?δ), V··O, Fe′Fe, and Fe·Fe. Calculations were made for the equilibrium constants Kox of the reaction and Ki for the reaction Using these constants, the defect concentrations were calculated as functions of PO2, temperature, and composition x. The present results are discussed with respect to previously reported results of conductivity measurements. 相似文献
16.
R. Ibañez A. Garcia C. Fouassier P. Hagenmuller 《Journal of solid state chemistry》1984,53(3):406-414
As a consequence of the weak phonon energies and the low crystal field, several excited states of Nd3+ are emitters in the NaxNdxM1?2xGa2G4 thiogallates (x ≤ 0.5 for M = Ca or Sr and ≤0.2 for M = Ba). The infrared emission is little affected by concentration quenching. NaNdGa4S8 is the first efficient stoichiometric sulfide so far reported. Unlike other sulfides previously investigated, the neodymium thiogallates show an intense excitation band, ascribed to electron transfer from the valence band to states constituted essentially by neodymium orbitals. 相似文献
17.
We present in this paper two new effects observed in the state of molecular iodine: a very high diamagnetic correction in the vibrational level υ′ = 62 and an important orientation of the optically excited molecules due to predissociation. Both effects can be interpreted by taking into consideration the perturbation of the B state by other electronic states. 相似文献
18.
The standard enthalpy of formation of γ-UO3 has been critically assessed; the value ?(292.5 ± 0.2) kcalth mol?1 is suggested.The enthalpies of solution of β-UO3 and γ-UO3 in 3 M H2SO4 have been measured and used to derive: 相似文献
19.
R. Reisfeld E. Greenberg C. Jacoboni R. De Pape C.K. Jørgensen 《Journal of solid state chemistry》1984,53(2):236-245
The fluorescence spectra and lifetimes of fluoride glasses of molar composition 36PbF2, 24MnF2 (or ZnF2), 35GaF3, 5 (or 7) Al(PO3)3, doped by ErF3 were investigated. The emission of Mn(II) in absence of Er(III) consists of a broad band centered around 630 nm and an integrated lifetime of 1.4 msec. In the presence of Er(III) the intensity and lifetimes are decreased as a result of energy transfer to the level of Er(III). The fluorescence of Er(III) arising from at 543 nm has an integrated lifetime of 0.06 ms in the absence of Mn(II) and is decreased to 0.01 ms in the presence of Mn(II) as a result of energy transfer to Mn(II). The 666-nm luminescence of Er(III) due to emission under excitation at 370 nm () is about 20 times weaker than the 543-nm emission when Mn(II) is absent. However, in the presence of Mn(II) this emission becomes 5 times stronger than the 543-nm emission. This intensified emission has a non-exponential time dependence. The longer component corresponds to the transfer of stored energy in Mn(II) to Er(III) while the short-lived component is probably due to cascading down Er(III) → Mn(II) → Er(III) through states above the Stokes threshold of Mn(II). This interpretation is backed up by weaker 543-nm emission and stronger 630-nm broad-band emission when the mixed system is excited in one of the upper excited states, of Mn(II) at 395 nm, or of Er(III). 相似文献
20.
B. Bochu M.N. Deschizeaux J.C. Joubert A. Collomb J. Chenavas M. Marezio 《Journal of solid state chemistry》1979,29(2):291-298
A series of titanates which have perovskite-like arrangements and are isostructural with [CaCu3](Mn4)O12 have been synthesized. The total charge of the A sites can be modified (1) by substituting the Ca2+ cations with monovalent ones and the tetravalent manganese cations of the B sites by a mixture of (Ti4+ + M5+) in which M = Ta, Nb, Sb, or (2) by substituting the Ca2+ cations by a combination of cations plus vacancies. In this case, if the total charge of the A sites is 2, one obtains compounds such as and ; on the contrary, if the charge is less than 2, then one has to compensate it by changing that of the B sites. This leads to compounds such as [□Cu3](Ti2M2)O12 (M = Ta, Nb, Sb). 相似文献