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1.
The emission of Ni2+ ions in MgO, KMgF3, KZnF3 and MgF2 crystals has been investigated. The fine structure on the bands at about 20 000 cm-1 and 13 000 cm-1 has been studied in detail and from this and the excitation spectra these bands are assigned to and transitions respectively. 相似文献
2.
The fluorescence and absorption spectra of Eu3+ in K5Eu(MoO4)4 have been measured at 300 K and 77 K. The fluorescence lifetime of the 5D0 state is 1.4 ms at 300 K. The largest cross section and the removal of degeneracies require to replace the nearest neighbour D3d symmetry of Eu3+ by the effective symmetries C1, C2 and Cs of the whole unit cell. It is shown that C1 dominates because of the statistical distribution of K+ and Eu3+. The corresponding inhomogeneous broadening is observed at 77 K. 相似文献
3.
Marek Danielewski Jaeosław Da̧bek Stanisł;aw Mrowec Grażyna Siemińska 《Solid State Ionics》1985,17(4):331-335
Using the re-equilibration kinetic method the chemical diffusion coefficient in nonstoichiometric chromium sesquisulfide, Cr2+yS3, has been determined as a function of temperature (1073–1373 K) and sulphur vapour pressure (10?104 Pa). It has been found that this coefficient is independent of sulphur pressure and can be described by the following empirical equation: . It has been shown that the mobility of the point defects inCr2+yS3 is independent of their concentration and that the self-diffusion coefficient of chromium in this sulfide has the following function of temperature and sulphur pressure: . (cm2s?1). 相似文献
4.
The emission spectra of Nd3+ ions in KNdxRE1?xP4O12 (RE = Y, La and Pr) and KNdxCr1?xP4O12 crystals were investigated. Under selective excitation into 2G + 4G multiples at 1.6 K the fluorescence of Nd3+ ions in non-equivalent crystal sites was observed. The excitation spectrum of the fluorescence had a complex satellite structure. Time resolved measurements showed the dependence of the fluorescence decay on the excitation wavelength. Selective excitation into the satellite lines at the wings of the main transition led to strongly non-exponential decay. The low temperature results indicated that there is no spectral energy transfer between ions in different types of sites. 相似文献
5.
By means of neutron diffraction measurements the structure parameters of polycrystalline Bi4Y3O12(Y = Ge, Si) crystallizing according to space group were determined at room temperature. With respect to the trigonal coordination of oxygen ions around Bi3+ the results are compared to EPR investigations on equivalent single-crystal specimens containing Gd3+ impurities on Bi sites. Corresponding approximations in the interpretation of the measurements are discussed. Although both methods yield similar systematic differences between the Ge- and Si-compounds, the influence of Gd on the structures appears to be substantial. Moreover point charge models should be improved with respect to details of the electron density distribution. 相似文献
6.
We report, for the first time, cw room temperature laser action of Cr3+:Gd3Sc2Al3O12. These crystals show a strong band fluorescence due to the transition with a lifetime of 150 μs. Laser pumping in the blue and red spectral range yields a minimum threshold of 170 mW and slope efficiencies up to 18.5%. The emission of the free running laser is centered at 784 nm with a FWHW of 5 nm. The extension of the Ga-garnets to Al-garnets as suitable host lattices for Cr3+ reveals the variety of garnet-structured crystals having an appropriate ligand field for continuously tunable laser operation. 相似文献
7.
Optical absorption spectra of Ni2+ in (NH4)2Mg(SO4)2·6H2O and Co2+ in Na2Zn(SO4)2·4H2O single crystals have been studied at room and liquid nitrogen temperatures. From the nature and position of the observed bands, a successful interpretation could be made assuming octahedral symmetry for both the ions in the crystals. The splitting observed for band in Ni2+ and band in Co2+ at liquid nitrogen temperature have been explained as due to spin-orbit interaction. The extra band observed at 16,325 cm-1 in the case of Ni2+ at low temperature has been interpreted to be the superposition of vibrational mode of SO2-4 radical on band. The observed band positions in both the crystals have been fitted with four parameters B, C, Dq and ζ. 相似文献
8.
Spectral luminescence characteristics of the Cs2Na(Er, Yb, Y)Cl6 type upconverter have been measured in the range 300–650 K. A nearly sixfold decrease of the emission intensity of an upconverter was observed in the green area. This emission corresponds to two luminescence transition of Er3+ ions: and . A mechanism of the luminescence intensity decrease has been proposed, in which deexcitation of the level to the level is caused by a neighbouring Er3+ ion being excited to the level. 相似文献
9.
V Malathy Devi B Fridovich G.D Jones D.G.S Snyder 《Journal of Molecular Spectroscopy》1983,97(2):333-342
Line strengths and self- and nitrogen-broadened half-widths were measured for spectral lines in the ν3 and ν2 + ν4 bands of 12CH4 and 13CH4 from 2870–2883 cm?1 using a tunable diode laser spectrometer. From measurements made over a temperature range from 215 to 297 K, on samples of 12CH4 broadened with N2, we deduced that the average temperature coefficients n, defined as , of the Lorentz broadening coefficients for the ν3 and ν2 + ν4 bands of 12CH4 were 0.97 ± 0.03 and 0.89 ± 0.04, respectively. A smaller increase is observed in line half-width with increasing pressure for E-species lines, for both self- and nitrogen-broadening, than for other symmetry species lines over the range of pressures measured, 70 to 100 Torr. 相似文献
10.
At temperatures below 59 K, coexistence of two types of satellite was observed in reciprocal lattice plane of b1?c1 as expressed by and . On the basis of nesting conditions by these q1 and q2, a feature of the Fermi surface for NbSe3 is discussed. 相似文献
11.
M. Drillon J. Darriet P. Hagenmuller R. Georges 《Journal of Physics and Chemistry of Solids》1980,41(5):507-515
A trinuclear cluster (Ru3O12)13? occurs in the Ba4NbRu3O12, and Ba4TaRu3O12 compounds where the oxydation states of ruthénium are +III and +IV. The exchange interaction between magnetic sites is described by a Hamiltonian, which takes account of the orbital degeneracy of the terms. For these ions, the spin-orbit coupling is the dominant effect and it appears that the low temperature magnetic susceptibility depends essentially on the orbital reduction factor and the distortion of the coordination octahedra. There is apparently no first order perturbation of the ground state due to the interaction between magnetic ions. 相似文献
12.
The cross-relaxation of YAG:Tb3+ has investigated by analysis of the 5D3 decay curve as a function of Tb3+ concentration. This technique is a more sensitive test of the mechanism than relative intensity measurements alone. It is shown that the relaxation is predominantly dipole-dipole in character (R0 ~ 1.3nm), and insensitive to temperature. The population of the 5D4 state following high energy excitation occurs almost entirely via cross-relaxation from the 5D3 state. 相似文献
13.
Comparison between experimental absorption due to the transition of substitutional Ni2+(d8) in GaP and theoretical predictions based on the Jahn-Teller model is presented. Numerical solution of the Hamiltonian, in which spin-orbit interaction and T2-mode Jahn-Teller coupling are included, is in very good agreement with the energy position and intensities of the observed absorption lines. 相似文献
14.
John W. Birks Steven D. Gabelnick Harold S. Johnston 《Journal of Molecular Spectroscopy》1975,57(1):23-46
Emission from both the state and the previously unreported state of IF has been observed in the gas phase reaction of I2 with F2 at low pressures. For the state the transition moment and vibrational populations were extracted from the spectra by a least-squares method whereby theoretical band shapes were fit to the experimental data. The effect of flow rates of reactants and Ar on the relative emission from the two electronic states, the effect of pressure on the state, and extinction of emission near 470 nm all favor the population of excited electronic states through a four-center reaction complex, rather than association of F and I atoms.It is argued that there is an avoided curve crossing between the lowest two 3Π0+ states of IF, and that the ground state dissociation energy is 23 229 ± 100 cm?1. The radiative lifetime of the state is estimated to be 10?3 sec and to be much shorter than that of the state. 相似文献
15.
M. Villedieu N. Devismes A.M. de Goër 《Journal of Physics and Chemistry of Solids》1977,38(9):1063-1070
The effect of γ irradiation at 300 K on the concentrations of vanadium ions V3+, V4+ and V2+ in Al2O3 has been studied quantitatively, using three techniques: optical absorption (V3+), low temperature thermal conductivity measurements (V4+) and EPR (V2+). Several single crystals of Al2O3 doped with vanadium in a large range of concentration have been measured. The evolution of the respective concentrations by γ irradiation as a function of the total vanadium content C is quite different in the two regions and C larger than this value. A consistent analysis of the results has nevertheless been achieved, leading to the determination of the absolute concentrations of the three ions in the as-received and γ irradiated states for all samples with (room temperature annealing is observed above this value). The concentrations of V4+ and V2+ ions are always small, but V4+ ions are more stable: they are present in the as-received state at a level of 1% of the total concentration and a maximum value of is observed in the γ irradiated state; on the other hand there are less than 4.7 × 1015V2+ ions per cm3 in the as-received state and the maximum value is only . Charge transfer between V ions only is not sufficient to explain the experimental results and other defects must be involved in the γ irradiation effect. 相似文献
16.
A frequency tunable infrared source has been constructed by using the (Ar-laser) - (dyelaser) difference frequency method developed by Pine and applied to the observation of the overtone bands of PH3 3ν2 ← 0 and 4ν2 ← ν2 in the 3.4 μm region and 4ν2 ← 0 in the 1.6-μm region. A Stark modulation method was used to increase the sensitivity of detection. For transitions which were well modulated, the minimum detectable absorption coefficient was estimated to be ~3 × 10?7 cm?1 using a 3-m cell. Emphasis was placed on the observation of the A1-A2 splitting for K = 3n rotational levels. For the 3ν2 state splittings were observed for K = 3, 6, and 9 because PH3 is a very nearly spherical top in this state. The magnitude and the J dependence of the observed K = 3n splittings have been analyzed by using a normal symmetric rotor Hamiltonian and a centrifugal distortion term of the form . 相似文献
17.
Mössbauer spectra were obtained of the paramagnetic spinels and susceptibilities were measured. The strong difference between the paramagnetic Fe2+ and Fe3+ spectrum, due to the different quadrupole splitting, is used for the distinction between the two species. At 300 K a superposition of the Fe3+ and the Fe2+ spectra is found for most of the iron and, in addition, some continuous absorption. The latter is strongest for equal Fe3+ and Fe2+ concentration while it disappears towards the end members (Fe3+ only or Fe2+ only) as well as with decreasing temperature (between 78 and 200 K). From this it is concluded that it arises from thermally activated electron exchange, the frequency of which passes a “critical” value of ~108 sec?1 for increasing temperature. Paramagnetic susceptibilities are found to obey a Curie-Weiss law down to low temperatures. From the dependence of the asymptotic Curie temperature on the composition the magnetic interaction parameters J11 = ?1.4 K, J22 = ?3.3 K and J12 = + 1.6 K for the Fe3+Fe3+, Fe2+Fe2+ and Fe3+Fe2+ interactions are derived. The experimental results are discussed in terms of a hopping model with an activation energy q ~- 0.12eV and a non-equivalence of the octahedral sites expressed by a varying potential energy difference U0 between neighbouring sites. The continuous absorption at 300 K for is attributed to about 17% of the iron on sites with U0 running from 0 to ??0.06 eV. The ferromagnetic Fe3+, Fe2+ interaction (J12) is attributed to electron transfer from localized Fe2+ ions to Fe3+ neighbours via a transfer integral b of the order of 0.05 eV. The magnitudes of J12 and b are tentatively explained. 相似文献
18.
Transition temperature to LRO state was found at TN=1.14K for nearly one-dimensional antiferromagnet CuCl2 · 2NC5H5. Intra- and inter-chain exchange constants J and J′ were estimated, and , respectively. Comparison with those of TMMC implies highly one-dimensional character. 相似文献
19.
The complex polar Kerr effect (rotation and ellipticity) of magnetite single crystals has been measured at room temperature between 0.5 and 4.3 eV. From the magneto-optical data and the optical constants, the off-diagonal elements (?xy) of the dielectric tensor has been derived. Three well separated magneto-optical transitions have been indentified. At about 0.75 eV one strong magneto-optical structure with a diamagnetic line shape is assigned to a transition from Fe2+ in octahedral sites. Two other structures with paramagnetic line shapes near 1.85 and 2.90 eV are assigned to the orbital promotion processes and , respectively, which take into account Fe 3dn?1 final state effects. 相似文献
20.
We report low temperatures ESR and Superconductivity experiments on Nd3+ and Gd3+ in the superconducting cubic intermetallic compound ZrIr2. The ratio of the squares of the effective 4f-conduction electron exchange parameters corresponding to Nd3+ and Gd3+ () were extracted both from the thermal broadening of the ESR linewidths and from the initial depression of the superconducting critical temperature, and were found to be comparable. Nd3+ was found to have a larger exchange parameter than of Gd3+. 相似文献