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AN INVESTIGATION FOR THE Cd2+-VACANCIES IN RbCdF3 and CsCdF3 CRYSTALS DOPED WITH Fe3+ IMPURITIES 下载免费PDF全文
余万伦 《物理学报(海外版)》1993,2(8):610-618
This paper presents high-order perturbation calculations for the zero-field splitting parameters D, F, and a of Fe3+-VCd pairs in RbCdF3 and CsCdF3 crystals doped with Fe3+ impurities. In comparison with experimental data, the present results are better than those obtained in previous work by using the phenomenological su-perposition model of spin-Hamiltonian. Moreover, the crystal fields arising from the Cd2+-vacancy and their induced crystal lattice distortion are analysed and calculated. It is found that the contribution from the Cd2+-vacancies cannot be ignored. Mena-while, we obtain that a ligand F- along the [001]-axis moves towards the central Fe3+ ion by Δ= 0.0020nm in RbCdF3 and 0.0028nm in CsCdF3. These results are quite different from Δ = 0.0104nm and Δ = 0.0112nm, respectively, obtained in previous work by using the superposition model of spin-Hamiltonian and ignoring the effect of the vacancy. 相似文献
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Three new Fe-defect complexes have been identified by ESR in Fe doped crystals of SrTiO3. These are an Fe3+ center with rhombic fine structure in the “as-grown” crystals, and the vacancy associated complexes Fe2+ -Vo and Fe1+ -Vo in “reduced” crystals. Photo-excited charge transfer effects are observed for these centers. 相似文献
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Seven absorption group-bands (1D2, 1G4, 3F2, 3F3, 3H4, 3H5, 3F4) of Tm3+ in YVO4 single crystals have been observed in the orientation absorption spectra recorded in the spectral range from 200 to 4000 nm at 300K. The integrated absorption cross section for each group-band was accurately evaluated. On the assumption that the anisotropy of this uni-axial crystal is small, the Judd-Ofelt theory was extended for the calculation of 4f-4f transition intensities of Tm3+ in YVO4. Two sets of phenomenological intensity parameters were derived from a least-squares-fit procedure. For c-axis cut sample we have Ω2=10.18 (10-20cm2), Ω4=1.96 (10-20cm2), Ω6=0.75 (10-20cm2).For a-axis cut sample we have Ω2=8.20 (10-20cm2), Ω4=2.47 (10-20cm2), Ω6=0.91 (10-20cm2). The anisotropy of the optical absorption intensities of Tm3+:YVO4 was theoretically analyzed in detail. 相似文献
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SPECTROSCOPIC INVESTIGATION ON THE PROPERTIES OF VISIBLE AND NEAR INFRARED EMISSIONS IN Tm3+, Ho3+ Co-DOPED YVO4 CRYSTALS 下载免费PDF全文
With the help of absorption and fluorescence spectra, the spectroscopic properties of Tm3+, Ho3+:YVO4 crystals have been investigated under different dopant concentrations. The absorption results show that the maximum absorption in the spectral range of currently available powerful laser diodes (LD) is at 796 nm, corresponding to the transition 3H6→3H4 of Tm3+ in the crystals. Upon the excitation with a LD at 808 nm, we have detected ten fluorescence bands in the spectral range spanning from visible to infrared. In visible region 4 upconversion bands have been observed centered at 475, 547, 660, and 701 nm. Discussions of the energy transfer processes suggest that cross relaxations and excited absorptions with the involvement of Tm3+ 3F4, 3H5 and Ho3+ 7I5 states are responsible for the four upconversion emissions. Comprising the relative integrated intersities of 2 μm (Ho3+: 5I7→5I8) and 1.8 μm (Tm3+: 3F_4→3H6) bands we have observed an efficient energy transfer from Tm3+ (3F4) to Ho3+ (5I7). Examination of the ratios of the intensity of 2 μm band to that of 1.8 μm band as a function of the ratios of Tm3+ concentration (cTm) to Ho3+ concentration (cHo) indicates that small concentration ratios (cTm/cHo) lead to high efficient energy transfers of Tm3+(3F4)→Ho3+(5I7). 相似文献
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DIELECTRIC AND PYROELECTRIC CHARACTERISTICS AND FERROELECTRIC SOFT MODES IN PbTiO3 POLYCRYSTALS DOPED WITH Ca2+ 下载免费PDF全文
The effects of Ca2+ ions on the structure and dielectric and pyroelectric characteristics of PbTiO3 polycrystals were investigated. With increasing content of Ca, a decrease in tetragonal axial ratio (c/a) was observed as a consequence of shrinkage of the lattice parameter c. The dielectric constant and pyroelectric coefficient increase and Curie temperature (TC) shifts toward lower temperature with increasing content of Ca. The theory of ferroelectric soft mode has been developed to illuminate the relationship between the structure and properties of the polycrystal. 相似文献
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Optical absorption and the enhancement and bleaching of Fe3+ and Fe5+ electron paramagnetic resonance in SrTiO3: Al measured as a function of wavelength and time show that the photochromic absorption bands are due to electron transfer from O2- valence states to Fe4+ and Fe5+. They occur at 2.09 and 2.82 eV for Fe4+ and at 1.99 and 2.53 eV for Fe5+. 相似文献
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M. Fischer 《Journal of Physics and Chemistry of Solids》1982,43(8):673-682
The hydrostatic dependence of the second order elastic constants of several fluoperovskites has been measured and studied from a macroscopic point of view and through a force field analysis. The first part of this paper is devoted to the experimental determination of some combinations of the third and fourth order elastic constants. The second part analyses the pressure dependence of the second order elastic constants from a macroscopic point of view. The large values of the second order anharmonicity coefficients are connected to the occurrence of a phase transition in some compounds, whereas the first order coefficients have an order of magnitude which agrees with a quasiharmonic hypothesis. The third part is devoted to the microscopic interpretation of the third order elastic constants. A rigid ion model is used with either classical Born Mayer potentials or a modification of these potentials with an axial term (Cowley and Rousseau's models). 相似文献
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Far infrared absorption in cubic KMgF3 doped with Fe2+ is reported . A line is observed at 87cm?1, which is assigned to the (Γ5g → Γ3g, Γ4g) transition in the Fe2+. The reduction in the spin-orbit coupling from the free ion value has been predicted by Ham, Schwarz and O'Brien. 相似文献
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本工作测量了室温下TbP3O14和EuP5O14晶体的吸收和发射光谱。根据吸收光谱和Judd-Ofelt理论计算了Tb3+和Eu3+的实验和理论的振子强度。用最小二乘法拟合实验与理论的振子强度得到唯象强度参量Ωλ。然后计算了Tb3+的5D3→7F5,5D4→7F4和5D4→7F6以及Eu3+的5D0→7F2,5D0→7F4的跃迁几率和寿命。同时用时间分辨光谱测量了不同温度下相应的荧光辐射寿命。计算与实验结果基本相符。理论和实验的结果表明Tb3+的5D3态的寿命主要取决于5D3→5D4和7F6→7F0两能级对之间的电偶极-电偶极交叉弛豫。
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The multiphonon sideband of the spin allowed transition 6T2g:A1 ? 2〉 → 6Eg:B3 ? 2〉 within the 3d6 orbital of Fe2+ in D2h symmetry was analyzed with respect to the one phonon absorption and density of states of the coupled phonon modes. Temperature dependence of the zero-phonon line shows, that the axial anisotropy of the S = 2 spin multiplet in the excited B3 state is about 0.9 cm-1. 相似文献
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In this work, double-center.doped luminescent material CaS:Bi3+, Eu2+ was made via flux NH4Cl by sintering in excess sulfur environment. The sample had a purplish red net luminescent color. Excitation spectra at both red, 650 nm and blue, 487 nrn were taken. The red emission from Eu2+ center was mainly come from the 4f65d1 absorption in the CaS host. The blue emission from the Bi3+ center on the other hand showed no big difference from the singly doped CaS:Bi3+ materials in excitation spectrum. Emission spectra were obtained at excitaton of 270nm and 300nm. Stokes shift was moved about 20-30nm, under different point excitation. Emission peaks of both Bi3+ and Eu2+ centers appeared at 463nm, 642.5nm by 270nm excitation and 487 nm, 620 nm by 300 nm excitation respectively. After-glow decay cures were also obtained and the shapes of decay curves are similar and it is due to the single hole-trap system by lattice defects. 相似文献
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A theoretical method for investigating the inter-relation between the electronic and the molecular structures of a 3d5 ion in a tetragonal ligand-field has been established on the basis of a 252×252 complete energy matrix. By means of this method, the local structure of the Fe3+-V cd and Fe3+-Li+ systems in RbCdF3:Fe3+ and CsCdF3:Fe3+ crystals are determined by the experimental EPR spectrum. Our calculation show that the local lattice structure around an octahedral Fe3+ center has a compression distortion along the crystalline axis in RbCdF3 as well as in CsCdF3 crystals, and that the compression magnitude of a tetragonal Fe3+-Li+ system is larger than that of the Fe3+-V cd system. This may be ascribed to the fact that a Fe3+ ion replaces a Cd2+ ion and a Li+ ion substitutes for another Cd2+ ion next to the Fe3+ ion in the Fe3+-Li+ system, and the Li+ ion will shift to the Fe3+ ion, which pushes the F1 ion toward the Fe3+ ion. Using this method, the experimental EPR parameters , and are also interpreted simultaneously. 相似文献
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T. Shinohara K. Sasaki H. Onodera M. Fujioka I. Kawasuji H. Watanabe 《Physics letters. A》1978,66(5):410-412
The charge densities of the 4s electrons in Fe2+ and Fe3+ ions in the ionic compound, NiO, were measured from an internal conversion experiment and compared with some predicted values on the basis of different theoretical methods. 相似文献
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Holographic measurements in LiNbO3: Ti waveguides are reported indicating a mode dependent enhancement of photoconductivity. This enhancement can be explained by a stabilization of Fe2+ centers in the waveguide which are responsible for optical damage effects. 相似文献