共查询到20条相似文献,搜索用时 765 毫秒
1.
The EPR spectra of the (BaF2)1 ? x (CeF3) x system are studied for the concentrations x = 0, 0.001, 0.002, 0.005, 0.01, and 0.02. The appearance of new tetragonal centers is detected beginning from x = 0.002, the intensity of these centers being maximal at x = 0.01. The (CaF2)1 ? x ? y (CeF3) x (YF3) y double solutions with x = 0.001 and y from 0 to 0.02 are also studied. In addition to the ordinary tetragonal center, beginning from y = 0.001, a new tetragonal center appears with the same structure as in the previously studied mixed crystals based on BaF2—namely, the Ce3+-□-R3+ chain elongated along the fourfold axis substitutes the Ca2+-Ca2+-Ca2+ and Ba2+-Ba2+-Ba2+ chains in regular CaF2 and BaF2 crystals (□ is the cation vacancy, and R3+ is the Ce3+, La3+, or Y3+ trivalent ion). 相似文献
2.
A. Casalot J. Claverie P. Hagenmuller 《Journal of Physics and Chemistry of Solids》1973,34(2):347-354
An investigation of the electrical conductivity of some oxyfluoride spinels of formula Znx2+Fe1?x3+[M2+ Fe3+]O4?xFx (M = Fe, Co, Ni) and Fe3+[Nx2+Fe2+Fe1?x3+]O4?xFx (N = Fe, Ni) shows that the conduction depends on the composition of the B sites: the activation energy increases, the conductivity and the Fe3O4 transition temperature decrease as the substitution rate of Fe3+ by N2+ in the B sites increases. The authors conclude to a hopping mechanism between the B cations; the anionic sublattice and the cationic A sublattice do not participate in the conduction. 相似文献
3.
J.W.D. Martens W.L. Peeters H.M. van Noort M. Erman 《Journal of Physics and Chemistry of Solids》1985,46(4):411-416
The magneto-optical spectra of Co1+xFe2?xO4 show with increasing Co3+ content an increasing intensity of the 4A2 ? 4T1(F) and 4A2 ? 4T1(P) transition of Co2+ at 0.8 and 2.0 eV. A decrease in the Co2+-Fe3+ charge transfer transitions on octahedral sites is found. In the optical spectra a strong increase in optical absorption is found with dominant transitions at 0.8, 1.6 and 2.6 eV due to Co3+ crystal field transitions on octahedral sites and a Co2+-Co3+ charge transfer. Conversion Electron Mössbauer Spectroscopy has been used to determine the cation distribution in the surface layer of the samples. The results indicate a shift of Co2+ from octahedral to tetrahedral sites when Co3+ is substituted in CoFe2O4. This results in enhanced optical absorption, enhanced magneto-optical effects and a lower Curie temperature. 相似文献
4.
Enhai Song Weiren Zhao Xihua Dou Yanjuan Zhu Shuangping Yi Huachu Min 《Journal of luminescence》2012,132(6):1462-1467
A series of color tunable phosphors K2Ca1?x?yP2O7:xMn2+, yEu3+ are synthesized by solid state reaction method. The energy transfer phenomenon from Mn2+ to Eu3+ has been observed in the Mn2+/Eu3+ codoped non-magnetic K2CaP2O7 host, which was confirmed by PL spectra and decay curves. The Mn2+→Eu3+ energy transfer is controlled by quadrupole–quadrupole interaction between sensitizer and activator. The maximum efficiency of energy transfer is estimated to be 33% with x=0.125 and y=0.03 in K2Ca1?x?yP2O7:xMn2+, yEu3+ phosphor. The phosphors can emit light from green to yellow and eventually to orange under 400 nm excitation by changing the Mn2+/Eu3+ content ratio, indicating that K2CaP2O7: Mn2+, Eu3+ would be potential candidates for use in lighting and displays applications. 相似文献
5.
The influence of local distortions on the structure and properties of copper and silver impurity Jahn-Teller complexes in mixed crystals, namely, CaxSr1?x F2: Me 2+ and Sr1?x BaxF2: Me 2+ (0≤x≤1, Me 2+=Cu2+ or Ag2+), is investigated using electron paramagnetic resonance (EPR) spectroscopy at frequencies of 9.3 and 37 GHz in the temperature range 4.2–250 K. Local distortions of the tensile and compressive types are induced by Ca2+, Sr2+, and Ba2+ impurity ions incorporated into the first or second coordination sphere of the cationic environment of the Me 2+ impurity ion during crystal growth. 相似文献
6.
Jingshan Hou Xin Yin Yongzheng Fang Fuqiang Huang Weizhong Jiang 《Journal of luminescence》2012,132(5):1307-1310
A series of single-composition phosphors Ca9MgM′(PO4)7:xEu2+, yMn2+ (CMM′ P:Eu2+, Mn2+; M′=Li, Na, K; 0.003≤x≤0.03; 0 ≤y≤0.1) were synthesized by solid state reactions. Upon excitation at 337 nm, phosphors Ca9MgM′ (PO4)7: Eu2+ exhibit strong blue emissions centered at 417 (Ca9MgLi(PO4)7:Eu2+), 457 (Ca9MgNa(PO4)7:Eu2+), and 453 (Ca9MgK(PO4)7:Eu2+) nm respectively, which correspond to the 4f65d1→4f7 transitions of Eu2+ ions, Through an effective resonance-type energy transfer, CMM′P:Eu2+,Mn2+ phosphors exhibit a series of colors by adjusting the concentration of Mn2+. The result indicates that CMM′P:Eu2+,Mn2+ can be potentially used as a UV excited phosphor for white light-emitting diodes (LEDs). 相似文献
7.
Abdolali Alemi Younes Hanifehpour Sang Woo Joo Aliakbar KhandarAli Morsali Bong-Ki Min 《Physica B: Condensed Matter》2011,406(14):2801-2806
New LnxSb2−xS3 (Ln: Lu3+, Ho3+, Nd3+)-based nanomaterials were synthesized by a co-reduction method. Powder XRD patterns indicate that the LnxSb2−xS3 crystals (Ln=Lu3+, Ho3+, x=0.00−0.1 and Ln=Nd3+, x=0.00−0.08) are isostructural with Sb2S3. SEM images show that doping of Lu3+ and Ho3+ ions in the lattice of Sb2S3 results in nanorods while that in Nd3+ leads to nanoflowers. UV-vis absorption and emission spectroscopy reveal mainly electronic transitions of the Ln3+ ions in case of Ho3+ and Nd3+ doped nanomaterials. Emission spectra show intense transitions from excited to ground state of Ln3+. Emission spectra of doped materials, in addition to the characteristic red emission peaks of Sb2S3, show other emission bands originating from f-f transitions of the Ho3+ ions. TGA curves indicated that Sb2S3 has the highest thermal stability. The electrical conductance of Ln-doped Sb2S3 is higher than undoped Sb2S3, and increase with temperature. 相似文献
8.
A. Bianconi A. Giovannelli I. Dovoli S. Stizza L. Palladino O. Gzowski L. Murawski 《Solid State Communications》1982,42(8):547-551
The X-ray Absorption Near-Edge Structure (XANES) of V in vanadium-iron glasses (50P2O5 + (50?x)FeO + xV2O5) have been measured. The effective charge of V ions in glasses has been determined. At low V2O5 concentration (x ~ 5) only V4+ with 6-fold coordination is present on the contrary a static mixed valence state (V4+, V5+) has been found at high concentrations 20?x?50. The results explain the electron hopping conductivity effects at high V2O5 concentration (x ~ 50) involving V4+ ? V5+ pairs and at low V2O5 concentration (x?10) involving V4+ ? Fe3+ pairs. 相似文献
9.
A. S. Nizamutdinov L. A. Nurtdinova V. V. Semashko S. L. Korableva 《Optics and Spectroscopy》2014,116(5):732-738
Differential gain spectra in the range 295–335 nm were measured in crystals of scheelite structure LiY1 ? x Lu x F4 (x = 0–1), doped by Ce3+ ions. It is shown that variation of Lu3+ and Y3+ ions relative content in LiY1 ? x Lu x F4 crystals allows to manipulate the spectral width of the amplification band. Cross-sections of excited-state absorption at the wavelengths of Ce3+ luminescence, probability ratios of formation and thermal destruction of color centers depending on the Y3+ ions content in LiY1 ? x Lu x F4 crystals were estimated. Even better gain characteristics have been demonstrated by LiLuF4:Ce3+, doped by Yb3+ ions. The highest optical gain coefficient with a wide amplification band among studied samples was observed in LiLuF4:Ce3+ crystal, codoped by Yb3+ ions. 相似文献
10.
Anisotropy of hexagonal ferrites with M,W and Y structures containing Fe3+ and Fe2+ as magnetic ions
F.K. Lotgering P.R. Locher R.P. van Stapele 《Journal of Physics and Chemistry of Solids》1980,41(5):481-487
The ferrimagnetic saturation moment and hexagonal anisotropy constant K1 have been measured at 4K on a Zn2Y single crystal and on polycrystalline BaFe2+2W and SrFe2+2W samples. The moment of Fe2W is in agreement with a collinear spin coupling and with the known site occupation for the Fe2+ ions. The moment of Zn2Y is 9% lower than the value for a collinear configuration.The uniaxial anisotropy of Fe2+ in hexagonal ferrites is discussed and compared with that of Co2+. No noticeable Fe2+ anisotropy is found in Fe2W in contrast to LaM = LaFe2+Fe3+11O19, in which the Fe2+ anisotropy is strong. The difference is attributed to the symmetry difference of the sites occupied by the Fe2+ ions in both compounds. The current theory does not satisfactorily explain the anisotropy and quadrupole splitting of Fe2+ in LaM. From this it is concluded that admixing of 5E states and (or) the influence of a dynamical Jahn-Teller effect cannot be neglected.The dipole-dipole anisotropy is computed for the M, W and Y structure and some deviation from the literature data is found. Using these results, a mean anisotropy of 1.3 to 2.3 cm?1 per Fe3+ ion is found for the three structures. 相似文献
11.
In manganese-doped PbWO4 crystals, low-intensity signals of triclinic clusters Mn4+-V O and Fe3+-V Pb have been revealed in addition to signals of Mn2+ tetragonal centers. The Mn4+-V O cluster is formed by a Mn4+ ion in the W6+ position, which is associated with a vacancy of the nearest neighbor O2?ion, and the Fe3+-V Pb cluster consists of a Fe3+ ion substituting for Pb2+ with a local compensation of by a lead vacancy. It has been shown that, in PbWO4: Mn, there is also a small amount of Mn4+ tetragonal centers located in the Pb2+ position with a nonlocal compensation of an excess charge. 相似文献
12.
Using luminol as the probe, the luminescence behavior of trivalent lanthanide ions (Ln3+=La3+, Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+, Yb3+ and Lu3+) in aqueous solution was first investigated by fluorescence, and the sensitivity enhanced by 3–5 orders of magnitude compared with the Ln3+ intrinsic fluorescence. It was found that Ln3+ with luminol could form a 1:1 association complex which remarkably enhanced the fluorescence signal of luminol. The increment of fluorescence intensity was proportional to the concentration of Ln3+ in the range of 1.0–70.0 nmol L?1, and the linear correlation equation, ΔIF=ACLn+B, was given. The relationships of A (defined as sensitivity factor) with some physical parameters (atomic number Z, ionic radius γ±, standard redox potential Eo and hydration enthalpy ΔHhyd) were discussed. The good symmetry of A vs. Z plot for light lanthanides (LLG) and the heavy lanthanides (HLG) and linear relations of A with Z, γ±, Eo and ΔHhyd should originate in the special features of Ln3+ electronic configurations [Xe]4fn (n=0–14). Using the proposed model of Ln3+–luminol interaction, lg[ΔIF/(IFo–ΔIF)]=rlg[Ln]+lg k, the association constant k was obtained over the range of 1.95×106–2.63×107 L mol?1. 相似文献
13.
An excitation band at 300 nm corresponding to Ce3+absorption is observed in pentaphosphate crystals containing Ce3+ and Nd3+ when the Nd3+ luminescence is monitored. The decay of excitation of Ce3+ in crystals of pure cerium pentaphosphate, CeP5O14, follows single exponential kinetics with a 22 ± 2 nsec lifetime. In Ce0.5Nd0.5P5O14 crystals, the Ce3+ lifetime is shortened to 3.8 ± 0.4 nsec as a result of efficient nonradiative energy transfer to the Nd3+ ions. 相似文献
14.
The hexagonal ferrite Fe2W = BaFe22+Fe3+16O27 exhibits a sharp 57Fe Mössbauer spectrum at 300 and 78 K. All seven sublattices in this complicated crystal structure are detected. Fast electron exchange between Fe2+ and Fe3+ ions gives rise to sharp lines and makes them indistinguishable. At 5 K the exchange is slow and the Fe2+ ions are detected from the presence of a weak subspectrum with broadened lines separated from the main spectrum of the Fe3+ ions. Analysis shows that the Fe2+ ions reside exclusively on one of the seven sublattices, which is occupied statistically by Fe2+ and Fe3+ ions in the ratio of 2 : 1. For SrFe2+2Fe3+16O27 the situation is the same. 相似文献
15.
The quenching of the Ce3+ emission and the increase of the Tb3+ emission with increasing x of Ce1-xTbxMgAl11O19 for x ? 0.35 is ascribed to energy transfer from Ce3+ to Tb3+, which is restricted to nearest rare earth neighbours. This transfer is almost complete at x ? 0.35. The decrease of the Tb3+ emission at higher Tb3+ concentrations is not due to Tb3+ concentrational quenching, but due to the limited solubility of Tb3+ in the CeMgAl11O19 phase. 相似文献
16.
P. Brauel T. Canzler D. Cords R. Felst G. Grindhammer M. Helm W.-D. Kollmann H. Krehbiel M. Schädlich 《Physics letters. [Part B]》1976,65(2):184-186
The reactionse + d → e' + pS + p + π?ande + d → e' + nS + n + π+ were measured detecting electron and pion in coincidence at an invariant hadronic mass of 2.19 GeV. The measurements were performed at electron four-momentum transfer squared of f2 = 0.70 and 1.35 GeV2 in the range of t = (γv?π)2 between tminand ?1.0 GeV2. The cross section d2σ/dtdφ of the reaction e + n → e' + p + π? was determined. 相似文献
17.
Xiansong Liu Pablo Hernández-Gómez Kai Huang Shengqiang Zhou Yong Wang Xia Cai Hongjun Sun Bao Ma 《Journal of magnetism and magnetic materials》2006
M-type strontium ferrites with substitution of Sr2+ by rare-earth La3+, and a little amount of Fe3+ by Co2+ according to the formula Sr1−xLaxFe12−xCoxO19, are prepared by the ceramic process. Effects of the substituted amount of La3+ and Co2+ on structure and magnetic properties of Sr1−xLaxFe12−xCoxO19 compounds have systematically been investigated by X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and B–H hysteresis curve measurements. In our results, the suitable amount of La3+–Co2+ substitution may remarkably increase saturation magnetization. Intrinsic coercive force (Hcj) of Sr ferrite magnets is evidently increased without significant decrease in residual flux density (Br) by La3+–Co2+ substitution. 相似文献
18.
Novel near infrared (NIR) phosphors CaxSr1−xS:Ce3+,Nd3+ were synthesized by a solid state reaction. The NIR emission was realized through an efficient absorption by the allowed 4f-5d transition of Ce3+ and efficient energy transfer to Nd3+ via well-matched energy levels. Ce3+ and Nd3+ content in CaS/SrS was optimized. It was found that CaS:Ce3+,Nd3+ gave much stronger NIR emission than that of SrS:Ce3+,Nd3+. Further studies on CaxSr1−xS:Ce3+,Nd3+ indicated that both visible emission of Ce3+ and NIR emission of Nd3+ were observably affected by Ca/Sr ratio. The energy transfer efficiency, which can be estimated from fluorescence lifetime of Ce3+, increased from 52% to 74% for the CaxSr1−xS:Ce3+,Nd3+ (x=0 to 1) series, accompanied with a shift of maximal emission wavelength of Ce3+ from 482 to 505 nm. The results showed that overlap between emission spectrum of Ce3+ and excitation spectrum of Nd3+ plays an important role in the energy transfer efficiency, and Ce3+ emitting in green or blue-greenish region sensitized the Nd3+ NIR fluorescence emission more efficiently than that in blue region. 相似文献
19.
V. A. Bezhanov V. V. Mikhaĭlin S. P. Chernov D. N. Karimov B. P. Sobolev 《Optics and Spectroscopy》2006,101(4):571-581
The short-wavelength transmission spectra of Na0.4 R 0.6F2.2 crystals with R = Y, Yb, or Lu have been investigated. For these crystals, the VUV transmission cutoffs are 78750, 58820, and 75200 cm?1, respectively. The 4f n–4f n?15d absorption and excitation spectra of Na0.4Y0.6F2.2 crystals activated with Ce3+, Pr3+, Nd3+, Er3+, Tm3+, and Yb3+ ions have been analyzed in the range 30000–80000 cm?1. The energy positions of the lowest levels of the 4f n?15d configurations of these ions in the fluorite crystal matrix Na0.4Y0.6F2.2 are determined. The absorption band in the spectral range 60600–70000 cm?1 in Na0.4(Y, Yb)0.6F2.2 crystals is due to the charge transfer from F? to Yb3+. It is shown that the environmental symmetry of Ce3+ ions in Na0.4R0.6F2.2 (R = Y, Yb, Lu) crystals is almost identical. 相似文献
20.
The six optical band positions and six spin-Hamiltonian parameters [g factors g∥, g⊥ and hyperfine structure constants A∥(171Yb3+), A⊥(171Yb3+), A∥(173Yb3+), A⊥(173Yb3+)] for Yb3+ ion at the tetragonal Y3+ site of KY3F10 crystal are calculated from a diagonalization (of energy matrix) method. In the method, the Hamiltonian of energy matrix contains the free-ion, crystal-field interaction, Zeeman (or magnetic) interaction and hyperfine interaction terms and so a 14×14 complete energy matrix for 4f13 ion in tetragonal crystal-field and under an external magnetic field is constructed. Diagonalizing the energy matrix, these optical and EPR spectral data are calculated together and the calculated results are in reasonable agreement with the experimental values. The signs of hyperfine structure constants A∥, A⊥ for the isotopes 171Yb3+ and 173Yb3+ in KY3F10 are suggested. The results are discussed. 相似文献