共查询到20条相似文献,搜索用时 15 毫秒
1.
《Materials Chemistry and Physics》2007,101(2-3):423-427
Electron paramagnetic resonance (EPR) and optical absorption studies have been carried out on Cu2+ ions doped in polyvinyl alcohol films (PVA). EPR spectrum at room temperature exhibits hyperfine structure characteristic of Cu2+ ions in tetragonal symmetry. The EPR spectra have also been recorded at various temperatures. The number of spins participating in the resonance is measured as a function of temperature and the activation energy is calculated. The paramagnetic susceptibility (χ) is calculated from the EPR data at various temperatures and the Curie constant is evaluated from 1/χ versus T graph. The optical absorption spectrum exhibits a broad band which has been assigned to the transition 2B1g → 2B2g. 相似文献
2.
Vijay Singh R. P. S. Chakradhar J. L. Rao Ho-Young Kwak 《Journal of Materials Science》2011,46(11):3928-3934
Manganese-doped BaAl12O19 green phosphor was prepared using a self-propagating (combustion) synthesis. Powder X-ray diffraction and scanning electron
microscopy were used to characterize the as-prepared combustion product. A room temperature photoluminescence study shows
an emission line at 513 nm corresponding to a transition from the upper 4T1 → 6A1 ground state of Mn2+ ions. The electron paramagnetic resonance (EPR) spectrum exhibits six line hyperfine structure at g = 1.981. From the EPR spectrum, the spin-Hamiltonian parameters have been evaluated. The g value indicates that the site symmetry around Mn2+ ions is distorted tetrahedral. The number of spins (N) participating in the resonance for g = 1.981 is measured as a function of temperature. The paramagnetic susceptibility (χ) is calculated from the EPR data at
various temperatures. From the plot 1/χ versus T, the Curie constant (C) and Curie paramagnetic temperature (θp) have been evaluated and discussed. 相似文献
3.
B. T. Raut M. A. Chougule A. A. Ghanwat R. C. Pawar C. S. Lee V. B. Patil 《Journal of Materials Science: Materials in Electronics》2012,23(12):2104-2109
Nanocomposites of CdS nanocrystals with conducting polyaniline doped with camphor sulfonic acid (CSA) have been prepared by spin coating technique and investigated by X-ray diffraction, field emission scanning electron microscopy (FESEM), fourier transform infra red spectroscopy (FTIR), UV–visible spectroscopy and electrical transport method. The X-ray diffraction patterns showed broad peaks due to formation of nanoparticles of CdS in polyaniline matrix. FESEM showed that the transformation of morphology from agglomeration to nanopetals. The FTIR spectra confirmed the interaction between CSA and polyaniline (PANi)–CdS nanocomposite. The UV–visible spectrums revealed the enhancement of doping level for the PANi–CdS nanocomposites which is assigned to the existence of greater number of charges on the polymer backbone. DC electrical conductivity studies showed an increase in conductivity of PANi–CdS nanocomposites from 6.9?×?10?6 to 3.14?×?10?4 due to addition of CSA (10–50?%). 相似文献
4.
Electron paramagnetic resonance (EPR) and optical absorption spectra of Cr3+ ions in Calcium alumino borate (CaAB) glasses have been studied. The EPR spectra exhibit weak resonance signal at g ≈ 4.50 and intense resonance signal at g ≈ 1.98. A sharp resonance signal at g ≈ 1.97 was also observed at lower concentrations of chromium. The concentration dependence of the linewidth of the resonance signal at g ≈ 1.98 suggests the formation of Cr3+ ion clusters by magnetic superexchange interactions. The temperature dependence of the peak to peak intensity and the linewidth of the resonance signal at g ≈ 1.98 suggests that the exchange interactions between Cr3+ ions in the present sample were antiferromagnetic in nature with Néel temperature, T N = 233 K. From the number of spins participating in the resonance at g ≈ 1.98, the paramagnetic susceptibility (χ) was calculated at different temperatures (233–295 K). A plot of 1/χ and T was found to obey Curie-Weiss law with negative Curie temperature. By measuring the relative intensities of the resonance signal at g ≈ 1.98, at different temperatures, the value of antiferromagnetic coupling constant (J) has been estimated. The optical absorption spectrum of chromium doped CaAB glass exhibits four bands, characteristic of Cr3+ ions, in nearly octahedral symmetry. From the band positions, the crystal field splitting parameter, Dq and the Racah interelectronic repulsion parameters, B and C were evaluated. The optical band gap (Eopt) and the Urbach energy (ΔE) were calculated from the ultraviolet absorption edges. 相似文献
5.
Electron paramagnetic resonance (EPR) and optical absorption spectra of Cu2+ ions in alkaline earth alumino borate glasses doped with different concentrations of CuO have been studied. The EPR spectra of all the glasses exhibit the resonance signals, characteristic of Cu2+ ions present in axially elongated octahedral sites. The number of spins participating in the resonance has been calculated as a function of temperature for calcium alumino borate (CaAB) glass doped with 0.1 mol% of CuO. From the EPR data, the paramagnetic susceptibility (χ) was calculated at different temperatures (T) and from the 1/χ-T graph, the Curie temperature of the glass has been evaluated. The optical absorption spectra of all the glasses show a single broad band, which has been assigned to the 2B1g → 2B2g transition of the Cu2+ ions. The variation in the intensity of optical absorption with the ionic radius of the alkaline earth ion has been explained based on the Coulombic forces. By correlating the EPR and optical absorption spectral data, the nature of the in-plane σ bonding between Cu2+ ion and the ligands is estimated. From the fundamental ultraviolet absorption edges of the glasses, the optical energy gap (Eopt) and the Urbach energy (ΔE) are evaluated. The variation in Eopt and ΔE is explained based on the number of defect centers in the glass. 相似文献
6.
Hexadecylamine-capped Mn-doped wurtzite CdSe nanoparticles have been successfully synthesized via a novel, facile method at low temperature. Optical spectroscopy, X-ray diffraction (XRD), electron paramagnetic resonance (EPR) transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selected area diffraction (SAD) and energy dispersive spectroscopy (EDS) measurements are presented to confirm successful doping of the wurtzite CdSe. The nanoparticles obtained show quantum confinement in their optical properties with band-edge luminescence. The reduction in the emission intensity of the doped CdSe compared to the pure CdSe indicates the presence of impurity (Mn2+ ions) in the pure CdSe nanoparticles. XRD analysis reveals that the nanoparticles are of wurtzite structure while the HRTEM image confirms the crystallinity of the doped material. 相似文献
7.
Electron paramagnetic resonance (EPR) of Mn2+ ions revealed their distribution on different structural units of a 2B2O3PbO glass matrix doped with MnO. Octahedral symmetric sites, tetragonally distorted, were detected. The progressive clustering of manganese ions was evidenced when the MnO content increased. EPR and magnetic susceptibility data revealed that both Mn2+ and Mn3+ ions are simultaneously present in the glass matrix and the transition from isolated ions in samples with x1 mol % to those involved in dipole–dipole interactions for samples with x30 mol % and antiferromagnetically coupled ions when x>30 mol %. 相似文献
8.
V. Natarajan A.R. Dhobale T.K. Seshagiri Chung-Hsin Lu 《Materials Research Bulletin》2004,39(13):2065-2075
Europium-ion doped strontium pyrophosphate was prepared via a chemical precipitation method to investigate the fluorescence of europium ions, the phosphate radical ions formed upon gamma-ray irradiation and their role in the thermally stimulated luminescence (TSL) of this compound. Fluorescence spectra revealed that europium ions were present in divalent as well as trivalent oxidation states. The measurements of fluorescence life time indicated that Eu3+ ions existed in two different types of environments in the lattice. Gamma irradiated europium-ion doped Sr2P2O7 showed the presence of two thermo-luminescence glow peaks at 465 and 565 K; however, no glow was observed in the undoped sample. Electron paramagnetic resonance (EPR) studies of europium-ion doped samples showed signals from Mn2+ ions (present as impurity) prior to and after gamma irradiation. Upon gamma irradiation, signals originating from PO22−, PO32− and O2− radical ions were observed in the undoped and doped samples. In the gamma irradiated europium-ion doped samples, additional low-field EPR signals, attributed to Eu2+ ions, were observed. By correlating the TSL and EPR results on europium-ion doped Sr2P2O7, the mechanism for the glow peak at 565 K was identified. 相似文献
9.
M. V. Vlasova N. G. Kakazey O. Milosevic D. P. Uskokovic D. Poleti D. Vasovc 《Journal of Materials Science》1990,25(10):4324-4330
The structure of ZnO varistors prepared by different chemical methods was studied by the electronic paramagnetic resonance (EPR) method. The presence of Mn2+ ions in both ZnO lattice and electroconductive phase was used as a sensitive probe for the analyses of structural changes which occur during sintering of ZnO varistors. Potential mechanisms which can contribute to the formation of resonant lines were considered. The concentration of paramagnetic centres was quantitatively analysed. The variation of EPR signals of Mn2+ ions in ZnO phase was registered as a function of the chemical methods used for the preparation of powders only when samples were sintered at lower temperatures and non-linear characteristics of varistor ceramics had not yet been reached. At higher sintering temperatures EPR signals of Mn2+ ions in electroconductive phase differed only in the case of powders obtained by NaOH coprecipitation. 相似文献
10.
The defect structure for Mn2+ in KTaO3 is theoretically studied by using perturbation formulas of the spin Hamiltonian (SH) parameters for 3d5 ions in tetragonal symmetry based on the strong-field scheme. By analyzing the electron paramagnetic resonance (EPR) data of the studied system, we suggest that the impurity Mn2+ ion occupy the dodecahedral K+ site, rather than the octahedral Ta5+ site. Based on the studies, it is found that the Mn2+ impurity undergoes an off-center displacement away from the ideal K+ site by about 0.60 Å along the C4 axis. The above displacement is qualitatively consistent with the recent result based on the generalized gradient approximation (GGA) and that obtained from EPR and dielectric spectroscopy studies. 相似文献
11.
A. Lecointre R. Ait Benhamou A. Bessiére G. Wallez M. Elaatmani B. Viana 《Optical Materials》2011,34(2):376-380
Mn-ion doped calcium phosphates namely Ca5(PO4)3(OH) hydroxyapatite (HAP), β-Ca3(PO4)2 (β-TCP) as well as Ca9.5Mn(PO4)7 whitlockite were synthesized and the optical properties of the Mn2+ cations were investigated. Annealing under reducing atmosphere enhances the emission of the divalent manganese species. Electron paramagnetic resonance (EPR) and optical spectroscopies confirm that Mn2+ ions are the active species. Orange and red emissions occur respectively for the Mn:HAP and Mn:TCP. For this latter, long-lasting phosphorescence (LLP) coming from the Mn2+ emission (4T1 → 6A1 transition) is observed at 640 nm but it appears that the traps depths are either two shallow or too deep to lead to an efficient long-lasting emission. 相似文献
12.
Diamond-like ZnGeP2 single crystals with a chalcopyrite structure highly doped with manganese have been obtained by means of reactive solid-phase diffusion. According to the EPR data, the concentration of Mn2+ ions reaches up to 1017?1018 cm?3. 相似文献
13.
Klaus Baberschke 《Journal of Superconductivity and Novel Magnetism》2006,19(1-2):77-84
Electron paramagnetic resonance (EPR) in metals has contributed a lot to the understanding of the electronic structure and
magnetic properties in dilute alloys as well as in concentrated ferromagnets. We recall some pioneering work of the Kazan
group and others, studying local moment EPR in superconductors. An SNS Josephson junction has been used as a microwave generator
and as an EPR detector at once. EPR was also used to study the Kondo effect in the EPR g-shift and linewidth. Moreover, the
high sensitivity of EPR (down to 1010 spins) allows to study single atomic layers of ferromagnets below and above the Curie temperature T
C as well as the spin fluctuations at T
C. The in situ ferromagnetic resonance (FMR) in ultrahigh vacuum (UHV) offers a unique possibility to study the interlayer exchange coupling
(IEC) and spin dynamics of coupled ferromagnetic films. Furthermore, the magnetic resonance enables us to measure basic parameters
of nanoscale magnets in absolute energy units (i.e., μeV/spin). The current status of the UHV-FMR in nanoscale ferromagnets
will be discussed. 相似文献
14.
High Current Injection into Dynamic p–n Homojunction in Polymer Light‐Emitting Electrochemical Cells
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Tomo Sakanoue Jinpeng Li Hisaaki Tanaka Ryota Ito Shimpei Ono Shin‐ichi Kuroda Taishi Takenobu 《Advanced materials (Deerfield Beach, Fla.)》2017,29(18)
Ions and electrons in blends of polymer–electrolyte can work in ensemble to operate light‐emitting electrochemical cells (LECs), in which the unique features of in situ formed p–n homojunctions offer efficient charge injection and transport. However, electrochemical features give rise to significant stability and speed issues due to limited electrochemical stability and low ion mobility, resulting in low brightness and a slow response of LECs. Here, these issues are overcome by the separate control of ionic and electronic charges, using a simple driving pulse superimposed on a small base voltage; ions with slow response are rearranged by a constant base voltage, while a high‐voltage pulse, superimposed upon the base, injects electrons/holes which have fast response, with minimal effect on the ions. This scheme successfully injects an extremely high current density of > 2 kA cm?2 with a balanced electron/hole ratio, at a high‐speed response time of ≈ 50 ns; both properties demonstrate advantages of LECs in making polymers brighter. An in situ electron spin resonance measurement on the LECs further revealed that this impressive performance is due to the highly doped polymers, whose spin density reached 7 × 1019 spins cm?3, and an ordered polymer structure in the active layer blend. 相似文献
15.
《Optical Materials》2014,36(12):2296-2302
The electron paramagnetic resonance (EPR) measurements of PbMoO4 single crystals doped with Co2+ ions (0.5 wt.%) carried out at temperature range 10–12 K are reported. The observed spectra reveal evidently two major groups of EPR spectra, each group consists of eight hyperfine structure components associated with the Co nuclear spin I = 7/2. Additionally, EPR spectra of the unintentional impurities have been observed, which have been assigned to Nd3+ ions in PbMoO4. The analysis of the various characteristic features of the EPR spectra as well as our earlier optical absorption studies of Co2+:PbMoO4 indicate that the Co2+ ions are located at two crystallographically distinct complexes, denoted Co2+(α) and Co2+(β). The fictitious ‘spin’ S′ = ½ has been assigned to the observed ground Kramers doublet state of each of the two Co2+ complexes tentatively identified as located at the Mo sites in PbMoO4. The spin Hamiltonian parameters for Co2+ (S′ = ½) ions in PbMoO4, including the components of the Zeeman and hyperfine structure tensors gij and Aij, respectively, are experimentally determined for the first time. Comparison of our results with the values of gij and Aij for Co2+ ions in other structurally similar compounds further strengthens this conclusion. Correlation of the present results with those obtained earlier from optical studies is discussed. Alternative assignments of the ground states and options for the origin of the ‘spin’ S′ = ½ for Co2+ ions in PbMoO4 will be considered in a subsequent paper. 相似文献
16.
R.P. Sreekanth Chakradhar K.P. Ramesh J. Ramakrishna 《Materials Research Bulletin》2005,40(6):1028-1043
Electron paramagnetic resonance (EPR) and optical investigations have been performed in the mixed alkali borate xNa2O-(30 − x)K2O-60B2O3 (5 ≤ x ≤ 25) glasses doped with 10 mol% of vanadyl ions in order to look for the effect of ‘mixed alkalis’ on the spectral properties of the glasses. The observed EPR spectra have structures for x > 5 mol% which are characteristic of a hyperfine interaction arising from an unpaired electron with the 51V nucleus and it builds up in intensity as x increases. It is observed that the mixed alkali play a significant role in accommodating the vanadyl ions in these mixed alkali glasses and for x > 5 mol%, shows a well resolved hyperfine structure typical for isolated VO2+ ions. The spin-Hamiltonian parameters (g and A), the dipolar hyperfine coupling parameter (P) and Fermi contact interaction parameter (k) have been evaluated. It is observed that the spin-Hamiltonian parameters do not vary much with the change in composition. It is observed that with increase of x, an increase occurs in tetragonal distortion for VO2+. The number of spins (N) participating in resonance and the paramagnetic susceptibility (χ) have been calculated. It is observed that N and χ increase with x. The optical bandgap energies evaluated for these glasses slightly increase with x and reach a maximum around x = 20 and thereafter decrease showing the mixed alkali effect. Optical band gap energies obtained in the present work vary from 2.73 to 3.10 eV for both the direct and indirect transitions. The physical parameters of the glasses are also determined with respect to the composition. 相似文献
17.
P. G. Baranov S. I. Goloshchapov G. A. Medvedkin T. Ishibashi K. Sato 《Journal of Superconductivity》2003,16(1):131-133
Electron paramagnetic (EPR) and ferromagnetic resonance (FMR) have been studied in the system of (Zn,Mn)GeP2 ferromagnetic layer grown on undoped ZnGeP2 single crystal. Strong FMR signals are registered in the wide temperature range up to room temperature. EPR and photo-EPR of intrinsic defects are observed in ZnGeP2 substrate. EPR spectra characteristic of Mn2+ ions on Zn2+ sites in the bulk appear after the growth of the ferromagnetic layer on ZnGeP2 crystal indicating the efficient Mn-diffusion into the bulk crystal by the annealing treatments. 相似文献
18.
P. G. Baranov S. I. Goloshchapov G. A. Medvedkin T. Ishibashi K. Sato 《Journal of Superconductivity and Novel Magnetism》2003,16(1):131-133
Electron paramagnetic (EPR) and ferromagnetic resonance (FMR) have been studied in the system of (Zn,Mn)GeP2 ferromagnetic layer grown on undoped ZnGeP2 single crystal. Strong FMR signals are registered in the wide temperature range up to room temperature. EPR and photo-EPR of intrinsic defects are observed in ZnGeP2 substrate. EPR spectra characteristic of Mn2+ ions on Zn2+ sites in the bulk appear after the growth of the ferromagnetic layer on ZnGeP2 crystal indicating the efficient Mn-diffusion into the bulk crystal by the annealing treatments. 相似文献
19.
S. Salimian S. Farjami Shayesteh 《Journal of Superconductivity and Novel Magnetism》2012,25(6):2009-2014
Diluted magnetic CdS:Mn nanoparticles were synthesized by the aqueous solution method with different manganese (Mn2+) concentrations (x=7?C10?atom?%) at room temperature in nitrogen atmosphere and capped with Thiogelycerol. The X-ray diffraction patterns of CdS nanoparticles with different Mn doping concentration indicated that samples have hexagonal structure at room temperature. Energy dispersive X-ray spectroscopy confirmed incorporative of Mn ions in CdS nanoparticles. UV-Visible spectroscopy is used to investigate optical absorption of Mn-doped CdS. From photoluminescence measurement it was found that the intensity of the luminescence spectra decreases by increasing Mn2+ dopant ions at high precursor concentration. Also, the room temperature ferromagnetic behavior of Mn-doped CdS nanoparticles is discussed by using hysteresis measurement results. 相似文献
20.
K. Tamizh Selvi K. Alamelu Mangai M. Priya P. Suresh Kumar M. Rathnakumari 《Journal of Materials Science: Materials in Electronics》2017,28(3):2317-2324
The present paper deals with the synthesis of Mn3O4/MgO nanocomposite through a simple sol–gel route and their electrical and magnetic properties are discussed for electrode applications. The grain size and particle morphology of the synthesized nanocomposite are characterized using XRD and HRSEM. The elemental compositions of the synthesized samples were analyzed using EDAX spectra. The dielectric constant, dielectric loss and AC conductivity of the synthesized samples were studied in the frequency range of 100 Hz–5 MHz at different temperatures (303–573 K) using impedance spectra. The activation energy was calculated using Arrhenius plot. The vibrating sample magnetometry (VSM) study shows that the nanocomposites are found to be paramagnetic at room temperature. 相似文献