EPR and optical absorption studies on Cr3+ ions doped in KZnClSO4 x 3H2O single crystals

EPR and optical absorption spectra of Cr3+ ions doped in KZnClSO4 x 3H2O single crystals have been studied at room temperature. The EPR spectrum exhibits a group of three fine structure transitions characteristic of Cr3+ ions. From the observed EPR spectra, the spin-Hamiltonian parameters have been determined. The optical absorption spectrum exhibits two broad bands characteristic of Cr3+ ions in an octahedral symmetry. From the observed band positions, the crystal field parameters have been evaluated.     

EPR studies of VO2+ ions in kainite single crystals

Electron paramagnetic resonance (EPR) spectra of VO2+ ions doped in Kainite (a mineral salt) single crystals and powder were recorded at room temperature at X-band frequencies.The angular variation studies of the spectra indicate that the VO2+ ion enters Mg2+ ion site substitutionally. The principal values of g and A-tensors were determined from the EPR spectral studies. Using these EPR parameters, the molecular orbital bonding parameters of VO2+ ion in the lattice have been evaluated and discussed.     

EPR and susceptibility studies of Zn1-xMnxTe crystals at room temperature

Single crystals of Zn1-xMnxTe for x = 0.1, 0.25, 0.45, 0.5 and 0.6 were prepared using vertical Bridgman technique. EPR (electron paramagnetic resonance) spectra were recorded at room temperature (303 K) between 0 and 6 kG magnetic field and range of frequency 8.8-9.6 GHz. As the concentration of Mn increases the line width (DeltaH) and the number of spins (Ns) were increased. Susceptibility studies were carried out at room temperature in the range of dc magnetic field 0-10 kG using vibrating sample magnetometer (VSM). Non-linear variation in susceptibility as a function of concentration (x) was observed and was explained on the basis of sp-d and d-d exchange interactions between Mn2+ ions and ZnTe lattice ions. Both EPR and susceptibility studies confirm the paramagnetic state of Zn1-xMnxTe system at RT.     

Preparation and structural characterization of rare-earth doped lead lanthanum zirconate titanate ceramics

A new preparation route towards rare-earth (RE) doped polycrystalline lead lanthanum zirconate titanate (PLZT) ceramics (RE = Y³⁺, Nd³⁺, Yb³⁺), based on the use of doped lanthanum oxide or zirconia, is reported. Structural characterization by X-ray powder diffraction reveals that secondary phase formation can be substantially diminished in comparison to conventional preparation methods. The distribution of the rare-earth dopants was investigated as a function of concentration by static ²⁰⁷Pb spin echo NMR spectra, using Fourier Transformation of Carr–Purcell–Meiboom–Gill spin echo trains. For the Nd- and Yb-doped materials, the interaction of the ²⁰⁷Pb nuclei with the unpaired electron spin density results in significant broadening and shifting of the NMR signal, whereas these effects are absent in the diamagnetic Y³⁺ doped materials. Based on different concentration dependences of the NMR lineshape parameters, we conclude that the structural role of the Nd³⁺ dopants differs significantly from that of Yb³⁺. While the Nd³⁺ ions appear to be statistically distributed in the PLZT lattice, incorporation of Yb³⁺ into PLZT appears to be limited by the appearance of doped cubic zirconia as a secondary phase.     

EPR spectra of Cu2+ and VO2+ ions in ammonium hydrogen oxalate hemihydrate [(NH4)HC2O4 . (1/2)H2O] single crystals

Cu(2+) and VO(2+) doped ammonium hydrogen oxalate hemihydrate, [(NH(4))HC(2)O(4) . (1/2)H(2)O], single crystals have been studied at room temperature and at 113K in three mutually perpendicular planes. Both ions yield unexpectedly large number of lines. The calculated results of the Cu(2+) and VO(2+) doped in [(NH(4))HC(2)O(4) . (1/2)H(2)O] indicate that both ions substitute with the NH(4)(+) ion in the structure. The EPR spectra of Cu(2+) ions are characteristic of tetragonally elongated octahedral site and the spectra of VO(2+) are characteristic of tetragonally compressed complex. The angular variation of the EPR spectra has shown that two different Cu(2+) and VO(2+) complexes are located in different chemical environments, and each environment contains two magnetically inequivalent Cu(2+) and VO(2+) sites in distinct orientations occupying substitutional positions in the lattice and show very high angular dependence. The principal g and the hyperfine (A) values of both ions are determined.     

Characterization of paramagnetic hole-centers in Al2O3 and Al2O3:Fe by optical and EPR absorption

The electron paramagnetic resonance (EPR) and optical absorption spectra of nominally pure and Fe-doped single crystals of Al₂O₃ have been examined before and after gamma-ray irradiation at 77°K. The EPR spectra for doped and irradiated crystals were found to be a function of the iron concentration. Analysis of the optical and EPR spectra observed on the same Fe-doped crystals which had been subjected to gamma-ray irradiations suggests that the center which accounts most satisfactorily for the details of these spectra is: a single trapped-hole localized on an anion which is adjacent to a substitutional divalent iron impurity atom. The optical absorption band ascribed to this center occurs at 3.08 eV.     

Electron Paramagnetic Resonance and optical absorption spectra of Cr3+ in zinc maleate tetrahydrate single crystals

Electron Paramagnetic Resonance (EPR) and optical absorption spectra of Cr³⁺ ions doped in single crystals of zinc maleate tetrahydrate (ZMTH) have been studied at room temperature (300 K). The EPR spectra exhibit a group of three fine structure transitions, characteristic of the Cr³⁺ ion. From the observed EPR spectra, the spin-Hamiltonian and zero-field splitting parameters have been determined. The optical absorption spectrum exhibits two broad bands characteristic of Cr³⁺ ions in octahedral symmetry. From the observed spectrum, the crystal field parameters have been evaluated.     

Multi‐frequency (S,X, Q and W‐band) EPR and ENDOR Study of Vanadium(IV) Incorporation in the Aluminium Metal–Organic Framework MIL‐53

Doping the well‐known metal–organic framework MIL‐53(Al) with vanadium(IV) ions leads to significant changes in the breathing behaviour and might have repercussions on the catalytic behaviour as well. To understand the properties of such a doped framework, it is necessary to determine where dopant ions are actually incorporated. Electron paramagnetic resonance (EPR) and electron–nuclear double resonance (ENDOR) are applied to reveal the nearest environment of the paramagnetic vanadium(IV) dopant ions. EPR spectra of as‐synthesised vanadium‐doped MIL‐53 are recorded at S‐, X‐, Q‐ and W‐band microwave frequencies. The EPR spectra suggest that at low dopant concentrations (1.0–2.6 mol %) the vanadium(IV) ions are well dispersed in the matrix. Varying the vanadium dopant concentration within this range or the dopant salt leads to the same dominant EPR component. In the ENDOR spectra, hyperfine (HF) interactions with ¹H, ²⁷Al and ⁵¹V nuclei are observed. The HF parameters extracted from simulations strongly suggest that the vanadium(IV) ions substitute Al in the framework.     

EPR and optical absorption studies on VO2+ ions in L-asparagine monohydrate single crystals

X-Band electron paramagnetic resonance (EPR) studies of VO(2+) ions in l-asparagine monohydrate single crystals have been done at room temperature. Detailed EPR analysis indicates the presence of two magnetically inequivalent VO(2+) sites. Both the vanadyl complexes are found to take up interstitial position. The angular variation of the EPR spectra in three planes ab, bc and ca are used to determine principal g and A tensors. For the two sites the spin Hamiltonian parameters are, site I: g(x)=1.9633, g(y)=2.0274, g(z)=1.9797, A(x)=88, A(y)=61, A(z)=161x10(-4)cm(-1); site II: g(x)=1.9627, g(y)=1.9880, g(z)=1.9425, A(x)=90, A(y)=66, A(z)=167x10(-4)cm(-1). The optical absorption study is also carried out at room temperature and absorption bands are assigned to various transitions. The theoretical band positions are obtained using energy expressions and a good agreement is found with the experimental values. By correlating EPR and optical data different molecular orbital coefficients are evaluated and the nature of bonding in the crystal is discussed.     

Correlation between Luminescence and EPR Spectroscopy as Evidence of Ytterbium Pair Formation in Li6Ln(BO3)3:Yb3+ (Ln=Gd,Y) Borate Single Crystals

Synthesized powders and grown single crystals of nominal compositions Li₆Ln(BO₃)₃:Yb³⁺ (Ln=Y, Gd) were investigated by means of powder and single‐crystal X‐ray diffraction (XRD), as well as optical near‐IR spectroscopy in conjunction with electron paramagnetic resonance (EPR) spectroscopy. The appearance of two distinct zero‐phonon lines suggests the existence of two kinds of Yb³⁺ ions in the single crystals. The XRD results exclude the possibility of a phase transition occurring between room and low temperatures. EPR spectra of single crystals show the presence of both isolated ions and pairs of ytterbium ions substituted for Y³⁺. A strong temperature dependence of the intensity of Yb–Yb pairs resonance lines coincides with temperature dependence of emission peak at 978 nm, confirming a common origin of the defect giving rise to these spectra. Calculated from EPR spectra, the distance between pairs of Yb³⁺ is in good agreement with crystallographic ones: R=3.856 Å, R_cryst=3.849 Å.     

Local lattice structure study of the octahedral (CrO6)9- clusters for Cr3+ ion doping in a variety of oxide crystals by simulating the corresponding EPR and optical spectra

On the basis of the 120 x 120 complete energy matrix, the local lattice structures of the octahedral (CrO6)9- clusters for Cr3+ ions doping in a variety of oxide crystals with D3d or C3v site symmetry have been studied by employing two distorted parameters, respectively. By simulating the calculated EPR and optical spectra data to the experimental results, the local lattice structure parameters are determined unambiguously. It is shown, by means of a series of calculations, that although the local lattice structures around the M (M = Al3+, Ga3+, Li+, Sc3+, etc.) ions in host crystals are obviously different, the local lattice structures of the octahedral (CrO6)9- clusters in a variety of oxide crystals doped with Cr3+ ions are similar and fluctuant in the vicinity of that of the Cr2O3. This may be ascribed to the fact that there is the similarly octahedral (CrO6)9- clusters in a variety of oxide crystals doped with Cr3+ and the Cr2O3 crystal. Our viewpoint is consistent with that of Gaudry et al. [Phys. Rev. B 2003, 67, 094108].     

EPR spectra of Cu(2+) in KH(2)PO(4) single crystals

Cu(2+) doped single crystals of KH(2)PO(4) were investigated using EPR technique at room temperature. The spectra of the complex contains large number of overlapping lines. Five sites are resolved and four of them are compatible with the tetragonal symmetry, and the fifth one belongs to an interstitial site. The results are discussed and compared with previous studies. Detailed investigation of the EPR spectra indicate that Cu(2+) substitute with K(+) ions. The principal values of the g and hyperfine tensors and the ground state wave function of Cu(2+) ions are obtained.     

EPR, optical and infrared absorption studies of Mn2+ ions doped in zinc malate trihydrate single crystal

Electron paramagnetic resonance (EPR) studies have been carried out on Mn2+ ions doped in zinc malate trihydrate single crystals in the temperature range 123-413 K on X-band frequency. The EPR spectrum at room temperature exhibits a group of five fine structure transitions each splits into six hyperfine components. Angular variation studies reveal that Mn2+ ions enter the lattice substitutionally. From the observed EPR spectrum, the spin-Hamiltonian parameters have been evaluated. The variation of zero-field splitting parameter (D) with temperature is measured. From the optical absorption spectrum, the crystal field splitting parameter Dq and the Racah interelectronic repulsion parameters B and C have been evaluated. The infrared spectrum exhibits bands characteristic of the carboxylic acid salts.     

Gd(Ⅲ)三元配合物EPR波谱研究

对Gd(Ⅲ)的三元配合物室温和低温的固体粉末以及低温THF溶液EPR波谱的研究发现,Gd(Ⅲ)三元配合物固体粉末在室温和低温EPR波谱各共振吸收峰差异不大,但在低温THF溶液中EPR波谱出现超精细分裂,甚至存在超超精细分裂.Gd(Ⅲ)三元配合物随协同配体改变,EPR各共振吸收峰位置、强度和数目均存在较大变化,且不对称参数λ随协同配体不同而改变;大多数Gd(Ⅲ)三元配合物表现“U”谱特征.     

BaFCl：Ce^3＋和BaFCl：Gd^3＋晶体中的发光中心

运用不同的固相反应条件制备或后处理了几种BaFCl:RE~(3+)(RE=Ce或Gd)晶体,测定了它们的荧光光谱,对照并分析光谱数据和不同条件下可能引入晶体缺陷的情况,推论出晶体中存在有2类发光中心,即由RE_(?)-F_(?)和RE_(?)-F_(?)缔合体构成的中心。     

Zeolite GdNaY nanoparticles with very high relaxivity for application as contrast agents in magnetic resonance imaging

In this paper we explore Gd(3+)-doped zeolite NaY nanoparticles for their potential application as a contrast agent in magnetic resonance imaging (MRI). The nanoparticles have an average size of 80-100 nm, as determined by TEM and XRD. A powdered sample loaded with La3+ was characterised by means of multinuclear solid-state NMR spectroscopy. The NMR dispersion (NMRD) profiles obtained from aqueous suspensions of samples with Gd3+ doping ratios of 1.3-5.4 wt% were obtaining at different temperatures. The relaxivity increases drastically as the Gd3+ loading decreases, with values ranging between 11.4 and 37.7 s-1 mM-1 at 60 MHz and 37 degrees C. EPR spectra of aqueous suspensions of the samples suggest that an interaction between neighbouring Gd3+ ions within the same particle produces a significant increase in the transversal electronic relaxation rates in samples with a high Gd3+ content. The experimental NMRD and EPR data are explained with the use of a model that considers the system as a concentrated aqueous solution of Gd3+ in the interior of the zeolite that is in exchange with the bulk water outside the zeolite. The results obtained indicate that the Gd3+ ion is immobilised in the interior of the zeolite and that the relaxivity is mainly limited by the relatively slow diffusion of water protons from the pores of the zeolite channels into the bulk water.     

Cu2+ ions as a paramagnetic probe to study the surface chemical modification process of layered double hydroxides and hydroxide salts with nitrate and carboxylate anions

A layered zinc hydroxide nitrate (Zn5(OH)8(NO3)2.2H2O) and a layered double hydroxide (Zn/Al-NO3) were synthesized by coprecipitation and doped with different amounts of Cu2+ (0.2, 1, and 10 mol%), as paramagnetic probe. Although the literature reports that the nitrate ion is free (with D3h symmetry) between the layers of these two structures, the FTIR spectra of two zinc hydroxide nitrate samples show the C2v symmetry for the nitrate ion, whereas the g ||/A || value in the EPR spectra of Cu2+ is high. This fact suggests bonding of some nitrate ions to the layers of the zinc hydroxide nitrate. The zinc hydroxide nitrate was used as matrix in the intercalation reaction with benzoate, o-chlorobenzoate, and o-iodobenzoate ions. FTIR spectra confirm the ionic exchange reaction and the EPR spectroscopy reveals bonding of the organic ions to the inorganic layers of the zinc hydroxide nitrate, while the layered double hydroxides show only exchange reactions.     

Ce0.8Gd0.2-xPrxO1.9固溶体的合成与表征

利用X射线衍射(XRD)、拉曼光谱(Raman)、X射线光电子能谱(XPS)和交流阻抗谱对溶胶-凝胶法制备的稀土双掺杂固溶体Ce0.8Cd0.2-xPrxO1.9(x=0,0.02,0.10)的结构和导电性进行了研究.XRD结果表明,经800℃焙烧所得样品都形成了单相立方萤石结构,平均晶粒尺寸在23～30 nm之间;X...     

EPR of copper ions in Pb<Subscript>2</Subscript>MoO<Subscript>5</Subscript> crystals

The article presents the results of EPR studies of Pb₂MoO₅ crystals containing a copper impurity. Based on the analysis of angular dependences of the EPR spectra, it is found that copper ions incorporate into the structure of the Pb₂MoO₅ crystal in the Cu²⁺ state and occupy the molybdenum site with the formation of a linear extended Cu(II)–V(O)–Pb(IV) defect along the а axis of the crystal. An oxygen vacancy appears in the structure of the defect to compensate the charge and the lead ion acquires the Pb⁴⁺ charge state. According to the structure of this center, one magnetically non-equivalent position with the direction of main values of А and g of A(Cu)_zz and g_zz tensors parallel to the а axis is observed in the EPR spectra. Moreover, the EPR spectra exhibit an addition hyperfine structure from one lead atom on which the unpaired electron density is 0.061%. The obtained data on the structure of the defect formed when the copper impurity incorporates into the Pb₂MoO₅ crystal provided the assumption that the observed light scattering when the light beam is directed perpendicular to the а axis may be due to the cooperative effect of the presence of di- and tetravalent ions substituting for molybdenum in the linear configuration of Pb–O–Mo bonds.     

Vibronic effects in Cu(II)-doped Ba2Zn(HCO2)6 x 4 H2O

The temperature-dependent electron paramagnetic resonance (EPR) spectrum of approximately 1% Cu(II) ions doped into Ba 2Zn(HCO2)6 x 4 H2O was analyzed at the Q-band frequencies over the temperature range 100-350 K to obtain structural information about the local environment. It can be concluded that the host crystal imparts a large orthorhombic strain which mainly corresponds to a tetragonal compression imposed onto the Cu(II)O6 species. This results in a copper center which adopts an orthorhombically distorted elongated geometry with the elongated axis perpendicular to the direction of the tetragonal compression due to the host crystal. There are two possible axes of elongation, and these represent two conformers separated by approximately 320 cm(-1). The thermal population of the higher energy level averages the g values, giving the observed temperature-dependent EPR spectra. The averaging process is between vibronic levels that are localized at two different minima of a single ground-state potential energy surface. These vibronic levels correspond to vibrational levels having different electronic properties. The determination of the host lattice strain parameters from the Cu(II) EPR spectra means that the guest ion is used as a probe of the environment of the Zn(II) site. The structural data derived from the lattice strain parameters are correlated with those from the Ba 2Zn(HCO2)6 x 4 H2O crystal structure.