EPR study of free radical in gamma-irradiated bis(cyclopentadienyl)zirconium dichloride single crystal

Bis(cyclopentadienyl)zirconium dichloride (BCZD; zirconocene dichloride) single crystals were exposed to ⁶⁰Co-γ irradiation at room temperature. The irradiated single crystals were investigated between 125 and 470?K by electron paramagnetic resonance spectroscopy. The spectra of the crystals were found to be temperature independent. The paramagnetic center was attributed to the cyclopentadienyl radical. The g values of the radiation damage center observed in BCZD single crystal and the hyperfine structure constants of the free electron with nearby protons were obtained.     

Electron paramagnetic resonance study of gamma-irradiated potassium hydroquinone monosulfonate single crystal

Gamma-irradiated potassium hydroquinone monosulfonate (PHM) single crystals were investigated between 125 and 300?K using the electron paramagnetic resonance (EPR) technique. Between 125 and 300?K no changes in the spectra have taken place. The spectra were found to be temperature independent. The investigation of EPR spectra of irradiated single crystals of PHM showed the presence of two PHM anion radicals. The g values of the radiation damage centers observed in the PHM single crystal and the hyperfine structure constants of the free electron with nearby protons were obtained.     

EPR study of Mn-implanted single crystal plates of TiO2 rutile

Single crystals of Mn-implanted TiO₂ rutile have been investigated by electron paramagnetic resonance (EPR) technique at room temperature. We have observed an EPR signal on Mn⁴⁺ ions (S=) in the manganese-implanted single crystal TiO₂ plates. Besides, weaker EPR signals due to Fe³⁺(S=, L=0) and Cr³⁺(S=) ions have also been observed. Characteristic six-line splitting of the manganese EPR lines due to hyper-fine interaction with ⁵⁵Mn nuclei (spin I=) has also been observed. Analysis of the EPR spectra shows that the manganese, iron and chromium ions substitute for Ti⁴⁺ ions in the TiO₂ rutile host. Two structurally equivalent groups of the centers have been observed in the EPR spectra in correspondence with two octahedral positions of the Ti ions in the rutile structure. Spin Hamiltonian parameters for the crystal field of orthorhombic symmetry on the Mn⁴⁺, Fe³⁺ and Cr³⁺ centers have been obtained as result of computer modelling.     

CuGeO3晶体自旋-佩尔斯态的EPR

报道了CuGeO₃单晶在96GHz频率,1 4K温度下的电子顺磁共振(EPR)实验,测量了主轴g因子.导出了Cu²⁺离子在CuGeO₃自旋佩尔斯系统中的混合d轨道基态波函数.采用近似自洽场方法计算了CuGeO₃的主轴g因子.使实验结果得到了解释.     

EPR study of Cu(II) dopant ions in single crystals of bis(l-asparaginato)Zn(II)

We report an electron paramagnetic resonance (EPR) study at 33.9 GHz and room temperature of oriented single crystal samples of bis(l-asparaginato)Zn(II) doped with Cu(II). The variation of the spectra with magnetic field orientation was measured in three crystal planes (a*b, bc and a*c, with a*=b×c). These spectra display two groups of four peaks arising from the hyperfine interaction with the I_Cu=3/2 nuclear spins of copper. They were assigned to Cu(II) ions in two lattice sites related by a 180° rotation around the b-crystal axis. The g and hyperfine coupling (A) tensors of the Cu(II) ions were evaluated from the single crystal data. Some indeterminacy in the assignment of the signals was avoided measuring the EPR spectrum of a powder sample. Their principal values are g₁=2.060(1), g₂=2.068(2), g₃=2.283(2), and A₁≈0.1×10⁻⁴, A₂=13×10⁻⁴ and A₃=165×10⁻⁴ cm⁻¹. The eigenvectors corresponding to g₃ and A₃ are coincident within the experimental error; the other eigenvectors are rotated 5.6° in the perpendicular plane. Considering the crystal structure of bis(l-asparaginato)Zn(II), our EPR results indicate that the Cu(II) impurities replace Zn(II) ions in the host crystal. We propose a molecular model based on the EPR data and the structural information, and analyse the results comparing the measured values with those obtained in similar systems.     

EPR characterization of Mn impurity ions in PbWO4 single crystals

The electron paramagnetic resonance (EPR) properties of the Mn²⁺ ions in PbWO₄ single crystals grown by the Czochralski method have been investigated in the X-band microwave frequency, at T=20 K. The angular dependence of the EPR line positions obtained by rotating the magnetic field in the main crystallographic planes shows that the local symmetry at the Mn²⁺ impurity ions is tetragonal, strongly suggesting that the Mn²⁺ ions substitute for the Pb²⁺ lattice cations, without charge compensation. The resulting spin Hamiltonian parameters compare well with the corresponding values for the Mn²⁺ ions in other isomorphous tungstates. The observed strong angular variation of the EPR linewidth has been quantitatively described considering a random distribution of lattice strains.     

Electron paramagnetic resonance study of exchange coupled Ce3+ ions in Lu2SiO5 single crystal scintillator

The Ce³⁺ ions incorporation inside lutetium oxyorthosilicate (Lu₂SiO₅) single crystals was studied by electron paramagnetic resonance. Already known Ce1 and Ce2 centers originating from the lattice peculiarity allowing two lutetium sites coordinated by different number of the oxygen ions were detected. Remarkably, for the Ce2 center, the determined g² tensor is asymmetric and could not be diagonalized as compared to the Ce1 center, for which the three principal values and corresponding axes orientation have been determined and reported previously. Besides, the much weaker resonance lines found in spectra close to those coming from the Ce1 and Ce2, and following them under crystal rotation with respect to the direction of an external magnetic field, have been revealed as well. They were classified as doublets produced by the exchange coupled Ce³⁺ ions, creating the Ce1–Ce1, Ce2–Ce2 and Ce1–Ce2-like dimers. The corresponding spin–spin coupling constants were estimated. They are in the range 0.04–0.4 cm⁻¹. The Ce1, Ce2 and total dimer centers populations were calculated as 89%, 4.5% and 6.5%, comparing integral intensities of corresponding resonance lines.     

EPR parameters and defect structure of the tetrahedral Ti3+ defect center in beryl crystal

The EPR parameters (g factors g _i and hyperfine structure constants A _i , where i=x, y, z) of Ti³⁺ ion at the tetrahedral Si⁴⁺ site of beryl crystals are calculated within the rhombic symmetry approximation from the high-order perturbation formulas based on the two-spin-orbit (SO)-parameter model. In these formulas both the contribution due to the SO coupling parameter of the central 3d¹ ion and that of ligand ions are considered. From the calculations, the defect structure of the Ti³⁺ defect center in beryl crystal is estimated and the EPR parameters g _x , g _y , g _z and A _y are reasonably explained. The values of the parameters A _x and A _z (which were not reported) are suggested and remain to be checked by the further experimental studies.     

Gamma-radiolysis of deaerated cysteine solutions

The electron paramagnetic resonance (EPR) spectra of gamma-irradiated single crystals of phenidone (fenidon C₉H₁₀N₂O) have been studied for different orientations of crystals in a magnetic field. Phenidone single crystals have been irradiated with ⁶⁰Co-γ rays at room temperature. The EPR spectra have been investigated at temperatures between 125 and 450 K. The spectra have been found to be temperature independent. The spin-Hamiltonian parameters have been obtained from the single-crystal EPR analysis. The principal values of the hyperfine coupling tensor of the unpaired electron and the principal values of the g-tensor have been determined.     

EPR,ENDOR and optical spectroscopy of Yb3+ ion in KZnF3 single crystals

The paramagnetic center of tetragonal symmetry formed by the Yb³⁺ ion in the KZnF₃ crystal has been studied using methods of EPR, ENDOR and optical spectroscopy. The location of the impurity ion and the structural model of the complex differing from the model of the Yb³⁺ center in KMgF₃ have been established. The empirical scheme of the energy levels of the Yb³⁺ ion has been found. The parameters of its interaction with the crystal electrostatic field and the hyperfine interaction with ligands of the nearest environment have been determined. The parameters of the crystal field were used for the analysis of the distortions of the crystal lattice in the vicinity of Yb³⁺. The parameters of the transferred hyperfine interaction have been calculated for the distances between Yb³⁺ and F⁻ ions of the nearest environment obtained taking into account the found distortions. They are in good agreement with the experimental values.     

EPR of radiation defects in LiBaF 3 crystals

EPR spectra of LiBaF 3 crystals have been investigated after X-irradiation at RT. A spectrum consisting of approximately 35 nearly equidistant EPR lines has a strong angular dependence on the line intensities. The spectrum is caused by a hyperfine interaction (hfs) of a spin S =1/2 with neighbouring groups of nuclei. The observed large number of hfs lines required Li nuclei being in the first shell and fluorine nuclei in the more distant second shell. We analysed the spectrum in the F -centre model, taking reduced hfs values of the F -centre in LiF and found qualitative explanation of the number of hfs lines. The angular dependence of the line intensities could be explained by an anisotropy of the g -tensor with its main axis along the [1 v 0 v 0] axis of the crystal.     

EPR and optical measurements of weakly doped LiNbO3: Er

Optical spectroscopy measurements of the congruent LiNbO₃ (LN) single crystals, weakly doped with Er (0.1–0.3 wt%) and Er (0.3 wt%) and Yb (0.5 wt%), have been carried out. The shape of the optical absorption and additional absorption bands registered after γ-irradiation suggests the presence of Er³⁺ ion pairs. EPR investigations were performed for LN single crystal doped with Er (0.1 wt%). Unusual behaviour of the temperature dependence of the intensity and linewidth of the main EPR line—corresponding to the fine transition of ^evenEr³⁺—ions, is reported. The main EPR line appears to be a superposition of several paramagnetic centres originating from isolated ^evenEr³⁺ ions and ^evenEr³⁺–^evenEr³⁺ pairs of ions. In low temperature region (below 20 K), the main EPR signal is dominated by signals arising from ^evenEr³⁺–^evenEr³⁺ pairs of ions. The inverse intensity of the EPR line at low temperature region fulfils the Curie–Weiss law and enabled to determine the Curie–Weiss constant Θ=1.5±0.5 K. The positive sign of Θ suggests that the ferromagnetic interactions arise in the system of ^evenEr³⁺–^evenEr³⁺ ion pairs in LN. Our results suggest that the distribution of Er ions in congruent LN is not homogeneous and Er impurity ions can form clusters in host lattice even in the case of weak erbium doping.     

ZnO:V3+晶体光谱和电子顺磁共振谱的理论研究

采用强场耦合图像,建立了3d2电子组态在三角对称中的45×45能量矩阵,通过对角化完全能量矩阵的方法,计算出了ZnO:V3 晶体的45条光谱能级和5个电子顺磁共振谱参量(零场分裂D,g因子g//,g⊥和超精细结构常数A//,A⊥),计算结果与实验数值能很好地符合.计算中还发现V3 杂质中心的局部结构与基质晶体的结构不一致,即V3 在ZnO中并不占据准确的Zn2 位置,而是沿c3轴方向位移一段距离△Z≈0.003 nm.作者对上述这些结果的合理性进行了讨论.     

EPR of Yb<Superscript>3+</Superscript> ions in a monoclinic KY(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> single crystal

The electron paramagnetic resonance (EPR) of Yb³⁺ ions in a KY(WO₄)₂ single crystal was investigated at T=4.2 K and fixed frequency of 9.38 GHz. The resonance absorption observed on the lowest Kramers doublet represents the complex superposition of three spectra, corresponding to the ytterbium isotopes with different nuclear moments. The EPR spectrum is characterized by a strong anisotropy of the g-factors. The temperature dependence of the g-factors is shown to be caused by the strong spin-orbital and orbital-lattice coupling. The resonance lines broaden with increasing temperature due to the short spin-lattice relaxation times.     

Theoretical examination of optical and EPR spectra for Cu ion in K2PdCl4 crystal

In this work, two d-d transition spectra and four EPR parameters g_∥, g_⊥, A_∥, A_⊥ of K₂PdCl₄/Cu²⁺ are uniformly interpreted based on Zhao's crystal-field model. The calculation result is in good agreement with the experiment findings. The ligand spin-orbit coupling is neglected on the calculation, which is consistent with the ab initio result by Hillier et al. [J. Am. Chem. Soc. 98 (1976) 95]     

EPR parameters and local lattice structure study of V ions in CdCl2 and CsMgCl3 crystals

The local lattice structure and EPR parameters (D, g_‖, g_⊥) have been studied systematically on the basis of the complete energy matrix for a d³ configuration ion in a trigonal ligand field. By simulating the calculated optical and EPR spectra data to the experimental results, the local distortion parameters (ΔR, Δθ) are determined for V²⁺ ions in CdCl₂ and CsMgCl₃ crystals, respectively. The results show that the local lattice structure of CdCl₂:V²⁺ system exhibits a compression distortion (ΔR=−0.0868 Å) while that of CsMgCl₃:V²⁺ system exists an elongation distortion (ΔR=0.0165 Å). The different distortion may be ascribed to the fact that the radius of V²⁺ ion is smaller than that of Cd²⁺ ion or larger than that of Mg²⁺ ion. Moreover, the relationships between EPR parameter D and local structure parameters (R, θ) as well as the orbital reduction factor k and g‐factors (g_‖, g_⊥) are discussed.     

Effect of temperature and high pressure on Mn2+ EPR spectra in K3H(SO4)2 fast-proton conductor

The linewidth ΔH _pp and spin-Hamiltonian parameters under temperature and high hydrostatic pressure by X-band continuous wave electron paramagnetic resonance in the K₃H(SO₄)₂ crystal were studied. Spin-Hamiltonian parameters, direction cosines and coordination of Mn²⁺ ion were determined at room temperature. The pressure at 300?MPa leads to the change of hydrogen bond potential and the transition from double well to single well potential moves about 10?K towards a higher temperature.