CsLiSO4/NH4LiSO4 system investigated by EPR

The single crystals of CsLiSO₄ and the solid solutions Cs _x (NH₄)_{(1? x )}LiSO₄ have been investigated using the EPR technique. Two kinds of vanadyl doped samples were considered – as-grown from the aqueous solutions of appropriate compounds and after a thermal treatment. It has been established that in as-grown crystals the EPR spectra of vanadyl ions were very complex due to the presence of more than one paramagnetic site in the lattice. At least two such sites were identified and spin Hamiltonian parameters were calculated for all the sites. After annealing the crystals at about 400?K, a significant decrease in the intensities of the EPR lines of VO²⁺ complexes was observed. In well-annealed samples the complexity of the EPR spectra has been found to disappear. Additionally, the third kind of vanadyl complexes were created during this treatment. It has also been shown that the EPR spectra of Cr³⁺ ions in CsLiSO₄ could be observed without any additional sample treatment reported in literature like an irradiation or thermal decomposition. It was established that the VO²⁺ and Cr³⁺, being sensitive to structural phase transition in the CsLiSO₄, can be used as a probe for the structural changes in the CsLiSO₄/NH₄LiSO₄ system.     

Electron paramagnetic resonance and thermally stimulated luminescence studies of uranyl doped calcium sulphate

Electron paramagnetic resonance (EPR) and thermally stimulated luminescence (TSL) studies were conducted onγ-irradiated CaSO₄:UO ₂ ²⁺ to elucidate the role of the electron/hole traps in thermally stimulated reactions and to obtain the trap parameters (trap depth and frequency factor). Intense TSL glow peaks around 140, 375, 400 and 438±2K are observed and their spectral characteristics have shown that UO ₂ ²⁺ and UO ₆ ⁶⁻ act as luminescent centres. EPR studies have shown the peaks at 140 and 400/438K to be associated with the thermal destruction of O⁻ and SO ₄ ⁻ radical ion in two stages respectively. The maximum rate of thermal destruction of SO ₄ ⁻ ions (as seen by EPR) in various alkaline earth sulphate matrices investigated in our laboratory is also summarized. The activation energy which characterizes the electron transfer reaction between SO ₄ ⁻ and the dopant ion lies in the range of (0.95±0.15 eV). This value is independent of the dopant and therefore seems to be characteristic of the binding energy of hole in the SO ₄ ⁻ radical ion.     

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.     

Electron paramagnetic resonance study of Mn2+ in kainite

epr measurements on kainite containing Mn²⁺ impurities are made at x-band microwave frequencies at room temperature. The fine structure transitions observed inac* plane have helped to extract the spin Hamiltonian parameters of Mn^{2 +} ions in the crystalline environment. The results indicate strong orthorhombic crystalline field and the rhombic field parameter is larger than those observed in the other similar systems. The z-axis of the D-tensor is determined with respect toac* plane by theoretically fitting the experimental fine structure transitions.     

Thermally stimulated luminescence and electron paramagnetic resonance studies on uranium doped K2Ca2(SO4)3

Thermally stimulated luminescence (TSL) studies of gamma-irradiated uraniumdoped K₂Ca₂(SO₄)₃ revealed two glow peaks around 400 K and 435 K. Electron paramagnetic resonance (EPR) studies carried out on these samples have shown the formation of the radical ions SO ₄ ⁻ , SO ₃ ⁻ , SO ₂ ⁻ and O ₃ ⁻ . From the study of the thermal stabilities of these radical ions, it was found that the thermal destruction of SO ₂ ⁻ and SO ₄ ⁻ radical ions are associated with the glow peaks observed around 400 K and 435 K respectively. Uranate ion was identified as the luminescent centre for the observed TSL glow. The trap depth values for the glow peaks have been determined from TSL data.     

Electron paramagnetic resonance study of copper impurity charge-states in PbWO4 scintillator

The study of two types of Cu²⁺ centres observed in nominally pure PbWO₄ crystals grown by Bridgman and Czochralski methods was carried out by electron paramagnetic resonance (EPR). One of centres, called Cu²⁺(I), arises after oxygen compensation, while the second one, called Cu²⁺(II) requires, in addition, infrared illumination at low temperatures, being thermally stable only up to 22–23 K. The EPR spectra of both Cu²⁺ centres are described by rhombic symmetry g-tensors with the Z-principal axis lying close to, or in the (ab) plane of the crystal. It is proposed that in both centres the Cu²⁺ ions substitute for Pb²⁺ ions. The additional reduction of the local crystal-field symmetry is connected with a CuWO₄ wolframite-type lattice distortion for the Cu(I) and a Jahn–Teller distortion of the regular PbWO₄ lattice for the Cu(II). It was also found that either IR irradiation or thermal heating activate the transfer of an electron between two closely spaced Cu²⁺ centres.     

基于电子顺磁共振的锶铁氧体磁特性研究

为了研究配料、温度、氧环境和掺杂等条件对锶铁氧体的磁性能的影响问题, 利用溶胶-凝胶法制备了锶铁氧体粉末, 建立了一种基于电子顺磁共振技术研究锶铁氧体粉末的磁特性的方法. 用电子顺磁共振波谱仪对烧结后的产物进行测试发现: 400 ℃预烧下, 锶铁摩尔比为1:9时, 中间产物顺磁相α-Fe₂O₃含量最多, 高于400 ℃时其含量减少, 亚铁磁相增加, 并确定最佳煅烧温度介于800-900 ℃. 这是由于外磁场和其他磁场综合作用产生亚铁磁相, 进而产生较强的磁矩相互作用所致. 结合工业实际应用, 发现缺氧退火环境下, 顺磁相α-Fe₂O₃含量较大, 不利于亚铁磁相生成; X-射线衍射(XRD)表征结果表明: 除了少量杂相, 其余均为顺磁相和亚铁磁相; 电子顺磁共振谱和XRD 谱检测结果综合表明, 锶铁摩尔比为1:9时, 最终产物的顺磁相含量最少, 亚铁磁相含量最多, 磁性最强; 毫特斯拉计的剩磁检测结果也证实了上述结果. 掺杂实验发现镧离子占锶镧总摩尔数的20% 至30% 时, 能够有效降低顺磁相的产生, 增强最终产物的亚铁磁性.     

Cryostat for low temperature x-irradiation and electron paramagnetic resonance

A cryostat for x-irradiation of solid samples at liquid air temperature is described. The design of the sample mount in the cryostat enables quick transfer of the sample after x-irradiation into EPR cavity to facilitate EPR study without warming the sample.     

Examination on the electron paramagnetic resonance spectra and the photoluminescence spectra of the Cr ions in the KMgF3 crystal

In this paper, the photoluminescence spectra and the electron paramagnetic resonance spectra of the Cr³⁺ ions in the KMgF₃ crystal are explained based on the complete energy matrix diagonalization procedure and a crystal-field like model. The results agree well with the experimental data. It is also shown that the nearest neighbor F⁻ ions deviate 1.3981 and −0.486° from their original position because of the K⁺ vacancy.     

Theoretical Studies of Electron Paramagnetic Resonance Parameters for Cr4+ Ions in Ca2GeO4 Crystals

The electron paramagnetic resonance (EPR) parameters (zero-field splitting D and g factors g_||, g_⊥) of Cr⁴⁺ ions in Ca₂GeO₄ crystals have been calculated from the complete high-order perturbation formulas of EPR parameters for a 3d² ion in trigonal MX₄ clusters. In these formulas, in addition to the contributions to EPR parameters from the widely used crystal-field (CF) mechanism, the contributions from the charge-transfer (CT) mechanism (which are often neglected) are included. From the calculations, it is found that for the high valence state 3dⁿ ions in crystals, the reasonable explanation of EPR parameters (in particular, the g factors) should take both the CF and CT mechanisms into account.     

Thermally stimulated luminescence and electron paramagnetic resonance studies of actinide doped calcium chloro phosphate

Electron paramagnetic resonance [EPR] and thermally stimulated luminescence [TSL] studies were conducted on self [α]-irradiated²³⁹Pu doped calcium chloro phosphate andγ-irradiated²³⁹Pu/²³⁸UO ₂ ²⁺ doped calcium chloro phosphate to elucidate the role of the electron/hole traps in thermally stimulated reactions and to obtain trap parameters from both TSL and EPR data. TSL glow peaks around 135 K (# peak 1), 190 K (# peak 2), 435 K (# peak 5) and 490 K (# peak 7) were observed and their spectral characteristics have shown that Pu³⁺ and UO ₆ ⁶⁻ act as luminescent centres in calcium chloro phosphate with respective dopants. EPR studies have shown the formation of the radical ions H⁰, PO ₄ ²⁻ , O⁻, O ₂ ⁻ and [ClO]²⁻ under different conditions. Whereas the [ClO]²⁻ radical being stable up to 700 K, was not found to have any role in TSL processes, the thermal destruction of other centres was found to be primarily responsible for the TSL peaks observed. The trap depth values were determined both by using the TSL data and also the temperature variation of EPR spectra of these centres.     

Radiation stabilization of U5+ in CaO matrix and its thermal stability: Electron paramagnetic resonance and thermally stimulated luminescence studies

Electron paramagnetic resonance (EPR) evidence is presented for the radiation stabilization of pentavalent uranium in CaO matrix. From the theoretical predictions ofg value for U⁵⁺ in axial symmetries, it was concluded that U⁵⁺ at Ca²⁺ site is associated with a second neighbour charge compensating Ca²⁺ vacancy. EPR measurements also revealed the presence of Mn²⁺, Mn⁴⁺ and Cu²⁺ impurities in the samples. The thermal stability of U⁵⁺ was investigated using EPR and thermally stimulated luminescence (TSL) techniques. The TSL and EPR studies on gamma irradiated uranium doped calcium oxide samples had shown that the intense glow peak at 540 K is associated with the reduction in the intensity of EPR signal of U⁵⁺ ion around this temperature. This peak is associated with the process U⁵⁺+hole→U^6+*→U⁶⁺+hv. The activation energy for this process was determined to be 1.4eV.     

An X-band time domain electron paramagnetic resonance spectrometer

A computer-controlled X-band time domain electron paramagnetic resonance (EPR) spectrometer, with a time resolution of the order of 0.5μsec, has been constructed with many of the crucial microwave components designed and fabricated by the Microwave Engineering Group of TIFR. The spectrometer operates either in a microwave power pulsed mode for determination of spin-lattice relaxation times by the saturation recovery technique or in the kinetic mode for determination of the time dependence of EPR signal after laser excitation. It has an automatic frequency control, an automatic phase control and, most importantly, a field-frequency lock which ensures good stability of the EPR line positions enabling signal averaging for extended periods. The constructional details of the spectrometer and its performance in both the modes are described here by reporting results on certain typical systems.     

Electron paramagnetic resonance of Dy3+ ions in lead thiogallate single crystals

The results of electron paramagnetic resonance (EPR) studies of Dy³⁺ ions in lead thiogallate PbGa₂S₄ single crystals have been presented. It has been shown that the ground state of these ions corresponds to the lowest Stark sublevel Γ₆ of the term ⁶ H _15/2. The spectra are well described by the axially symmetric spin Hamiltonian with the effective spin S = 1/2 with the factors g _‖ = 15.06 and g _⊥ = 2.47. The Dy³⁺ ions substitute Pb²⁺ ions in the crystal lattice of PbGa₂S₄. The observed hyperfine structure has allowed to unambiguously interpret the EPR spectra. The hyperfine interaction constants of two odd isotopes of dysprosium in lead thiogallate single crystals have been found to be A _‖ = 675 × 10^?4 cm^?1 and A _⊥ = 111 × 10^?4 cm^?1 for ¹⁶³Dy and A _‖ = 472 × 10^?4 cm^?1 and A _⊥ = 77 × 10^?4 cm^?1 for ¹⁶¹Dy.     

Electron paramagnetic resonance of Ce3+ ions in lead thiogallate single crystals

The results of electron paramagnetic resonance (EPR) studies of Ce³⁺ impurity ions in single crystals of lead thiogallate PbGa₂S₄ have been reported. The Ce³⁺ ions substitute for Pb²⁺ ions in the crystal lattice of PbGa₂S₄. A number of paramagnetic cerium centers in lead thiogallate have been observed. The spectra are described by the spin Hamiltonian of rhombic symmetry with the effective spin S = 1/2. The g factors of the main cerium centers have been determined. A large number of paramagnetic centers are due to both nonequivalent positions of lead and local charge compensation under the substitution Ce³⁺ ?? Pb²⁺.     

Electron paramagnetic resonance investigation of K3H(SO4)2 proton conductor doped with Cr ion

The proton arrangement around SO₄ units in K₃H(SO₄)₂ (KHS) was studied in detail by X-band CW EPR spectra of CrO₄³⁻ paramagnetic centre incorporated into KHS during the crystal growth process. The EPR data prove the theoretical model of coherent motion of protons and SO₄ units at the fast-proton conducting phase proposed by Ito and Kamimura.     

Electron paramagnetic resonance of Gd3+ ions in powders of LaF3:Gd3+ nanocrystals

The observation of electron paramagnetic resonance of Gd³⁺ ions in nanosized powders of rare-earth fluorides LaF₃:Gd³⁺ has been reported. The measurements have been performed on a single crystal and micro- and nanosized powders at room temperature. Electron paramagnetic resonance spectra and spin-Hamiltonian parameters of Gd³⁺ ions have been obtained. A qualitative difference of spectra in nano- and micropowders due to the increase in the spread of the crystal field parameters with the decrease in the particle size has been found. The relationship between the single-crystal domain size and the hydrothermal treatment time has been established.     

Electron paramagnetic resonance study of Fe3+ centres in KTiOAsO4

An EPR study of Fe³⁺ centres in single crystal KTiOAsO₄ (KTA) has been performed at the Q-band frequency. Two Fe³⁺ centres have been observed for which all spin-Hamiltonian parameters were calculated. The comparison of the pseudosymmetries obtained from fourth-order constants of the spin-Hamiltonian and from a fourth-order crystal field calculation for the two Ti-octahedra, allowed us to locate one Fe³⁺ at both Ti sites in KTA. The deviation from cubic symmetry is similar and not very large for the two centres showing that the charge compensation mechanism is not at short distance.     

Investigation of the local structure of Cu2+ ions doped in alkali lead tetraborate glasses by their electron paramagnetic resonance and optical spectra

The local structure of the Cu²⁺ centers in alkali lead tetraborate glasses was theoretically studied based on the optical spectra data and high-order perturbation formulas of the spin Hamiltonian parameters (electron paramagnetic resonance g factors g_∥, g_⊥ and hyperfine structure constants A_∥, A_⊥) for a 3d⁹ ion in a tetragonally elongated octahedron. In these formulas, the relative axial elongation of the ligand O^2? octahedron around the Cu²⁺ due to the Jahn–Teller effect is taken into account by considering the contributions to the g factors from the tetragonal distortion which is characterized by the tetragonal crystal-field parameters Ds and Dt. From the calculations, the ligand O^2? octahedral around Cu²⁺ is determined to suffer about 19.2% relative elongation along the C₄ axis of the alkali lead tetraborate glass system, and a negative sign for A_∥ and a positive sign for A_⊥ for these Cu²⁺ centers are suggested in the discussion.