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.     

Supertransferred hyperfine structure in EPR of V4+ ion in Ca3In2Ge3O12 garnet

Interaction of an unpaired electron of the tetrahedral V⁴⁺ ion in Ca₃In₂Ge₃O₁₂ garnet with the four nearest In nuclei gives rise to clearly resolved structure of EPR spectra. We report the observation and analysis of these spectra at three frequencies and at temperature 77 K. The temperature dependence between liquid helium and the room temperatures was also studied. Parameters of the spin Hamiltonian are g_∥=1·8735; g_⊥=1·9825; ∣ ¦A∥|=150·4×10^?4cm^?1; ¦ A_⊥¦ = 36·7 × 10^?4 cm^?1. The supertransferred hyperfine interaction was found to be isotropic, absolute value of the corresponding parameter a is 22·1 × 10^?4 cm^?1.     

Hyperfine-structure measurements on Dy161 and Dy163

In an atomic beam magnetic resonance experiment the hyperfine interaction constantsA andB of the⁵ I ₈ groundstate of Dy¹⁶¹ and Dy¹⁶³ were found to be Dy¹⁶¹:A=?(115.8±1)MHz, Dy¹⁶³:A=(162.9±0.6)MHz,B=(1102±15)MHz,B=(1150±20)MHz. Using an effective value for 〈r^?3〉, the magnetic moments and electric quadrupole moments of the Dy¹⁶¹ and Dy¹⁶³ nuclei were calculated to be Dy¹⁶¹:μ _I=?(0.47±0.09) n.m., Dy¹⁶³:μ _I=(0.66±0.13)n.m.,Q=(2.36±0.4)barns,Q=(2.46±0.4)barns.     

EPR study of Fe3+ and Mn2+ in CeO2 and ThO2

Attempts were made to grow CeO₂ and ThO₂ single crystals doped with transition metal ions. Only Fe³⁺ and Mn²⁺ could be detected by the EPR technique. The EPR spectrum of Fe³⁺ in CeO₂ exhibits the well-known fine structure in cubic fields. The parameters areg=2.0044(1) anda=15.6(1)·10^?4 cm^?1. The hyperfine constantA for⁵⁷Fe in hexahedral coordination was found to be 8.9(1)·10^?4 cm^?1. The EPR spectrum of Mn²⁺ in CeO₂ reveals two cubic Mn²⁺ centers. The parameters for center 1 areg=1.9999(1) andA=86.9(1)·10^?4 cm^?1 and for center 2g=1.9984(1) andA=87.0(1)·10^?4 cm^?1. Heating the Mn doped CeO₂ samples in hydrogen, the Mn²⁺ centers transform from cubic into trigonal centers with approximate values ofg=1.9988(2),A=84.5(6)·10^?4 cm^?1 andD=203(1)·10^?4 cm^?1. The two observed Mn²⁺ centers in ThO₂ exhibita priori axial symmetry with approximate values ofg=2.0006(2),A=88.9(4)·10^?4 cm^?1 andD=33(3)·10^?4 cm^?1.     

ESR study of vanadyl ion in tripotassium citrate

ESR spectra of VO²⁺ doped tripotassium citrate are recorded at room temperature. The observed spectra are fitted to a spin Hamiltonian of orthorhombic symmetry with g_x = 2.001 ± 0.001, g_y = 1.997 ± 0.001, g_z = 1.945 ± 0.001, A_x = (49.0 ± 1) × 10⁻⁴ cm⁻¹, A_y = (66.8 ± 1) × 10⁻⁴ cm⁻¹ and A_z = (168.4 ± 1) × 10⁻⁴ cm⁻¹. The covalency and Fermi contact terms are evaluated and compared with those of other lattices.     

EPR of Cu2+ Impurities in Cytosine Hydrochloride: A Case of Superhyperfine Structure

Electron paramagnetic resonance spectra of Cu²⁺ impurities in cytosine hydrochloride single crystals are observed at liquid nitrogen temperature. Two magnetically equivalent sites for Cu²⁺ have been observed. The parameters of ⁶³Cu obtained with the fitting of spectra to rhombic symmetry spin Hamiltonian are: g _x  = 2.047 ± 0.002, g _y  = 2.187 ± 0.002, g _z  = 2.390 ± 0.002, A _x  = (86 ± 3) × 10^?4 cm^?1, A _y  = (87 ± 3) × 10^?4 cm^?1, and A _z  = (138 ± 3) × 10^?4 cm^?1. The observed bands in optical spectra of the single crystal recorded at room temperature are assigned to various d–d and charge-transfer transitions. Using both EPR and optical data, the nature of bonding of metal ion with different ligands is discussed.     

ESR study of vanadyl ion in trisodium citrate pentahydrate

ESR study of VO²⁺ doped trisodium citrate pentahydrate is undertaken at room temperature. The observed spectra are correlated with the available crystal structure data and are fitted to a spin Hamiltonian of orthorhombic symmetry with g_x = 1.998 ± 0.001, g_y = 1.992 ± 0.001, g_z = 1.934 ± 0.001, A_x = (70.0 ± 1) × 10^-4cm^-1, A_y = (66.6 ± 1) × 10^-4cm^-1 and A_z = (175.4 ± 1) × 10^-4cm^-1. The covalency and Fermi contact parameters are evaluated and compared with those of VO²⁺ in other lattices.     

X-ray determination of the mean-square vibrational amplitudes of atoms in nearly perfect CdS crystals

The mean-square amplitudes of Cd and S atoms in CdS were determined for vibrations parallel as well as perpendicular to the c-axis. The results were obtained by measuring the temperature dependence of X-ray integrated intensities for reflections from both basal and prismatic planes in nearly perfect crystals. The analysis of the experimental data is given in detail. The following results were found for T = 295°K: 〈u²_Cd〉_∥ = 2.85±0.04×10^?18cm², 〈u²_s〉_∥ = 1.94 ± 0.08 × 10^?18cm², 〈u²_Cd〉_⊥= 2.39 ± 0.04 × 10^?18cm² and 〈u²_s〉⊥ = 1.63 ± 0.08 × 10^?18cm². The fact that Cd atoms have a larger vibrational amplitude than the S atoms is briefly discussed.     

Spin-spin interaction of Dy3+ ions in KY(WO4)2

The spin-spin interaction of Dy³⁺ ions in a KY(WO₄)₂ single crystal is investigated by electron paramagnetic resonance (EPR) spectroscopy at a temperature of 4.2 K and a frequency of 9.2 GHz. The EPR spectra of ion pairs located in different coordination shells are analyzed. It is revealed that the considerable contribution to the spin-spin interaction of the nearest neighbor ion pair nn is made not only by the magnetic dipole-dipole interaction but also by the isotropic exchange interaction with the parameter I _nn = (+601 ± 17) × 10^?4cm^?1. The exchange interaction in pairs of more widely spaced ions is substantially weaker: I _5n = (?38 ± 3) × 10^?4cm^?1 and I _9n = (+18 ± 4) × 10^?4cm^?1. For the other ion pairs, the magnetic dipole-dipole interaction dominates. It is found that the EPR spectra of single ions and ion pairs exhibit a superhyperfine structure associated with tungsten nuclei.     

EPR and Optical Absorption Study of VO2+-Doped Lithium Hydroxylammonium Sulphate

ABSTRACT

Single-crystal and powder EPR studies of VO²⁺-doped lithium hydroxylammonium sulphate (LiNH₃OHSO₄) were carried out at room temperature. The results indicate the presence of two magnetically inequivalent VO²⁺ sites. The VO²⁺ ion takes up a substitutional position in the host lattice. The angular variation of EPR spectra in three mutually perpendicular planes were used to determine the spin Hamiltonian parameters, and the values obtained were the following: For Site 1, g_x = 2.0249 ± 0.0002, g_y = 1.9698 ± 0.0002, g_z = 1.9552 ± 0.0002, A_x = (51 ± 2) × 10^?4 cm^?1, A_y = (93 ± 2) × 10^?4 cm^?1, and A_z = (165 ± 2) × 10^?4 cm^?1; and for Site 2, g_x = 2.0267 ± 0.0002, g_y = 1.9743 ± 0.0002, g_z = 1.9213 ± 0.0002, A_x = (40 ± 2) × 10^?4 cm^?1, A_y = (80 ± 2) × 10^?4 cm^?1, and A_z = (155 ± 2) × 10^?4 cm^?1. The optical absorption spectrum recorded at room temperature shows four bands. From the optical and EPR data, various molecular coefficients are evaluated, and the nature of bonding in the crystal is discussed.     

EPR, Optical Absorption and Superposition Model Study of Fe3+-Doped Ammonium Dihydrogen Phosphate Single Crystals

X-band electron paramagnetic resonance (EPR) studies are carried out on Fe³⁺ ions doped in ammonium dihydrogen phosphate (ADP) single crystals at room temperature. The crystal field and spin Hamiltonian parameters are evaluated from the resonance lines obtained at different angular rotations. The obtained values of spin Hamiltonian and zero-field parameters of the Fe³⁺ ion in ADP are: g = 1.994 ± 0.002, |D| = (220 ± 5) × 10^?4 cm^?1 and a = (640 ± 5) × 10^?4 cm^?1. On the basis of EPR data, the site symmetry of the Fe³⁺ ion in the crystal is discussed. The Fe³⁺ ion enters the lattice substitutionally replacing the NH₄ ⁺ sites. The optical absorption of the crystal is also studied at room temperature in the wavelength range of 195–925 nm. The energy values of different orbital levels are calculated. The observed bands are assigned as transitions from the ⁶ A _1g (S) ground state to various excited quartet levels of the Fe³⁺ ion in a cubic crystalline field. From the observed band positions, Racah interelectronic repulsion parameters (B and C), cubic crystal field splitting parameter (D _q ) and Trees correction are calculated. There values are: B = 970, C = 1,923, D _q  = 1,380 cm^?1 and α = 90 cm^?1, respectively. On the basis of EPR and optical data, the nature of bonding in the crystal is discussed. The zero-field splitting (ZFS) parameters are also determined theoretically using B _kq parameters estimated from the superposition model. The values of ZFS parameters thus obtained are |D| = (213 ± 5) × 10^?4 cm^?1 and |E| = (21 ± 5) × 10^?4 cm^?1.     

Absorption of Dy3+ and Nd3+ ions in BaR 2F8 single crystals

The Dy³⁺ absorption and excitation spectra of BaY₂F₈ and BaYb₂F₈ single crystals are investigated in the ultraviolet, vacuum ultraviolet, and visible ranges at a temperature of 300 K. These crystals exhibit intense broad absorption bands due to the spin-allowed 4f-5d transitions in the range (56–78) × 10^?3 cm^?1 and less intense absorption bands that correspond to the spin-forbidden transitions in the range (50–56) × 10^?3 cm^?1. The Nd³⁺ absorption spectra of BaY₂F₈ single crystals are studied in the range (34–82) × 10^?3 cm^?1 at 300 K for different crystal orientations.     

Analysis of the optical spectrum of Ho3+ in LiYF4

The energy levels for Ho³⁺ in single crystal LiYF₄ from 0–21,300 cm^?1 have been determined from polarized absorption and fluorescence spectra using crystals at temperatures between 4 and 300°K. Energy level assignments were made initially by comparing the crystal spectra with energy levels calculated by using crystal field parameters interpolated from previously reported analyses of Nd³⁺, Er³⁺ and Tm³⁺ in LiYF₄. The energy level scheme identifies energy levels in the 10 lowest J-multiplets and gives calculated energies for the next six higher J-multiplets. The crystal field parameters were varied to obtain a best fit between experimental and theoretical energies, and the final values B₂₀ = 410, B₄₀ = ? 615, B₄₄ = 819, B₆₀ = ? 27.9 and B₆₄ = 677 ± i32.8 cm^?1 give an r.m.s. fit of 2.78 cm^?1. The calculations were made by diagonalizing the crystal field Hamiltonian, H_x = Σ_kmB_kmC_km, in the space of ten lowest J-multiplets spanned by intermediate coupled free-ion wavefunctions calculated using the free-ion parameters of Carnall et al. for Ho in aqueous solution. The calculated g_∥ for the Γ_3.4 ground state of 13.63 compares favorably with a previously reported value of 13.3 ± 0.1.     

Analysis of the ground configuration of Tm3+ in YVO4

An analysis has been made of the optical spectrum of Tm³⁺ in YVO₄ reported by K. D. Knoll. The approach taken was to describe the Tm³⁺ free ion as completely as possible and then to describe the effects of the crystal field on these levels. Parameters were obtained that gave an r.m.s. deviatioa of 10.6 cm^?1 in a least squares fit. In Knolls' earlier analysis, which did not describe the free ion adequately, several sets of parameters were given that are consistent with different portions of the spectrum. The results computed with our parameters gave a new interpretation of the ³F₄ and ³H₅ multiplets and gave g_∥ factors in good agreement with the measurements. The efiects of the hyperfine interaction and the spin-crystal field interaction on the energy levels resulted in displacements of smaller than 0.1 cm^?1.     

Luminescence and defect studies of YAlO3:Dy3+, Sm3+ single crystals exposed to 100 MeV Si7+ ion beam

Ionoluminescence (IL) and photoluminescence (PL) spectra for different rare earth ions (Sm³⁺ and Dy³⁺) activated YAlO₃ single crystals have been induced with 100 MeV Si⁷⁺ ions with fluence of 7.81×10¹² ions cm^?2. Prominent IL and PL emission peaks in the range 550–725 nm in Sm³⁺ and 482–574 nm in Dy³⁺ were recorded. Variation of IL intensity in Dy³⁺ doped YAlO₃ single crystals was studied in the fluence range 7.81×10¹²–11.71×10¹² ions cm^?2. IL intensity is found to be high in lower ion fluences and it decreases with increase in ion fluence due to thermal quenching as a result of an increase in the sample temperature caused by ion beam irradiation. Thermoluminescence (TL) spectra were recorded for fluence of 5.2×10¹² ions cm^?2 on pure and doped crystals at a warming rate of 5 °C s^?1 at room temperature. Pure crystals show two glow peaks at 232 (Tg₁) and 328 °C (Tg₂). However, in Sm³⁺ doped crystals three glow peaks at 278 (Tg₁), 332 (Tg₂) and 384 °C (Tg₃) and two glow peaks at 278 (Tg₁) and 331 °C (Tg₂) in Dy³⁺ was recorded. The kinetic parameters (E, b s) were estimated using glow peak shape method. The decay of IL intensity was explained by excitation spike model.     

Dipolar studies in CaF2 with Ce3+

Dielectric relaxation in CaF₂ doped with various amounts of Ce³⁺ (0·01 to 1·0 mol%) was measured. The value of the activation energy for orientation of the dipoles {Ce³⁺-F^? interstitial} was determined to be H = (0·46 ± 0·01) eV. The frequency factor was found to have the value τ_o = (5 ± 1) × 10^?15 sec, giving for the vibrational frequency of the interstitial the value ν_o = (5 ± 1) × 10¹³ sec^?1.The number of dipoles contributing to the dielectric loss peak was determined to be between 10¹⁷ and 8 × 10¹⁷ cm^?3 for the different doping amounts of Ce³⁺. Optical absorption measurements showed the existence of large aggregate bands. We could verify that there exists a second-order reaction of aggregation, which is responsible for the non-linearity found between optical absorption at 305 nm and the nominal concentration of Ce³⁺ in the samples. On the other hand, if we assume that the centers which contribute to optical absorption at 305 nm are those also responsible for the relaxation peak, we find that the number contributing to each process is not the same. We can define an interaction radius R as the minimum separation between two dipoles allowing them to contribute to the relaxation peak. From our experimental data R ? 3·8 × 10^?7 cm.     

EPR of V2+ in SrCl2

The X-band EPR spectrum of SrCl₂:V has been measured at liquid nitrogen temperature. A signal associated with V²⁺ in a site of trigonal symmetry is observed. The EPR data have been explained using the spin hamiltonian $\textcolor{red}{}\text{= μ}{}_{\mathrm{\beta }}\text{H}\text{g}\text{?}\text{S}\text{+ D[S}{}^2{}_{\mathrm{z}}\text{?}\text{1}\text{3}\text{S(SH)] +}\text{S}\text{A}\text{?}\text{I}$, with D ? hv, g_∥ = 1.957 ± 0.004, g₆ = 1.954 ± 0.004, A_∥ = 230 ± 5 MHz, A₆ = 235 ± 5 MHz. This V²⁺ defect is similar to those previously reported in fluoride crystals with the fluorite structure.     

EPR and Optical Absorption Study of Cr3+-Doped Dipotassium Tetrachloropalladate

X-band electron paramagnetic resonance (EPR) study of Cr³⁺-doped dipotassium tetrachloropalladate single crystal is done at liquid nitrogen temperature. EPR spectrum shows two sites. The spin-Hamiltonian parameters have been evaluated by employing hyperfine resonance lines observed in EPR spectra for different orientations of crystal in externally applied magnetic field. The values of spin-Hamiltonian and zero-field splitting (ZFS) parameters of Cr³⁺ ion-doped DTP for site I are: g _x  = 2.096 ± 0.002, g _y  = 2.167 ± 0.002, g _z  = 2.220 ± 0.002, D = (89 ± 2) × 10^?4 cm^?1, E = (16 ± 2) × 10^?4 cm^?1. EPR study indicates that Cr³⁺ ion enters the host lattice substitutionally replacing K⁺ ion and local site symmetry reduces to orthorhombic. Optical absorption spectra are recorded at room temperature. From the optical absorption study, the Racah parameters (B = 521 cm^?1, C = 2,861 cm^?1), cubic crystal field splitting parameter (Dq = 1,851 cm^?1) and nephelauxetic parameters (h = 2.06, k = 0.21) are determined. These parameters together with EPR data are used to discuss the nature of bonding in the crystal.     

Temperature dependence of Mn2+ EPR in Sn2P2S6 near the phase transition

The X-band EPR spectrum of Mn²⁺ in Sn₂P₂S₆ was studied in the temperature rangeT=223–363 K. At room temperature the spin-Hamiltonian constants areg=2.00±0.01,B ₂ ⁰ =(163±3)·10^?4 cm^?1,B ₂ ² =(159±3)·10^?4 cm^?1,A=?(75±1)·10^?4 cm^?1. The effect of the invariance in temperature of the resonance magnetic fields in the narrow temperature rangeT=337–340 K and the model of the paramagnetic centre are discussed. According to EPR data a phase transition occurs atT=337 K. This transition from the paraelectric phase to the ferroelectric one is accompanied by a dramatic change in value of the spin-Hamiltonian constantB ₂ ⁰ .     

Hyperfine and nuclear quadrupole interactions in copper-doped cadmium oxalate trihydrate single crystals

Electron spin resonance experiments on Cu²⁺ doped in a single crystal of cadmium oxalate trihydrate grown by a slow diffusion technique have been carried out at 77 K. The major features of the ESR spectra can be attributed to divalent copper (3d⁹) in substitutional Cd²⁺ sites. Information has been gained about the hyperfine and quadrupole interactions concerning the ion. The spin-Hamiltonian parameters in the $\text{S =}\text{1}\text{2}$, $\text{I =}\text{3}\text{2}$ manifold are: g_x = 2.0211; g_y = 2.2249; g_z = 2.4536; A_x = +84.5 × 10^?4cm^?1; A_y = +16.8 × 10^?4cm^?1; $\text{A}{}_{\mathrm{z}}\text{= ?40.8 × 10 ×}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$; P_x = ?7.4 × 10^?4cm^?1; P_y = ?0.4 × 10^?4cm^?1; and P_z = +7.8 × 10^?4cm^?1. An evaluation of the asymmetry and quadrupole coupling parameters revealed that the ground state of the guest ion in Cd(COO)₂ · 3H₂O is 0.97|x² ?y₂ > +0.24 |3z² ? r² >.