Electron paramagnetic resonance studies of GdMnO3 single crystal and thin film deposited onto a LaAlO3 substrate

Electronic paramagnetic resonance (EPR) spectra of a GdMnO₃ single crystal and GdMnO₃/LaAlO₃ thin film have been measured at X- and Q-band frequencies in the temperature range from 4.2 to 300 K. It is found that the EPR spectrum of a GdMnO₃ single crystal consists of only one broad exchange-narrowed line. Unusual magnetism is observed at the interface between the GdMnO₃ thin film and LaAlO₃ substrate, where it is possible to see the fine structure of the EPR spectrum for a Gd³⁺ ion. The parameters characterizing the fine structure related to the Gd³⁺ ion in the GdMnO₃ film deposited onto the LaAlO₃ substrate are determined.     

EPR of Gd3+ in single crystal colquiriite and analysis of the spin Hamiltonian tensorsB 4 andB 6

In single crystal colquiriite LiCaAlF₆ doped with Gd³⁺ ions two EPR spectra of the Gd³⁺ ions with the Laue site-symmetry groups C_i and C_3i were observed. The spectrum angular dependence for trigonal Gd³⁺ centre was investigated in detail and corresponding spin Hamiltonian parameters were fitted. From analysis of the spin Hamiltonian tensorsB ₄ andB ₆ it was established that Gd³⁺ with the Laue group C_3i substitutes at Ca²⁺ site with the excess charge compensation by an ion located along the threefold axis from this site. The transformation formulas for a sixth-rank irreducible Hermitian tensor under coordinate rotation are tabulated in an explicit form. By using the EPR data for Gd³⁺ substituted in a variety of host crystals, the fourth-rank and sixth-rank tensors of Gd³⁺ spin Hamiltonians were tabulated and correlated with structures of the coordination polyhedra at substitution sites. The results suppose a predominance of quadratic crystal field contributions into the spin Hamiltonian tensorB ₄ of Gd³⁺.     

Pulsed EPR spectroscopy of Gd3+ centers in Ca1−x R x F2+x (R=La, Y) mixed crystals

A study of Gd³⁺ centers in Ca_1?x R _x F_2+x (R=La, Y) crystals using pulsed EPR spectroscopy is presented. The echo-induced EPR (ESE-EPR) spectrum shows, besides the signal of slightly perturbed cubic Gd³⁺ centers, a broad signal at g≈2 due to Gd³⁺ centers at low symmetry sites. To describe the effects of R³⁺ ions on the EPR Gd³⁺, a model, including cubic and linear R³⁺?2F _i ^? centers, is developed. Its predictions are compared with the experimental results. The composition dependence of the EPR signal due to slightly perturbed cubic Gd³⁺ centers in mixed Ca_1?x R _x F_2+x crystals is explained taking into account the different clustering tendency in La and Y crystals. Moreover, the formation of mixed clusters involving R³⁺ and Gd³⁺ ions is proposed for both series of samples. A greater clustering trend is found in the Y crystals than in the La ones. Gd³⁺ ions are found to be a “non innocent” paramagnetic probe for structural studies in these mixed crystals.     

Electron paramagnetic resonance of Mn2+ and Gd3+ in Pr2Zn3(NO3)12.24 H2O single crystals

The electron paramagnetic resonance of Mn²⁺ and Gd³⁺ doped in Pr₂Zn₃(NO₃)₁₂.24H₂O single crystals has been studied at X-band. Mn²⁺ substitutes for two Zn²⁺ sites, while Gd³⁺ substitutes for single type of Pr³⁺ sites. The spin-Hamiltonian analysis of the EPR spectra is presented at 298 K as well as 77 K.     

The domain structure of ferroelastic BiVO4 crystal studied by Gd EPR

The domain structure of ferroelastic BiVO₄ single crystal has been investigated using the electron paramagnetic resonance (EPR) of the Gd³⁺ ions existing as an impurity in the crystal. Two sets of Gd³⁺ EPR signals were obtained in the crystallographic ca-plane. These two sets of signals originated not from the two kinds of substitutional sites but from the twin-domain structure in the host crystal. It is found that the BiVO₄ crystal investigated with Gd³⁺ EPR has the prominent (W-plane) domain wall. The domain structure is stable in contrast with a previous report by Baran et al. From the observed W-plane of the domain wall, it is suggested that a ferroelastic transition in BiVO₄ is 4/mmm F 2/m instead of 4/m F 2/m. The model of twinning mechanism improved in a previous report by Mn²⁺ EPR is confirmed by Gd³⁺ EPR.     

Nonlinear properties of Pb5Ge3O11:Gd3+ in an electric field: Paramagnetic resonance

This paper discusses the field and temperature dependences of the shift in position of EPR signals in an external electric field, which is linearly related to the polarization in the paraelectric phase of Pb₅Ge₃O₁₁:Gd³⁺. Fiz. Tverd. Tela (St. Petersburg) 39, 1643–1644 (September 1997)     

Electron paramagnetic resonance of Gd<Superscript>3+</Superscript> aqua complexes in vitrified aqueous solutions and Gd<Superscript>3+</Superscript> aqua ions adsorbed on the capillary surface

Electron paramagnetic resonance (EPR) spectra of Gd³⁺ aqua complexes are measured in dilute aqueous solutions of Gd(NO₃)₃ (C<0.2 M) at room temperature. A partial resolution of the fine structure observed in the spectra is characteristic of solid disordered systems and results in an increase in the effective width of the EPR line with a decrease in the Gd³⁺ concentration. This phenomenon is explained in terms of adsorption of Gd³⁺ aqua ions on the surface of the measuring capillaries. The fine structure is revealed in the EPR spectra of Gd(NO₃)₃ aqueous solutions, namely, the Gd(NO₃)₃ solutions vitrified at a temperature of 77 K (with an addition of 10–15 vol % glycerol) and Gd(NO₃)₃ solutions quasi-vitrified at 298 K (with an addition of 70–90 vol % glycerol). Analysis of the EPR spectra demonstrates that these solutions contain two types of aqua complexes with fine structure parameters D₁=180 G and D₂=580 G. Reasoning from a comparison with x-ray diffraction data, the fine structure parameters D₁ and D₂ are assigned to higher symmetric eight-coordinate and lower symmetric nine-coordinate Gd³⁺ aqua complexes, respectively.     

掺Gd3+,Y3+对PbWO_4低温热释光的影响

通过热释光方法研究了PbWO₄(PWO),PWO:Y³⁺,PWO:Gd³⁺多晶粉末及PWO,PWO:Y单晶的低温(<300K)热释光现象.多晶粉末中,掺杂Y³⁺或Gd³⁺都会大大降低甚至消除200K附近的热释光峰,同时产生新的热释光峰,分别位于125和150K(掺Y掺Gd).这表明掺三价离子除了起到电荷补偿作用以减少Pb³⁺,O^-浓度外,还可以产生新的陷阱能级.对于PWO:Y单晶,掺杂Y³⁺可以消除253K的热释光峰,即消除较深(～0.89eV)的陷阱,但PWO单晶中较浅的陷阱(～0.42eV)对应130K热释光峰仍然存在,对此进行讨论,它最可能源于氧空位缺陷.根据Pb³⁺,Gd³⁺,Y³⁺的电子库仑势不同,在PWO晶体中替代Pb²⁺后形成的电子陷阱深度有别(E_Pb>E_Gd>E_Y),从而解释了相应的热释光峰值温度的不同 关键词： 4')" href="#">PbWO₄ Y和Gd掺杂 热释光 陷阱     

EPR of Gd3+ - doped CeF3 single crystal: Linewidth variation with temperature

Detailed X-band EPR study of a Gd³⁺-doped CeF₃ single crystal has been made from 4.2 to 473 K, with particular attention to EPR linewidths. In general, it is found that there are four regions over which the log-log plot of the linewidth versus temperature is linear, implying separate power-law dependences of the linewidth. Gd³⁺ spin Hamiltonian parameters in CeF₃ have been estimated at various temperatures from the line positions. From the linewidth variation with temperature the Debye temperature has determined to be about 140 K.     

EPR, Optical Absorption and Superposition Model Studies of Fe3+-Doped Diammonium Hexaaqua Magnesium Sulfate: A Case of Hyperfine Structure

An electron paramagnetic resonance (EPR) study of Fe³⁺-doped diammonium hexaaqua magnesium sulphate single crystal is carried out at liquid nitrogen temperature. EPR spectrum shows two sites. The spin-Hamiltonian parameters are evaluated from angular variation of observed hyperfine lines. Fe³⁺ ion enters the host lattice substitutionally at site I, replacing Mg²⁺, whereas it enters interstitially at site II. The local site symmetry of Fe³⁺ ion within the host lattice is orthorhombic. An optical absorption study is performed at room temperature. Using the optical absorption spectrum the bands are assigned and the Racah parameters (B and C) and cubic crystal field splitting parameter Dq are determined. The nature of metal–ligand bonding in the crystal is determined using EPR and optical data. Crystal field parameters and zero-field splitting parameters (ZFSPs) are evaluated theoretically for both the sites using superposition model and microscopic spin Hamiltonian together with perturbation equations, respectively. The theoretically evaluated ZFSPs are in good agreement with the experimental values.     

Temperature and pressure dependences of EPR spectra of Gd ion doped in the EuAl3(BO3)4 monocrystal

The ground state of Gd³⁺ ions substituting for trivalent europium in the EuAl₃(BO₃)₄ single crystal was studied by electron paramagnetic resonance (EPR) over the temperature range of 300-4.2 K and at pressures up to 9 kbar. The EPR spectra were analysed using the spin Hamiltonian of axial symmetry. The following parameters are reported: g=1.981±0.002, b₂⁰=280.18±0.12, b₄⁰=−12.95±0.08 and b₆⁰=0.61±0.12 (at Т=298 K). The distortions of the nearest environment of Gd³⁺ ion were analysed within the framework of the superposition model of crystal field.     

An EPR study of different Gd3+ centers in LiNbO3

Electron Paramagnetic Resonance (EPR) and Zero-(magnetic)-Field (paramagnetic) Resonance (ZFR) spectra have been observed for LiNbO₃:Gd. EPR spectra measured at 9 and 35 GHz consisted of at least seven independent patterns; all of predominantly axial symmetry and all ascribed to Gd³⁺. The two most intense patterns have been analyzed in detail, and while one was found to be axially symmetric the other, though predominantly axial, had a small rhombic crystal field term. The ZFR spectrum, measured between 1 and 18 GHz, consisted of at least two patterns of zero field transitions. Both EPR and ZFR spectra were found to be insensitive to variations in LiNbO₃ stoichiometry, c- of a-axis crystal growth direction, and various sample treatments.     

Observation of defect clustering in Gd-doped calcium fluoride

Abstract

Solid solutions Ca_1-xGd_xF_2+x for 3 × 10^?7≤ x ≤10^?1 have been studied by electron paramagnetic resonance (EPR) and ionic thermal currents (ITC). The EPR experiments show the presence of two single-ion sites a cubic and a tetragonal Gd³⁺ center which co-exist with comparable abundances for intermediate impurity concentrations. The cubic center predominates at very low and high concentrations. Seven different relaxation processes have been identified from the ITC spectra and the variation of their intensity vs. x was measured. The absolute concentrations of the cubic and nn Gd³⁺ dipoles were calculated. The scavenging of interstitial fluorines by the neutral clusters explains both the abundance of cubic sites at high concentration and the variety of orientable clusters detected by ITC.     

Temperature features of the EPR spectrum of GdMnO3: Single crystal and thin film GdMnO3/LaAlO3

Electron paramagnetic resonance (EPR) spectra of GdMnO₃ single crystal and GdMnO₃/LaAlO₃ thin film are measured at Q-band frequency in the temperature range of 4.2 to 300 K. The temperature dependence of parameters of the spin Hamiltonian corresponding to the monoclinic symmetry of such paramagnetic centers as Gd³⁺ ions in the GdMnO₃/LaAlO₃ film is determined.     

Pecularities of EPR spectra of the Gd impurity in the Sn-Rich Pb1−x Sn x Te(Gd) solid solutions

An electron paramagnetic resonance (EPR) experimental study of crystalline and powder p-Pb_1?x?y Sn _y Gd _y Te samples for various matrix compositionx and Gd contenty has been carried out. The study reveals that grinding the crystals into powder as well as their low-temperature annealing turns Gd impurity ions from the EPR-silent Gd²⁺ state to the EPR-active Gd³⁺ state, whereas high-temperature annealing in vacuum quenches EPR signals from Gd³⁺ ions. The experimental results are interpreted in terms of a model assuming that the trivalent charge state of the Gd impurity ions in lead and tin tellurides is a component part of the “substituting Gd impurity-Te vacancy” complex.     

Electron paramagnetic resonance and luminescence of Gd3+ in the mixed fluorides Ca1-xLaxF2+x and Ca1

Abstract

In this paper we present an study on the EPR and photoluminiscence spectra of Gd³⁺ in the mixed crystals Ca_0.998-xR_xGd_0.002F_0.002+x(x≤0.35, R=La or Y). For x <0.1 the EPR spectrum shows a main signal due to cubic Gd³⁺ that is broadened as x increases. Different broadenings are found for La and Y samples For high x values the EPR spectrum is similar to that in glass matrices. The results are explained taking to account a random second rank crystal field due to the extra charges associated with R³⁺ and fluorine intersitials. The ⁶P→⁶S emission of Gd³⁺ also has been measured. The influence of R concentration on this luminiscence has been studied.     

EPR and dielectric properties of Pb5Ge3O11 crystals with off-center Cu2+ ions

The electron paramagnetic resonance (EPR) and dielectric properties of Pb₅Ge₃O₁₁ crystals activated by copper ion are investigated. It is shown that Cu²⁺ ions replace Pb²⁺ in trigonal symmetry positions and occupy three off-center positions displaced from a crystal lattice site in a plane perpendicular to the polar axis C. The temperature variation of EPR spectra and dielectric properties indicates the presence of thermally activated jumps of Cu²⁺ ions between off-center positions. The EPR and dielectric data are used to determine the activation energy W=0.24 eV and the eigenfrequency τ ₀ ^?1 ～ 10¹² Hz of local dynamics of Cu²⁺ ions.     

The Formation of Dimeric Centers of Copper,Iron and Gadolinium in Modified Pb<Subscript>5</Subscript>Ge<Subscript>3</Subscript>O<Subscript>11</Subscript>

It is discovered that the electron paramagnetic resonance (EPR) spectrum of the doubly charged copper centers occurs in single crystals of Pb₅Ge₃O₁₁ doped with gadolinium or iron after annealing in an atmosphere containing chlorine and bromine. Similar annealing of the crystals doped with copper in a chlorine and fluorine atmosphere leads to redistribution of the intensities of the EPR spectra of two types of Cu²⁺ centers. The influence of annealing on the ongoing intensity of spectra of the dimeric triclinic centers Fe³⁺–A, Gd³⁺–A (where A represent Cl^?, Br^?, O^2?, F^?) was the subject of this research. Consideration is given to the mechanisms for changing the charge state and association of copper center with defects.     

Light-induced intrinsic defects in PLZT ceramics

This paper reports on an EPR study of a ferroelectric, 1.8/65/35, and an antiferroelectric, 2/95/5, of optically transparent Pb_1?y La_yZr_1?x Ti_xO₃ (PLZT) ceramics within a broad temperature range (20–300 K) after illumination at a wavelength of 365–725 nm. Illumination with ultraviolet light, whose photon energy corresponds to the band gap of these materials, at T<50 K creates a number of photoinduced centers: Ti³⁺, Pb⁺, and Pb³⁺. It is shown that these centers are generated near a lanthanum impurity, which substitutes for both the Pb²⁺ and, partially, Ti⁴⁺ ions through carrier trapping from the conduction or valence band into lattice sites. The temperature ranges of the stability of these centers are measured, and the position of their local energy levels in the band gap is determined. The most shallow center is Ti³⁺, with its energy level lying 47 meV below the conduction band bottom. The Pb³⁺ and Pb⁺ centers produce deeper local levels and remain stable in the 2/95/5 PLZT ceramics up to room temperature. The migration of localized carriers is studied for both ceramic compositions. It is demonstrated that, under exposure to increased temperature or red light, the electrons ionized into the conduction band from Ti³⁺ are retrapped by the deeper Pb⁺ centers, thus hampering the carrier drift in the band and the onset of photoconduction. The part played by localized charges in the electrooptic phenomena occurring in the PLZT ceramics is discussed.     

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.