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.     

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⁺.     

Optical absorption by Nd<Superscript>3+</Superscript> and Gd<Superscript>3+</Superscript> ions in epitaxial films grown on Gd<Subscript>3</Subscript>Ga<Subscript>5</Subscript>O<Subscript>12</Subscript> substrates from a lead-containing solution melt

Epitaxial films of composition (Gd,Nd)₃Ga₅O₁₂ or (Gd,Y,Nd)₃Ga₅O₁₂ with a neodymium content varying from 0.3 to 15 at. % are grown by liquid-phase epitaxy from a supercooled PbO-B₂O₃-based solution melt on Gd₃Ga₅O₁₂(111) substrates. The optical absorption spectra of the epitaxial films grown are measured in the wavelength range 0.2–1.0 µm. The results of interpreting the absorption bands observed in the spectra are used to construct the energy level diagrams of Nd³⁺ and Gd³⁺ ions in the matrices of the epitaxial films.     

PL Properties of Sr<Subscript>2</Subscript>CeO<Subscript>4</Subscript> With Eu<Superscript>3+</Superscript> and Dy<Superscript>3+</Superscript> for Solid State Lighting Prepared by Precipitation Method

Photoluminescence studies of pure and Dy³⁺, Eu³⁺ doped Sr₂CeO₄ compounds are presented by oxalate precipitation method for solid state lighting. The prepared samples also characterized by XRD, SEM (EDS) and FTIR spectroscopy. The pure Sr₂CeO₄ compound displays a broad band in its emission spectrum when excited with 280 nm wavelength, which peaks centered at 488 nm, which is due to the energy transfer between the molecular orbital of the ligand and charge transfer state of the Ce⁴⁺ ions. Emission spectra of Sr₂CeO₄ with different concentration of Dy³⁺ ions under near UV radiation excitation, shows that intensity of luminescence spectra is found to be affected by Dy³⁺ ions, and it increases with adding some percentages of Dy³⁺ ions. The maximum doping concentration for quenching is found to be Dy³⁺?=?0.2 mol % to Sr²⁺ions. The observed broad spectrum from 400 to 560 nm is mainly due to CT transitions in Sr₂CeO₄ matrix and some fractional contribution of transitions between ⁴F_9/2 → ⁶H_15/2 of Dy³⁺ ions. Secondly the effect of Eu³⁺ doping at the Sr²⁺ site in Sr₂CeO₄, have been studied. The results obtained by doping Eu³⁺ concentrations (0.2 mol% to 1.5 mol%), the observed excitation and emission spectra reveal excellent energy transfer between Ce⁴⁺ and Eu³⁺. The phenomena of concentration quenching are explained on the basis of electron phonon coupling and multipolar interaction. This energy transfer generates white light with a color tuning from blue to red, the tuning being dependent on the Eu³⁺ concentration. The results establish that the compound Sr₂CeO₄ with Eu³⁺?=?1 mol% is an efficient “single host lattice” for the generation of white lights under near UV-LED and blue LED irradiation. The commission internationale de I’Eclairage (CIE) coordinates were calculated by Spectrophotometric method using the spectral energy distribution of prepared phosphors.     

Effects of Gd<Superscript>3+</Superscript> modifications on the photoelectrochemical properties of TiO<Subscript>2</Subscript>-based dye-sensitized solar cells

In this paper, TiO₂ particles (~30 nm) modified with Gd₂O₃-coating layer (~2 nm) for dye-sensitized solar cells (DSSCs) were fabricated via the hydrothermal method. Among the solar cells based on the Gd³⁺-doped TiO₂ photoanodes, the optimal conversion efficiency was obtained from the 0.025Gd³⁺-modified TiO₂-based cell, with a 17.7% improvement in the efficiency as compared to the unmodified one (7.18%). This enhancement was probably due to the improved UV radiation harvesting via a down-conversion luminescence process by Gd³⁺ ions, enhancement of visible light absorption and improved dye loading capacity. In addition, after Gd modification, a thin coating could be formed on the TiO₂ nanoparticles, which worked as an energy barrier and resulted in a lower charge recombination.     

Electrical properties of heavily doped fluorite-structured BaF2:RF3 (R=La, Pr, Nd, Gd, Tb, Y, Sc) single crystals

The superionic conductivity and dielectric response of heavily doped fluorite-structured Ba_1−xR_xF_2+x (R=La, Pr, Nd, Gd, Tb, Y, Sc; x=0.005–0.45) crystals are reported. The highest ionic conductivity is found for R=Sc and x=0.1. Upon ScF₃ doping, small Sc³⁺ ions rearrange their surroundings, create excessive fluoride interstitial ions and bring about a high ionic conductivity. For each dopant, the concentration dependence of the ionic conductivity is non-linear. A monotonous concentration dependence of the ionic conductivity is found only for La³⁺ doping. Upon doping with Nd³⁺, Gd³⁺, Tb³⁺, Y³⁺ and Sc³⁺ ions, a conductivity maximum is observed at x=0.1–0.2. Upon Pr³⁺ doping, this maximum is split. The influence of defect clustering on the concentration dependence of the conductivity is discussed. Paper presented at the 6th Euroconference on Solid State Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999.     

Submillimeter ESR spectra of Fe<Superscript>2+</Superscript> ions in synthetic and natural beryl crystals

Electron spin resonance spectra of non-Kramers bivalent iron (Fe²⁺) ions have been detected in synthetic and natural beryl crystals with an iron impurity. The observed ESR spectra have been attributed to resonance transitions of Fe²⁺ ions from the ground (singlet) state to excited (doublet) levels with the splitting Δ = 12.7 cm^–1 between the levels. The experimental angular and frequency dependences of the resonance field of the ESR signal have been described by the spin Hamiltonian with the effective spin S = 1. The analysis of the ESR data and optical absorption spectra indicates that the Fe²⁺ ions are situated in tetrahedral positions and substitute Be²⁺ cations in the beryl structure.     

Microstructural and magnetic properties of Ax:Zn1-xO (A=Mn,Gd and Mn/Gd) nanocrystals

We report the microstructural and magnetic properties of transition (3d) and rare earth (4f) metal substituted into the A_x:Zn_1?xO (A=Mn, Gd and Mn/Gd) nanocrystal samples synthesized by solgel method. The structural properties and morphology of all samples have been analysed using X-ray diffraction (XRD) method and scanning electron microscopy. The impurity phase in the XRD patterns for all samples is not seen, except (Mn/Gd):ZnO sample where a very weak secondary phase of Gd₂O₃ is observed. Due to the large mismatch of the ionic radii between Mn²⁺ and Gd³⁺ ions, the strain inside the matrix increases, unlike the crystallite size decreases with the substitution of Mn and Gd into ZnO system. A couple of additional vibration modes due to the dopant have been observed in Raman spectrum. The magnetic properties have been studied by vibrating sample magnetometer. The magnetic hysteresis shows that Mn:ZnO and Gd:ZnO have soft ferromagnetic (FM) behaviour, whereas (Mn/Gd):ZnO has strong FM behaviour at room temperature (RT). The enhancement of ferromagnetism (FM) in (Mn/Gd):ZnO sample might be related to short-range FM coupling between Mn²⁺ and Gd³⁺ ions via defects potential and/or strain-induced FM coupling due to the expansion lattice by doping. The experimental results indicate that RTFM can be achieved by co-substitution of 3d and 4f metals in ZnO which can be used in spintronics applications.     

Effect of Gd doping on structural, electrical and magnetic properties of BiFeO3 electroceramic

Room temperature multiferroic electroceramics of Gd doped BiFeO₃ monophasic materials have been synthesized adopting a slow step sintering schedule. Incorporation of Gd nucleates the development of orthorhombic grain growth habit without the appearance of any significant impurity phases with respect to original rhombohedral (R3c) phase of un-doped BiFeO₃. It is observed that, the materials showed room temperature enhanced electric polarization as well as ferromagnetism when rare earth ions like Gd doping is critically optimized (x=0.15) in the composition formula of Bi_1+2xGd_2x/2Fe_1−2xO₃. We believe that magnetic moment of Gd⁺³ ions in Gd doped BiFeO₃ tends to align in the same direction with respect to ferromagnetic component associated with the iron sub lattice. The dielectric constant as well as loss factor shows strong dispersion at lower frequencies and the value of leakage current is greatly suppressed with the increase in concentration of x in the above composition. Addition of excess bismuth and Gd (x=0.1 and 0.15) caused structural transformation as well as compensated bismuth loss during high temperature sintering. Doping of Gd in BiFeO₃ also suppresses spiral spin modulation structure, which can change Fe-O-Fe bond angle or spin order resulting in enhanced ferromagnetic property.     

Photoluminescence properties of Y0.75-xGdxAl0.10BO3:Eu3+0.10, 0.05R3+ (R= Sc, Bi) (0.00≤x≤0.45)

Y$_{0.75 - x}$Gd_xAl_0.10BO$₃:Eu$^{3+}_0.10, 0.05R³⁺ ($R$=Sc, Bi) ($0.00 ≤ x ≤ 0.45$) powder samples are prepared by solid-state reaction and their luminescence properties are investigated. With the replacement of Y³⁺$ ions by Sc³⁺$ (or Bi³⁺)$ and Gd³⁺$ ions in (Y,Al)BO$₃:Eu, the intensities of emission at 254 and 147~nm are remarkably improved, because Sc³⁺$ ions can absorb UV light and transfer the energy to Eu³⁺$ ions efficiently. Moreover, Gd³⁺$ and Bi$^{3 + }$ ions act as an intermediate ``bridge' between the sensitizer and the activator (Eu³⁺)$ in energy transfer to produce light in the (Y, Gd)BO$₃:Bi³⁺$, Eu³⁺$ system more effectively. After doping an appropriate concentration of Gd³⁺$ into Y$_{0.50}$Gd$_{0.25}$Al_0.10BO$₃:Eu³⁺_{0.01}$, Bi$^{3+}_{0.05}$, the emission intensity reaches its maximum, which is nearly 110{\%} compared with the red commercial phosphor (Y,Gd)BO$₃:Eu and better chromaticity coordinates (0.650, 0.350) are obtained.     

Luminescence and time-resolved spectroscopy properties of (Gd1−xEux)(BO2)3 multicrystals

(Gd_1?xEu_x)(BO₂)₃ (0≤x≤1) phosphors are synthesized by traditional high temperature solid state reaction. The photoluminescence (PL) properties of Gd(BO₂)₃ and Gd(BO₂)₃ activated with Eu³⁺ are investigated. The PL spectra exhibit the typical characteristic emission and excitation of Gd³⁺ and Eu³⁺ ions, and support the energy transfer taking place from Gd³⁺ to Eu³⁺ ions. The relationship between Eu³⁺ doping concentration and emission intensity is also studied. Even if all of the Gd³⁺ ions are substituted by Eu³⁺ ions, the concentration quenching between Eu³⁺ happens. However, the quenching is not complete. The luminescence decay curves are measured, and the lifetimes become short with the Eu³⁺ content increasing. The decreasing Gd³⁺ lifetimes also indicates that there exists efficient energy transfer between Gd³⁺ and Eu³⁺ ions.     

中子探测晶体Li6Gd(BO3)3:Ce的光谱特性研究

文章用提拉法生长出Li₆Gd(BO₃)₃:Ce晶体,并对其光谱性能与发光过程进行了探索. 借助于真空紫外-紫外透过光谱测试,发现晶体的透过光谱中存在Ce³⁺离子和Gd³⁺的特征吸收峰,同时还存在与Ce⁴⁺离子相关的电荷迁移带. 对晶体的真空紫外-紫外激发发射光谱进行研究发现,在晶体存在着Ce³⁺离子的5d→4f辐射跃迁发光与Gd³⁺离子的4f→4f辐射跃迁发光,而且存在着Gd³⁺→Ce³⁺之间的能量传递. 对Li₆Gd(BO₃)₃:Ce晶体的X射线与γ射线激发发射光谱研究可知,晶体在高能射线激发下的闪烁光主要是Ce³⁺离子的发光. 关键词： 6Gd(BO₃)₃:Ce晶体')" href="#">Li₆Gd(BO₃)₃:Ce晶体 真空紫外-紫外透过光谱 真空紫外-紫外激发发射光谱 能量传递     

Luminescence and thermally stimulated recombination processes in Li<Subscript>6</Subscript>Gd(BO<Subscript>3</Subscript>)<Subscript>3</Subscript>:Ce<Superscript>3+</Superscript> crystals

The luminescence and thermally stimulated recombination processes in lithium borate crystals Li₆Gd(BO₃)₃ and Li₆Gd(BO₃)₃:Ce have been studied. The steady-state luminescence spectra under X-ray excitation (X-ray luminescence), temperature dependences of the intensity of steady-state X-ray luminescence (XL), and thermally stimulated luminescence (TSL) spectra of these compounds have been investigated in the temperature range of 90–500 K. The intrinsic-luminescence 312-nm band, which is due to the ⁶ P _J → ⁸ S _7/2 transitions in Gd³⁺ matrix ions, dominates in the X-ray luminescence spectra of these crystals; in addition, there is a wide complex band at 400–420 nm, which is due to the d → f transitions in Ce³⁺ impurity ions. It is found that the steady-state XL intensity in these bands increases several times upon heating from 100 to 400 K. The possible mechanisms of the observed temperature dependence of the steady-state XL intensity and their correlation with the features of electronic-excitation energy transfer in these crystals are discussed. The main complex TSL peak at 110–160 K and a number of minor peaks, whose composition and structure depend on the crystal type, have been found in all crystals studied. The nature of the shallow traps that are responsible for TSL at temperatures below room temperature and their relation with defects in the lithium cation sublattice are discussed.     

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     

Thermo and photoluminescence properties of Eu activated hexagonal, monoclinic and cubic gadolinium oxide nanorods

Different phases of Eu³⁺ activated gadolinium oxide (Gd (OH)₃, GdOOH and Gd₂O₃) nanorods have been prepared by the hydrothermal method with and without cityl trimethyl ammonium bromide (CTAB) surfactant. Cubic Gd₂O₃:Eu (8 mol%) red phosphor has been prepared by the dehydration of corresponding hydroxide Gd(OH)₃:Eu after calcinations at 350 and 600 °C for 3 h, respectively. When Eu³⁺ ions were introduced into Gd(OH)₃, lattice sites which replace the original Gd³⁺ ions, a strong red emission centered at 613 nm has been observed upon UV illumination, due to the intrinsic Eu³⁺ transition between ⁵D₀ and ⁷F configurations. Thermoluminescence glow curves of Gd (OH)₃: Eu and Gd₂O₃:Eu phosphors have been recorded by irradiating with gamma source (⁶⁰CO) in the dose range 10-60 Gy at a heating rate of 6.7 °C sec⁻¹. Well resolved glow peaks in the range 42-45, 67-76, 95-103 and 102-125 °C were observed. When γ-irradiation dose increased to 40 Gy, the glow peaks were reduced and with increase in γ-dose (50 and 60 Gy) results the shift in first two glow peak temperatures at about 20 °C and a new shouldered peak at 86 °C was observed. It is observed that there is a shift in glow peak temperatures and variation in intensity, which is mainly attributed to different phases of gadolinium oxide. The trapping parameters namely activation energy (E), order of kinetics (b) and frequency factor were calculated using peak shape and the results are discussed.     

ESR study of Mn2+ in sodium β″-alumina

ESR measurements are reported on Mn²⁺ diffused into sodium β″-alumina. The spin Hamiltonian parameters obtained are g₁₁ = 2.0000(2), $\text{g}{}_{\mathrm{?}}\text{= 2.0019(2)}$, A₁₁ = ?8.39(3) mT, $\text{A}{}_{\mathrm{?}}\text{= ?8.33(3)}\text{mT}$ and D = ?7.20(5) mT. The site position of the Mn²⁺ ions is discussed and compared to published results for Mn²⁺ in sodium β-alumina.     

Electron magnetic resonance of gadolinium-doped calcium fluoride

Electron magnetic resonance (EMR) spectra of gadolinium-doped calcium fluoride have been studied at room temperature for Gd concentrations between 0.01 and 2.00 mol%. Gd³⁺ ions in sites with two different symmetries were observed. One of the sites, with cubic symmetry, is unstable at room temperature and decays with a time constant of 2.2 day⁻¹. The other site, with tetragonal symmetry, is stable and is attributed to Gd³⁺ ions in substitutional sites next to a charge-compensating F⁻ interstitial ion. The linewidth and intensity of the EMR spectrum with tetragonal symmetry increase with increasing Gd concentration. A theoretical calculation based on the concentration dependence of the EMR linewidth yields an effective range of the exchange interaction between Gd³⁺ ions in CaF₂ of 0.774 nm, of the same order as that of Gd³⁺ ions in other cubic ionic compounds.     

VUV 5<Emphasis Type="Italic">d</Emphasis>-4<Emphasis Type="Italic">f</Emphasis> luminescence of Gd<Superscript>3+</Superscript> and Lu<Superscript>3+</Superscript> ions in the CaF<Subscript>2</Subscript> host

The first observation and characterization of Lu³⁺ 4f ¹³5d-4f ¹⁴ luminescence from the CaF₂: Lu³⁺ crystal are reported, and the multisite structure in the spectra of Ce³⁺, Gd³⁺, and Lu³⁺ ions in the CaF₂ host is analyzed with the high-resolution VUV spectroscopy technique using synchrotron radiation. It is shown that vibronic structure in the emission and excitation spectra of interconfigurational transitions in Gd³⁺ and Lu³⁺ ions doped into CaF₂ differs from that observed for Ce³⁺ ions entering mainly at the tetragonal (C _4v ) sites. However, the exact types of sites in which the Gd³⁺ and Lu³⁺ ions reside in a CaF₂ lattice cannot be identified using only the obtained experimental spectroscopid data. The text was submitted by the authors in English.     

Growth defect W<Superscript>3+</Superscript>-W<Superscript>2+</Superscript> of CdWO<Subscript>4</Subscript> crystals

CdWO₄ crystals grown by the Czochralski method at the low-temperature gradient were investigated with electron spin resonance (ESR) spectroscopy. ESR spectra did not contain the spectra of impurity ions typical for the CdWO₄ structure, i.e., Fe³⁺, Mn²⁺, and Cr³⁺. At the same time, in the studied crystals a complex ESR spectrum having the hyperfine structure due to two nonequivalent tungsten atoms was observed (W¹⁸³;I=1/2; natural abundance, 14.28%). Angular dependence analysis and simulation of ESR spectra have shown that this novel spectrum is described by a spin-Hamiltonian with the following parameters:D=839 G,E=80 G,g _xx=2.01,g _yy=1.97,g _zz=1.987 and electron spinS=7/2. There is one magnetically nonequivalent position of the center in the crystal structure and the direction ofD _zz andg _zz corresponds to the direction of W_n-W_n+2 (or Cd_n-Cd_n+2) in the crystal structure. Because of the fact that it is in principle impossible to achieve the electron stateS=7/2 for the d-shell of one transition metal ion and taking into account the fact that such electron state is realized for two nonequivalent tungsten atoms, we suppose the defect structure to be the chain W²⁺-M⁺-W³⁺. In the structure of this defect the ion M⁺ is diamagnetic, the ions W²⁺ and W³⁺ have electron spinS=2 andS=3/2, respectively. The necessary condition for such defect to exist is to place this chain of ions in cadmium positions for the charge compensation. the reason for such defects to form is supposed to be the incorporation of M⁺ ions into the CdWO₄ lattice. The presence of W²⁺ and W³⁺ in Cd positions in the defect structure provides the charge compensation and the lowering of the lattice stress.     

Effective hyperfine temperature in frustrated Gd 2Sn 2O 7: two level model and 155Gd Mössbauer measurements

Using ¹⁵⁵Gd M?ssbauer spectroscopy down to 27 mK, we show that, in the geometrically frustrated pyrochlore Gd₂Sn₂O₇, the Gd³⁺ hyperfine levels are populated out of equilibrium. From this, we deduce that the hyperfine field, and the correlated Gd³⁺ moments which produce this field, continue to fluctuate as T ↦ 0. With a model of a spin 1/2 system experiencing a magnetic field which reverses randomly in time, we obtain an analytical expression for the steady state probability distribution of the level populations. This distribution is a simple function of the ratio of the nuclear spin relaxation time to the average electronic spin-flip time. In Gd₂Sn₂O₇, we find the two time scales are of the same order of magnitude. We discuss the mechanism giving rise to the nuclear spin relaxation and the influence of the electronic spin fluctuations on the hyperfine specific heat. The corresponding low temperature measurements in Gd₂Ti₂O₇ are presented and discussed. Received 17 October 2001 Published online 6 June 2002