The ground state and EPR spectrum in monoclinic KY(WO4)2:Nd single crystal

The electron paramagnetic resonance (EPR) of Nd³⁺ ion in KY(WO₄)₂ single crystal was investigated at T=4.2 K using an X-band spectrometer. The observed resonance absorption represents the complex superposition of three spectra corresponding to neodymium isotopes with different nuclear momenta. The EPR spectrum is characterized by a strong g-factor anisotropy. The temperature dependences of the g-factor were caused by strong spin-orbit and orbit-lattice coupling. The resonance lines become broader as temperature increases due to the short spin-lattice relaxation time.     

An optically detected electron-paramagnetic-resonance study of the luminescent triplet state of fresnoite,Ba2TiSi2O8

The luminescent center of the fresnoite crystal has been studied by electron paramagnetic resonance with optical detection at temperatures between 0.5 and 10 K. The results prove that the strong blue-green luminescence originates from a spin triplet state that is centered on the Ti ion. The C₄ symmetry of the Ti site is lost on excitation through a static Jahn-Teller effect, and eight sets of equivalent, strongly inhomogeneously broadened optically detected EPR signals appear. The signals are described by a spin hamiltonian withS=1, |D| ≈ 70 GHz, |E|=3.02 GHz, g_zz=1.93, and g_xx=g_yy ≡ g₃=2.0023. The lifetimes of the three sublevels aret _x =3.4,t _y=30,t _z=23 ms; the dominant radiative decay is from τ_x and polarized perpendicular to thec axis.     

EPR and optical absorption studies of Fe ions in sodium borophosphate glasses

Electron paramagnetic resonance (EPR) and optical absorption spectral investigations have been carried out on Fe³⁺ ions doped sodium borophosphate glasses (NaH₂PO₄-B₂O₃-Fe₂O₃). The EPR spectra exhibit resonance signals with effective g values at g=2.02, g=4.2 and g=6.4. The resonance signal at g=4.2 is due to isolated Fe³⁺ ions in site with rhombic symmetry whereas the g=2.02 resonance is due to Fe³⁺ ions coupled by exchange interaction in a distorted octahedral environment. The EPR spectra at different temperatures (123-295 K) have also been studied. The intensity of the resonance signals decreases with increase in temperature whereas linewidth is found to be independent of temperature. The paramagnetic susceptibility (χ) was calculated from the EPR data at various temperatures and the Curie constant (C) and paramagnetic Curie temperature (θ_p) have been evaluated from the 1/χ versus T graph. The optical absorption spectrum exhibits bands characteristic of Fe³⁺ ions in octahedral symmetry. The crystal field parameter (Dq) and the Racah interelectronic repulsion parameters (B and C) have also been evaluated and discussed.     

Die Hyperfeinstruktur des 32 P 1/2-Zustandes von Natrium im starken Magnetfeld

The hyperfine structure of the 3² P _1/2-state of²³Na has been measured by the optical double resonance technique in a magnetic field sufficiently strong to decoubleI andJ. The magnetic interaction constantA _1/2 and the Landég-factor were found to be:A _1/2=94.3(2) MHz,g=0.66581(12).     

Light-induced metastable defects in a-Si:H as elucidated by optically detected magnetic resonance measurements at 2K

We observed a gradual increase of a nonradiative recombination channel in a-Si:H by strong light exposure at 2K, i.e., an increase in the intensity of the quenching optically detected magnetic resonance (ODMR) line at g=2.005 and no change of the other quenching lines at g=2.004 and g=2.013. The sample with previous light soaking at 300K still showed a degradation of photoluminescence (PL) efficiency as much as that for the sample without previous light soaking, but no obvious change of the quelching ODMR lines. An increase of silicon dangling bond (db) density and the other nonradiative recombination process are suggested to explain the experimental results.     

The rate matching effect: A hidden property of aperiodic stochastic resonance

We study a system S generating Poisson events, and a corresponding dichotomous signal as well, perturbed by a system P, also generating Poisson events and a corresponding dichotomous signal. The rates of events productions for system and perturbation are gS and gP, respectively. We call S events the events produced by the system S and P events those produced by the perturbation P. We show that this simple model reproduces the essence of recent experimental and theoretical results on aperiodic stochastic resonance. More remarkably, this simplified version of aperiodic stochastic resonance allows us to discover a property that has been overlooked by the earlier research work. The rate matching condition gS=gP is the border between two distinctly different conditions: For gS<gP, the P events are attractors of the S events and for gS>gP they become repellers of the S events. The transition from the former to the latter condition is very marked and takes place in a short region of either gS or gP, depending on which is the parameter changed, thereby resulting in a discontinuous transition.     

EPR of Pb3+ in ZnO

The influence of doping zinc oxide with lead has been studied by electron paramagnetic resonance technique. Beside the signal nearg=1.956 (electron trapped in an oxygen vacancy) the resonances of Pb³⁺-ions are observed. Due to the strong Fermi-contact-hyperfine interaction of the 6s-electron with the Pb-207-nucleus the Breit-Rabi-diagram is evaluated with the experimentally obtainedA-value. The dependences of the resonances on optical illumination and temperature are investigated.     

Submillimeter-wave ESR measurements of Ca1−xCuO2 (x = 0.164) with edge-sharing CuO2 chains

Quasi-one-dimensional (1-D) cupric oxide Ca_1?xCuO₂ (x = 0.164) is the system with 25–40% hole-doped edge-sharing CuO₂ chains. However, the holes are almost localized in Ca_1?xCuO₂ and its magnetic susceptibility with a peak at 30 K was explained by the model considering both 1-D antiferromagnetic chains and spin dimers (Z. Hiroi, M. Okumura, Y. Nabeshima, T. Yamada, M. Takano: J. Phys. Soc. Jpn.69, 1824, 2000). To clarify the magnetic nature of Ca_1?xCuO₂, we performed submillimeter-wave electron spin resonance (ESR) measurements on a powder sample of Ca_0.83?6CuO₂. The resonance above 12 K showed typical powder ESR of Cu²⁺ and theg-values were determined to be g∥= 2.33 and g_⊥ = 2.06 from the analysis. The resonance below 12 K changed completely from ESR. The frequency-field relation of ESR at 1.8 K clearly showed the easy-axis type antiferromagnetic resonance.     

The oscillator strength of the πg shape resonance in the absorption K-spectrum of a nitrogen molecule

Magnitudes of the absorption cross sections of a nitrogen molecule are measured by the transmission method near the ionization K-threshold. Based on these data, the partial absorption NK cross sections are obtained and the oscillator strength of the π_g shape resonance is determined. It is found that the oscillator strength of the π_g-resonance increases as the optical density of nitrogen decreases. This phenomenon is interpreted as a result of the instrumental distortion effect (the thickness effect). By extrapolating to zero pressure, the oscillator strength of the π_g shape resonance is determined to be 0.29.     

Synthesis and characterization of chemically anchored adenosine with PHEMA grafted gold nanoparticles

The synthesis of chemically anchored adenosine with biocompatible poly(2-hydroxylethyl methacrylate) grafted gold nanoparticles (Ado-i-PHEMA-g-AuNPs) was realized by employing a simple strategy. Disulfide-containing poly(2-hydroxylethyl methacrylate) (DT-PHEMA) was initially synthesized by atom transfer radical polymerization (ATRP). The formation of DT-PHEMA was confirmed by ¹H-NMR and FT-IR. The molecular weight and molecular weight distribution were found to be 9.6 kg/mol and 1.40 from GPC analysis. DT-PHEMA was subsequently used for the synthesis of PHEMA-g-AuNPs by a grafting to protocol. The grafting of DT-PHEMA on the surface of AuNPs was confirmed by FT-IR, TGA, XPS, and EDX analyses. The particle size of the PHEMA-g-AuNPs was found to be ca. 5.0 nm from HR-TEM analysis. Boronic acid was used for functionalization of PHEMA-g-AuNPs, which was then subjected for covalent immobilization with adenosine via strong interaction between free hydroxyl groups of adenosine and boronic acid. Characterization and properties of the Ado-i-PHEMA-g-AuNPs were investigated by taking advantage from FT-IR, XPS, EDX, and UV-visible spectroscopy. The Ado-i-PHEMA-g-AuNPs nanocomposite exhibits a surface plasmon resonance peak at 586 nm which is red shifted from AuNPs (521 nm), indicating significant changes of surface property upon PHEMA-adenosine immobilization onto the surface of AuNPs.     

Theg-factor of the 9/2+ [624] ground state of183Os

The hyperfine interaction of¹⁸³OsFe has been studied with nuclear magnetic resonance on oriented nuclei after recoil implantation. Taking into account the resonance displacement due to quadrupole interaction |gμ _N H _HF/h|=149.9(2) MHz has been found. WithH _HF=?1,115(20) kG theg-factor of the 9/2⁺ [624] ground state of¹⁸³Os is deduced asg=(?)0.176(3).     

Theg-tensor anisotropy of the triplet state of the primary electron donor in the photosynthetic bacteriumRhodobacter sphaeroides by high-field (95 GHz) EPR

The anisotropy of theg-tensor of the light-induced triplet state of the primary electron donor (D) of the photosynthetic bacteriumRhodobacter sphaeroides is determined by electron-spin-echo-detected electron paramagnetic resonance at 95 GHz. Measurements on frozen solutions of quinone-depleted reaction centers yield g-values along the principal directions of the zero-field splitting tensor (Norris J.R., Budil D.E., Gast P., Chang C.H., ElKabbani O., Schiffer M.: Proc. Natl. Acad. Sci. USA86, 4335–4339, 1989).g-Values determined are: 2.00308, 2.00238, and 2.00138. The deviation from axial symmetry and thez-component of the g-tensor are smaller than observed in the cation radical of D.     

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.     

Quantum interference effects in a multi-driven transition Fg = 3 ↔ Fe = 2

We calculated and studied the quantum coherence effects of a degenerate transition F_g = 3 ↔ F_e = 2 system interacting with a weak linearly polarized (with σ_± components) probe light and a strong linearly polarized (with σ_± components) coupling field. Due to the competition between the drive Rabi frequency and the Zeeman splitting, electromagnetically induced transparency (EIT) and electromagnetically induced absorption (EIA) are appeared at the different values of applied magnetic field in both cases that the Zeeman splitting of excited state Δe is smaller than the Zeeman splitting of ground state Δg (i.e., Δe < Δg) and Δe > Δg. It is shown that the resonance is broader and contrasts are higher for Δe < Δg than that for Δe > Δg at the same Rabi frequencies of probe and coupling fields.     

EPR study of Gd3+ in a ferroelastic BiVO4 single crystal

Electron paramagnetic resonance of the Gd³⁺ ion in a ferroelastic BiVO₄ single crystal with a single domain, grown by the Czochralski method, has been investigated at room temperature using a Q-band spectrometer. The rotation patterns of the resonance fields measured in the crystallographic planes are analyzed using a monoclinic spin Hamiltonian. The principal Z-axis of the second-order zero-field splitting tensorD is found to be along the crystallographicb-axis. Spin Hamiltonian parameters together with the principal axes ofg andD tensors in the monoclinic plane show that the local site symmetry of Gd³⁺ ion in BiVO₄ crystal is monoclinic and that the Gd³⁺ ion substitutes for Bi³⁺ ion.     

Suppression of the local Jahn-Teller effect in nanostructures: Self-trapped holes and excitons in AgCl nanocrystals

A strong decrease in the g-factor anisotropy was revealed by optically detected magnetic resonance for self-trapped Jahn-Teller holes (both isolated and forming self-trapped excitons) in AgCl nanocrystals embedded into the KCl crystal lattice. This is evidence for considerable suppression of the Jahn-Teller effect in nanoobjects. The suggested mechanism of suppression of the Jahn-Teller effect in nanocrystals is associated with an additional deformation field arising in nanocrystals owing to a strong vibronic interaction at the interface.     

EPR and photoluminescence properties of green light emitting LaAl11O18:Mn phosphors

The LaAl₁₁O₁₈:Mn²⁺ powder phosphor has been prepared using a self-propagating synthesis. Formation and homogeneity of the LaAl₁₁O₁₈:Mn²⁺ phosphor has been verified by X-ray diffraction and energy dispersive X-ray analysis respectively. The EPR spectra of Mn²⁺ ions exhibit resonance signals with effective g values at g≈4.8 and g≈1.978. The signal at g≈1.978 exhibits six-line hyperfine structure and is due to Mn²⁺ ions in an environment close to tetrahedral symmetry, whereas the resonance at g≈4.8 is attributed to the rhombic surroundings of the Mn²⁺ ions. It is observed that the number of spins participating in resonance for g≈1.978 increases with decreasing temperature obeying the Boltzmann law. Upon 451 nm excitation, the photoluminescence spectrum exhibits a green emission peak at 514 nm due to ⁴T₁ (G)→⁶A₁ (S) transition of Mn²⁺ ions. The crystal field parameter Dq and Racah inter-electronic repulsion parameters B and C have been evaluated from the excitation spectrum.     

Method for measuring the anomalous magnetic moment of free electrons

It is shown that a previously described method for measuring the spin resonance of free electrons in a trap can also be used to measure their (g-2) anomaly. The electrons are trapped in an electrostatic quadrupole field with a superimposed homogeneous axial magnetic field, and are polarized by spin exchange. The spin and (g-2) resonance are monitored through the spin dependence of the excitation processe+Na (3S)→e+Na(3P). Calculations are made of the energy levels and transition probabilities of the trapped electrons.     

A naturally induced hole center in the mineral hypersthene

In natural hypersthene a paramagnetic center in triclinic site symmetry was detected by electron paramagnetic resonance with the following spin. Hamiltonian parameters:g _xx=2.0104,g _yy=2.0256,g _zz=2.0090. This center is most likely formed as a hole on an oxygen of the SiO₄ unit. No hyperfine splitting was detected at room temperature. The EPR signal disappears after heating the crystal at 773 K for 1 h although the colour does not bleach.     

ESR experiments with egg shells of chickens

The electron spin resonance spectra fromGallus domesticus egg shells exhibit a strong free radical singlet, a spectrum due to Mn²⁺ ions in a calcite site, a low field line line atg≈30/7 due to Mn²⁺ in a rhombic site, and spectral lines arising from Fe³⁺ ions. Details of the ESR spectral lines did not correlate with fertile, non-fertile or color type egg-shell characteristics.