Towards Determination of Distances Between Nanoparticles and Grafted Paramagnetic Ions by NMR Relaxation

We developed an approach for determining distances between carbon nanoparticles and grafted paramagnetic ions and molecules by means of nuclear spin–lattice relaxation data. The approach was applied to copper-, cobalt- and gadolinium-grafted nanodiamonds, iron-grafted graphenes, manganese-grafted graphene oxide and activated carbon fibers that adsorb paramagnetic oxygen molecules. Our findings show that the aforementioned distances vary in the range of 2.7–5.4 Å and that the fixation of paramagnetic ions to nanoparticles is most likely implemented by means of the surface functional groups. The nuclear magnetic resonance data data are compared with the results of electron paramagnetic resonance measurements and density functional theory calculations.     

The Role of Metal Ions in the Study of Ancient Paper by Electron Paramagnetic Resonance

Samples from covers and endleaves of sixteenth to eighteenth century books in good conservation state from the Biblioteca Nazionale Marciana in Venice have been investigated by means of electron paramagnetic resonance (EPR) spectroscopy and optical microscopy to characterize the embedded paramagnetic species and to test differences and similarities of the materials in the two types of book components. We detected the Mn(II), Fe(III), and Cu(II) paramagnetic ions, and analyzed their EPR signals by comparing them with previous results in literature of EPR studies on paper. Interestingly, the Mn(II) EPR spectrum profile appears as a fingerprint for samples coming from the same book, either from cover or endleaf, and it looks different for samples extracted from different books. We discuss the role of EPR as a spectroscopic tool for characterizing the interaction of the ions with the paper components and as possible agents of degradation.     

Induced Intersystem Crossing at the Fluorescence Quenching of Laser Dye 7-Amino-1,3-Naphthalenedisulfonic Acid by Paramagnetic Metal Ions

The fluorescence and triplet state quenching of 7-amino-1,3-naphthalenesulfonic acid by paramagnetic metal ions have been investigated in an aqueous medium. The basic mechanism of the fluorescence quenching involves the static and dynamic electron transfer to the paramagnetic cation. The induced S₁→T₁ intersystem crossing at fluorescence quenching of the fluorophore by Cu²⁺ cation has been found. There is a correlation between triplet state quenching rate constants and values of the efficient paramagnetic susceptibility and spin of the cations. The rate constants for the quenching pathways have been calculated.     

Dispersion Relations for Proton Relaxation in Solid Dielectrics

Russian Physics Journal - Frequency-temperature spectra of the complex permittivity are studied for proton semiconductors and dielectrics using the methods of a quasi-classical kinetic theory of...     

Paramagnetic Ions in Distorted Perovskite YAlO3 Doped with Europium

Physics of the Solid State - In crystals of yttrium orthoaluminate doped with the 151Eu isotope, Eu2+, Cr3+, Gd3+, and Мо3+ paramagnetic centers are detected. The fine structure...     

Relaxation of Paramagnetic Centers during Modulation of a Stationary Magnetic Field

It has been found that the phase shift _min in the synchronous detection block that ensures the minimum amplitude of the EPR lines of ruby, diphenylpicrylhydrazyl, and MnSO₄·5H₂O, depends on the amplitude of the modulationH _m of a stationary magnetic field. The dependence of _min on H _m is explained by the inertial nature of the recovery of the stationary states of paramagnetic centers on a change in the magnetic field strength.     

Constructing Efficient and Thermostable Red-NIR Emitter via Cross Relaxation and Crystal-Field Engineering of Holmium-Based Perovskite-Type Half Metal

Lanthanide ions, as dopants, have evoked widespread research interest owing to the rich optical, magnetic, and electrical properties, but their luminescent intensity is always limited by typical concentration quenching. Herein, a holmium-based double perovskite of Cs₂NaHoCl₆ is reported, which surprisingly breaks through this barrier and achieves efficient red-NIR emission by virtue of the large unit cell, low phonon energy, high content of activators, and cross relaxation phenomenon between Ho³⁺. The heavy Ho³⁺ also endows the intriguing half-metallic nature with a down-spin conducting band and an up-spin insulating band. After performing ion doping on crystallographic sites of Na⁺ and Ho³⁺, the photoluminescence quantum yield of such red-NIR emitter under 450 nm excitation is dramatically promoted to 82.3%, benefiting from the improved crystal field environment that alleviates the parity forbidden rule and suppresses non-radiative recombination loss. Furthermore, the heat-favorable phonon-assisted population processes enable the robust photostability against thermal quenching. By combining a 450 nm chip, the red-NIR light-emitting diodes are fabricated, in which the wide-coverage NIR emissions are ideally suited for medical light source, night vision, nondestructive examination, and transmission imaging. It is believed that this work will open an avenue for enhancing the fluorescence of lanthanide ions and developing advanced spintronic materials.     

The Determination of Plutonium in the Presence of Fluorides Ions

The possibility of a direct determination of plutoniutn in the presence of hydrofluoric acid was studied.

Two redox titration methods based on the oxidation of Pu(III) and reduction of Pu(VI) were verified. Both methods were compared and an optimal procedure for determination of plutonium in the presence of fluoride ions was elaborated.     

Local NMR Relaxation of Dendrimers in the Presence of Hydrodynamic Interactions

We study the role of hydrodynamic interactions for the relaxation of segments’ orientations in dendrimers. The dynamics is considered in the Zimm framework. It is shown that inclusion of correlations between segments’ orientations plays a major role for the segments’ mobility, which reveals itself in the nuclear magnetic resonance relaxation functions. The enhancement of the reorientation dynamics of segments due to the hydrodynamic interactions is more significant for the inner segments. This effect is clearly pronounced in the reduced spectral density \(\omega J(\omega )\), maximum of which shifts to higher frequencies when the hydrodynamic interactions are taken into account.     

Rabi Oscillations of Paramagnetic Ions in Solids: Role of Electrostatic Interactions

We study the decay of Rabi oscillations of magnetically coupled impurity ions diluted in the solid. Electrostatic interactions between the ions treated as charged defects shift their g-factors and result in valuable correlations of their Larmor frequencies if the ions are close enough. We find an increase in the decay time of Rabi oscillations in comparison with the case of uncharged defects. The magnitude of the effect depends on the ratio between the impurity and the total defect concentrations, as well as on the type of the electron paramagnetic resonance line broadening mechanism (by random electric fields, electric field gradients, etc.). We present results in the arbitrary order of multipole expansion with respect to valence electron coordinates of the paramagnetic ion. Corresponding corrections to the decay times of Rabi oscillations of Nd³⁺ ions in CaWO₄ crystal are obtained.     

Determination of Very Slow Diffusion of Paramagnetic Ions by NMR Spectroscopy

In this paper, we propose a new method of measuring the very slow paramagnetic ion diffusion coefficient using a commercial high-resolution spectrometer. If there are distinct paramagnetic ions influencing the hydrogen nuclear magnetic relaxation time differently, their diffusion coefficients can be measured separately. A cylindrical phantom filled with Fricke xylenol gel solution and irradiated with gamma rays was used to validate the method. The Fricke xylenol gel solution was prepared with 270 Bloom porcine gelatin, the phantom was irradiated with gamma rays originated from a ⁶⁰Co source and a high-resolution 200 MHz nuclear magnetic resonance (NMR) spectrometer was used to obtain the phantom ¹H profile in the presence of a linear magnetic field gradient. By observing the temporal evolution of the phantom NMR profile, an apparent ferric ion diffusion coefficient of 0.50 μm²/ms due to ferric ions diffusion was obtained. In any medical process where the ionizing radiation is used, the dose planning and the dose delivery are the key elements for the patient safety and success of treatment. These points become even more important in modern conformal radio therapy techniques, such as stereotactic radiosurgery, where the delivered dose in a single session of treatment can be an order of magnitude higher than the regular doses of radiotherapy. Several methods have been proposed to obtain the three-dimensional (3-D) dose distribution. Recently, we proposed an alternative method for the 3-D radiation dose mapping, where the ionizing radiation modifies the local relative concentration of Fe²⁺/Fe³⁺ in a phantom containing Fricke gel and this variation is associated to the MR image intensity. The smearing of the intensity gradient is proportional to the diffusion coefficient of the Fe³⁺ and Fe²⁺ in the phantom. There are several methods for measurement of the ionic diffusion using NMR, however, they are applicable when the diffusion is not very slow.     

Phonon Scattering by Paramagnetic Ions of Europium and Samarium in Bismuth Ferrite

Physics of the Solid State - Temperature dependences of the thermal diffusivity and thermal conductivity in multiferroic materials BiFeO3, Bi0.90Sm0.10FeO3, and Bi0.90Eu0.10FeO3 were studied....     

A Modified Technique for the Determination of Hydration Numbers of Metal Ions in Concentrated Aqueous Solutions by Means of Proton Magnetic Resonance

Quite recently much attention has been devoted to the direct determination of hydration numbers of cations in both aqueous solutions and in mixed solvent systems by means of PMR (proton magnetic resonance).^1-10     

强磁场下顺磁掺杂离子的光谱扩散

采用一种简明的解析方法从纯粹频域的角度讨论强磁场下顺磁离子掺杂体系的光谱扩散过程。一般说来光谱扩散遵循[1-exp(-WT_w)]^x的形式,W是跳变速率,T_w为等待时间。在不存在冷冻核时,对于频域和时域x分别为1/2和1。考虑到冷冻核效应,光谱扩散的速率将近似地以因子(ω_eff/ω₀)²减慢,这里ω₀是描述冷冻核的特征频率。当冷冻核充分大时,频域和时域的光谱扩散的行为趋于一致x≈0.22。     

Proton Transport in Hydrogen-Bonded Chains in the Presence of an External Field

The motion of a kink pair consisting of kink soliton in different sublattices in hydrogen-bonded chains in the presence of an external force and damping is discussed based on a new soliton model. The scattering cross-section of a kink pair for an electromagnetic wave and the mobility of a kink pair are found.     

Temperature- and Concentration-Dependence of the Spin-Lattice Relaxation Time of Chromium Ions in GASH

Investigations of the temperature- and concentration dependence of the spin-lattice relaxation time T₁ in ferroelectric GASH (= Guanidinium aluminium sulfate hexahydrate) single crystals doped with Cr³⁺-ions are reported. The concentration-dependence found on the higher concentrated crystals C 0.1% Cr³⁺) as well as the observed cross-relaxation are explained in terms of spin-lattice relaxation via exchange pairs. Using the VAN VLECK formalism T₁ has been estimated for Cr³⁺: GASH by comparision of the present system and K-Cr-alum.     

Magnetization of Paramagnetic Ions by Phase-Modulated Microwave Pulses in a Zero Magnetic Field

Physics of the Solid State - The effect of magnetization formation for paramagnetic ions with spin S = 1 in a solid under a zero magnetic field by pulsed manipulations with electron spins has been...     

Consequences of Xe–H Cross Relaxation in Aqueous Solutions

We have investigated the transfer of polarization from ¹²⁹Xe to solute protons in aqueous solutions to determine the feasibility of using hyperpolarized xenon to enhance ¹H sensitivity in aqueous systems at or near room temperatures. Several solutes, each of different molecular weight, were dissolved in deuterium oxide and although large xenon polarizations were created, no significant proton signal enhancement was detected in -tyrosine, α-cyclodextrin, β-cyclodextrin, apomyoglobin, or myoglobin. Solute-induced enhancement of the ¹²⁹Xe spin–lattice relaxation rate was observed and depended on the size and structure of the solute molecule. The significant increase of the apparent spin–lattice relaxation rate of the solution phase ¹²⁹Xe by α-cyclodextrin and apomyoglobin indicates efficient cross relaxation. The slow relaxation of xenon in β-cyclodextrin and -tyrosine indicates weak coupling and inefficient cross relaxation. Despite the apparent cross-relaxation effects, all attempts to detect the proton enhancement directly were unsuccessful. Spin–lattice relaxation rates were also measured for Boltzmann ¹²⁹Xe in myoglobin. The cross-relaxation rates were determined from changes in ¹²⁹Xe relaxation rates in the α-cyclodextrin and myoglobin solutions. These cross-relaxation rates were then used to model ¹H signal gains for a range of ¹²⁹Xe to ¹H spin population ratios. These models suggest that in spite of very large ¹²⁹Xe polarizations, the ¹H gains will be less than 10% and often substantially smaller. In particular, dramatic ¹H signal enhancements in lung tissue signals are unlikely.