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Impurity Centers (impurity + center)

Distribution by Scientific Domains
Physics and Astronomy50%

Selected Abstracts

Investigations of the g -factors and local phase-transition behavior for Ni3+ ion in the tetragonal phase of RbCaF3 crystal

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2008
Shun-Ru Zhang
Abstract The EPR g factors g, and g, for Ni3+ ion (created by room-temperature X-irradiation of nickel-doped RbCaF3) in the tetragonal phase of RbCaF3 crystal are calculated from the second-order perturbation formulas based on a cluster approach for high-spin 3d7 ions in tetragonal octahedral clusters. The calculated results are in reasonable agreement with the experimental values. The local phase-transition behavior of the Ni3+ impurity center in RbCaF3 is also estimated from the calculation. It is found that the local phase-transition behavior in the Ni3+ center is unlike the intrinsic one in the host crystal (in particular, the fluorine octahedra surrounding the cations change from tetragonal compression in the host crystal to tetragonal elongation in the Ni3+ impurity center). The results are discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Spin-lattice relaxation of spin-½ nuclei in solids containing diluted paramagnetic impurity centers.

CONCEPTS IN MAGNETIC RESONANCE, Issue 1 2003

Abstract Dynamic nuclear polarization of nuclear spins via the solid-state and thermal mixing effects is discussed. Continuous-wave S- and X-band microwave radiation have been employed to measure 13C signal enhancements and polarization times for 13C nuclei in a natural type Ib diamond as a function of magnetic field. It was found that thermal mixing plays an important role in the 13C signal enhancement because the central electron spin resonance (ESR) line width HL , H0,C/,e, resulting in flip-flip and flip-flop forbidden transitions taking place simultaneously. On the other hand, the 13C spin-lattice relaxation rate is determined to a large extent by the solid-state effect (forbidden transitions). 13C polarization rates have also been measured for a suite of natural diamonds. It is shown that the polarization rate is proportional to the paramagnetic impurity concentration, in agreement with the theory. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson 19A: 36,43, 2003. [source]

Spin-lattice relaxation of spin-½ nuclei in solids containing diluted paramagnetic impurity centers.

CONCEPTS IN MAGNETIC RESONANCE, Issue 1 2003

Abstract Dynamic nuclear polarization of nuclei by means of paramagnetic electron spin locking (Hartmann-Hahn cross-polarization between paramagnetic electrons and nuclei, or NOVEL) is discussed. The theory is demonstrated by experiments executed at 2.4 and 9.6 GHz on a natural type Ib diamond. It is shown that the 13C polarization rate is independent of the microwave frequency, in agreement with theory. NOVEL polarization takes place only while the spin-locking pulse is on. The rate at which the nuclei are polarized is proportional to the electron polarization in the rotating frame. Therefore, the length of the spin-locking pulse is limited by the value of T1,(e), and because T1,(e) , T1(e) for diamond the effective NOVEL polarization rate of 13C nuclei is usually relatively low. A comparison between the relative effectiveness of 13C polarization rates between NOVEL and the solid-state effect is made for high and low paramagnetic impurity concentrations. The dependence of the 13C polarization rate on the paramagnetic impurity concentration has been determined for a suite of natural diamonds. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson 19A: 44,49, 2003. [source]

Energy structure and micromechanism of photo-electromotive force effect in V-doped CdTe crystals

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2007
Yu. P. Gnatenko
Abstract For the first time photo-electromotive force (photo-EMF) measurements were carried out for CdTe crystals doped with V atoms as a result of the photogeneration of carriers from deep impurity centers to the conduction band. Tilted geometry was applied that allowed two-dimensional monitoring of the vi- bration source. The CdTe:V crystals were excited by a He,Ne laser with a wavelength of 1.15 ,m (,, = 1.08 eV) and P = 2 mW. The mechanism of the appearance of the holographic current in the CdTe:V crystals taking into account real defect structure was proposed. The frequency dependence of the ac photo-EMF (holographic) current for the CdTe:V crystals was measured. It was shown that a low cut-off frequency for a laser intensity I = 0.2 mW/mm2 equals 6.0 kHz, which corresponds to a response time of 26 ,s. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]