Impurity Defect Induced Ferromagnetism Investigation of SiO2-Supported NiO Particles

This study examines amorphous SiO2-supported NiO particles by nickel concentration and calcination temperature arrangement to determine photoluminescence emission peaks and magnetic properties. Conventional co-precipitation with thermal calcination was used to produce NiO nanoparticles. Cubic NiO crystallization with single phase was improved by doubling the nickel concentration by calcination at 500 ºC and 600 ºC. Average crystalline size of 72 nm was obtained in the samples where double nickel concentration with calcination temperature at 600 ºC. Granular forms have been observed in all samples, and nickel clusters were shown in the samples where the nickel concentration is twice as high. Green band emission intensity increases with improved NiO crystallinity due to surface oxygen vacancies at 505 nm. It is interesting to observe ferrimagnetism for SiO2-supported NiO particles calcined at 500 ºC. From these results, optimal synthesis procedure and reduction in nucleation growth of NiO nanoparticles was achieved by double nickel concentration with calcination temperature at 600 ºC. Resumen. Este estudio examina partículas de NiO soportadas en SiO2. El estudio comprende la variación de la concentración de níquel y la temperatura de calcinación para determinar los picos de emisión de fotoluminiscencia y las propiedades magnéticas. Se utilizó la coprecipitación convencional con calcinación para producir nanopartículas de NiO. Se mejoró la cristalización cúbica de NiO con fase única al duplicar la concentración de níquel y calcinación a 500 ºC y 600 ºC. Se obtuvo un tamaño cristalino promedio de 72 nm en las muestras donde se duplicó la concentración de níquel con temperatura de calcinación a 600 ºC. Se observaron formas granulares en todas las muestras, y se encontraron agregados de níquel en las muestras donde la concentración de níquel fue el doble. La intensidad de la banda de emisión aumenta con la cristalinidad de NiO debido a las vacantes de oxígeno en la superficie. Es interesante observar el ferrimagnetismo de las partículas de NiO soportadas en SiO2 calcinadas a 500 ºC. A partir de estos resultados, se logró un procedimiento de síntesis óptimo y la reducción del crecimiento de nucleación de nanopartículas de NiO mediante una concentración doble de níquel con una temperatura de calcinación de 600 ºC.

Structural, Electronic and Magnetic Properties of Impurities Defected Graphene/MoS2 Van Der Waals Heterostructure: First-principles Study

Two-dimensional (2D) pristine and defected van der Waals (vdW) heterostructure (HS) materials open up fortune in nanoelectronic and optoelectronic devices. So, they are compatible for designing in the fields of device applications. In the present work, we studied structural, electronic and magnetic properties of vdW (HS) graphene/MoS2 ((HS)G/MoS2), Nb impurity defect in vdW (HS) graphene/MoS2 (Nb-(HS)G/MoS2), and Tc impurity defect in vdW (HS) graphene/MoS2 (Tc-(HS)G/MoS2) materials by using spin-polarized DFT-D2 method. We examined the structure of these materials, and found that they are stable. Based on band structure analysis, we found that (HS)G/MoS2, Nb-(HS)G/MoS2 and Tc-(HS)G/MoS2 have metallic characteristics. Also, (HS)G/MoS2 and Tc-(HS)G/MoS2 materials have n-type Schottky contact, while Nb-(HS)G/MoS2 material has p-type Schottky contact. To understand the magnetic properties of materials, we have used DoS, IDoS and PDoS calculations. We found that (HS)G/MoS2 is a non-magnetic material, but Nb-(HS)G/MoS2 and Tc-(HS)G/MoS2 are magnetic materials. Magnetic moment of Nb-(HS)G/MoS2 and Tc-(HS)G/MoS2 materials are -0.24 μB/cell and +0.07μB/cell values respectively from DoS/PDoS calculations, and 0.26 μB/cell and 0.08μB/cell values respectively from IDoS calculations. Up-spin and down-spin states of electrons in 2p orbital of C atoms, 3p orbital of S atoms, 4d orbital of Mo atoms, 4d orbital of Tc atom in Tc-(HS)G/MoS2, and 2p orbital of C atoms, 3p orbital of S atoms, 4p & 4d orbitals of Mo atoms, 4p & 4d orbitals of Nb atom in Nb-(HS)G/MoS2 have major contribution for the development of magnetic moment.

Structures of Impurity Defects in Lithium Niobate and Tantalate Derived from Electron Paramagnetic and Electron Nuclear Double Resonance Data

Point intrinsic and extrinsic defects, especially paramagnetic ions of transition metals and rare-earth elements, have essential influence on properties of lithium niobate, LN and tantalate, LT, and often determine their suitability for numerous applications. Discussions about structures of the defects in LN/LT have lasted for decades. Many experimental methods facilitate progress in determining the structures of impurity centers. This paper gives current bird’s eye view on contributions of Electron Paramagnetic Resonance (EPR), and Electron Nuclear Double Resonance (ENDOR) studies to the determination of impurity defect structures in LN and LT crystals for a broad audience of researchers and students. Symmetry and charge compensation considerations restrict a number of possible structures. Comparison of measured angular dependences of ENDOR frequencies with calculated ones for Li and Nb substitution using dipole–dipole approximation allows unambiguously to determine the exact location of paramagnetic impurities. Models with two lithium vacancies explain angular dependencies of EPR spectra for Me3+ ions substituting for Li+ like Cr, Er, Fe, Gd, Nd, and Yb. Self-compensation of excessive charges through equalization of concentrations of Me3+(Li+) and Me3+(Nb5+) and appearance of interstitial Li+ in the structural vacancy near Me3+(Nb5+) take place in stoichiometric LN/LT due to lack of intrinsic defects.

Применение метода матрицы рассеяния для расчета примесных состояний в полупроводниковых структурах

We adapted S-matrix method for calculation of energy levels and carrier wavefunctions near impurity/defect states. We demonstrate the possibility of implying this method for multiband models on the example of Luttinger Hamiltonian with Coulomb acceptor in the spherical symmetry approximation. The obtained energies of discrete levels are in well agreement with results of calculations performed by other methods.

Analysis of doping influence on structural defects in LiNbO3.

Changes in a structural state of homogeneous doped lithium niobate crystals with magnesium in the region of 5 mol. % were studied by X-ray diffraction methods. It was found that the changes in the structure of LiNbO3: Mg occured not only in the region of the impurity defect, but also in the region of the main motive of the structure. Bond lengths in the octahedra of the main motive and the Nb–Li distance along the polar axis of the crystal changed. The magnesium introduced into the vacant lithium octahedron distorted the shape of the octahedron more strongly than niobium.

Исследование мощности люминесценции экситонов и примесно-дефектных центров, возбуждаемых с помощью двухфотонного поглощения

In the present work, using as an example ZnSe: Fe2+ single crystals, it was experimentally and theoretically studied the effect of the average power of femtosecond laser radiation on the average luminescence power of excitons and impurity-defect centers upon two-photon excitation of the electronic system of a crystal. It has been experimentally shown that the average luminescence power of crystal excitons in the studied range of excitation powers is proportional to 4 degrees of the average excitation radiation power. The average luminescence power of impurity-defect centers has a quadratic character. A theory is constructed that explains the experimentally observed dependencies. It is noted that the nature of the dependence of the crystal luminescence on the pump power during two-photon excitation can be used to estimate the degree of contamination of the crystal by impurity-defect centers.