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Mikhail G. Brik - One of the best experts on this subject based on the ideXlab platform.
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mn4 doped heterodialkaline fluorogermanate red phosphor with high quantum yield and spectral luminous efficacy for warm white light emitting device application
Inorganic Chemistry, 2018Co-Authors: Chunyan Jiang, Mikhail G. Brik, Mingying Peng, Alok M. SrivastavaAbstract:Narrow band red-emitting Mn4+-doped fluoride phosphor is an essential red component of modern white-light-emitting-diode (WLED) devices. Its luminescence has sensitivity to structure and influences the performance of WLED. In this paper, we report a high-performance Mn4+ phosphor based on a new heterodialkaline fluorogermanate, CsNaGeF6:Mn4+. As determined by the single-Crystal X-ray diffraction analysis, the CsNaGeF6 compound Crystallizes in the orthorhombic Crystal system with space group Pbcm (No. 57). Under excitation by 360 and 470 nm photons, CsNaGeF6:Mn4+ emits intense red light near 630 nm with a high quantum yield of 95.6%. The electronic energy levels of the Mn4+ ion in Cs2GeF6, Na2GeF6, and CsNaGeF6 are calculated using the exchange charge model of Crystal-Field Theory. The local Mn4+ environment inducing different zero-phonon-line emissions in the structures is probed by electron paramagnetic resonance. The Mn4+-doped heterodialkaline fluorogermanate CsNaGeF6:Mn4+ exhibits broader emission as ...
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Mn4+-Doped Heterodialkaline Fluorogermanate Red Phosphor with High Quantum Yield and Spectral Luminous Efficacy for Warm-White-Light-Emitting Device Application
2018Co-Authors: Chunyan Jiang, Mingying Peng, Alok M. Srivastava, Mikhail G. BrikAbstract:Narrow band red-emitting Mn4+-doped fluoride phosphor is an essential red component of modern white-light-emitting-diode (WLED) devices. Its luminescence has sensitivity to structure and influences the performance of WLED. In this paper, we report a high-performance Mn4+ phosphor based on a new heterodialkaline fluorogermanate, CsNaGeF6:Mn4+. As determined by the single-Crystal X-ray diffraction analysis, the CsNaGeF6 compound Crystallizes in the orthorhombic Crystal system with space group Pbcm (No. 57). Under excitation by 360 and 470 nm photons, CsNaGeF6:Mn4+ emits intense red light near 630 nm with a high quantum yield of 95.6%. The electronic energy levels of the Mn4+ ion in Cs2GeF6, Na2GeF6, and CsNaGeF6 are calculated using the exchange charge model of Crystal-Field Theory. The local Mn4+ environment inducing different zero-phonon-line emissions in the structures is probed by electron paramagnetic resonance. The Mn4+-doped heterodialkaline fluorogermanate CsNaGeF6:Mn4+ exhibits broader emission as a result of the lowest symmetry. It has higher quantum yield than Na2GeF6:Mn4+ and higher spectral luminous efficacy than Cs2GeF6:Mn4+. Given the good thermal stability and efficient luminescence, a prototype warm-WLED device with a color rendering index of 92.5, a correlated color temperature of 3783 K, and a luminous efficacy of 176.3 lm/W has been fabricated by employing the CsNaGeF6:Mn4+ phosphor as the red component. Our results not only reveal that a high-performance Mn4+ red phosphor is achieved through cationic substitutions but also construct a relationship of performance–structure to guide the design of Mn4+ phosphors in the future
B Z Malkin - One of the best experts on this subject based on the ideXlab platform.
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structural and magnetic investigations of single Crystalline neodymium zirconate pyrochlore nd 2 zr 2 o 7
Physical Review B, 2015Co-Authors: Ciomaga M Hatnean, M R Lees, O A Petrenko, Dean S Keeble, G Balakrishnan, Matthias J Gutmann, V V Klekovkina, B Z MalkinAbstract:We report structural and magnetic properties studies of large high-quality single Crystals of the frustrated magnet ${\mathrm{Nd}}_{2}{\mathrm{Zr}}_{2}{\mathrm{O}}_{7}$. Powder x-ray diffraction analysis confirms that ${\mathrm{Nd}}_{2}{\mathrm{Zr}}_{2}{\mathrm{O}}_{7}$ adopts the pyrochlore structure. Room-temperature x-ray diffraction and time-of-flight neutron-scattering experiments show that the Crystals are stoichiometric in composition with no measurable site disorder. The temperature dependence of the magnetic susceptibility shows no magnetic ordering at temperatures down to 0.5 K. Fits to the magnetic susceptibility data using a Curie-Weiss law reveal a ferromagnetic coupling between the Nd moments. Magnetization versus Field measurements show a local Ising anisotropy along the $\ensuremath{\langle}111\ensuremath{\rangle}$ axes of the ${\mathrm{Nd}}^{3+}$ ions in the ground state. Specific heat versus temperature measurements in zero applied magnetic Field indicate the presence of a thermal anomaly below $T\ensuremath{\sim}7$ K, but no evidence of magnetic ordering is observed down to 0.5 K. The experimental temperature dependence of the single-Crystal bulk dc susceptibility and isothermal magnetization are analyzed using Crystal Field Theory and the Crystal Field parameters and exchange coupling constants determined.
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static magnetic susceptibility Crystal Field and exchange interactions in rare earth titanate pyrochlores
Journal of Physics: Condensed Matter, 2010Co-Authors: B Z Malkin, Tom T A Lummen, G Dhalenne, P H M Van Loosdrecht, A R ZakirovAbstract:The experimental temperature dependence (T = 2–300 K) of single Crystal bulk and site susceptibilities of rare earth titanate pyrochlores R2Ti2O7 (R = Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb) is analyzed in the framework of Crystal Field Theory and a mean Field approximation. Analytical expressions for the site and bulk susceptibilities of the pyrochlore lattice are derived taking into account long range dipole–dipole interactions and anisotropic exchange interactions between the nearest neighbor rare earth ions. The sets of Crystal Field parameters and anisotropic exchange coupling constants have been determined and their variations along the lanthanide series are discussed.
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epr and optical spectra of yb 3 in cscdbr 3 charge transfer effects on the energy level structure of yb 3 in the symmetrical pair centers
Physical Review B, 2000Co-Authors: B Z Malkin, A M Leushin, A I Iskhakova, J Heber, M Altwein, K Moller, I I Fazlizhanov, V A UlanovAbstract:Electron paramagnetic resonance (EPR), optical absorption, fluorescence, and excitation spectra of ${\mathrm{CsCdBr}}_{3}:1%$ ${\mathrm{Yb}}^{3+}$ single Crystals were taken at 4.2 K. An analysis of the dependence of the EPR spectrum on the magnetic-Field direction and a comparison of the recorded signal shapes with simulated envelopes over the magnetic dipole transitions of the expected dimers containing all ytterbium isotopes were performed. This allowed us to assign the measured EPR spectra unambiguously to the symmetrical pair center of the type ${\mathrm{Yb}}^{3+}{\ensuremath{-}\mathrm{C}\mathrm{d}}^{2+}$ vacancy-${\mathrm{Yb}}^{3+}$ substituting for three adjacent ${\mathrm{Cd}}^{2+}$ ions in the bromine octahedra chains. A distance of 0.596 nm between the magnetically equivalent ${\mathrm{Yb}}^{3+}$ ions was determined from the line splitting due to magnetic dipole-dipole interaction. An interpretation of the optical spectra in compounds containing $({\mathrm{YbBr}}_{6}{)}^{3\mathrm{\ensuremath{-}}}$ complexes is presented, which is based on a Crystal-Field Theory accounting for an interaction between the ground ${4f}^{13}({\mathrm{Yb}}^{3+})[{4p}^{6}({\mathrm{Br}}^{\mathrm{\ensuremath{-}}}){]}_{6}$ and excited ${4f}^{14}({\mathrm{Yb}}^{2+}{)4p}^{5}(\mathrm{Br})[{4p}^{6}({\mathrm{Br}}^{\mathrm{\ensuremath{-}}}){]}_{5}$ charge-transfer configurations. The observed large splitting of the excited ${}^{2}{F}_{5/2}{(4f}^{13})$ Crystal-Field multiplet is explained on the basis of a quasiresonant hybridization of the $4f$-hole state with the spin orbitals of the charge-transfer states. With physically reasonable values of the fitted model parameters, the calculated energy level diagram of the ${4f}^{13}$ configuration and the g tensor of the ${\mathrm{Yb}}^{3+}$ ion in the Crystal-Field ground state are in good agreement with the experimental data.
Wen-chen Zheng - One of the best experts on this subject based on the ideXlab platform.
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investigations of the optical and epr data and local structure for the trigonal tetrahedral co 2 centers in liga 5 o 8 co 2 Crystal
Physica B-condensed Matter, 2018Co-Authors: Jian He, Bitao Liao, Wen-chen ZhengAbstract:Abstract In this paper, we calculate uniformly the optical and EPR data for Co2+ ion at the trigonal tetrahedral Ga3+ site in LiGa5O8 Crystal from the complete diagonalization (of energy matrix) method founded on the two-spin-orbit-parameter model, where the contributions to the spectroscopic data from both the spin-orbit parameter of dn ion (in the classical Crystal Field Theory) and that of ligand ions are contained. The calculated ten spectroscopic data (seven optical bands and three spin-Hamiltonian parameters g//, g⊥ and D) with only four adjustable parameters are in good agreement with the available observed values. Compared with the host (GaO4)5− cluster, the great angular distortion and hence the great trigonal distortion of (CoO4)6− impurity center obtained from the calculations are referred to the large charge and size mismatch substitution. This explains reasonably the observed great g-anisotropy Δg (= g// − g⊥) and zero-Field splitting D for the (CoO4)6− cluster in LiGa5O8: Co2+ Crystal.
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uniform calculation of the optical and epr spectral data for the trigonal cro6 9 octahedral clusters in y3al5o12 Crystal
Polyhedron, 2017Co-Authors: Chang Liu, Yang Mei, Bowei Chen, Honggang Liu, Wen-chen ZhengAbstract:Abstract The complete diagonalization (of the energy matrix) method is applied in this paper for the unified calculation of optical and EPR spectral data of the trigonal (CrO 6 ) 9− octahedral clusters in Y 3 Al 5 O 12 (YAG) Crystal. The method is based on the two-spin–orbit-parameter model where, besides the contributions from the spin–orbit parameter of central d n ion in the traditional Crystal-Field Theory, those from the spin–orbit parameter of ligand ions via the covalence effect are considered. The computed 32 spectroscopic data values (29 Crystal Field energy levels and three spin-Hamiltonian parameters, namely the g factors g // and g ⊥ , and the zero-Field splitting D ) are in reasonable agreement with the experimental values, despite using only four adjustable parameters. This suggests that the method is valid in the uniform calculation of optical and EPR spectral data for d 3 ions in Crystals. The impurity-induced angular distortion of the (CrO 6 ) 9− clusters in YAG Crystal was also evaluated.
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research on the optical band positions spin hamiltonian parameters and atom position parameter of co2 ion in cdse Crystal
Journal of Magnetism and Magnetic Materials, 2015Co-Authors: Yang Mei, Wen-chen Zheng, Renming Peng, Chengfu WeiAbstract:Abstract The optical band positions and EPR (or spin-Hamiltonian) parameters (g factors g//, g⊥ and zero-Field splitting D) of Co2+ ion in the trigonally-distorted tetrahedral Cd2+ site of CdSe Crystal are calculated simultaneously from the complete diagonalization (of energy matrix) method (CDM) based on the two-spin–orbit-parameter model. This model contains the contributions to the spectral data from both the spin–orbit parameters of central dn ion (i.e., one-spin–orbit-parameter model) in the conventional Crystal-Field Theory and that of ligand ions via covalence effect. The calculated 12 optical band positions and three spin-Hamiltonian parameters using four adjustable parameters show reasonable agreement with the experimental values. The local atom-position parameter uloc (where the corresponding parameter u in the host CdSe Crystal is unlikely) in the Co2+ center is also estimated from the calculations. The calculations of these spectral data from the CDM based on the conventional one-spin–orbit parameter model are also made for comparison. It is found that the calculated optical band positions are also close to the experimental values, but the calculated spin-Hamiltonian parameters are in poor agreement with the observed values. So, for the unified and reasonable calculations of optical and EPR data of dn ions in Crystals (in particular, in the cases of ligand with large spin–orbit parameter), the CDM based on the two-spin–orbit-parameter model should be applied.
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calculations of the optical and epr spectral data for cr3 ion in y3ga5o12 Crystal from the complete diagonalisation method
Molecular Physics, 2015Co-Authors: Yang Mei, Renming Peng, Chengfu Wei, Wen-chen ZhengAbstract:The complete diagonalisation (of energy matrix) method is applied in this paper to calculate together the optical and electron paramagnetic resonance (EPR) spectral data for Cr3+ ion at the trigonal Ga3+ site of Y3Ga5O12 Crystal. The method is founded on the two-spin-orbit-parameter model where in addition to the contributions from the spin-orbit parameter of central dn ion (i.e., one-spin-orbit-parameter model) in the traditional Crystal Field Theory, those from the spin-orbit parameter of ligand ion via covalence effect is also considered. The calculated results propose that by using only four adjustable parameters, the 12 observed spectral data (nine optical band positions and three EPR parameters g//, g⊥ and D) in Y3Ga5O12: Cr3+ are reasonably explained. The impurity-induced local lattice distortion of Cr3+ in Y3Ga5O12 Crystal is also estimated through the calculations. The results are discussed.
N M Avram - One of the best experts on this subject based on the ideXlab platform.
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comparative analysis of Crystal Field effects and optical spectroscopy of six coordinated mn4 ion in the y2ti2o7 and y2sn2o7 pyrochlores
Optical Materials, 2011Co-Authors: M G Brik, A M Srivastava, N M AvramAbstract:Abstract The electronic energy levels of the six-coordinated Mn 4+ ion in the pyrochlores Y 2 B 2 O 7 ( B = Sn 4+ , Ti 4+ ) have been computed using the exchange charge model of Crystal Field Theory. The calculated Mn 4+ energy levels and their trigonal splitting are in good agreement with the experimental spectra. The calculated Crystal Field parameters show that the higher Crystal Field strength in Y 2 Sn 2 O 7 arises from an increased orbital overlap effect between the Mn 4+ ion and the nearest oxygen ions, which are located at the 48 f Crystallographic position of the pyrochlore lattice. This increased overlap in Y 2 Sn 2 O 7 occurs despite the fact that the Mn 4+ –O 2− bond distance in Y 2 Sn 2 O 7 is longer than in Y 2 Ti 2 O 7 and is attributed to a lack of hybridization (covalent bonding) between the filled 2 p orbital of oxygen ion occupying the 48 f site of the pyrochlore lattice and the filled Sn 4+ 4 d 10 orbital. The low temperature emission spectrum of Mn 4+ activated Y 2 Sn 2 O 7 is analyzed in terms of a weak zero phonon line (R-line) with accompanying vibrational side bands.
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Crystal Field analysis of energy level structure of lialo2 v3 and ligao2 v3
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2006Co-Authors: N M Avram, C N AvramAbstract:Abstract A detailed analysis of the energy level structure of tetrahedrally coordinated V3+ ion in lithium aluminum oxide LiAlO2 (γ-phase) and lithium dioxogallate LiGaO2 is performed using the exchange charge model of the Crystal Field Theory. The parameters of the Crystal Field acting on the V3+ optical electrons are calculated from Crystal structure data assuming C1 point symmetry of the [VO4]5− impurity center in LiAlO2 and LiGaO2. Crystal Field splitting of all five LS terms of the V3+ ion (3F, 3P, 1S, 1D, 1G) is calculated. The energy levels obtained are compared with experimental absorption spectra and results of application of other Crystal Field models (the angular overlap model and Racah Theory) to the considered Crystals; though only one fitting parameter of the exchange charge model was used, a good agreement with experimental data on the ground and excited state absorption is demonstrated.
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Crystal Field analysis of energy level structure of the cr2o3 antiferromagnet
Solid State Communications, 2004Co-Authors: N M Avram, C N AvramAbstract:Abstract A detailed analysis of the energy level structure of the six-fold coordinated Cr3+ ion in the chromium oxide Cr2O3 is performed using the exchange charge model of the Crystal Field Theory. Parameters of the Crystal Field acting on the Cr3+ optical electrons are calculated from the Crystal structure data for the [CrO6]9− impurity center. The energy levels obtained are compared with the experimental absorption spectra for the considered Crystal; a good agreement with experimental data is demonstrated. One possible explanation for the ultraviolet p1 absorption band is proposed based on the results of Crystal Field calculations.
V A Ulanov - One of the best experts on this subject based on the ideXlab platform.
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epr and optical spectra of yb 3 in cscdbr 3 charge transfer effects on the energy level structure of yb 3 in the symmetrical pair centers
Physical Review B, 2000Co-Authors: B Z Malkin, A M Leushin, A I Iskhakova, J Heber, M Altwein, K Moller, I I Fazlizhanov, V A UlanovAbstract:Electron paramagnetic resonance (EPR), optical absorption, fluorescence, and excitation spectra of ${\mathrm{CsCdBr}}_{3}:1%$ ${\mathrm{Yb}}^{3+}$ single Crystals were taken at 4.2 K. An analysis of the dependence of the EPR spectrum on the magnetic-Field direction and a comparison of the recorded signal shapes with simulated envelopes over the magnetic dipole transitions of the expected dimers containing all ytterbium isotopes were performed. This allowed us to assign the measured EPR spectra unambiguously to the symmetrical pair center of the type ${\mathrm{Yb}}^{3+}{\ensuremath{-}\mathrm{C}\mathrm{d}}^{2+}$ vacancy-${\mathrm{Yb}}^{3+}$ substituting for three adjacent ${\mathrm{Cd}}^{2+}$ ions in the bromine octahedra chains. A distance of 0.596 nm between the magnetically equivalent ${\mathrm{Yb}}^{3+}$ ions was determined from the line splitting due to magnetic dipole-dipole interaction. An interpretation of the optical spectra in compounds containing $({\mathrm{YbBr}}_{6}{)}^{3\mathrm{\ensuremath{-}}}$ complexes is presented, which is based on a Crystal-Field Theory accounting for an interaction between the ground ${4f}^{13}({\mathrm{Yb}}^{3+})[{4p}^{6}({\mathrm{Br}}^{\mathrm{\ensuremath{-}}}){]}_{6}$ and excited ${4f}^{14}({\mathrm{Yb}}^{2+}{)4p}^{5}(\mathrm{Br})[{4p}^{6}({\mathrm{Br}}^{\mathrm{\ensuremath{-}}}){]}_{5}$ charge-transfer configurations. The observed large splitting of the excited ${}^{2}{F}_{5/2}{(4f}^{13})$ Crystal-Field multiplet is explained on the basis of a quasiresonant hybridization of the $4f$-hole state with the spin orbitals of the charge-transfer states. With physically reasonable values of the fitted model parameters, the calculated energy level diagram of the ${4f}^{13}$ configuration and the g tensor of the ${\mathrm{Yb}}^{3+}$ ion in the Crystal-Field ground state are in good agreement with the experimental data.