Crystal Field Effects Research Articles

Luminescence studies of Eu3+ doped calcium magnesium silicate phosphor prepared at different annealing temperatures for fine color tunability

This research article explores the possibility of fine-tuning of the color monochromaticity of Eu3+ doped calcium magnesium silicate: CaMgSi2O6: Eu3+, Ca3MgSi2O8: Eu3+, and Ca2MgSi2O7: Eu3+ (CMS: Eu3+) phosphor by introducing a crystal field effect in the luminescence emission spectra. The effect of Eu doping and annealing temperature on modifying the morphology, crystal structure, bonding nature, luminescent properties, and color monochromaticity of calcium magnesium silicate; CaMgSi2O6, Ca3MgSi2O8, and Ca2MgSi2O7 (CMS) phosphor is analyzed in detail. CMS and CMS: Eu3+ were separately prepared by the sol-gel method, employing five different annealing temperatures. Morphological analysis using FESEM confirmed agglomerated porous structures at annealing temperatures of 800 °C, 900 °C, and 1000 °C, whereas clear particle formation was observed at 1100 °C and 1200 °C, both in CMS and CMS: Eu3+. An increase in the particle size with temperature and reduction in the growth kinetics with Eu3+ doping was noticed. The non-stoichiometric composition identified during the chemical analysis was in agreement with the XRD findings of the formation of merwinite, diopside, and akermanite phases in CMS and CMS: Eu3+. The XRD analysis further confirmed that Eu3+ doping favor merwinite over diopside structure. The structural modifications in the CMS due to the presence of Eu3+ appeared as blue and redshift in the vibrational wavenumbers of Ca–O and Mg–O in FTIR studies. Luminescence studies confirmed an increase in the peak splitting with the annealing temperature in the excitation and the emission spectra due to the crystal field effect. The possible reasons for the peak splitting are the formation of multiple phases with multiple site occupancy, preferably with the octahedral coordination, and the J mixing due to the effective charge balancing expected due to higher oxygen capture occurring at the higher annealing temperature. With the increase in annealing temperature, color chromaticity coordinates varied from (0.61, 0.39) to (0.63, 0.37) due to better charge compensation which is in agreement with the luminescence studies.

Numerical Calculation of the Thermodynamic Properties of Silver Erbium Alloys for Use in Metallic Magnetic Calorimeters

Using dilute silver erbium alloys as a paramagnetic temperature sensor in metallic magnetic calorimeters (MMCs) has the advantage of the host material not having a nuclear quadrupole moment, in contrast to the alternative of using gold erbium alloys. We present numerical calculations of the specific heat and magnetization of Ag:Er, which are necessary for designing and optimizing MMCs using this type of alloy as sensor material. The parameter ranges we consider are temperatures between 1,{text {{mK}}} and 1,{text {{K}}}, external magnetic fields of up to 20,{text {{mT}}}, and erbium concentrations of up to 2000,{text {{ppm}}}. The system is dominated by an interplay of crystal field effects, Zeeman splitting, and the RKKY interaction between erbium ions, with certain specific constellations of erbium ions having noticeable effects on the specific heat. Increasing the external magnetic field or assuming a decreased strength of the RKKY interaction leads to a higher magnetization and a narrowing of the main Schottky peak, while changes in the erbium concentration can be well described by parameter scaling.

Second-Order Nonlinear Optical Responses of AlN Two-Dimensional Monolayer: A Real-Time First-Principles Study.

Two-dimensional materials have recently attracted attention due to their unique physical properties and promising applications. This work reports the electronic, linear and second-order nonlinear optical properties of aluminum nitride (AlN) monolayer by using a real-time first-principles approach based on Green's function theory. In this approach, quasi-particle corrections, crystal local field effects, and excitonic contributions are considered for investigating the linear and nonlinear responses. As a two-dimensional material with a wide direct gap of around 6.45 eV, the AlN monolayer exhibits strong resonances of absorption and second-harmonic spectra in the ultraviolet range. In the transparent spectral range from blue to deep ultraviolet (2.8-5.3 eV), strong peaks of second-order nonlinear susceptibility appear in the AlN monolayer with a large peak value of around 430 pm/V, which is one or two orders-of-magnitude larger than the nonlinear materials used in the ultraviolet range. The results presented in this work will find important applications for nonlinear imaging, spectroscopy, and nonlinear nanophotonics in the ultraviolet range.

Tetraanionicarachno‐Carboranyl Ligand Imparts Strong Axiality to Terbium(III) Single‐Molecule Magnets

AbstractA family of fully sandwichedarachno‐lanthanacarborane complexes formulated as {η6‐[μ‐1,2‐[o‐C6H4(CH2)2]‐1,2‐C2B10H10]2Ln}{Li5(THF)10} (Ln=Tb, Dy, Ho, Er, Y) is successfully synthesized, where the “carbons‐adjacent” carboranyl ligand (arachno‐R2‐C2B10H104−) bears four negative charges and coordinates to the central lanthanide ions using the hexagonal η6C2B4face. Thus, the central lanthanide cations are pseudo‐twelve‐coordinate and have an approximate pseudo‐D6hsymmetry or hexagonal‐prismatic geometry. As the crystal field effect imparted by this geometry is still unknown, we thoroughly investigated the magnetic properties of this series of complexes and found that the crystal field imposed by this ligand causes a relation of Tb>Dy>Ho>Er for the energy gaps between the ground and the first excited states, which is of striking resemblance to the ferrocenophane and phthalocyanine ligands although the latter two ligands give disparate local coordination geometries. Moreover, the effective energy barrier to magnetization reversal of 445(10) K, the observable hysteresis loop up to 4 K and the relaxation time of the yttrium‐diluted sample reaching 193(17) seconds at 2 K under an optimized field for the Tb analogue of this family ofarachno‐lanthanacarborane complexes, render a new benchmark for Tb3+‐based single‐molecule magnets.

Tetraanionic arachno-Carboranyl Ligand Imparts Strong Axiality to Terbium(III) Single-Molecule Magnets.

A family of fully sandwiched arachno-lanthanacarborane complexes formulated as {η6 -[μ-1,2-[o-C6 H4 (CH2 )2 ]-1,2-C2 B10 H10 ]2 Ln}{Li5 (THF)10 } (Ln=Tb, Dy, Ho, Er, Y) is successfully synthesized, where the "carbons-adjacent" carboranyl ligand (arachno-R2 -C2 B10 H10 4- ) bears four negative charges and coordinates to the central lanthanide ions using the hexagonal η6 C2 B4 face. Thus, the central lanthanide cations are pseudo-twelve-coordinate and have an approximate pseudo-D6h symmetry or hexagonal-prismatic geometry. As the crystal field effect imparted by this geometry is still unknown, we thoroughly investigated the magnetic properties of this series of complexes and found that the crystal field imposed by this ligand causes a relation of Tb>Dy>Ho>Er for the energy gaps between the ground and the first excited states, which is of striking resemblance to the ferrocenophane and phthalocyanine ligands although the latter two ligands give disparate local coordination geometries. Moreover, the effective energy barrier to magnetization reversal of 445(10) K, the observable hysteresis loop up to 4 K and the relaxation time of the yttrium-diluted sample reaching 193(17) seconds at 2 K under an optimized field for the Tb analogue of this family of arachno-lanthanacarborane complexes, render a new benchmark for Tb3+ -based single-molecule magnets.

Spectral broadening mechanism of Yb3+-doped cubic LuxSc2-xO3 sesquioxide crystals for ultrafast lasers

Over the past decades, Yb3+-doped cubic sesquioxide crystals have been considered as ideal gain materials for ultrafast laser generation, owing to their high thermal conductivity and adequate optical characteristics. The broadening of spectra by mixing host crystals to obtain short pulses has been extensively explored; however, few studies have examined the mechanism of the crystal field effect on spectral broadening. This paper describes the spectral broadening process caused by the combination of the discrete transition peaks induced by the crystal field effect and electron-phonon coupling widening based on Yb:LuxSc2-xO3 crystals. The energy level splitting induced by the crystal field effect not only determines the emission peak positions, but also broadens the emission spectra in the mixed host materials through the increasing spin-orbit coupling effect. Moreover, with the involvement of the electron-phonon coupling and the crystal field effect, the spectral broadening is much more obvious at room temperature. These results not only explain the spectral broadening mechanism of Yb3+-doped sesquioxides but also provide important insights for the improvement of new ultrafast laser materials.

The Role of Radical Bridges in Polynuclear Single-Molecule Magnets.

Employing radical bridges between anisotropic metal ions has been a viable route to achieve high-performance single-molecule magnets (SMMs). While the bridges have been mainly considered for their ability to promote exchange interactions, the crystal-field effect arising from them has not been taken into account explicitly. This lack of consideration may distort the understanding and limit the development of the entire family. To shed light on this aspect, herein we report a theoretical investigation of a series of N -radical-bridged diterbium complexes. It is found that while promoting strong exchange coupling between the terbium ions, the N -radical induces a crystal field that interferes destructively with that of the outer ligands, and thus reduces the overall SMM behavior. Based on the theoretical results, we conclude that the SMM behavior in this series could be further maximized if the crystal field of the outer ligands is designed to be collinear with that of the radical bridge. This conclusion can be generalized to all exchange-coupled SMMs.

Magnetic glassiness and crystal field effects on thermal and electrical properties of Er5Pd2-type compounds

Magnetic properties, thermal expansion, heat capacity, and electrical resistivity of the cluster-glass compound Er4.8Pd2 and its paramagnetic isostructural counterpart Lu4.8Pd2 have been studied in the temperature range 2–300 K and in applied magnetic fields up to 140 kOe. Short-range antiferromagnetic (AFM) correlations of localized magnetic moments of Er3+ ions were found to develop in Er4.8Pd2 on cooling below T* ≈ 40 K. A cluster-glass magnetic state was observed below freezing temperature Tf ≈ 13.3 K, while Lu4.8Pd2 showed paramagnetic behavior. The crystal electric field (CEF) was found to substantially affect both the heat capacity and the thermal expansion of Er4.8Pd2. The CEF splitting of the Er3+ ion multiplet 4I15/2 was estimated to be as high as 280 K with a doublet ground state. Both the Schottky-type anomaly and short-range antiferromagnetic order contributions were found to give rise to a large volumetric heat capacity of Er4.8Pd2 at low temperatures. High direct magnetocaloric effect with −ΔSM(T)60kOe = 18.8 J mole−1 K−1 was confirmed to exist in Er4.8Pd2 while no inverse magnetocaloric effect was observed at low temperatures. Electrical resistivity of Er4.8Pd2 revealed a non-metallic behavior at low temperatures which was ascribed to an inhomogeneous electronic state due to the formation of clusters with the AFM short-range correlations.

Effect of crystal field on the critical exponent of the magnetocaloric property of the mixed spin (7/2, 3/2) Ising system

Effect of crystal field on the critical exponent of the magnetocaloric property of the mixed spin (7/2, 3/2) Ising system

Random Crystal Field Effect on the Critical Properties of the Mixed Spin-(52,12) Anisotropic Heisenberg Model in the Oguchi Approximation

We have employed the Oguchi approximation (OA) to investigate the effects of a random crystal field which is active (inactive) with probability [Formula: see text] [Formula: see text] for given lattice sites on the thermodynamic properties of the mixed spin-[Formula: see text] anisotropic Heisenberg model in the presence of an external magnetic field. By exploiting the thermal variations of the order parameters, interesting phase diagrams are produced on various planes. The phase diagrams show first- and second-order transition lines and also tricritical points. In addition to the reentrant behavior which is localized in a certain range of [Formula: see text] at very low temperature, the magnetic exponent [Formula: see text] calculated near the critical point exhibits interesting behaviors depending on the crystal field interaction. The hysteresis behavior of the model is also investigated and it reveals that the width of hysteresis loop decreases or increases, respectively, for negative or positive crystal field region as the probability [Formula: see text] increases.

Investigation on thermal and electron transport properties combined with the low-temperature scaling behaviour of strongly correlated Ce2Rh3Al9

The paper presents some new aspects of the heat transport properties and thermoelectric characteristic of the heavy fermion Kondo lattice Ce2Rh3Al9. A thorough analysis of the obtained experimental data was presented along with their detailed discussion, paying particular attention to the range of low temperatures. The temperature dependence of thermoelectric power shows large values and reveals several well formed extrema, which reflect the crystal electric field effects and the Kondo scale, respectively. The giant positive slope of the Seebeck coefficient displayed in the form of the ratio S(T)/T is observed at low temperatures. Different to the thermoelectric power, the absolute values of thermal conductivity in Ce2Rh3Al9 are quite low. In addition, we have investigated the response of thermal and electron transport on the presence of a perpendicular static magnetic field of B = 9 T. For the sake of completeness, the field dependence of the transverse magnetoresistance data recorded between 0.4 ≤ T ≤ 20 K is presented and discussed as well.

Crystal field and lattice disorder effects on the low-temperature thermodynamic properties of TmF3

The temperature dependence of the heat capacity Cp(T), (2–300 K), and the lattice parameters a(T), b(T), and c(T) (5–300 K) TmF3 were experimentally studied. Anomalies in the studied characteristics were identified due to the influence on the thermal properties of trifluoride of the crystal field, and at the lowest temperatures (2–10 K), of a possible glass-like contribution due to disorder in the crystal lattice. As a result of our analysis of the excess contribution to the heat capacity (Schottky contribution, CSch(T)), we proposed a simplified scheme based on 1-1-7-5 splitting of the ground state of the Tm3+ ion, and determined the splitting parameters. The influence of the crystal field is also manifested through anomalies in the thermal expansion of TmF3. The temperature dependences of the unit cell volume of thulium trifluoride, and its heat capacity, were analysed using the Debye-Einstein model, and the model parameters are determined.

Low-field magnetic anisotropy of Sr2IrO4

Magnetic anisotropy in strontium iridate (Sr2IrO4) is essential because of its strong spin–orbit coupling and crystal field effect. In this paper, we present a detailed mapping of the out-of-plane (OOP) magnetic anisotropy in Sr2IrO4 for different sample orientations using torque magnetometry measurements in the low-magnetic-field region before the isospins are completely ordered. Dominant in-plane anisotropy was identified at low fields, confirming the b axis as an easy magnetization axis. Based on the fitting analysis of the strong uniaxial magnetic anisotropy, we observed that the main anisotropic effect arises from a spin–orbit-coupled magnetic exchange interaction affecting the OOP interaction. The effect of interlayer exchange interaction results in additional anisotropic terms owing to the tilting of the isospins. The results are relevant for understanding OOP magnetic anisotropy and provide a new way to analyze the effects of spin–orbit-coupling and interlayer magnetic exchange interactions. This study provides insight into the understanding of bulk magnetic, magnetotransport, and spintronic behavior on Sr2IrO4 for future studies.

Effect of crystal field on the magnetic and thermodynamic properties of the Ising mixed spin (1-1/2-1) three layers system of cubic structure

This work implemented Monte Carlo (MC) simulation to study the phase diagrams and magnetic properties of a mixed spin (1-1/2-1) three-layer system with a cubic structure. The effect of the crystal field on the system compensation, critical temperatures, magnetic and thermodynamic properties of the system have been explored. The crystal field was found to have a profound impact on the system compensation and critical temperatures. Our results suggest that the presence of the crystal field will cause the compensation temperature to exist for a short range of negative crystal field values. Furthermore, the threshold values of the crystal field were found to determine the change in both the compensation and critical temperatures with the variation of the crystal field. Moreover, a first-order phase transition presents at the threshold values of D. Finally, the system reveals the presence of two-step hysteresis loops for some temperatures and crystal field values.

Crystal field effect on the magnetic field dependence cooling exponent of 3D simple cubic spin-7/2 Ising model: A Monte Carlo study

Based on the Monte Carlo simulation, the magneto caloric effect of a spin-7/2 3D-Ising system with pure ferromagnetic interaction was studied. The effective magnetic field h dependent entropy change ΔS was examined and result shows that ΔS follows a quadratic polynomial of hn where n is the cooling exponent. In the high field region the quadratic term h2n becomes comparable with the linear term hn. The quadratic term is strongly suppressed by the increment of the crystal field coefficient D. The ratio of the coefficient of the linear and quadratic term B/C is nearly 250 for D = 4 J (J is the exchange coefficient) and the quadratic term becomes negligibly small compared with the linear term. Furthermore in this ferromagnetic Ising system n continuously decreases from 0.71 to 0.62 for the rise of effective crystal field coefficient De from 0 to 4. This happens due to the enhancement of the + 7/2 spin from 70% to 87% for the increment of the same amount of De. It turns the system from spin-σ to spin-1/2 3D-Ising in nature.

Magnetic anisotropy of transition metal and lanthanide ions in pentagonal bipyramidal geometry.

The magnetic anisotropy associated with a pentagonal bipyramidal (PBP) coordination sphere is examined on the basis of experimental and theoretical investigations. The origin and the characteristics of this anisotropy are discussed in relation to the electronic configuration of the metal ions. The effects of crystal field, structural distortion, and a second-coordination sphere on the observed anisotropies for transition meal and lanthanide ions are outlined. For the Ln derivatives, we focus on compounds showing SMM-like behavior (i.e. slow relaxation of their magnetization) in order to highlight the essential chemical and structural parameters for achieving strong axial anisotropy. The use of PBP complexes to impart controlled magnetic anisotropy in polynuclear species such as SMMs or SCMs is also addressed. This review of the magnetic anisotropies associated with a pentagonal bipyramidal coordination sphere for transition metal and lanthanide ions is intended to highlight some general trends that can guide chemists towards designing a compound with specific properties.

Об экспериментальном определении параметров интенсивности 4f-4f-переходов по спектрам излучения соединений европия (III)

Eu3+ complexes and specially β-diketonate compounds are well known and studied in several areas due to their luminescence properties, such as sensors and lightning devices. A unique feature of the Eu3+ ion is the experimental determination of the 4f-4f intensity parameters Ωλ directly from the emission spectrum. The equations for determining Ωλ from the emission spectra are different for the detection of emitted power compared to modern equipment that detects photons per second. It is shown that the differences between Ωλ determined by misusing the equations are sizable for Ω4 (ca. 15.5%) for several Eu3+β-diketonate complexes and leads to differences of ca. 5% in the intrinsic quantum yields Q_Ln^Ln. Due to the unique features of trivalent lanthanide ions, such as the shielding of 4f-electrons, which lead to small covalency and crystal field effects, a linear correlation was observed between Ωλ obtained using the emitted power and photon counting equations. We stress that care should be exercised with the type of detection should be taken and provide the correction factors for the intensity parameters. In addition, we suggest that the integrated intensity (proportional to the areas of the emission band) and the centroid (or barycenter) of the transition for obtaining Ωλ should be determined in the properly Jacobian-transformed spectrum in wavenumbers (or energy). Due to the small widths of the emission bands of typical 4f-4f transitions, the areas and centroids of the bands do not depend on the transformation within the experimental uncertainties. These assessments are relevant because they validate previously determined Ωλ without the proper spectral transformation.

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Eu3+ complexes and specially β-diketonate compounds are well known and studied in several areas due to their luminescence properties, such as sensors and lightning devices. A unique feature of the Eu3+ ion is the experimental determination of the 4f-4f intensity parameters Ωλ directly from the emission spectrum. The equations for determining Ωλ from the emission spectra are different for the detection of emitted power compared to modern equipment that detects photons per second. It is shown that the differences between Ωλ determined by misusing the equations are sizable for Ω4 (ca. 15.5%) for several Eu3+β-diketonate complexes and leads to differences of ca. 5% in the intrinsic quantum yields Q_Ln^Ln. Due to the unique features of trivalent lanthanide ions, such as the shielding of 4f-electrons, which lead to small covalency and crystal field effects, a linear correlation was observed between Ωλ obtained using the emitted power and photon counting equations. We stress that care should be exercised with the type of detection should be taken and provide the correction factors for the intensity parameters. In addition, we suggest that the integrated intensity (proportional to the areas of the emission band) and the centroid (or barycenter) of the transition for obtaining Ωλ should be determined in the properly Jacobian-transformed spectrum in wavenumbers (or energy). Due to the small widths of the emission bands of typical 4f-4f transitions, the areas and centroids of the bands do not depend on the transformation within the experimental uncertainties. These assessments are relevant because they validate previously determined Ωλ without the proper spectral transformation.

Crystal field-induced lattice expansion upon reversible oxygen uptake/release in YbMnxFe2−xO4

The mechanism for oxygen release and uptake is influenced by crystal field effects in the solid solution YbMnxFe2−xO4.

On the optical anisotropy in 2D metal-halide perovskites.

Two-dimensional metal-halide perovskites (MHPs) are versatile solution-processed organic/inorganic quantum wells where the structural anisotropy creates profound anisotropy in their electronic and excitonic properties and associated optical constants. We here employ a wholistic framework, based on semiempirical modeling (k·p/effective mass theory calculations) informed by hybrid density functional theory (DFT) and multimodal spectroscopic ellipsometry on (C6H5(CH2)2NH3)2PbI4 films and crystals, that allows us to link the observed optical properties and anisotropy precisely to the underlying physical parameters that shape the electronic structure of a layered MHP. We find substantial frequency-dependent anisotropy in the optical constants and close correspondence between experiment and theory, demonstrating a high degree of in-plane alignment of the two-dimensional planes in both spin-coated thin films and cleaved single crystals made in this study. Hybrid DFT results elucidate the degree to which organic and inorganic frontier orbitals contribute to optical transitions polarized along a particular axis. The combined experimental and theoretical approach enables us to estimate the fundamental electronic bandgap of 2.65-2.68 eV in this prototypical 2D perovskite and to determine the spin-orbit coupling (ΔSO = 1.20 eV) and effective crystal field (δ = -1.36 eV) which break the degeneracy of the frontier conduction band states and determine the exciton fine structure. The methods and results described here afford a better understanding of the connection between structure and induced optical anisotropy in quantum-confined MHPs, an important structure-property relationship for optoelectronic applications and devices.