Co-doped System Research Articles

Improvement of the Electroluminescence Performance of Exciplex‐Based OLEDs by Effective Utilization of Long‐Range Coupled Electron–Hole Pairs

AbstractAn effective method to utilize the radiation of long‐range coupled electron–hole pairs to improve the electroluminescence performance of exciplex‐based organic light‐emitting diodes (OLEDs) is realized by codoping an organic spacer into the bulk‐heterojunction exciplex emitter. The photoluminescence properties of the codoped films reveal that the fraction of delayed fluorescence will be clearly strengthened with an increasing codoping ratio, indicating that more triplet excitons can be utilized effectively, thus greatly enhancing the efficiency of exciplex‐based OLEDs. The maximum external quantum efficiency is improved by ≈105%, from 3.9% to 8.0%, and maintains 7.5% at a luminance of 1000 cd m−2; the codoped devices with the spacer also exhibit excellent spectrum stability under various applied voltages. Magneto‐electroluminescence properties are also investigated to verify the radiative process of long‐range coupled electron–hole pairs. Furthermore, based on this codoped system, low driving voltage, high efficiency, and low efficiency roll‐off are achieved in the orange phosphorescence OLEDs, indicating the advantage of this method in exciton regulation and utilization. This work can assist for further research to achieve high‐performance exciplex‐based OLEDs by adjusting the exciton behavior in device structure design.

Effect of Co doping on mechanism and kinetics of ammonia synthesis on Fe(1 1 1) surface

With the aim of improving the efficiency of the Haber-Bosch industrial process for the synthesis of ammonia, here we explore doping the traditional Fe-based Haber-Bosch catalyst with an impurity element. Starting from a previous experimentally-validated theoretical investigation of the reaction mechanism for Haber-Bosch synthesis of ammonia on the Fe bcc(1 1 1) surface, we focus on changes in mechanism and kinetics brought about by substitutional doping of 25% top layer iron with cobalt. The choice of Co is justified by the analysis of the wave functions of the critical reaction steps on the Fe(1 1 1) surface which showed that large changes in the net spin (magnetization) of the Fe atoms are thereby involved, and suggested that dopants with modified spins might accelerate rates. Quantum Mechanics values of free energies and reaction barriers are calculated for the Co-doped system for a set of 20 important surface configurations of adsorbates, and used as input to kinetic Monte Carlo (kMC) simulations to obtain final ammonia production. We find that at T = 673 K, P(H2) = 15 atm, P(N2) = 5 atm, and P(NH3) = 1 atm, target conditions to drastically reduce the extreme energy cost of industrial ammonia synthesis process, top-layer Co doping leads to an acceleration by a factor of 2.3 in reaction rates of ammonia synthesis, and therefore an expected corresponding decrease in production costs.

Influence of Zr–S co-doping on the electronic structure and optical properties of anatase TiO2: first-principles GGA + U method

Titanium dioxide has received much attraction in the field of photocatalysts applied for hydrogen production from the water splitting due to its unique set of desirable properties of non-toxicity, chemical and thermal stability, efficient photocatalytic activity and low cost. However, it is only active under ultraviolet irradiation because of the wide band gap, which limits its photocatalytic efficiency. In the present paper, the geometrical structure, dopant formation energy, electronic structure and optical properties of a series of Zr–S co-doped anatase TiO2 were calculated by the GGA + U method based on density functional theory to narrow the band gap and expand its light absorption edge. The results show that the hybridization of O2p and S3p changes the energy levels near the top of valence band and Zr4d orbital makes a certain separation of the O2p and Ti3d orbital in conduction bands, which is helpful to prevent the recombination of electron and hole. The distance between S and Zr atom in the supercell has a significant influence on the electronic structure and optical properties of the co-doped system. The edge of co-doped TiO2 absorption band has a certain degree of redshift. This study may provide theoretical guidance for its application in photocatalysts.

Investigation of Upconversion Photoluminescence of Yb3+/Er3+:NaLaMgWO6 Noncytotoxic Double-Perovskite Nanophosphors.

Bright fluorescent rare-earth-ion-doped upconversion nanomaterials are attractive choices for photonic devices. A remarkable green upconversion emission has been obtained by the sensitizing effect of Yb3+ in a Yb3+/Er3+:NaLaMgWO6 (NLMWO) nanophosphor under near-infrared (NIR) excitation. A citrate sol-gel method was employed to synthesize the nanophosphor samples. The lack of a secondary phase in the X-ray diffraction pattern confirms that the Er3+ and Yb3+ ions are incorporated in the ordered double-perovskite structure. Surface analysis and particle evaluation are performed by field-emission scanning electron microscopy and transmission electron microscopy analysis. Upconversion and downconversion emission performances were systematically studied by varying the dopant concentrations. A strong upconversion green emission can be observed with the naked eye, and it resembles the upconversion spectra of Er3+-doped phosphors. Remarkably, because of an energy-transfer process, the green upconversion emission can be converted into a strong red emission by codoping with Yb3+ ions. We observed the color tuning effect from green to red, which can be controlled by varying the Yb3+ concentration in the codoped phosphors during NIR excitation. A systematic investigation of the upconversion mechanism from Yb3+ to Er3+ doubly doped NLMWO nanocrystals is demonstrated. The upconversion mechanism was evaluated only by varying the excitation power of the laser as well. A strong NIR emission at 1.57 μm corresponding to Er3+ can be significantly enhanced by increasing the codoping concentration of Yb3+ ions. The energy migration pathway is accurately presented. The Commission internationale de l'éclairage color coordinates were analyzed for singly and doubly doped nanophosphors. The cytotoxicity of the codoped nanophosphor system was evaluated using WI-38 cell lines. This optimized codoped nanophosphor material is noncytotoxic; thus, it can be useful for in vitro studies in biological studies. On the basis of the obtained results, the NLMWO:Yb3+/Er3+ nanophosphors can be a promising choice for novel upconversion photonic applications.

Investigation of energy transfer in Pr3+, Yb3+ co-doped phosphate phosphor: The role of 3P0 and 1D2

The synthesis, crystal structure and photoluminescence and decay kinetics properties have been carried out for the Pr3+-Yb3+ co-doped YPO4 phosphors. Upon excitation with 447 nm, the intense emissions from 3P0, 1D2 and 1G4 excited states are all observed in the Pr3+ singly doped phosphors. The population of 1D2 state is attributed to cross-relaxation 3P0+3H4 → 1D2+3H6 and/or non-radiative multiphonon relaxation from 3P0 because of the larger maximum phonon energy of YPO4 host (1080 cm−1),which needs only 3–4 phonons to balance the energy gap between 3P0 and 1D2 excited states. For the Pr3+-Yb3+ codoped samples, the effect of Yb3+ concentration on the luminescence and decay kinetics of Pr3+ are investigated for the interpretation of observed experimental results. The observations and discussions manifest that the efficient energy transfer from Pr3+ to Yb3+ occurs, involving mainly 1D2 and 1G4 levels of Pr3+ ions instead of 3P0 level, which is not in accordance with many reported results. It is hoped that our results may give a new insights into the energy transfer mechanism in Pr3+-Yb3+ codoped system.

ANÁLISIS DE LAS PROPIEDADES ÓPTICAS DE TiO2 ANATASE DOPADO CON N y F EN BASE A CÁLCULOS DE PRIMEROS PRINCIPIOS

El uso de TiO2 en la construcción de celdas solares tiene una severa limitación; su band gap amplio de aproximadamente 3.2 eV que solo le permite absorber radiación en la región ultravioleta (UV) λ<380 nm. Esto reduce gravemente la utilidad de la energía solar al 5 %. En la presente investigación se usó el potencial de Perdew-Burke-Ernzerhof (PBE) en el marco de la teoría funcional de la densidad (DFT) implementada en el código WIEN2k que usa las ondas planas aumentadas linearizadas (FP-LAPW) como aproximación de la base para los orbitales de Kohn-Sham, para calcular las propiedades ópticas y estructura electrónica de TiO2 dopado con N y/o F. Se ha observado que la fase anatasa de TiO2 dopada con F, N o el codopado F-N exhibe una disminución en el band gap hasta en un 17% para el dopado con N a una concentración de 10.4 %, y que esta reducción del gap está asociada a la mejor absorción en la zona visible del espectro de los sistemas estudiados. Los resultados indican que TiO2 anatasa dopado en distintas concentraciones puede aumentar la eficiencia de celdas fotovoltaicas y que este aumento en la eficiencia es proporcional a la concentración del elemento dopante para los sistemas monodopados. El codopado, que continuamente es reportado como mejor, en cuanto a la reducción del gap y la absorción de radiación, en comparación con el monodopado, no ha mostrado serlo en el sistema de codopado por sustitución con N y F.

Exploration of Atomic Scale Changes during Oxygen Vacancy Dissociation Mechanism in Nanostructure Co-Doped Ceria: As Electrolytes for IT-SOFC

The work provides key insight of extrinsic and intrinsic oxygen vacancies clustering, dissociation mechanism and their influence on oxy-ion conductivity in co-doped ceria system. For present attempt, we develop aliovalent co-doped ceria system Ce0.85Ca0.15/2M0.15/2O2-δ (M = Sm, Gd, Nd Dy and Sr) with optimize compositions as electrolytes for IT-SOFCs. Structure of all samples are confirmed by X-ray diffraction (XRD) and analyzed by Rietveld refinement using Full-Prof suite. Oxygen vacancies clustering are observed by X-ray absorption techniques (EXAFS & XANES) and Raman spectroscopy. Two separate Raman mode related to extrinsic and intrinsic oxygen vacancies defect spaces are detected; dissociation of oxygen vacancies from the defect clustering are realized from systematic decrease in intensity of the respective Raman mode with temperature. The EXAFS study demonstrates reduction in coordination number with enhancement in interatomic spacing, and disorder factor with increasing temperature. The results are evidenced for oxygen vacancies dissociation from cluster. XANES study reveals co-dopants in ceria causes: (i) suppression of reducing ability of Ce4+ to Ce3+ and (ii) asymmetric distribution of Ce-O in CeO8 polyhedron. Oxy-ion conductivity of co-doped ceria systems are determined by using complex impedance spectroscopy. Co-dopant induced atomic-scale restructuring and oxygen vacancies dissociations are found strongly influence on conduction mechanism.

Electronic and optical properties of n-pr co-doped anatase TiO<sub>2</sub> from first-principles

ZnO is a wide bandgap semiconductor with the advantages of good stability, strong radiation resistance, and low cost. It has become a hot material in the field of photocatalysis, but it can only absorb purple light. Therefore, it is a valuable problem to study how to expand the response range of ZnO to visible light. Doping modification is a common method to solve this problem. In order to carry out the relevant research, the calculation in this paper are carried out by the CASTEP tool in Materials Studio software based on the first-principles of ultrasoft pseudopotential of density functional theory, the geometric structures of ZnO, Zn<sub>0.875</sub>Pr<sub>0.125</sub>O, ZnO<sub>0.875</sub>N<sub>0.125</sub>, Zn<sub>0.875</sub>Pr<sub>0.125</sub>O<sub>0.875</sub>N<sub>0.125</sub>, Zn<sub>0.75</sub>Pr<sub>0.25</sub>O<sub>0.875</sub>N<sub>0.125</sub>, Zn<sub>0.625</sub>Pr<sub>0.375</sub>O<sub>0.875</sub>N<sub>0.125</sub> are constructed. All the models are based on the optimization of the geometry structure. By using the method of generalized gradient approximation plus U, we calculate the band structure, density of states, population, absorption spectra and dielectric functions of the models. The results show Co-doped system is easier to form than single-doped system, and the stability of the co-doped system increases first and then decreases with the increase of Pr concentration. The population ratio of the shortest Zn-O bond to the longest Zn-O bond in the same system increases first and then decreases with the impurity concentration, which shows that the doping of impurities has a great influence on the lattice distortion of the system, and the distortion is benefit for the separation of photogenerated hole-electron pairs. Therefore, the photocatalytic activity of the materials can be improved. Hybridization of N-2p and Pr-4f states destroys the integrity of crystals and forms crystal fields around impurity atoms, which results in splitting of energy levels and narrowing of bandgap. Compared with intrinsic ZnO, the static dielectric constant of all doped systems increases, especially the constant of Pr-N co-doped systems increases with the increase of doped Pr concentration, which indicates that the polarization ability of the co-doped systems increases with the increase of doped Pr atomic concentration. The main peaks of the dielectric function imaginary part of the doping systems move to the low energy region, and the absorption spectrums are red-shifted. As the concentration of impurity Pr atom increases, in the visible region, the absorption capacity of each co-doped system increases, their response range is enlarged in turn, showing the co-doping of N and Pr is benefit for improving the photocatalytic activity of ZnO.

Sb3+ and Gd3+ co-doped Cerium oxide Nanocrystalline Ceramic system: Structural and Dielectric Studies

Nanostructured ceramic materials have high conductivity compared to bulk materials. Ceria based systems, with fluorite structure, [samarium doped ceria (SDC) and gadolinium doped ceria (GDC)] are found to be the best electrolyte materials for intermediate temperature solid oxide fuel cells (IT-SOFC). In the present study, Ce0.8Gd0.1Sb0.1O2-δ nanostructured materials were synthesized by wet co-precipitation method. X ray diffraction pattern confirms the crystallization of the sample in the most conducting cubic fluorite phase. The presence of Ce, Gd, and Sb in the sample is qualitatively confirmed by Fourier transform infrared spectroscopy. Scanning electron spectroscopy image shows mesoporous nature of the sample. The addition of Sb3+ to the GDC system reduces the sintering temperature by 33.33%. The dielectric studies show that the prepared sample is an ionic material with two types of conduction mechanisms – grain interior and grain boundary. Hence, two different activation energies for ionic conduction are obtained for the sample at low and high temperature region.

Electronic structures and optical properties of Ce-doped anatase TiO<sub>2</sub> with oxygen vacancy

<sec> The crystal structures, defect formation energy, electronic structures and optical properties of oxygen vacancy and/or Ce-(co)doped anatase TiO<sub>2</sub> are investigated by using density functional theory plus <i>U</i> calculations. </sec><sec> The calculated results indicate that lattice distortion induces the enhanced octahedral dipole moment in Ce doped TiO<sub>2</sub> crystal when introducing oxygen vacancy into the lattice of the TiO<sub>2</sub> crystal, which is effective for separating the photo-excited electron-hole pairs; meanwhile, compared with the valence band of pure TiO<sub>2</sub> and TiO<sub>2</sub> mono-doped separately with Ce and oxygen vacancy, the valence band of TiO<sub>2</sub> co-doped with Ce and oxygen vacancy broadens drastically, which is mainly contributed from the electronic states of Ce 5d, Ti 4s and O 2p in the valence band shifting toward the lower energy direction. As a result, Ce doped TiO<sub>2</sub> with oxygen vacancy is beneficial to the mobility of photo-generated carriers in TiO<sub>2</sub>. Similarly, the anti-bonding states also move toward the lower band energy direction, which are formed by the mixture of Ce 4f, Ce 5d, Ti 3d, and O 2p orbits in the conduction band. Due to these shifts, the energy gap of Ce and oxygen vacancy codoped TiO<sub>2</sub> is narrowed to 2.67 eV with the emerge of the occupied impurity energy levels near Fermi level. Because of the above-mentioned excellence features, the absorption spectra for doped systems exhibit remarkable red-shift, especially, the intensity of optical absorption of TiO<sub>2</sub> co-doped with Ce and oxygen vacancy in the visible region and the infra-red region are obviously stronger than those of the Ce mono-doped TiO<sub>2</sub>. </sec><sec> When introducing oxygen vacancy into the Ce-doped system, the calculated conduction band energy edge position changes from −0.27 eV to −0.32 eV, which implies that the reducing power of the conduction band edge of TiO<sub>2</sub> is remarkably enhanced. More fascinatingly, the calculated band energy edges for the Ce and oxygen vacancy codoped TiO<sub>2</sub> can satisfy the basic requirement for water splitting under visible light irradiation.</sec><sec> In conclusion, Ce and oxygen vacancy co-doped system can effectively strengthen the photo-catalytic activity of TiO<sub>2</sub> and improve the utilization of the solar light; and our calculated results provide a powerful theoretical basis for the applications of the Ce and oxygen vacancy co-doped anatase TiO<sub>2</sub> in visible-light-driven water splitting in the future research. </sec>

Effects of Se substitution and transition metal doping on the electronic and magnetic properties of a MoSxSe2-x/h-BN heterostructure.

The van der Waals heterostructures created by stacking two monolayer semiconductors have been rapidly developed experimentally and exhibit various unique physical properties. In this work, we investigate the effects of Se atom substitution and 3d-TM atom doping on the structural, electronic, and magnetic properties of the MoSe2/h-BN heterostructure, by using first-principles calculations based on density functional theory (DFT). It is found that Se atom substitution could considerably enhance the band gaps of MoSe2/h-BN heterostructures. With an increase in the substitution concentration, the energy band changes from an indirect to a direct band gap when the substitution concentration exceeds a critical value. For 3d-TM atom doping, it is shown that V-, Mn-, Fe-, and Co-doped systems exhibit a half-metallic state and magnetic behavior, while there is no spin polarization in the Ni-doped case. The results provide a theoretical basis for the development of diluted magnetic semiconductors and spin devices based on the MoSxSe2-x/h-BN heterostructure.

Efficient Visible-to-NIR Spectral Conversion for Polycrystalline Si Solar Cells and Revisiting the Energy Transfer Mechanism from Ce3+ to Yb3+ in Lu3Al5O12 Host.

The so-called Shockley-Queisser converting efficiency limit of Si solar cells is believed to be surpassed by using the spectral converter. However, searching for efficient spectral converting materials is still a challenging task. In this paper, efficient visible-to-NIR spectral conversion for polycrystalline Si solar cells has been demonstrated in Ce3+ and Yb3+ codoped Lu3Al5O12. Moreover, the underlying energy transfermechanism from Ce3+ to Yb3+ is systematically re-investigated by the detailed excitation and emission spectra as well as fluorescent decay curves, and our results demonstrate that fast metal-to-metal charge transfer from Ce3+ to nearby Yb3+ is the dominant energy transfermechanism. Finally, we provide new evidence that Ce4+-Yb2+ charge-transfer state is responsible for the relatively low quantum efficiency of NIR emission in Ce3+ and Yb3+ codoped system.

Photoluminescence properties and crystal structure of BaSiO3:xEu3+, yBi3+ red phosphor synthesized by co-precipitation method

The Ba1-xSiO3:xEu3+ (x = 0.0025, 0.02, 0.04, 0.06, 0.08, 0.09), Ba0.996SiO3:0.004Bi3+ and Ba0.92-ySiO3:0.08Eu3+, yBi3+ (y = 0, 0.001, 0.0025, 0.004, 0.005, 0.01) phosphors have been synthesized by chemical co-precipitation method combined with one calcination of the corresponding precursors in air. Then the XRD, XPS and spectrophotometer have been carried out to analyze the crystal structure and photoluminescence properties of the phosphor. The structure of samples is orthorhombic and the space group is P212121. Meanwhile, Bi3+ co-doped system shows a broadened charge transfer band (CTB) and the highest peak of CTB has red shifted from 246 to 274 nm due to an overlap of the transition from O2− to Bi3+. The symmetry of Eu3+ ions is distorted by co-doping Bi3+ ion and the efficient energy transfer from Bi3+ to Eu3+ ions enhances the photoluminescence intensities of the BaSiO3:Eu3+, Bi3+ phosphors significantly. The optimum concentration of Eu3+ and Bi3+ ions in BaSiO3 is 8 mol% and 0.4 mol%, respectively. Additionally, the CIE 1931 chromaticity coordinates of Ba0.916SiO3:0.08Eu3+, 0.004Bi3+ excited by 274 and 393 nm are located at red region. The PL emission spectra of the optimized phosphor at different temperatures show an excellent thermal stability, it remains 87.6% of photoluminescence intensity at 25 °C when the temperature reaches 100 °C. Moreover, the activation energy (Ea) is calculated to be 0.27 eV. These results indicate that BaSiO3:Eu3+, Bi3+ phosphors are the suitable candidates for commercial red phosphor.

The mechanism of photocatalyst and the effects of co-doping CeO2 on refractive index and reflectivity from DFT calculation

In this paper, the structural, electronic and optical properties of (N, P), (N, S), (C, P) and (C, S) co-doped CeO2 are studied by using the method of density functional theory (DFT) + U method. The calculated lattice constant, the charge, the bond order, the cell volume and the bond length of CeO2 are consistent with previous experimental and theoretical results. For co-doped CeO2 systems, the calculated results show that the lattice constants, the bond order of CeO as well as the cell volume increase, while the charge of Ce decrease. Due to co-doping, the energy gap (Eg) between valence band and conduction band becomes narrower than that of pure CeO2. Meanwhile, the electron structures of the co-doped CeO2 are changed, which may lead to transformation of optical properties. Nonmetallic atomic orbital (C 2p, N 2p, P 3p, S 3p) and metal atomic orbital (Ce 4f and 5d) are hybridized, except for the hybridization between Ce (4f and 5d) and O (2p). Compared with CeO2, Eg between Ce 4f and Ce 5d becomes smaller. Further, the optical absorption, refractive index and reflectivity of them are investigated. The calculated results reveal that their absorption edges have a red shift. Co-doping enhances visible light photocatalytic activity, which is related to the transition of valence band → conduction band, and Ce 4f → Ce 5d. The co-doped CeO2 has high refractive index and reflectivity. Therefore they may be becoming an important materials in single (or multilayered) optical coatings and optical reflective pigments.

Spectroscopic evaluation a new and novel Nd3+/Yb3+ co-doped CdO-V2O5 glass system for 1 μm laser application

Structural and spectral evaluations of Nd3+ and Nd3+/Yb3+ doped CdO-V2O5 glasses based on X-Ray diffraction, Raman spectroscopy, absorption, excitation and emission spectra and decay time profiles, are performed. X-Ray diffraction patterns and Raman spectroscopy revealed that all samples are amorphous (glassy phase) up to 4 mol% of Yb3+, without segregation of any crystalline phase. The optical band gap values determined from the absorption spectra, assuming direct optical band gap, were in the range of 2.13–2.07 eV, depending on the Yb3+ concentration. The emission spectra of the Nd3+ and Nd3+/Yb3+ doped glasses upon Nd3+ excitation at 585 nm, displayed the NIR Nd3+ feature emissions centered at 880, 1060 and 1342 nm, and Yb3+ emission at 977 nm, being the latter one achieved at expenses of energy transfer from Nd3+. According to the shortening of the Nd3+ emission decay profiles such process is not radiative with efficiency in the range of 0.181–0.521, depending on the Yb3+ content. The 880 nm Nd3+ decay fitting using the Inokuti-Hirayama model considering, energy migration among donors, suggested that an electric dipole-dipole interaction might mediate the energy transfer process, within Nd3+-Yb3+ clusters.

Influence of Co Doping on the Structural, Dielectric and Raman Properties of Ba0.75Sr0.25Ti1−xCoxO3

We synthesized Ba1−xSrxTiO3 (BST) and Co doped Ba0.75Sr0.25CoxTi1−xO3 (BSCTx) compositions (x = 0.03, 0.05, 0.07) by the solid state reaction route and probed the effect of Co-doping on the structural, microstructural, dielectric and phonon behaviour. Room temperature x-ray diffraction patterns of sintered ceramics reveal perovskite type average cubic crystalline structure (space group Pm-3m) for all doped compositions, whereas, pure BST composition stabilizes in the tetragonal crystalline phase (space group P4mm). Absence of any impurity peaks in the doped samples reveals that Co-ions are entering into the lattice without any metal clustering. Quantitative full profile fitting using Reitveld refinement fits well in the cubic phase giving a small value of goodness of the fitting parameter (Rwp). The real part of the dielectric permittivity as well as dielectric loss (tan δ) decreases with Co-doping indicating that intrinsic defects get annealed with doping. \( (\varepsilon^{\prime}/\varepsilon^{\prime\prime} - T) \) plots clearly show the cubic to tetragonal phase transition in BST at around 50°C, whereas Co-doped samples show no such transition in the temperature range studied. Temperature dependent Raman spectra reveal the characteristic phonon modes associated with the tetragonal phase at room temperature, whereas, Co-doped samples exhibit only bands associated with local disorder in the cubic phase. The spectral features of tetragonal phase appear around − 10°C in the 3% Co-doped system indicating the decrease of transition temperature with Co-doping. The analysis of deconvoluted Raman parameters using two sub-lattice models clearly reveals the structural disorder due to doping with slightly distorted TiO6 octahedra getting almost perfect thus giving rise to a cubic phase in the doped system.

First-principles investigation on the interlayer doping of SnSe2 bilayer

Using density functional theory calculations, we systematically investigated the effects of numbers and types of transition metals (TM) on the magnetic property of SnSe2 bilayer nanosheet. Our results revealed that, when one TM is introduced into the interlayer, the magnetic moment induced by the Co and Ni is tiny while it is largely strengthened with the doping of V, Cr, Mn, and Fe. When two TMs are inserted into the interlayer, V and Cr make the system change into a weak antiferromagnetism (AFM) state while Mn-, Fe-, Co-doped systems display a weak ferromagnetism (FM) ground state. These FM states have the magnetic moments which double those of the one TM–doping systems. With the TM numbers further increasing to four, the robust AFM and FM features appear with the doping of Fe and Mn, respectively. Ni cannot induce any magnetism whatever the numbers of Ni are filling in. Interestingly, with the increase of the numbers of dopants, transitions from FM to AFM and AFM to FM are predicted to be realized on Fe-SnSe2 and Cr-SnSe2 systems, respectively. This kind of transition may be important for the applications in spintronic devices.

Monodisperse Na0.39Y0.61F2.35:Ln3+ (Ln=Dy, Tb, Eu) and NaYF4 nano-/micromaterials: Controllable morphology, porous structure, tunable multicolor and energy transfer

In this paper, monodisperse and uniform Na0.39Y0.61F2.35 (denoted as NYF hereafter) and NaYF4 nano-/micromaterials were synthesized by trisodium citrate (labeled as Cit3-) assisted one-step hydrothermal method. Various morphologies and sizes could be easily modulated by changing the ratio of reactants under the alkaline conditions, including porous nanoparticles, microrods stacked by nanospheres, turtle shell-like and hexagonal microprisms. XRD, SEM, photoluminescence (PL) and nitrogen adsorption desorption were used to characterize the prepared samples. Additionally, by co-doping the Tb3+, Eu3+ and tri-doping Dy3+, Tb3+, Eu3+ ions into the NYF host and tuning their relative concentration ratio, multicolor tunable emissions were obtained. The energy transfer process from Tb3+ to Eu3+ was studied in co-doped and tri-doped systems and demonstrated to be an exchange interaction mechanism. These results show that the NYF porous nanomaterials may have potential applications in the field of luminescence.

Electronic and magnetic properties of new half-metallic ferromagnetic rutile Ti1–x–yVxNiyO2 (x = y = 6.25%): A first-principles study

We report electronic and magnetic properties of the new half-metallic ferromagnetic co-doped system of rutile Ti1–x–yVxNiyO2 (x = y = 6.25%). The semiconductor ferromagnetic doped system of rutile Ti1–xVxO2 (x = 6.25%) system is revisited as the reference. The plane-wave GGA + U method was used after choosing U at Ti 3d site in the fully-optimized rutile TiO2. The co-doped system exhibits the total magnetic moment of 1.41 μB/Ni atom localized at the V and Ni sites which is significantly higher than that of the doped system. Interestingly, the local ferrimagnetism centered at the cations of V4+ and Ni3+ is found with the minor contribution from their nearest-neighboring O2− ions bound via the p-d hybridization. The Ni3+ ion induces the half-metallic behavior by introducing spin-up hole O 2p states above the Fermi energy level. Finally, the GGA + U provides accurate energy positions of sub-V 3d and Ni 3d states under the elongation Jahn-Teller distortion at the VO6 and NiO6 octahedra. Our result shows the significant effect of Ni3+ ion in modifying the electronic and magnetic properties of the rutile Ti1–xVxO2 system. This study presents the essentials properties which can be a guide for experiments.

Chrome influence on the physical properties of Bi0.90Ba0.10Fe0.90Ti0.10O3 multiferroic ceramic system

Bi0.90Ba0.10Fe0.90Ti0.10O3 and Bi0.90Ba0.10Fe0.88Cr0.02Ti0.10O3 multiferroic ceramics were prepared, in order to evaluate the chrome influence on the physical properties of Ba2+ and Ti4+ co-doped BiFeO3 system. The structural properties revealed, at room temperature, a rhombohedral (R3c) ferroelectric phase for the studied compositions. The dielectric analysis was carried out in a wide temperature and frequency ranges. The dielectric results have shown a clear magneto-electric coupling, which is associated to the presence of a dielectric anomaly around the antiferromagnetic-paramagnetic transition temperature. Additionally, the Cr3+ ions play an important role decreasing the electrical conductivity of the studied compositions. The doping element has also shown an important influence on the magnetic hysteresis results.