Search

By means of ab initio density functional theory calculations taking into account electronic correlation and van der Waals force, we conducted comprehensive studies of the electronic and magnetic properties, as well as structural and magnetic ordering evolution under pressure of the square lattice antiferromagnets AMoOPO4Cl (A = K, Rb) containing Mo5+ ions with S = 1/2, theoretically predicted as the potential candidates for achieving quantum phases, existing in the boundary regimes for spin-1/2 J1 - J2 square lattice magnets. Our results indicate that the columnar antiferromagnetic ordering, experimentally determined, is the magnetic ground state of the ambient P4/nmm phase, stabilized by the predominant antiferromagnetic next nearest neighbor interaction J2 in the diagonal directions of the square lattice, regardless of the effective Hubbard amendment values. More importantly, the P4/n phase, involving the mutual twisting of the MoO5Cl and PO4 polyhedra, satisfactorily reproduces the experimentally observed structural transition and the subsequent magnetic ordering transition from columnar antiferromagnetic ordering to Néel antiferromagnetic one, identified to be the appropriate high pressure structure. Furthermore, the mechanism underlined responsible for the magnetic ordering transition at high pressure has been disclosed in terms of density of states and spin density isosurface analysis across the transition. The loss of mirror plane symmetry in the P4/n phase activates the P 3s orbitals to participate in the magnetic interaction, giving rise to a competitive ferromagnetic superexchange interaction, in addition to antiferromagnetic direct one, and consequently initiating the magnetic ordering transition. The insights revealed here not only deepen our understanding of the electronic properties and structural and magnetic ordering transitions under high pressure of square lattice antiferromagnets AMoOPO4Cl (A = K, Rb), but also push the boundaries of knowledge by recognizing the role of nonmagnetic ions P 3s in magnetic exchange coupling. [ABSTRACT FROM AUTHOR]

Monodisperse β-NaYF4:Ln3+ (Ln = Yb/Er, Yb/Tm) single micro/ nanocrystals were first one-pot fabricated at 50 °C through a novel synthetic route containing two pivotal processes: (a) synthesis of a β-NaYF4 {0001} unit layer through a novel style of ion-exchange from Y2(OH)5NO3nH2O (LYH) and (b) the subsequent oriented- assembly process. [ABSTRACT FROM AUTHOR]

A series of Ca2SrAl2O6:Ce3+,Li+,Mn2+ phosphors have been synthesized by traditional solid state reactions. The structure and photoluminescence properties of the samples together with the energy transfer from Ce3+ to Mn2+ ions have been investigated in detail. The obtained phosphors can be excited efficiently by UV excitation and exhibit a broad blue-green emission band peaking at 470 nm and an orange-red emission band at 610 nm, which result from the f-d transition of the Ce3+ and the 4T1-6A1 transition of the Mn2+ ions, respectively. By varying the doping concentration of the Mn2+ ion, a series of tunable colors including white are obtained at an irradiation of 355 nm. The possible energy transfer mechanism was proposed in terms of the experimental results and analysis of photoluminescence spectra and decay curves of the phosphors. The critical distance between the Ce3+ and Mn2+ ions has been calculated by both the concentration quenching method and the spectral overlap method. Preliminary studies on the properties of the phosphor indicated that our prepared Ca2SrAl2O6:Ce3+,Li+,Mn2+ phosphor might have potential application as a single-phase white-emitting phosphor for WLEDs. [ABSTRACT FROM AUTHOR]

Well-defined t-LaVO4:Eu3+ microcrystals have been synthesized through a facile hydrothermal route using La0.95Eu0.05(1,3,5-BTC)(H2O)6 as a precursor for the first time. It was found that the pH value and temperature have a remarkable influence on the morphology determination. By tuning the initial pH value, uniform micro cubes and cuboid rods can be obtained. The possible growth mechanism has been discussed, underlying the systematic time-dependent phase transition and morphological evolution. In addition, the luminescence properties showed that the cuboid rod-shaped LaVO4:Eu3+ sample shows a slightly stronger red emission than the cube-shape one. Our novel synthetic route may provide some new guidance in the design and controlled synthesis of inorganic nano/micromaterials. [ABSTRACT FROM AUTHOR]

Presently considerable interest in phosphor-converted warm LEDs which meet the stringent requirements of general illumination is stimulated. Here we report warm white LEDs made by altering the crystal structure and doping ions, which can govern the luminescence pattern to modulate the correlated color temperature and color-rendering index. [ABSTRACT FROM AUTHOR]

The Eu2+ → Tb3+ → Sm3+ energy transfer scheme has been proposed to realize the sensitization of Sm3+ ion emission by Eu3+ ions. Following this energy transfer model, near-UV convertible Sm3+-activated orange phosphors have been obtained in Sr3Y(PO4)3:Eu2+, Tb3+, Sm3+ powders. [ABSTRACT FROM AUTHOR]

By direct precipitation in solution at room temperature, cerium benzendicarboxylate complexes with various morphologies have been obtained facilely for the first time. After calcination, CeO2with large surface areas can be obtained, which inherited their parents' morphologies and exhibited better catalytic properties for CH4oxidation than commercial CeO2. [ABSTRACT FROM AUTHOR]