Yeju Huang

Ca9Lu(PO4)(7):Eu2+,Mn2+: A Potential Single-Phased White-Light-Emitting Phosphor Suitable for White-Light-Emitting Diodes

A novel white-light-emitting phosphor Ca(9)Lu(PO(4))(7):Eu(2+),Mn(2+) has been prepared by solid-state reaction. The photoluminescence properties indicate that there is an efficient energy transfer from the Eu(2+) to Mn(2+) ions via a dipole-quadrupole reaction. The obtained phosphor exhibits a strong excitation band between 250 and 430 nm, matching well with the dominant emission band of a UV light-emitting-diode (LED) chip. Upon excitation of UV light, white light is realized by combining a broad blue-green emission band at 480 nm and a red emission band at 645 nm attributed to the Eu(2+) and Mn(2+) ions. The energy-transfer efficiency and critical distance were also calculated. Furthermore, the phosphors can generate lights from blue-green through white and eventually to red by properly tuning the relative ratio of the Eu(2+) to Mn(2+) ions through the principle of energy transfer. Preliminary studies showed that the phosphor might be promising as a single-phased white-light-emitting phosphor for a UV white-light LED.

White-light emission from a single-emitting-component Ca9Gd(PO4)7:Eu2+,Mn2+ phosphor with tunable luminescent properties for near-UV light-emitting diodes

Ca9Gd(PO4)7 and Ca9Gd(PO4)7:xEu2+,yMn2+ were synthesized by solid-state reaction. The refinement confirmed that Ca9Gd(PO4)7 belongs to space group R3c (No. 161) with unit cell parameters a = 10.4526 A, c = 37.3769 A, V = 3536.61 A3, and Z = 6. Upon the excitation from 250 to 430 nm, the Ca9Gd(PO4)7:xEu2+,yMn2+ phosphors exhibit a broad blue-green emission band at 490 nm and a red emission band at 645 nm, which originate from the Eu2+ and Mn2+ ions, respectively. The varied emitted color from blue-green through white and eventually to red can be achieved by properly tuning the relative ratio of the Eu2+ to Mn2+ ions in the phosphors through the energy transfer from the Eu2+ and Mn2+ ions. The energy transfer from Eu2+ to Mn2+ was demonstrated to be a resonant type via a dipole-quadrupole reaction by the luminescence spectra, energy transfer efficiency, and decay curves of the phosphors. Furthermore, the critical distance of the Eu2+ and Mn2+ ions has also been calculated. More importantly, compared to the multiple emitting components of white LEDs system, single-emitting-component phosphors would enable easy fabrication with perfect stability and color reproducibility.

Sr3Al2O5Cl2:Ce3+,Eu2+: A potential tunable yellow-to-white-emitting phosphor for ultraviolet light emitting diodes

The Sr3Al2O5Cl2:Ce3+,Eu2+ phosphors were prepared by solid state reaction. The obtained phosphors exhibit a strong absorption in the UV-visible region and have two intense emission bands at 444 and 609 nm. The energy transfer from the Ce3+ to Eu2+ ions was observed, and the critical distance has been estimated to be about 24.5 A by spectral overlap method. Furthermore, the developed phosphors can generate lights from yellow-to-white region under the excitation of UV radiation by appropriately tuning the activator content, indicating that they have potential applications as an UV-convertible phosphor for white light emitting diodes.

Facile and rapid fabrication of metal―organic framework nanobelts and color-tunable photoluminescence properties

Novel one-dimensional terbium 1,3,5-benzenetricarboxylate nanobelts have been synthesized on a large scale through direct precipitation in solution phase without the assistance of any surfactant, catalyst, or template. The as-obtained nanobelts present crystallinity in spite of the moderate reaction conditions, exhibiting 1D helical strands and a 3D network framework. The influence of the reaction temperature, concentration, molar ratio of reactants, and solvent on the belt-like nanostructure has been discussed in detail. A possible mechanism based on the crystal structure of the compound is proposed to account for the formation of the nanobelts. A detailed investigation of the photoluminescence of Tb(1,3,5-BTC)(H2O)·3H2O nanobelts indicates that the optical properties of these phosphors are dependent on their size. More interestingly, the luminescence color of the Tb(1,3,5-BTC)(H2O)·3H2O:Eu3+ nanobelts can be easily tuned from green to green-yellow, yellow, orange and red-orange due to the energy transfer from the Tb3+ to Eu3+ ions by changing the doping concentration of activator ions.

Color point tuning of Y3Al5O12:Ce3+ phosphor via Mn2+-Si4+ incorporation for white light generation

In this paper, the color point tuning of Y3Al5O12 : Ce3+ phosphor has been realized by the incorporation of Mn2+–Si4+. The Mn2+ ions occupy the dodecahedral crystallographic Y3+ site, while the Si4+ ions substitute the tetrahedral Al3+ crystallographic site in the obtained powder. Under 450 nm excitation, the YAG : Ce3+,Mn2+,Si4+ samples exhibit the typical yellowish-green emission band of the Ce3+ ions, as well as an orange emission band of the Mn2+ ions. Furthermore, the intensity ratio of the orange/yellowish-green band can be enhanced through the increase of Mn2+–Si4+ content. The intense orange emission band of the Mn2+ ions is attributed to the effective energy transfer from the Ce3+ to Mn2+ ions, which has been justified through the luminescence spectra and the fluorescence decay dynamics. The related mechanism was demonstrated to be the electric dipole–quadrupole interaction based on the Inokuti–Hirayama theoretical model, and critical distance is calculated to be 8.6 A by the spectral overlap method.

Sacrificial Template Method for Fabrication of Submicrometer-Sized YPO4:Eu3+ Hierarchical Hollow Spheres

Large-scale good-quality submicrometer-sized YPO(4):Eu(3+) hollow spheres were synthesized by utilizing the colloidal spheres of Y(OH)CO(3):Eu(3+) as a sacrificial template and NH(4)H(2)PO(4) as a phosphorus source, for the first time. The whole process mainly consists of the hydrothermal reaction and acid erosion. The YPO(4):Eu(3+)@Y(OH)CO(3):Eu(3+) core-shell structures were first obtained after the hydrothermal process. Then, the remaining Y(OH)CO(3):Eu(3+) was removed by selective dissolution in a dilute nitric acid solution. The YPO(4):Eu(3+) hollow spheres were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence (PL). The formation mechanism was also investigated. The obtained YPO(4):Eu(3+) hollow spheres may have potential applications in cell biology, drug release, and diagnosis, due to high chemical stability and luminescence functionality.

Facile synthesis and luminescence of uniform Y2O3 hollow spheres by a sacrificial template route.

Uniform Y(2)O(3) hollow microspheres have been successfully prepared via a urea-based homogeneous precipitation technique with colloidal melamine formaldehyde (MF) microspheres as templates followed by a subsequent calcination process. X-ray diffraction, energy dispersive X-ray analysis, and Fourier transform infrared spectroscopy results show that the MF templates can be effectively removed, and the amorphous precursor has converted to crystalline Y(2)O(3) during the annealing process. Scanning electron microscopy and transmission electron microscopy images indicate that the Y(2)O(3) hollow spheres inherit a spherical shape and good dispersion of MF templates, and the shell of the hollow spheres is composed of a large amount of uniform nanoparticles. The lanthanide activator ion Ln(3+)-doped Y(2)O(3) hollow microspheres exhibit bright down- and upconversion luminescence with different colors coming from different activator ions under ultraviolet or 980 nm light excitation, which may find potential applications in fields such as light phosphor powders, advanced flat panel displays, or drug delivery.

Highly Uniform and Monodisperse Gd2O2S:Ln3+ (Ln = Eu, Tb) Submicrospheres: Solvothermal Synthesis and Luminescence Properties

Gd(2)O(2)S:Ln(3+) (Ln = Eu, Tb) submicrospheres were successfully prepared through a facile and mild solvothermal method followed by a subsequent heat treatment. X-ray diffraction (XRD) results demonstrate that all the diffraction peaks of the samples can be well indexed to the pure hexagonal phase of Gd(2)O(2)S. The energy dispersive spectroscopy (EDS), element analysis, and FT-IR results show that the precursors are composed of the Gd, Eu, O, S, C, H, and N elements. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results show that these spheres are actually composed of randomly aggregated nanoparticles. The formation mechanism for the Gd(2)O(2)S:Ln(3+)(Ln = Eu, Tb) spheres has been proposed on an isotropic growth mechanism. Under ultraviolet excitation, Gd(2)O(2)S:Ln(3+)(Ln = Eu, Tb) spheres show red and green emission corresponding to the (5)D(0)→(7)F(2) transition of the Eu(3+) ions and the (5)D(4)→(7)F(5) transition of the Tb(3+) ions. Furthermore, this synthetic route may have potential applications for fabricating other lanthanide oxysulfides.

Mutifuntional GdPO4:Eu3+ Hollow Spheres: Synthesis and Magnetic and Luminescent Properties

Mondispersed submicrometer GdPO(4):Eu(3+) hollow spheres were synthesized via an effective one-pot hydrothermal process. These hollow spheres have the average diameter of 200 nm, and the shell thickness is about 20 nm. The surface of the spheres consists of a number of nanorods with diameters of about 10 nm and lengths of about 50-80 nm. Both magnetic and luminescent properties of the obtained Eu(3+)-doped GdPO(4) hollow spheres were investigated. The hysteresis plot (M-H) analysis result indicates their paramagnetic property. The fluorescence spectra demonstrate that they emit orange-red color light originated from the (5)D(0) → (7)F(J) transitions of the Eu(3+) ions. Therefore, the obtained GdPO(4) hollow spheres hold promise for encapsulate drugs with controlled release. Moreover, the GdPO(4):Eu(3+) hollow spheres are attributes for bimodal magnetic resonance imaging (MRI)/optical bioimaging labeling.

Facile selective synthesis and luminescence behavior of hierarchical NaY(WO4)2:Eu3+ and Y6WO12:Eu3+

Two kinds of Eu3+-doped tungstate precursors with uniform bowknot and flower morphologies have been synthesized with the assistance of disodium ethylenediamine tetraacetate (Na2H2L). The precursors with distinct morphologies and constituents were obtained selectively by simply changing the amount of the identical reagents. After calcinations, the precursors were successfully transformed into morphology-preserved Eu3+-doped NaY(WO4)2 and Y6WO12 respectively. The formation of these structures was proposed based on the evolution of the morphology. Under UV excitation, the bowknot-like precursor of NaY(WO4)2 exhibits white emission due to a broad band and the characteristic transitions of Eu3+ ions, while both the annealed products show strong red emission when excited at the O–W charge transfer band.