Wei Lü

Sr3GdNa(PO4)3F:Eu2+,Mn2+: a potential color tunable phosphor for white LEDs

A series of Eu2+ and Mn2+ activated novel Sr3GdNa(PO4)3F phosphors have been prepared through a high temperature solid state reaction. The investigation revealed that Sr3GdNa(PO4)3F crystallized in a hexagonal crystal system with the space group P (no. 147). The Eu2+ activated phosphors can be efficiently excited in the range of 250 to 420 nm, which matches well with the commercial n-UV LED chips, and give intense blue emission centering at 470 nm. By codoping the Eu2+ and Mn2+ ions into the SGNPF host and singly varying the doping content of the Mn2+ ion, tunable colors from blue to white and then to yellow are obtained in SGNPF:Eu2+,Mn2+ phosphors under the irradiation of 390 nm. The energy transfer from the Eu2+ to Mn2+ ions is demonstrated to be a dipole–quadrupole mechanism in terms of the experimental results and analysis of photoluminescence spectra and decay curves of the phosphors. The critical distance between the Eu2+ and Mn2+ ions in SGNPF:Eu2+,Mn2+ was determined by the spectral overlap method. The investigation indicates that our prepared samples might have potential application in WLEDs.

Eu2+ & Mn2+-Coactivated Ba3Gd(PO4)(3) Orange-Yellow-Emitting Phosphor with Tunable Color Tone for UV-Excited White LEDs

A novel orange-yellow-emitting Ba(3)Gd(PO(4))(3):xEu(2+),yMn(2+) phosphor is prepared by high-temperature solid-state reaction. The crystal structure of Ba(3)Gd(PO(4))(3):0.005 Eu(2+),0.04 Mn(2+) is determined by Rietveld refinement analysis on powder X-ray diffraction data, which shows that the cations are disordered on a single crystallographic site and the oxygen atoms are distributed over two partially occupied sites. The photoluminescence excitation spectra show that the developed phosphor has an efficient broad absorption band ranging from 230 to 420 nm, perfectly matching the characteristic emission of UV-light emitting diode (LED) chips. The emission spectra show that the obtained phosphors possess tunable color emissions from yellowish-green through yellow and ultimately to reddish-orange by simply adjusting the Mn(2+) content (y) in Ba(3)Gd(PO(4))(3):0.005 Eu(2+),y Mn(2+) host. The tunable color emissions origin from the change in intensity between the 4f-5d transitions in the Eu(2+) ions and the (4)T(1)-(6)A(1) transitions of the Mn(2+) ions through the energy transfer from the Eu(2+) to the Mn(2+) ions. In addition, the mechanism of the energy transfer between the Eu(2+) and Mn(2+) ions are also studied in terms of the Inokuti-Hirayama theoretical model. The present results indicate that this novel orange-yellow-emitting phosphor can be used as a potential candidate for the application in white LEDs.

Structure and photoluminescence properties of novel Ca2NaSiO4F:Re (Re = Eu2+, Ce3+, Tb3+) phosphors with energy transfer for white emitting LEDs

A series of Eu2+ and Ce3+/Tb3+ doped Ca2NaSiO4F (CNSOF) phosphors have been synthesized and their structure and photoluminescence properties have been investigated in detail. Rietveld structure refinement indicates that the phosphors crystalized in an orthorhombic system with a space group of Pnma (no. 62) and there are two kinds of cation sites for the doped ions to occupy in forming emission centers. The CNSOF:Eu2+ and CNSOF:Ce3+ phosphors both have broad excitation bands, which match well with the commercial UV LED chips. The CNSOF:Eu2+ phosphor can have intense green emission with a maximum at 530 nm under irradiation at 380 nm, while the CNSOF:Ce3+ sample can emit intense blue light, peaking at 470 nm with excitation at 365 nm. By codoping the Tb3+ and Ce3+ ions into an CNSOF host and varying their relative ratio, tunable blue-green colors are obtained due to efficient energy transfer from the Ce3+ to Tb3+ ions. Moreover, energy transfer mechanisms for the Eu2+ ions in CNSOF:Eu2+ and Ce3+ → Tb3+ in CNSOF:Ce3+,Tb3+ have been studied systematically. Our investigation indicates that CNSOF:Eu2+ and CNSOF:Ce3+,Tb3+ may be potential green and blue-green phosphors for UV WLEDs, respectively.

Crystal structure and luminescent properties of a novel high efficiency blue-orange emitting NaCa2LuSi2O7F2:Ce3+,Mn2+ phosphor for ultraviolet light-emitting diodes

A series of NaCa2LuSi2O7F2:xCe(3+),yMn(2+) phosphors are firstly prepared by a high-temperature solid-state reaction technique. The Rietveld refinement analysis confirmed that the obtained phosphors have a pure crystalline phase with cuspidine-group structure. NaCa2LuSi2O7F2:xCe(3+),yMn(2+) phosphors can be efficiently excited by UV light and have two emission bands at about 410 and 600 nm. The luminescent properties of the singly-doped samples reveal that the Ce(3+) ions occupy two different Lu(3+) sites in the host lattice. We observed an efficient energy transfer from the Ce(3+) to Mn(2+) ions. The investigation revealed that the mechanism of the energy transfer was a resonant type via a nonradiative dipole-quadrupole interaction. The hues can be adjusted and white light can be obtained by tuning the concentration of Mn(2+) ions in the codoped phosphors through the energy transfer from the Ce(3+) to Mn(2+) ions, hinting a promising application of NaCa2LuSi2O7F2:xCe(3+),yMn(2+) as a single-component phosphor that can produce white light from UV-based LEDs.

Mussel-inspired multifunctional supramolecular hydrogels with self-healing, shape memory and adhesive properties

A novel multifunctional supramolecular hydrogel with self-healing, shape memory and adhesive properties is successfully developed on the basis of dynamic phenylboronic acid (PBA)–catechol interactions. The reversible nature of PBA–catechol bonds renders the hydrogel with outstanding self-healing and shape memory behavior, and the mussel-inspired catechol moieties generate fascinating adhesive properties.

UV light-initiated RAFT polymerization induced self-assembly

Unlike conventional polymerization induced self-assembly (PISA) trigged by thermal stimuli, reversible addition–fragmentation chain transfer (RAFT) PISA initiated by UV light, as an environmentally friendly and easily manipulated method, is exploited as a new strategy to prepare polymeric micelles at room temperature.

Monodisperse YVO4:Eu3+ submicrocrystals: controlled synthesis and luminescence properties

Monodisperse YVO4:Eu3+ submicrocrystals with uniform morphologies have been successfully synthesized via a facile ethylene glycol (EG) assisted hydrothermal route. The particle shape and size could be effectively manipulated by tuning the thermodynamic (e.g. temperature) and kinetic (e.g. reactant concentration, pH value) parameters. Flower-like, spherical, octahedral, and revolving door-like YVO4:Eu3+ submicrocrystals were obtained by fine-tuning the pH values. The possible growth mechanism of octahedral YVO4:Eu3+ submicrocrystals was presented on the basis of systematic time-dependent experiments. The luminescent spectra reveal that both the post-calcinated spherical and octahedral YVO4:Eu3+ samples show a typical red emission of the Eu3+ ions dominated by strong 617 nm peak with dramatic difference in intensity. This difference may arise from the changes of the adsorbates, surface defects, and crystallinity. Our facile hydrothermal route may provide some new guidance in the design and controlled synthesis of inorganic nano/micromaterials.

Color tuning and energy transfer investigation in Na2Ca4Mg2Si4O15:Eu2+, Mn2+ phosphor and its potential application for UV-excited UV-WLEDs

In this paper, a novel single-phased white light emitting phosphor Na2Ca4Mg2Si4O15:Eu2+, Mn2+ was prepared successfully via the high temperature solid state reaction. The obtained Na2Ca4Mg2Si4O15:Eu2+ phosphor exhibits a broad excitation band ranging from 200 to 450 nm and a blue light emission band peaking at 480 nm, originating from 4f7 ↔ 4f65 d1 (f-d) electric dipole allowed transitions of Eu2+ ions. Due to the energy transfer from Eu2+ to Mn2+ ions, the co-doped Eu2+ ions in the Na2Ca4Mg2Si4O15:Eu2+, Mn2+ phosphors markedly enhances the luminescence intensity of Mn2+ ions, providing highly attractive tunable color. The luminescent mechanism invoking the energy transfer between Eu2+ ions and Mn2+ ions has been certified to be dipole–quadrupole interaction predominantly through the investigations of the luminescence spectra and the fluorescence decay curves. Our results show that the novel Na2Ca4Mg2Si4O15:Eu2+, Mn2+ phosphor is a very promising candidate for UV white light emitting diodes.

Novel synthesis and luminescence properties of t-LaVO4:Eu3+ micro cube

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.

Efficient sensitization of Mn2+ emission by Eu2+ in Ca12Al14O33Cl2 host under UV excitation

A new blue-green emitting phosphor Ca12Al14O33Cl2:Eu2+,Mn2+ has been synthesized by the solid-state reaction technique method under a reductive atmosphere. The X-ray diffraction measurement results indicate that the crystal structure of the phosphor is a single phase of Ca12Al14O33Cl2. The phosphors can be efficiently excited by near ultraviolet (n-UV) light and show a blue emission band at about 450 nm and a green emission band at about 550 nm, which originated from the Eu2+ ions and the Mn2+ ions. The efficient energy transfer from the Eu2+ ions and the Mn2+ ions was observed and its mechanism should be a resonant type via a nonradiative dipole–quadrupole interaction. The critical distance between the Eu2+ ions and Mn2+ ions has been calculated to be about 10.83 A as well. In addition, the temperature dependent photoluminescence of the as-prepared phosphors has been investigated in detail. Our results indicate that the developed phosphor may be used as a potential blue-green emitting phosphor for UV-based white LEDs.