Weitao Gong

Tunable white-light emission via energy transfer in single-phase LiGd(WO4)2:Re3+ (Re = Tm, Tb, Dy, Eu) phosphors for UV-excited WLEDs

A series of novel single-phase color tunable LiGd(WO4)2(LGW):Re3+ (Re = Tm, Tb, Dy, Eu) phosphors have been synthesized by a solid-state reaction. X-ray diffraction (XRD), FT-IR, photoluminescence (PL) and fluorescence decay curves were utilized to characterize the as-prepared samples. Under the excitation of UV light, LGW:Tm3+, LGW:Tb3+, LGW:Dy3+ and LGW:Eu3+ exhibit the characteristic emissions of Tm3+ (blue), Tb3+ (green), Dy3+ (yellow) and Eu3+ (red), respectively. On the one hand, by simply adjusting the doping concentration of Eu3+ ions in the LGW:2% Tm3+, 4% Tb3+, x% Eu3+ system, a white emission in a single-phase was achieved by blending simultaneously the blue, green, and red emissions of Tm3+, Tb3+, and Eu3+ ions in the LGW host, in which the energy transfer from Tb3+ to Eu3+ ions was found to play an important role. On the other hand, a white emission can also be realized based on the energy transfer from Tm3+ to Dy3+ ions in the LGW:2% Tm3+, x% Dy3+ system. The energy transfer mechanism from Tm3+ to Dy3+ ions has been demonstrated to be through dipole–quadrupole interaction and the critical distance (RTm–Dy) calculated by the concentration quenching method is 16.03 A. The PL properties of as-prepared materials indicate that LGW:Re3+ (Re = Tm, Tb, Dy, Eu) may be potentially applied as single-phase white-light-emitting phosphors for UV-excited WLEDs.

A new single-phase white-light-emitting CaWO4:Dy3+ phosphor: synthesis, luminescence and energy transfer

A series of single-phase CaWO4:Dy3+ phosphors have been prepared via a conventional solid state reaction process. X-Ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), and fluorescent decay curves were used to characterize the synthesized samples. Under UV light excitation, the CaWO4 sample shows a blue emission in a broad band centered at about 415 nm originating from the WO42− groups, while the Dy3+ ions doped CaWO4 samples show strong line emissions coming from the characteristic f–f transitions due to an efficient energy transfer from WO42− to Dy3+. The decreases of decay lifetimes of host emissions in CaWO4:Dy3+ demonstrated the energy transfer from the host to Dy3+. The energy transfer mechanism in CaWO4:Dy3+ phosphors has been determined to be a resonant type via a dipole–dipole mechanism. By simply controlling the doping concentration of Dy3+, the PL color of CaWO4:Dy3+ phosphors varies from blue to yellow-green, and especially the white light emission is realized in CaWO4:xDy3+ (x = 0.06). The PL properties of the as-prepared materials indicate that CaWO4:Dy3+ could potentially serve as a single-phase white-light-emitting phosphor in solid-state lighting and display fields.

Multi-color luminescence properties and energy transfer behaviour in host-sensitized CaWO4:Tb3+,Eu3+ phosphors

A series of host-sensitized and color-tunable CaWO4:Tb3+,Eu3+ phosphors were prepared via a high-temperature solid-state reaction route, and the crystal structure and luminescence properties, especially the energy transfer behavior, were investigated in detail. Under UV radiation, the CaWO4 host presents a broad emission band from about 320 to 600 nm centered around 415 nm, ascribed to the charge transfer in WO42− groups; while Eu3+ and Tb3+ ion doped CaWO4 samples show both host emission and respective emission lines derived from the characteristic f–f transitions of activators, which present abundant emission colors owing to an efficient energy transfer from the host to Eu3+/Tb3+ ions. The energy transfer from the host to Eu3+ and Tb3+ was evidenced by directly observing appreciable overlap between the excitation spectrum of the host and the emission spectrum of Eu3+/Tb3+, as well as by the decreased decay time of host emission with increasing Eu3+/Tb3+ concentration. The energy transfer mechanisms in CaWO4:Eu3+/Tb3+ phosphors have been determined to be a resonant type via dipole–dipole interaction. In the Eu3+ and Tb3+ co-doped system, CaWO4:Eu3+,Tb3+, the energy transfer phenomenon not only occurs from host to activators, but also from Tb3+ to Eu3+, resulting in color-tunable emission including white light by simply adjusting the doping concentration of Eu3+ and Tb3+ ions. The PL properties of the as-prepared materials indicate their promising application in solid-state lighting fields.

Novel red-emitting LiGd(WO4)2:Eu3+ phosphor with high thermal stability and high color purity for application in white light-emitting diodes

An excellent light-emitting diodes phosphor must possess effective absorption, high quantum efficiency, high quenching temperatures, and high color purity. Our synthesized LiGd(WO4)2:Eu3+ materials possess all of these properties. Excitation of these phosphors with ultraviolet radiation yields bright red emission at 617 nm due to the 5D0 → 7F2 transition of Eu3+ ions. Compared with different Eu3+ doping concentrations, LiGd(WO4)2:80%Eu3+ phosphor has optimal photoluminescence properties and shows internal quantum efficiency as high as 69%. More impressive is its good thermal stability; when heated up to 150 °C, the LiGd(WO4)2:80%Eu3+ phosphor still has 81% of its initial emission intensity at room temperature. Furthermore, the LiGd(WO4)2:80%Eu3+ phosphor shows high purity of red emission with coordinate values (x = 0.656, y = 0.334). The abovementioned results suggest that the LiGd(WO4)2:80%Eu3+ phosphor can be a suitable red-emitting candidate for ultraviolet-excited white light-emitting diodes.

Fluorescent Cross‐Linked Supramolecular Polymer Constructed by Orthogonal Self‐Assembly of Metal–Ligand Coordination and Host–Guest Interaction

A new host molecule consists of four terpyridine groups as the binding sites with zinc(II) ion and a copillar[5]arene incorporated in the center as a spacer to interact with guest molecule was designed and synthesized. Due to the 120u2009° angle of the rigid aromatic segment, a cross-linked dimeric hexagonal supramolecular polymer was therefore generated as the result of the orthogonal self-assembly of metal-ligand coordination and host-guest interaction. UV/Vis spectroscopy, (1) Hu2005NMR spectroscopy, viscosity and dynamic light-scattering techniques were employed to characterize and understand the cross-linking process with the introduction of zinc(II) ion and guest molecule. More importantly, well-defined morphology of the self-assembled supramolecular structure can be tuned by altering the adding sequence of the two components, that is, the zinc(II) ion and the guest molecule. In addition, introduction of a competitive ligand suggested the dynamic nature of the supramolecular structure.

Fabrication of nanostructured V2O5 via urea combustion for high-performance Li-ion battery cathode

Nanostructured vanadium pentoxide (V2O5) crusts were facilely synthesized via the combustion of a precursor by mixing commercial V2O5 with molten urea. The nanocrusts were transferred to nanorods during further annealing at 630 °C. Both the V2O5 nanocrusts and V2O5 nanorods were used preliminarily as a cathode material for Li-ion batteries. Their electrode performance was highly improved compared to commercial V2O5.

Construction of fluorescence-tunable pyrido-fused benzimidazoles via direct intramolecular C–H amination under transition-metal-free conditions

A novel methodology was discovered to construct multi-phenyl substituted pyrido-fused benzimidazole (PBI) core frameworks via direct oxidative intramolecular C–H amination of α-unsubstituted pyridinium salts under transition-metal free conditions. The resulting highly π-conjugated PBI derivatives exhibited highly tunable fluorescent emission not only in solution but also in the solid state.

Aggregation-Induced Emission (AIE) Fluorophore Exhibits a Highly Ratiometric Fluorescent Response to Zn2+ in vitro and in Human Liver Cancer Cells

Two novel organic fluorophores, containing bis-naphthylamide and quinoline motifs, have been designed and synthesized. One of the fluorophores contains an isobutylene unit and exhibits a significant aggregation-induced emission (AIE) and a remarkable highly selective ratiometric fluorescence response towards Zn2+ in solution as well as in human liver cancer cells. The AIE behavior of this fluorophore was fully verified by fluorescence and UV/Vis spectroscopy, quantum yield calculations, and single-crystal X-ray diffraction, which revealed an intricate crystal packing system. Conversely, a fluorophore that lacks the isobutylene moiety did not exhibit any significant fluorescent properties as a result of its more flexible molecular structure that presumably allows free intramolecular rotational processes to occur.

Configuration-independent AIE-active supramolecular polymers of cyanostilbene through the photo-stable host–guest interaction of pillar[5]arene

Supramolecular polymerization-enabled, configuration-independent aggregation-induced emission (AIE) systems of cyanostilbene were achieved through host–guest interactions between pillar[5]arene and nitrile triazole guests. Interestingly, host, control and control-guest lost its AIE upon photo-isomerization due to the absence of host–guest interaction. 1H NMR, DOSY NMR and fluorescence studies of the supramolecular polymers before and after UV irradiation clearly indicated the significant role of photo-stable host–guest interaction in enhancing and retaining AIE.

Construction of a novel INHIBIT logic gate through a fine-tuned assembly of anthryl fluorophores via selective anion recognition and host–guest interactions

A novel ligand (AAP) based on an anthryl fluorophore was rationally designed and synthesized. The presence of H2PO4− (Pi) could induce the effective assembly of the ligand which leads to a strong excimer emission, while β-cyclodextrin (β-CD) disassembled the Pi–ligand complex through a host–guest interaction with terminal adamantane groups. This disassembly causes a considerable decrement in emissive intensity as well as a clear blue-shift in emissive wavelength. By manipulating the assembly and disassembly of anthryl fluorophores with Pi and β-CD, a novel INHIBIT logic gate was constructed using Pi and β-CD as the chemical inputs and fluorescence emission as the output.