Highly enhanced luminescence from single-crystalline C-60 center dot 1m-xylene nanorods

Single-crystalline C-60 center dot 1m-xylene nanorods with a hexagonal structure were successfully synthesized by evaporating a C-60 solution in m-xylene at room temperature. The ratio of the length to the diameter of the nanorods can be controlled in the range of approximate to 10 to over 1000 for different applications. The photoluminescence (PL) intensity of the nanorods is about 2 orders of magnitude higher than that for pristine C-60 crystals in air. Both UV and Raman results indicate that there is no charge transfer between C-60 and m-xylene. It was found that the interaction between C-60 and m-xylene molecules is of the van der Waals type. This interaction reduces the icosahedral symmetry of C-60 molecule and induces strong PL from the solvate nanorods.

Blue light-emitting polymer with polyfluorene as the host and highly fluorescent 4-dimethylamino-1,8-naphthalimide as the dopant in the sidechain

The dopant/host concept, which is an efficient approach to enhance the electroluminescence (EL) efficiency and stability for organic light-emitting diodes (OLEDs) devices, has been applied to design efficient and stable blue light-emitting polymers. By covalently attaching 0.2 mol % highly fluorescent 4-dimethylamino-1,8-naphthalimide (DMAN) unit (photoluminescence quantum efficiency: Phi(PL)=0.84) to the pendant chain of polyfluorene, an efficient and colorfast blue light-emitting polymer with a dopant/host system and a molecular dispersion feature was developed. The single-layer device (indium tin oxide/PEDOT/polymer/Ca/Al) exhibited the maximum luminance efficiency of 6.85 cd/A and maximum power efficiency of 5.38 lm/W with the CIE coordinates of (0.15, 0.19). Moreover, no undesired long-wavelength green emission was observed in the EL spectra when the device was thermal annealed in air at 180 degrees C for 1 h before cathode deposition. These significant improvements in both efficiency and color stability are due to the charge trapping and energy transfer from polyfluorene host to highly fluorescent DMAN dopant in the molecular level.

Efficient blue electroluminescence from neutral alcohol-soluble polyfluorenes with aluminum cathode

Efficient blue polymer light-emitting diodes (PLEDs) have been fabricated with a neutral alcohol-soluble polyfluorene, i.e., poly(9,9-bis(6(')-diethoxylphosphorylhexyl)fluorene) (PF-EP), as the emitting layer, high work-function Al as the cathode, and poly(vinyl carbazole) as the hole-transporting layer. The PLEDs display a maximum luminous efficiency of 4.0 cd/A and the luminous efficiency > 2.4 cd/A in a wide range of current densities. It is found that the promising performance of the devices is attributed to the fact that the PF-EP is not only an efficient blue light-emitting polymer, but it also can facilitate efficient electron injection at the Al/PF-EP interface.

Poly(aryl ether)s containing ter- and pentafluorene pendants for efficient blue light emission

Four novel thermally stable poly(aryl ether)s, e.g., P3F, P5F, P2A3F, and P2A5K containing ter- or pentafluorene units in the side chains for efficient blue light emission have been designed and synthesized. All the polymers show the optical properties identical to the corresponding monomers and are amorphous with higher glass transition temperature (T-g) than their monomeric Counterparts. The polymer light-emitting diodes (PLEDs) were fabricated with the device structure of ITO/(PEDOT:PSS)/polymer/Ca/Al. The incorporation of diphenylamine group to oligofluorene terminals significantly reduces the hole-injection energy barrier in PLEDs. The devices based on P2A3F and P2A5F show the luminous efficiencies of 1.2 and 2.0 cd/A at a brightness of 300 cd/m(2) with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.15, 0.13) and (0.19, 0.20), respectively. All these indicate that the high-performance light-emitting polymers can be synthesized with the traditional condensation polymerization through careful design of polymer structures.

Synthesis and characterization of blue-light-emitting poly(aryl ether)s containing oligofluorenes in the main chain

A series of blue light-emitting poly(aryl ether)s (PAEs) containing ter- or pentafluorenes in the main chain have been synthesized via nucleophilic substitution polycondensation reaction. The energy levels of the polymers were tuned by introducing hole-transporting triaryamine groups in the side chains and/or incorporating electron-transporting oxadiazole segments in the main chain. The optical properties of the polymers are dominantly determined by the well-defined oligofluorene segments, and therefore all polymers show high photoluminescence quantum yield. Differential scanning calorimeter (DSC) characterizations indicate that they are vitrified polymers with high glass transition temperature (up to 156 degrees C). The polymers comprising pentafluorenes exhibit electroluminescent properties equal to or better than fully conjugated fluorene homopolymers. With the device structure of ITO/PEDOT:PSS/polymer/Ca/Al, an external quantum efficiency of 1.4% along with Commission Internationale de L'Eclairage (CIE) coordinates of (0.17, 0.09) has

Facile separation and determination of Aconitine alkaloids in traditional Chinese medicines by CE with tris(2,2 '-bipyridyl) ruthenium(II)-based electrochemi-luminescence detection

A facile CE method coupled with tris(2,2'-bipyridyl) ruthenium(ll)-based electrochem iluminescence [Ru(bpy)(3)(2+)] detection was developed for simultaneous determination of Aconitum alkaloids, i.e., hypaconitine (HA), aconitine (AC), and mesaconitine (MA) in baseline separation. The optimal separation of these Aconitum alkaloids was achieved in a fused-silica capillary column (50 cm x 25 mu m id) with 30 mM phosphate solution (pH 8.40) as running buffer at 12 kV applied voltage. The three alkaloids can be determined within 10 min by a single run. The calibration curves showed a linear range from 2.0 x 10(-7) to 2.0 x 10(-5) M for HA, 3.4 x 10(-7) to 1.7 x 10(-5) M for AC, and 3.8 x 10(-7) to 1.9 x 10(-5) M for MA. The RSDs; for all analytes were below 3.01%. Good linear relationships were found with correlation coefficients for all analytes exceeding 0.993. The detection limits were 2.0 x 10(-8) M for HA, 1.7 x 10(-7) M for AC, and 1.9 x 10(-7) M for MA under optimal conditions. This method was successfully applied to determine the three alkaloids in Aconitum plants.

Sol-gel synthesis and characterization of SiO2@CaWO4, SiO2@CaWO4 : Eu3+/Tb3+ core-shell structured spherical particles

Nanocrystalline CaWO4 and Eu3+ (Tb3+)-doped CaWO4 phosphor layers were coated on non-aggregated, monodisperse and spherical SiO2 particles by the Pechini sol-gel method, resulting in the formation of SiO2@CaWO4, SiO2@CaWO4:Eu3+/Tb3+, core-shell structured particles. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), photoluminescence (PL), low-voltage cathodoluminescence (CL), time-resolved PL spectra and lifetimes were used to characterize the core-shell structured materials. Both XRD and FT-IR indicate that CaWO4 layers have been successfully coated on the SiO2 particles, which can be further verified by the FESEM and TEM images. The PL and CL demonstrate that the SiO2@CaWO4 sample exhibits blue emission band WO42- with a maximum at 420 nm (lifetime = 12.8 mu s) originated from the 4 groups, while SiO2@CaWO4:Eu3+ and SiO2@CaWO4:Tb3+ show additional red emission dominated by 614 nm (Eu3+:D-5(0)-F-7(2) transition, lifetime = 1.04 ms) and green emission at 544 nm (Tb3+:D-5(4)-F-7(5) transition, lifetime = 1.38 ms), respectively.

Silica supported submicron SiO2@Y2SiO5 : Eu3+ and SiO2@Y2SiO5 : Ce3+/Tb3+ spherical particles with a core-shell structure: Sol-gel synthesis and characterization

X-1-y(2)SiO(5):Eu3+ and X-1-Y2SiO5:Ce3+ and/or Tb3+ phosphor layers have been coated on nonaggregated, monodisperse, submicron spherical SiO2 particles by a sol-gel process, followed by surface reaction at high temperature (1000 degrees C), to give core/shell structured SiO2@Y2SiO5:Eu3+ and SiO2@Y2SiO5:Ce3+/Tb3+ particles. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), TEM, photoluminescence (PL), low voltage cathodoluminescence (CL), and time-resolved PL spectra and lifetimes are used to characterize these materials. The XRD results indicate that X-1-Y2SiO5 layers have been successfully coated on the sur- face Of SiO2 particles, as further verified by the FESEM and TEM images. The PL and CL studies suggest that SiO2@Y2SiO5:Eu3+, SiO2@Y2SiO5:Tb3+ (or Ce3+/Tb3+), and SiO2@Y2SiO5:Ce3+ core/shell particles exhibit red (Eu3+, 613 rim: D-5(0)-F-7(2)), green (Tb3+, 542nm: D-5(4)-F-7(5)), or blue (Ce3+, 450nm: 5d-4f) luminescence, respectively. Pl, excitation, emission, and time-resolved spectra demonstrate that there is an energy transfer from Ce3+ to Tb3+ in the SiO2@Y2SiO5:Ce3+,Tb3+ core/shell particles.

Dy3+- and Eu3+-doped LaGaO3 nanocrystalline phosphors for field emission displays

Nanocyrstalline LaGaO3 and Dy3+- and Eu3+-doped LaGaO3 were prepared through a Pechini-type sol-gel process. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), photoluminescence, cathodoluminescence spectra, and lifetimes were utilized to characterize the samples. XRD reveals that the samples begin to crystallize at 900 degrees C and pure LaGaO3 phase can be obtained at 1000 degrees C. FE-SEM images indicate that the Dy3+- and Eu3+-doped LaGaO3 samples are both composed of aggregated spherical particles with sizes ranging from 40 to 80 nm. Under the excitation of ultraviolet light and low voltage electron beams (1-5 kV), the undoped LaGaO3 sample shows a strong blue emission peaking at 433 nm, and the Dy3+- and Eu3+-doped LaGaO3 samples show their characteristic emissions of Dy3+ (F-4(9/2)-H-6(15/2) and F-4(9/2)-H-6(13/2) transitions) and Eu3+ (D-5(0,1,2)-F-7(1,2,3,4) transitions), respectively. The relevant luminescence mechanisms are discussed.

Luminescence properties of sol-gel derived spherical SiO2@Gd-2(WO4)(3): Eu3+ particles with core-shell structure

Monodisperse, core-shell structured SiO2@Gd-2(WO4)(3):Eu3+ particles were prepared by the sol-gel method. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy, transmission electron microscopy, photoluminescence (PL) and low-voltage cathodoluntinescence (CL). PL and CL study revealed that the core-shell structured SiO2@Gd-2(WO4)(3):Eu3+ particles show strong red emission dominated by the D-5(0)-F-7(2) transition of Eu3+ at 615 nm with a lifetime of 0.89 ins. The PL and CL emission intensity can be tuned by the coating number of Gd-2(WO4)(3):Eu3+ phosphor layers on SiO2 particles, the size of the SiO2 core particles, and by accelerating voltage and the filament current, respectively.

Synthesis and characterization of spherical Sr2CeO4 phosphors by spray pyrolysis for field emission displays

A blue emitting Sr2CeO4 phosphor with a one-dimensional structure has been prepared by a two-step spray pyrolysis (SP) method, starting from the aqueous solutions of metal nitrates with citric acid and polyethylene glycol (PEG) as additives. The material is ultimately designed for field emission displays (FEDs). X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA), field emission scanning electron microscope pictures (FE-SEM) as well as photoluminescence (PL) and cathodoluminescence (CL) spectroscopy and lifetime measurements have been employed to characterize the samples. The morphology, PL and low voltage CL properties of Sr2CeO4 phosphors as-prepared using the SP method have been investigated by changing the concentration of the precursor solution, concentration of PEG, annealing temperature, acceleration voltage and filament current. The obtained Sr2CeO4 phosphor particles are spherical and of submicron size, 0.5-2 mu m. The emission spectrum of the phosphors shows a broad band with maximum at 467 nm (lifetime = 37.4 mu s; CIE chromaticity coordinates: x = 0.15 and y = 0.21), presumably due to a ligand-to-metal charge-transfer transition.

Assembly of Prussian blue onto SiO2 nanoparticles and carbon nanotubes by electrostatic interaction

Prussian blue (PB) was modified onto surface of SiO2 nanoparticles and multiwall carbon nanotubes (MWNTs) by electrostatic assembled method. SiO2 nanoparticles and MWNTs firstly modified by polyelectrolyte exhibited positive charges and negative charged PB could be assembled onto them. UV-vs spectroscopy, Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), field-emitted scanning electron microscopy (FE-SEM) and electrochemical methods were used to characterize these composite nanomaterials. TEM and FE-SEM images showed that PB was easily assembled onto polyelectrolyte modified SiO2 nanoparticles and MWNTs. Moreover, PB on the surface of nanomaterials was stable and still kept its intrinsic electrochemical properties and high electrocatalytic activity towards hydrogen peroxide.

Syntheses, structures and luminescence of silver(I) sulfonate complexes with PPh3 ligand

In this paper, four new luminescent silver(I) sulfonate complexes with PPh3, namely Ag(L1)(PPh3)(2) (1), Ag(L2)(PPh3)(3) (2), [Ag-2(L3)(PPh3)(4) (H2O)center dot 1.5CH(3)CN center dot 0.5H(2)O (3) and [Ag-4(L4)(PPh3)(10)]center dot 8H(2)O (4), where L1=p-toluenesulfonate, L2=1-naphthalenesulfonate, L3=3-carboxylate-4-hydroxybenzenesulfonate, L4=1, 3, 6, 8-pyrenetetrasulfonatc and PPh3=triphenylphosphine, have been synthesized and characterized. The crystal structures were determined by single-crystal X-ray diffraction method. Compounds 1, 2, 3 and 4 adopt discrete structures rather than polymeric structures. Compounds I and 2 show mononuclear structures while 3 and 4 are dinuclear and tetranuclear molecules, respectively. Moreover the numbers of PPh3 molecules coordinating to one silver center are two or three. The photoluminescent properties of 1, 2 and 3 are discussed.

Up-conversion spectrum properties of the oxy-fluoride glass co-doped with Er3+ and Yb3+

Up-conversion of 45PbF(2)-45GeO(2)-10WO(3) oxy-fluoride glasses co-doped with Yb3+ and Er3+ ions were prepared by fusion method through melting at 1223 K and then annealing at 653 K for 4 h. Transmittance of the undoped host glass was beyond 73% in a range of 0.6-2.5 mu m and the co-doped glasses still provided good transmittance beyond 50%. Refractive indices of the host and co-doped glasses were 1.517 and 1.650, respectively. Blue, green and red fluorescence spectra were observed in a range of 400-700 nm under 980 nm diode laser excitation. Up-conversion spectra at about 410, 518, 530and 650 nm were assigned to the 4f electron transitions of H-2(9/2) -> I-4(15)/(2), H-2(15/2) -> I-4(15/2) S-4(3/2) -> I-4(15/2) and F-4(9/2) -> I-4(15/2) of Er3+ ion, respectively. The mechanism of energy transfer between Yb3+ and Er3+ ions in the glass was analyzed. Raman shift shows the non-radiative relaxation of the glass sample is low.

A new blue phosphorescent glass-ceramic: Rare-earth-doped calcium aluminoborate

A new blue phosphorescent glass-ceramic, Eu2+ and Nd3+, co-doped CaO-Al2O3-B2O3, was synthesized. After the irradiation with ultraviolet (UV) light, the glass-ceramic emitted blue long-lasting phosphorescence (LLP) with a spectrum peaking at about 464 nm ascribed to the characteristic 4f(6)5d(1) -> 8S(7/2) transition of Eu2+. This phosphorescence can be seen in the dark 1 h after the irradiation. However, the transparent Eu2+ and Nd3+ co-doped CaO-Al2O3-B2O3 glass did not show the phosphorescence. By the X-ray diffraction diffusion (XRD) data, alpha-CaAl2B2O7 was demonstrated to be the crystallites in the glass-ceramic. We think that alpha-CaAl2B2O7:Eu2+ Nd3+ crystallites produced during the heat treatment of the glass contribute to the LLP of the glass-ceramic.