One-Pot Exfoliation of Graphitic C3 N4 Quantum Dots for Blue QLEDs by Methylamine Intercalation.

Here, a simplified synthesis of graphitic carbon nitride quantum dots (g-C3 N4 -QDs) with improved solution and electroluminescent properties using a one-pot methylamine intercalation-stripping method (OMIM) to hydrothermally exfoliate QDs from bulk graphitic carbon nitride (g-C3 N4 ) is presented. The quantum dots synthesized by this method retain the blue photoluminescence with extremely high fluorescent quantum yield (47.0%). As compared to previously reported quantum dots, the g-C3 N4 -QDs synthesized herein have lower polydispersity and improved solution stability due to high absolute zeta-potential (-41.23 mV), which combine to create a much more tractable material for solution processed thin film fabrication. Spin coating of these QDs yields uniform films with full coverage and low surface roughness ideal for quantum dot light-emitting diode (QLED) fabrication. When incorporated into a functional QLED with OMIM g-C3 N4 -QDs as the emitting layer, the LED demonstrates ≈60× higher luminance (605 vs 11 Cd m-2 ) at lower operating voltage (9 vs 21 V), as compared to the previously reported first generation g-C3 N4 QLEDs, though further work is needed to improve device stability.

The Bond-Energy Method in Site Occupancy and Property of Eu3+ Doped in SrAl2B2O7 Phosphors.

The SrAl2B2O7:1%Eu3+ phosphors were obtained by solid-state reaction. Photoluminescence (PL) spectra are characterized the property of samples, and under the excitation of 394 nm, the sharp emission lines of SrAl2B2O7:1%Eu3+ can be assigned to Judd-Ofelt transitions (5D0-7FJ) of Eu3+, which are 5D0-7F1, 5D0-7F2, 5D0-7F3, and 5D0-7F4. The bond energy method is used to determine the site occupancy, and the occupancy of Eu3+ can be determined by comparing the deviation of its bond energy in different locations at Sr2+, Al3+ and B3+ sites. Theoretical calculation result indicates that Eu3+ would preferentially occupy the smaller energy variation sites Sr2+.

The Bond-Energy Method in Site Occupancy and Property of High Concentration Eu3+ in Sr2CeO4 Phosphors.

The low concentration of Eu3+ doped Sr2CeO4 phosphors has been widely studied in recent years and in this paper, we researched the properties of high concentration Eu3+ doped in Sr2CeO4. The Sr2Ce(1-x)Eu4-x/2 (x = 0, 1%, 10%, 20%) phosphors were obtained by traditional solid-state reaction. Photoluminescence (PL) spectra are characterized the property of samples. PL spectra illustrate that the concentration of Eu3+ increased, the intensity of 5D0-7F1, 5D0-7F2 increased and intensity of Sr2CeO4 host emission intensity was decreased. The phenomenon can be ascribed to the energy transfer from Ce4+ to Eu3+. When the concentration of Eu3+ is 20%, the completely red emission can be obtained even if no other ions are doped under the excitation wavelength of 350 nm, it is proved that Eu3+ occupied Ce sites rather than Sr site in Sr2CeO4 samples. The conclusion we make is due to the value of |ΔEEuCe-O| and |ΔEEuSr-O| calculated by bond-energy method, the smaller the value, the easier it is for the doped ions Eu3+ to enter the site.

Spectral and energy transfer in Bi3+-Ren+ (n = 2, 3, 4) co-doped phosphors: extended optical applications.

Bismuth with [Xe]4f145d106s26p3 electronic configuration is considered as 'a wonder metal' due to its diverse oxidation states and multi-type electronic structures. This review article summarizes the spectral properties of phosphors doped with Bi3+ or co-doped with Bi3+-Ren+ (n = 2, 3, 4), and highlights the critical role of Bi3+ in spectral modification. The energy transfer processes are discussed in detail, including (1) Bi3+ and metal-to-metal charge, (2) Bi3+ and tetravalent cation, (3) Bi3+ and trivalent cation, (4) Bi3+ and divalent cation, and (5) Bi3+ and two kinds of rare earth ions. The most important results obtained in each case are summarized, and the emerging challenges and future development of Bi3+-doped phosphors are discussed. We introduce a method for spectral modification based on the energy transfer between Bi3+ and other cations, with the perspective of development and application in the fields of phosphors, telecommunication, optical temperature sensing, biomedicine, and lasers.

Preparation and Luminescent Properties of Sm3+-Doped High Thermal Stable Sodium Yttrium Orthosilicate Phosphor.

Orange-red-emitting sodium yttrium orthosilicate NaYSiO4:xSm3+ (x = 0.005, 0.01, 0.02, 0.05, 0.10, 0.15, and 0.20) were synthesized. The phase structure and photoluminescence properties of these phosphors were investigated. The emission spectrum obtained by excitation into 406 nm contains exclusively the characteristic emissions of Sm3+ at 571 nm, 602 nm, 648 nm, and 710 nm, which correspond to the transitions from 4G5/2 to 6H5/2, 6H7/2, 6H9/2, and 6H11/2 of Sm3+, respectively. The strongest one is located at 602 nm due to the 4G5/2 --> 6H7/2 transition of Sm3+, generating bright orange-red light. The optimum dopant concentration of Sm3+ ions in NaYSiO4:xSm3+ is around 2 mol%, and the critical transfer distance of Sm3+ is calculated as 23 Å. The thermal quenching temperature is above 500 K. The fluorescence lifetime of Sm3+ in NaYSiO4:0.02Sm3+ is 1.83 ms. The NaYSiO4:Sm3+ phosphors may be potentially used as red phosphors for white light emitting diodes.

Ce(3+) /Tb(3+) non-/single-/co-doped K-Lu-F materials: synthesis, optical properties, and energy transfer.

Using a hydrothermal method, Ce(3+) /Tb(3+) non-/single-/co-doped K-Lu-F materials have been synthesized. The X-ray diffraction (XRD) results suggest that the Ce(3+) and/or Tb(3+) doping had great effects on the crystalline phases of the final samples. The field emission scanning electron microscopy (FE-SEM) images indicated that the samples were in hexagonal disk or polyhedron morphologies in addition to some nanoparticles, which also indicated that the doping also had great effects on the sizes and the morphologies of the samples. The energy-dispersive spectroscopy (EDS) patterns illustrated the constituents of different samples. The enhanced emissions of Tb(3+) were observed in the Ce(3+) /Tb(3+) co-doped K-Lu-F materials. The energy transfer (ET) efficiency ηT were calculated based on the fluorescence yield. The ET mechanism from Ce(3+) to Tb(3+) was confirmed to be the dipole-quadrupole interaction inferred from the theoretical analysis and the experimental data. Copyright © 2015 John Wiley & Sons, Ltd.

Synthesis, phase evolution and optical properties of Tb(3+)-doped KF-YbF3 system materials.

KF-YbF3 system materials have been synthesized by a hydrothermal method without any surfactant or template. By controlling the reactant ratios of KF:Yb(3+), the hydrothermal temperature and the pH of the prepared solutions, the final products can evolve among the orthorhombic phase of YbF3, the cubic phase of KYb3F10 and the cubic phase of KYbF4. The X-ray diffraction (XRD) patterns of the samples prove the phase evolution of the final products. The morphologies of the samples were characterized using field emission scanning electron microscopy (FE-SEM) images and the evolution of the morphology is consistent with that of the crystalline phases. The optical properties of Tb(3+) in the samples were characterized by PL excitation and emission spectra, as well as luminescent decay curves.

Simultaneous realization of two approaches to white light in single-component phosphors.

A novel single-component warm white light-emitting Sr(2)Ca(0.995)MoO(6): Sm(3+) (0.005) phosphor was synthesized by solid-state reaction. The photoluminescence excitation spectra ranging from 300 to 450 nm and 460 to 500 nm broadly are observed. Direct full-color warm white light [(x, y) = 0.3221, 0.3525] was realized in this single-phase phosphor with exposure to 380 nm UV light. When this phosphor is pumped by 466 nm radiation we obtained yellow emission with an intense red component, suggesting that this material is also competitive as a blue-pumped yellow phosphor. Thus two approaches to white light are realized simultaneously in Sm(3+) doped single-component phosphor for the first time. The quantum yield and the reliability of the as-synthesized phosphors for White LED applications were also investigated.

Photoluminescence properties and spectral structure analysis of NaLn(MoO4)2:Eu3+ (Ln = Gd, Y) phosphors.

In this paper, a facile synthetic route for the preparation of NaLn(MoO4)2:Eu3+ (Ln = Gd, Y) nanocrystals by a hydrothermal method is reported. The NaLn(MoO4)2:Eu3+ (Ln = Gd, Y) micro-powders were synthesized by a high temperature solid-state reaction. The optical properties of Eu3+ as a local structural probe are analyzed when being incorporated into NaLn(MoO4)2 (Ln = Gd, Y) micro-powders and nanocrystals. In NaLn(MoO4)2:Eu3+ (Ln = Gd, Y), the substitution of Ln3+ by Eu3+ is confirmed and the point symmetry of the site and crystal structure are analyzed. The luminescence mechanism and the size dependence of their fluorescence properties in NaLn(MoO4)2:Eu3+ (Ln = Gd, Y) micro-powders and nanocrystals are also discussed in detail.

One-pot synthesis of conducting poly(3-methylthiophene)-grafted-graphene nanosheets.

We report a simple one-pot synthesis of graphene nanosheets wrapped poly(3-methylthiophene) (GNs-f-P3MT) composites. At first, natural graphite was oxidized using the Hummer's method followed by chemical reduction with hydrazine monohydrate to yield GNs. Subsequently, in-situ chemical oxidative polymerization of 3-methylthiophene was carried out to obtain noncovalently bonded GNs-f-P3MT composites. The morphology and microstructure of the composites together with pure graphene oxide and GNs were characterized using XPS, XRD, FT-IR, FESEM, HRTEM and TGA. The microscopic results indicated the homogeneous dispersion of GNs throughout the polymer matrix. Furthermore, thermogravimetric results illustrated that the addition of GNs into the P3MT matrix led to improvement in the thermal stability of the composites.

Hydrothermal synthesis and photoluminescence investigation of NaY(MoO4)2:Eu3+ nanophosphor.

An intense red-emitting NaY(MoO4)2:Eu3+ nanophosphor was developed using a hydrothermal technique. A highly pure and single-phase NaY(MoO4)2:Eu3+ nanopowder was obtained after sintering the as-prepared sample at 800 degrees C. The crystal structure and photoluminescence properties of this double molybdate were investigated. X-ray diffraction analysis showed that the NaY(MoO4)2 nanoparticles have a scheelite-type tetragonal structure, without mixed phases. Rietveld analysis provided the atomic coordinates and Mo-O-rare-earth angles. The morphology of the molybdate precursor was controlled by adjusting the synthesis conditions. The pH was found to play a crucial role in the particle size and morphology distribution. The crystalline powder phosphor exhibited intense and efficient red emissions attributed to efficient energy-transfer from MoO4(2-) to Eu3+. The chromaticity coordinates (x,y) of the NaY(MoO4)2:Eu3+ phosphor sample correspond to (0.662, 0.337). The NaY(MoO4)2:Eu3+ powder exhibited a deep-red emission under near-ultraviolet (UV) excitation, indicating a promising red phosphor for white-light-emitting diodes based on near-UV light-emitting diodes.

Wide-band excited Y6(WMo)(0.5)O12:Eu red phosphor for white light emitting diode: structure evolution, photoluminescence properties, and energy transfer mechanisms involved.

Y6(WMo)(0.5)O12 activated with Eu(3+) ions was investigated as a red-emitting conversion phosphor for white light emitting diodes (WLEDs). The phosphors were synthesized by calcining a citrate-complexation precursor at different temperatures. The photoluminescence properties of the phosphors and the energy transfer mechanisms involved were studied as a function of structure evolution. It was found that the host lattices were crystallized in a cubic or a hexagonal phase depending on the synthesis conditions. Although all the phosphors showed intensive red emission under an excitation of near-UV or blue light due to energy transfer from the host lattices to Eu(3+) ions, the photoluminescence spectra and temporal decay features were found to vary significantly with the structure and crystallinity of the host lattice. The mechanisms of the energy transfer from the host lattices to Eu(3+) ions and energy quenching among Eu(3+) ions were discussed on the basis of structure evolution of the host lattice. Phosphors calcined at 800 and 1300 °C were suggested to be promising candidates for blue and near-UV light excited WLEDs, respectively.

Crystal growth and photoluminescence properties of Sm3+ doped CeO2 nanophosphors by solvothermal method.

The phosphor of CeO2 activated with the trivalent rare-earth Sm3+ ions were synthesized by using a solvothermal method. The CeO2:Sm3+ powders were finally obtained through calcination process sintered in the air at 800-1200 degrees C. The synthesized phosphors were characterized systematically by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), photoluminescence (PL) and photoluminescence excitation spectra (PLE). The XRD and FE-SEM results reveal that the phosphor exhibit agglomerated spherical shape and with the increase of sintering temperature peaks become sharper and narrower and the crystal sizes also increase, respectively. The room temperature photoluminescence spectra of Sm3+ doped CeO2 powders were recorded on a PTI (Photon Technology International) flurimeter using a Xe-arc lamp with a power of 60 W. The emitted radiation was dominated by the orange light with the characteristic emission of Sm3+ from the transitions of 4G5/2 --> 6H5/2,7/2. The sharp emission properties show that the CeO2 has the potential to serve as a host material for rare-earth doped laser crystal and phosphor material.

Encapsulation of TiO2 nanoparticles with poly(4-vinylpyridine) using surface functionalized thiol-lactam initiated radical polymerization.

A nanocomposite of TiO2 nanoparticle with an electroactive poly(4-vinylpyridine) (PVP) was synthesized via a simple surface thiol-lactam initiated radical polymerization upon grafting from protocol. This can be achieved through the primary modification of the TiO2 surface with a silane coupling agent leading to thiol functionalized TiO2 (TiO2-SH). Subsequently, a controlled radical polymerization of 4-vinylpyridine in the presence of TiO2-SH and butyrolactam afforded PVP-g-TiO2 nanocomposites. The grafting of PVP on the surface of TiO2 was confirmed by FT-IR, TGA, XPS, EDX, TEM and SEM analyses. The UV-vis studies of the synthesized PVP-g-TiO2 nanocomposite demonstrated an exceptionally good dispersibility in organic solvents.

Photoluminescence properties of NaSr(P, V)O4:Eu3+ phosphors.

Eu3+ activated NaSr(P,V)O4 phosphors have been synthesized using solid state reaction method and further characterized for their structure and optical properties using different techniques such as X-ray diffraction, scanning electron microscopy, photolumniscenec excitation, emission, and chromaticity coorrdinate analysis, etc. Material shows a broad excitation peak (monitored for lambda(ems) = 613 nm) lying in the 300-360 nm region and gives intense transitions (lambda(exc) = 320 nm) namely 5D0 --> 7F1 at 590 nm, 5D0 --> 7F2 at 613 nm, 5D0 --> 7F3 at 650 nm, and 5D0 --> 7F4 at 700 nm due to Eu3+ ion. Our results show that replacement of the PO4(3-) ions with isomorphic VO4(3-) ions improves the structural stability and the overall intensity of the emission. The maxium emission intensity is achieved for the NaSr(P0.4, V0.6)O4:Eu3+ phosphor. An estimated increase of an order is attained for the NaSr(P0.4, V0.6)O4:Eu3+ phosphor as compared to NaSrPO4:Eu3+ or NaSrVO4:Eu3+ phosphor. The chromaticity coordinate of the phosphor (0.68, 0.31) lies well within the red region and suggest that the material could be an alternative red phosphor for lighting and display applications.

Enhancement in the microstructure and photoluminescence properties of YVO4:Eu3+ by Al doping.

Al contents have been doped as a sensitizer to improve the luminescent brightness, and the conventional solid state reaction method has been used to synthesize the phosphors. Al doping effects on the microstructures of YVO4:Eu3+ phosphors were measured by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The luminescent characteristics were characterized by photoluminescence excitation (PLE) and emission (PL) measurements. Incorporation of Al3+ ions into the YVO4:Eu phosphors has greatly enhanced the crystallinity, particle size and hence the luminescence properties and the optimum concentration in Al dopants are found to be 0.05 mol. The photoluminescence intensity of 0.05 mol Al(3+)-doped YVO4:Eu3+ phosphors was improved by a factor of 1.41, in comparison with undoped Y0.95Eu0.05VO4 phosphor. The improvement in photoluminescence properties with Al doping may result from the improved crystallinity and from the enlarged grain sizes inducing lower scattering loss.

Concentration enhanced upconversion luminescence in ZrO2:Ho3+, Yb3+ nanophosphors.

The upconversion luminescence properties of ZrO2:Ho3+ and co-doped ZrO2:Ho3+, Yb3+ nanophosphors with various concentrations of Yb3+ ions were synthesized via a solvothermal reaction method. Our samples have a nearby spherical shape and an average crystal size was about 80 nm. For low concentrations of Yb3+ ion, the crystalline structure changed from tetragonal to monoclinic phase as the Yb3+ concentration increased to 3 mol% Yb3+ ions. As the Yb3+ concentration increased to above 5 mol%, ZrO2 nanophosphors displayed a very stable tetragonal phase. The sample shows a strong green (550 nm) and weak red (660 nm) and near infrared (757 nm) upconversion emission corresponding to the transitions of Ho3+:5F4/5S2 --> 5I8, 5F5 --> 5I8 and 5S2 --> 5I7, respectively. The energy transfer (ET) processes between the Ho3+ and Yb3+ ions and the involved mechanisms have been investigated. Experimental results suggest that two-photon upconversion processes are taking place under excitation by a 975 nm.

Optical characterization of Eu3+ doped ZnO nanocomposites.

A rare-earth metal ion (Eu3+) doped ZnO nanocomposites have been successfully synthesized by employing wet chemical procedure using multi-wall carbon nanotubes (MWCNT's) as removable template. The preparation was carried out by immersing empty and dried MWCNT's in a stoichiometric composition of zinc nitrate and europium nitrate solution followed by filtration and sintering. The synthesized Eu3+ doped ZnO nanocomposites were characterized by means of different characterization techniques namely XRD, SEM, EDS, FT-IR and Raman spectroscopy. The XRD profile of the Eu3+ doped ZnO nanocomposites indicated its hexagonal nature while the photoluminescent analysis reveals that the prepared nanocomposite exhibits a strong red emission peak at 619 nm due to 5D0 --> 7F2 forced electric dipole transition of Eu3+ ions. Such luminescent materials are expected to find potential applications in display devices.

An investigation on Eu3+ doped CaLa2ZnO5 novel red emitting phosphors for white light-emitting diodes.

A novel phosphor namely CaLa2ZnO5 doped with Eu3+ ions were prepared by conventional solid state reaction method. We have studied and optimized various constraints like sintering temperature, sintering time and dopant concentration. XRD, SEM profiles have been studied to explore its structural properties. Luminescence properties of these phosphors have been characterized by means of their photoluminescence (PL) spectra. We have noticed that the emission intensity of CaLa2ZnO5:Eu3+ phosphors strongly depend on its sintering temperature and Eu3+ concentration. Moreover, their PL spectra reveals that CaLa2ZnO5:Eu3+ phosphors exhibits a strong luminescence of 5D(0)_7F(2) transition at 627 nm under the excitation of 468 nm, which correspond to the popular emission line from a GaN based blue light-emitting diode (LED) chip. The obtained results of the prepared Eu3+ doped phosphors are very much encouraging and they are potentially useful in the development of new solid-state lightning devices.

Controlled fabrication and shape-dependent luminescence properties of hexagonal NaCeF4, NaCeF4:Tb3+ nanorods via polyol-mediated solvothermal route.

Hexagonal monodisperse NaCeF(4) and NaCeF(4):Tb(3+) nanorods have been successfully synthesized by a polyol-mediated solvothermal route with ethylene glycol (EG) as solvent. The crystalline phase, size, morphology, and luminescence properties were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence (PL) spectra as well as dynamic decays. The experimental results indicate that the content of NH(4)F and NaNO(3) are crucial in controlling product morphology and size. Nanorods with different aspect ratios could be controllably obtained under settled conditions. Shape-dependent luminescence and energy transfer routes from Ce(3+) to Tb(3+) in NaCeF(4):Tb(3+) nanorods were observed by the modified local crystal field environment around rare earth ions. The 4f-5d transitions of Ce(3+) ions have much higher sensitivity to the anisotropic shape of samples than that of Tb(3+) ions.