Intense Broad Emission Research Articles

Facile fabrication of single-phase multifunctional BaGdF5 nanospheres as drug carriers.

Multifunctional BaGdF5 nanospheres with mesoporous, luminescent, and magnetic properties have been successfully synthesized with the assistance of trisodium citrate by a hydrothermal method. The mesoporous structure is revealed by scanning electron microscope and transmission electron microscope images as well as N2 adsorption-desorption isotherm. The as-synthesized BaGdF5 nanospheres exhibit an intense broad bluish emission (centered at 450 nm) under the excitation of 390 nm, which might originate from the CO2·(-) radical-related defect produced by Cit(3-) groups. It is also shown that these BaGdF5 nanospheres brightened the T1-weighted images, suggesting that they could act as T1 contrast agents for magnetic resonance imaging. Using metformin hydrochloride as the model drug, the luminescent porous spheres show good drug storage/release capability. Furthermore, the emission intensity varies as a function of the cumulative drug release, making the drug-carrying system easily trackable and monitorable by detecting the luminescence intensity. Additionally, the paramagnetic property, originating from the unpaired electrons of Gd(3+) ions, opens the possibility of directing the magnetic targeted carrier to the pathological site by magnetic field gradient.

Synthesis, Crystal Structure, and Fluorescent Property of a New Two-Dimensional Zn(II) Coordination Polymer Based on Oxalic Acid and 1,4-Bis(imidazol-1-ylmethyl)-butane

A new compound [Zn(C2O4)(bimb)]n·nH2O (1) (H2C2O4 = oxalic acid, bimb = 1,4-bis(imidazol-1-yl)-butane) has been synthesized by hydrothermal reaction and characterized by elemental analysis, IR, and single-crystal X-ray diffraction. Compound 1 exhibits two-dimensioanl layer structure. The intermolecular O-H···O interactions extend the compound 1 into 3D supramolecular architectures and play an important role in stabilizing compound 1. Furthermore, the solid-state fluorescence spectrum of the compound 1 was studied. The compound 1 exhibits intense broad emission at 520 nm at room temperature.

Luminescence properties of Ba3Si6O9N4:Eu2+ green-emitting phosphors for white LEDs

A green-emitting phosphor, Eu2+-activated Ba3Si6O9N4 phosphor, was synthesized by a conventional solid state reaction method. X-ray diffraction patterns showed that the synthesized phosphor sintered at 1300°C for 6h was a Ba3Si6O9N4 pure phase. It could be efficiently excited by UV–blue light (280–500nm) and showed a single intense broad emission band (470–625nm). Suitable excitation range makes it match well with the emission of near-UV or blue LEDs. Concentration quenching of the doped-Eu2+ ions occurred at x=0.15, and the critical distance is calculated to be about 1.807nm by theory of energy transfer. The result indicates that Ba3Si6O9N4:Eu2+ is a promising green-emitting phosphor for white LEDs.

CdS nanoparticles incorporated onion-like mesoporous silica films: Ageing-induced large stokes shifted intense PL emission

CdS nanoparticles (NPs) were generated in onion-like ordered mesoporous SiO2 films through a modified sol–gel process using P123 as a structure directing agent. Initially Cd2+ doped (12 equivalent mol% with respect to the SiO2) mesoporous SiO2 films were prepared on glass substrate. These films after heat-treatment at 350°C in air yielded transparent mesoporous SiO2 films having hexagonally ordered onion-like pore channels embedded with uniformly dispersed CdO NPs. The generated CdO NPs were transformed into CdS NPs after exposing the films in H2S gas at 200°C for 2h. The as-prepared CdS NPs incorporated mesoporous SiO2 films (transparent and bright yellow in color) showed a band-edge emission at 485nm and a weak surface defect related emission at 530nm. During ageing of the films in ambient condition the band-edge emission gradually weakened with time and almost disappeared after about 15days with concomitant increase of defect related strong surface state emission band near 615nm. This transformation was related to the decay of initially formed well crystalline CdS to relatively smaller and weakly crystalline CdS NPs with surface defects due to gradual oxidation of surface sulfide. At this condition the embedded CdS NPs show large Stokes shifted (∼180nm) intense broad emission which could be useful for luminescent solar concentrators. The detailed process was monitored by UV–Visible, FTIR and Raman spectroscopy, XPS, XRD and TEM studies. The evolution of photoluminescence (PL) and life times of CdS/SiO2 films were monitored with respect to the ageing time.

Deep Red to Near‐Infrared Emitting Rhenium(I) Complexes: Synthesis, Characterization, Electrochemistry, Photophysics, and Electroluminescence Studies

A series of triarylamine-containing tricarbonyl rhenium(I) complexes, [BrRe(CO)3 (N^N)] (N^N=5,5'-bis(N,N-diaryl-4-[ethen-1-yl]-aniline)-2,2'-bipyridine), has been designed and synthesized by introducing a rhenium(I) metal center into a donor-π-acceptor-π-donor structure. All of the complexes showed an intense broad structureless emission band in dichloromethane at around 680-708 nm, which originated from an excited state of intraligand charge transfer ((3)ILCT) character from the triarylamine to the bipyridine moiety. Upon introduction of the bulky and electron-donating pentaphenylbenzene units attached to the aniline groups, the emission bands were found to be red shifted. The nanosecond transient absorption spectra of two selected complexes were studied, which were suggestive of the formation of an initial charge-separated state. Computational studies have been performed to provide further insight into the origin of the absorption and emission. One of the rhenium(I) complexes has been utilized in the fabrication of organic light-emitting diodes (OLEDs), representing the first example of the realization of deep red to near-infrared rhenium(I)-based OLEDs with an emission extending up to 800 nm.

Structure and luminescence properties of Bi3+ activated Ca12Al14O32Cl2 phosphors

Bi3+ doped Ca12Al14O32Cl2 series were successfully synthesized by conventional solid-state reaction method and their luminescence properties have been investigated in detail. Crystallographic parameters of the refinement structure with cubic space group I-43d were obtained by XRD refinement as a=12.0183(3)Å and V (cell volume)=1735.93(1)Å3. The resulting phosphors absorb ultraviolet (UV) light (240–400nm) and show a single intense broad emission band in the wavelength range of 400–600nm with maximum intensity at 483nm. The Commission Internationale de 1’Eclairage (CIE) chromaticity coordinates are about x=0.185, y=0.306. Thus, the novel light blue-emitting phosphor Ca12Al14O32Cl2:Bi3+ could be potentially applied in UV white light-emitting diodes.

Electrochemical and Photophysical Study in Solution and on Ruthenium(II) Polypyridyl Complexes Containing Thiophenylethynylphenanthrolines Self-assembled on Gold Surfaces

Abstract Novel ruthenium(II) polypyridyl complexes with diethynylphenanthrolines containing acetylthiophenyl unit(s) have been prepared and characterized by photophysical measurements. These complexes showed the MLCT and the lowest energy π–π* absorption bands, and also intensive broad emission bands assignable to a triplet MLCT transition were observed in the deaerated solution. The electrochemistry of these complexes in the solution and on self-assembled monolayers on the gold electrode clearly showed Ru(II)/R(III) redox waves.

Full-color photoluminescence of ZnO nanorod arrays based on annealing processes

Vertically well-aligned ZnO nanorod arrays with highly crystalline wurtzite structures were synthesized on ITO glass substrates by a two-step hydrothermal method, and then, annealed at different temperatures and under different atmospheres. Photoluminescence spectra showed a near-band-edge (NBE) emission peak and an intense broad visible emission band for as-grown and annealed samples. These visible emission bands exhibited dependences on post-annealing conditions and excitation energies. Emission shifting in the visible region was investigated and explained in terms of the presence of defects. Based on these findings, we demonstrate that the visible emission in these materials can be tailored by controlling the defects in ZnO. Under different annealing conditions, it is possible to manipulate the emission in the visible region, which has important implications for the production of optoelectronic devices.

Synthesis and luminescence properties of broad band greenish-yellow emitting LnVO4:Bi3+ and (Ln1, Ln2)VO4:Bi3+ (Ln=La, Gd and Y) as down conversion phosphors

Ln0.97VO4:Bi0.033+ and (Ln10.5, Ln20.5)0.97VO4:Bi0.033+ (where Ln=La, Gd and Y) down conversion (DC) phosphors have been synthesized by a novel co-precipitation technique followed by heat-treatment. The influence of lanthanide host composition on crystal structure, luminescence and pertinent optical properties have been investigated by various spectroscopic techniques: XRD, SEM, FT-IR and PL. The produced phosphors have exhibited an intense greenish-yellow emission, upon UV-irradiation. A broad band excitation (280–350nm) ascribed to 1S0→3P1 and an intense broad greenish-yellow emission band (400–700nm) attributed to 3P1→1S0 transition, owing to Bi3+ ions have been observed. PL spectra revealed that the phosphors with Gd – containing host has exhibited a better luminescence among the others. The luminescence intensity sequence in descending order was as follows: GdVO4→(Gd, Y)VO4→(La, Gd)VO4→(La, Y)VO4→YVO4→LaVO4: Bi3+. These phosphors can efficiently convert the UV-photons in a broad range from 280–350nm of feckless UV-rays into the absorbable visible emission for c-Si solar cells, based on the spectral matching phenomena. In view of the better fluorescence and pertinent optical properties, the phosphor with composition Gd0.97VO4: Bi0.033+ is a suggestible sought UV-absorbing spectral converter, in its thin transparent DC form for c-Si solar cells for better harvesting the solar energy.

Synthesis, structure and photoluminescence properties of fine yellow-orange Ca-α-SiAlON: Eu2+ phosphors

Yellow-orange oxynitride Ca-α-SiAlON: Eu2+ phosphors with the compositions of Ca0.8Si9.2Al2.8O1.2N14.8: xEu2+ (x=0–0.24) were obtained via carbothermal reduction and nitridation method. Crystallographic parameters of the refinement structure with triclinic space group P31c (159) were obtained by XRD refinement as a=b=7.8859(3)Å, c=5.7336(2)Å, V=308.7915(3)Å3, Z=1. The resulting phosphors can absorb light in the range of 300–500nm efficiently and show a single intense broad emission band in the wavelength range of 500–700nm with maximum intensity at 580–601nm. The chromaticity coordinates of the synthesized Ca-α-SiAlON: Eu2+ phosphors can be tailored by simply controlling the activator concentration. All the results show that Ca-α-SiAlON: Eu2+ phosphors can be a candidate for warm white LEDs.

Preparation and photoluminescence properties of the Sr1.56Ba0.4SiO4:0.04Eu2+ phosphor

The Sr1.56Ba0.4SiO4:0.04Eu2+ phosphors were prepared via a combustion reaction and following the calcination method at low temperature. The influences of the amount of the uncommonly used SrCl2 flux, different calcination temperatures and time on the structure and the photoluminescence (PL) properties of the phosphors were investigated. Under the excitation of 450nm blue light, the phosphor shows the intense broad emission band from 490nm to 650nm, and the emission peak is centered at 553nm. The luminescence intensity of Sr1.56Ba0.4SiO4:0.04Eu2+ was very sensitive to the crystallinity and morphology characteristics of the phosphor. The phosphor calcined at 950°C for 3h in 20%H2/80%Ar atmosphere exhibits improved PL properties due to its high crystallinity and excellent morphology characteristics. The use of the SrCl2 flux provides a novel way to improve the crystallinity of the silicates phosphors at low preparation temperature.

A dual-mode solar spectral converter CaLaGa3S6O:Ce3+,Pr3+: UV-Vis-NIR luminescence properties and solar spectral converting mechanism

A promising dual-mode solar spectral converter CaLaGa3S6O:Ce3+,Pr3+ for Si solar cells has been successfully developed. The structure, photoluminescence excitation and emission spectra in the UV-Vis-NIR region, and the decay curves have been systematically investigated. The results show that CaLaGa3S6O:Ce3+,Pr3+ exhibits two distinct solar spectral converting behaviors, quantum cutting (QC) (3PJ = 0,1,2 → 1G4 → 3H4) and downshift (DS) processes (1D2 → 3FJ = 3,4), depending on different excited levels of Pr3+ and Ce3+. It can almost harvest UV-blue-red (250–625 nm) photons, greatly enhancing the utilization of solar spectrum especially in UV-Vis spectrum region, and convert into an intense broad NIR emission (930–1060 nm), perfectly matching the maximum spectral response of Si solar cells. We demonstrate that Ce3+/Pr3+ ions can form an efficient donor–acceptor pair, with high potential as full spectrum solar converter for Si solar cells, and Ce3+ ion can be an efficient sensitizer for harvesting UV photon and greatly enhancing the NIR emission of Pr3+ ion through efficient energy feeding by allowed 4f–5d absorption of Ce3+ ion with high oscillator strength. The NIR integrated emission intensity of CaLaGa3S6O:Ce3+,Pr3+ is 7.78 times as intense as that of a NIR quantum cutting phosphor Ca2BO3Cl:Ce3+,Tb3+,Yb3+ (CBC). We believe this new dual-mode solar spectral converter may open a new route to the design of advanced UV-Vis–NIR phosphors for Si based solar cell applications.

Synthesis and luminescence properties of Bi 3+-doped YVO 4 phosphors

YVO 4:Bi 3+ phosphors have been prepared by a convenient high-temperature solid-state method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) technologies are used to study the luminescence properties of YVO 4:Bi 3+ phosphors. The emission and excitation spectra of Bi 3+ in the YVO 4 lattice have been investigated at room temperature. The excitation band peaks at 330 nm in a region among 250–400 nm, and the emission spectrum exhibits an intense yellowish-white broad emission centered at about 543 nm covering from 400 nm to 800 nm. The full width at half maximum (FWHM) is about 144 nm. The color coordinates of the as-synthesized YVO 4:Bi 3+ phosphors are in a range of x = 0.358–0.374, y = 0.482–0.496. The dependence of the luminescence intensity on Bi 3+ concentrations and heat treatment condition has also been discussed. In addition, we found that a little amount of flux NH 4Cl could enhance the Bi 3+ luminescence intensity.

Syntheses, structures, and properties of two novel cadmium coordination polymers with 1D and 2D structures

Two novel complexes [Cd 2(MIP) 2(BDC) 2]n ( 1) [MIP = 2-(3-methoxyphenyl)-1H-imidazo[4,5-f][1,10]phenanthroline, BDC = terephthalic acid] and [Cd(IPM)(NDC)]n ( 2) [IPM = 4-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)-2-methoxyphenol, NDC = naphthalene-1,4-dicarboxylic acid] have been synthesized by hydrothermal reaction and characterized by elemental analysis, IR, single-crystal X-ray diffraction and thermogravimetric analysis (TGA). Complex 1 exhibits 1D zigzag chain structure and complex 2 shows 2D layer topology. The intermolecular C H⋯O interactions extend the complex 1 into 2D networks, and the existing H-bonds further stabilized the complexes 1–2, which can be proved by TGA experiment. Furthermore, the solid-state fluorescence spectrum of the complex 2 was studied, as well as the ligand IPM. The complex 2 exhibits intense broad emission at 540 nm at room temperature, which is red-shifted by 45 nm relative to that of free ligand IPM.

Synthesis and luminescence properties of a broad-band red phosphor Ca 3Si 2O 7:Eu 2+ for warm white light-emitting diodes

Single-phase broad-band red-emitting Ca 3Si 2O 7:Eu 2+ phosphors, with photoluminescence features that qualify them as candidates for white light-emitting diodes applications, were successfully synthesized via a modified solid-state reaction method that employed H 3BO 3 as a flux. The phosphors produced have an intense broad red emission band, with a peak at 603 nm, a full width at half maximum of 110 nm, and color coordinates of (0.550, 0.438). Concentration quenching occurred at 0.01 mol Eu 2+. The discussion of the results shows that Eu 2+ ions should be accommodated at the Ca-sites of the lattice, dipole–dipole interactions should predominantly govern the energy transfer mechanism among them, and the critical distance between them is ∼31 Å.

Effect of annealing on the structural and luminescent properties of ZnO nanorod arrays grown at low temperature

Vertically well-aligned ZnO nanorod arrays were synthesized on glass substrates by a two-step chemical bath deposition method. The structural and luminescent properties of as-grown and air annealed samples were investigated. Scanning electron microscopy, x-ray diffraction and Raman spectra demonstrate that ZnO nanorods are well oriented with c-axis perpendicular to the substrates. Photoluminescence spectra show a weak ultraviolet emission and an intense broad visible emission band for as-grown and air annealed samples. These visible emission bands exhibit dependences of post annealing temperatures and excitation energies: (1) as the annealing temperature increases, the visible emission band gradually red-shifts from yellow to orange-red; (2) the optimal excitation energy for yellow and orange-red emission band is near the band-gap energy; (3) green emission band can be excited only by the energies lower than the band-gap energy and this emission becomes weak after high temperature annealing. A depletion region model is presented to explain the origins and red-shift of the visible emission bands. The recombination of a delocalized electron in the interstitial zinc close to the conduction band with a deeply trapped hole in the single negatively charged interstitial oxygen center in the deletion region (in the bulk) is responsible for the yellow (orange-red) emission.

Luminescent Properties of Eu-Doped Transparent Glass-Ceramics Containing YPO4 Nanocrystals

Eu-doped transparent glass–ceramics containing YPO4 nanocrystals were prepared, and their structural and luminescent properties were investigated. Excited by 365 nm light, the precursor glass and glass–ceramics all emit an intense broad blue emission ascribing to 5d–4f transition of Eu2+ as well as characteristic sharp red emissions of Eu3+. The prominent Stark splitting, low forced electric dipole 5D0→7F2 transition and long decay lifetimes of Eu3+ emission demonstrated that Eu3+ had entered into YPO4 nanocrystals, while Eu2+ still reside in glass matrix. Our results indicate that YPO4-based glass–ceramics doped with lanthanide ions may find application in photonics.

Novel green-emitting Na 2CaPO 4F:Eu 2+ phosphors for near-ultraviolet white light-emitting diodes

In this study, green-emitting Na 2CaPO 4F:Eu 2+ phosphors were synthesized by solid-state reactions. The excitation spectra of the phosphors showed a broad hump between 250 and 450 nm; the spectra match well with the near-ultraviolet (NUV) emission spectra of light-emitting diodes (LEDs). The emission spectrum showed an intense broad emission band centered at 506 nm. White LEDs were fabricated by integrating a 390 nm NUV chip comprising blue-emitting BaMgAl 10O 17:Eu 2+, green-emitting Na 2CaPO 4F:0.02 Eu 2+, and red-emitting CaAlSiN 3:Eu 2+ phosphors into a single package; the white LEDs exhibited white light with a correlated color temperature of 5540 K, a color-rendering index of 90.75, and color coordinates (0.332, 0.365) close to those of ideal white light.

Luminescent Porous Silica Fibers as Drug Carriers

Luminescent and porous silica fibers have been successfully prepared by using the electrospinning process. The obtained multifunctional silica fibers, which possess a porous structure and display blue luminescence, can serve as a drug delivery host carrier, using ibuprofen (IBU) as a model drug, allowing the investigation of storage/release properties. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), N(2) adsorption/desorption, photoluminescence (PL) spectra, and kinetic decay were used to characterize the structural, morphological, and optical properties of the as-obtained samples. The results reveal that the multifunctional silica materials exhibit an irregular porous structure, and display a fiberlike morphology with dimensions of several hundred nanometers in width and several millimeters in length. The obtained silica fibers exhibit an intense broad bluish emission, which might be attributed to impurities and/or defects in the silica fibers. The IBU-loaded silica fiber system shows blue luminescence under UV irradiation and controlled release behavior for IBU. In addition, the emission intensities of silica fibers in the drug carrier system vary with the released amount of IBU, thus allowing the drug release to be easily tracked and monitored by the change of the luminescence intensity.

Conformational Isomerism of 1,2-Bis(imidazol-1′-yl)ethane Affected by the Orientation of Functional Carboxylate Groups in Cadmium and Cobalt Helical Coordination Polymers

Four helical coordination polymers, [Cd(anti-bime)(1,3-pda)]n (1), [Cd(gauche-bime)(1,4-pda)]n (2), [Co(anti-bime)(1,2-pda)]n (3), and [Co(gauche-bime)(1,4-pda)]n (4), have been solvothermally prepared by the assembly of mixed flexible ligands, bime and 1,3-H2pda, 1,4-H2pda, 1,2-H2pda with Cd(NO3)2·4H2O and Co(NO3)2·6H2O, respectively (bime = 1,2-bis(imidazol-1′-yl)ethane, 1,3-H2pda = 1,3-phenylenediacetic acid, 1,4-H2pda = 1,4-phenylenediacetic acid, 1,2-H2pda = 1,2-phenylenediacetic acid). Single-crystal X-ray diffraction analyses reveal that all of the complexes possess helical structures owing to the use of mixed flexible ligands; the conformations of flexible bime are entirely different, anti-bime occurs in 1 and 3, while gauche-bime occurs in 2 and 4. The fluorescent properties of 1 and 2 suggest that the intense broad photoluminescence emission at 387 nm for 1 and 389 nm for 2, 3, and 4 exhibit similar weak antiferromagnetic coupling between the Co2+ centers.