Synthesis and Spectroscopic Studies of Endohedral Metallofullerenes Tb@C2N

Endohedral metallofullerenes Tb@C_2n were synthesized and extracted with high-yield by K-H carbon-are evaporation and an effective pyridine extraction technique at high-temperature high-pressure. Laser-desorption-ionization time-of-flight (LD-TOF) mass spectrometry, X-ray photoelectron spectroscopy (XPS), solid-state fluorescent emission spectroscopy and gas phase derivation reaction with the self-chemical ionization mass spectrometric ion system of vinyl acetate were employed for studying the electronic structures, fluorescent properties and gas phase reactivities of metallofullerenes Tb@C_2n. The experimental results suggest that endohedral metallofullerenes Tb@C_2n would have the approximate structures of Tb³⁺@C_2n³⁺ similar to other metallofullerenes, good fluorescent emission properties and active reactivities in gas phase ion-molecular reactions.     

ISOLATION AND SPECTROSCOPIC STUDY OF A SERIES OF MONOTERBIUM ENDOHEDRAL METALLOFULLERENES

ABSTRACT

A series of monoterbium endohedral metallofullerenes Tb@C₈₀, Tb@C₈₆, and the second isomer of Tb@C₈₂ (II) has been produced and isolated from various hollow fullerenes and endohedral metallofullerenes by an efficient multi-stage chromatographic separation process for the first time. All these newly isolated metallofullerenes are characterized by laser-desorption time-of-flight (LD-TOF) mass spectrometry and UV-Vis-NIR absorption spectroscopy. Their possible molecular symmetries are discussed according to their HPLC retention time and absorption spectra.     

Gas Phase Derivations of Endohedral Metallofullerenes by Ion-Molecular Reactions

Gas phase ion-molecular reactions of endohedral metallofullerenes with the self-chemical ionization ion system of vinyl acetate, benzene and acetone in the ion source of the mass spectrometer have been studied. Several derivatized endohedral metallofullerene cations [M@C₈₂-C₂H₃O]⁺, [M₂@C₈₀-C₂H₃O]⁺, [M@C₈₂-C₆H₆]⁺ and [M@C₈₂-CO-CH₃]⁺ are observed as the major products. The experimental results indicate that endohedral metallofullerenes have active gas phase reactivities and can be efficiently derivatized by some small organic cations.     

Fabrication and characterization of the photoluminescent properties of Tb doped one-dimensional GdPO4 nanorods

In this letter, one-dimensional GdPO₄:Tb³⁺ nanostructures were successfully synthesized by an easy hydrothermal method at 120 °C and 150 °C. Their morphology and structure were characterized and their photoluminescent properties were investigated, including excitation and emission spectra as well as fluorescent dynamics. Results indicated that one-dimensional GdPO₄:Tb³⁺ nanorods formed at low temperature. The hydrothermal temperature did not affect their morphology and size. The crystal structure of GdPO₄:Tb³⁺ nanostructures belongs to monoclinic phase. According to excitation and emission spectra, the strong green emission of Tb³⁺ ions from ⁵D₄-⁷F₅ transitions and the energy transfer from Gd³⁺ to Tb³⁺ ions were observed.     

Controllable synthesis and luminescence properties of TiO2:Eu3+ nanorods,nanoparticles and submicrospheres by hydrothermal method

Eu³⁺-doped TiO₂ nanocrystals with three kinds of morphologies (nanorods, nanoparticles, and submicrospheres) have been successfully fabricated in cetyltrimethylammonium bromide (CTAB)/water/cyclohexane/n-pentanol reverse micelle by hydrothermal method for the first time and their photoluminescence (PL) properties have also been studied. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), FT-IR, and PL spectra were used to characterize the samples. The acidic and alkaline conditions of the microemulsion play an important role in determining the geometric morphologies of the final products. TiO₂:Eu³⁺ with three different morphologies all exist only in anatase phase and show high luminescence intensity without further calcinations, which show its advantages of energy saving. The shape of emission spectra was independent of the morphologies of the products but the luminescence intensity of the TiO₂:Eu³⁺ materials is strongly dependent on their morphology. The results show that TiO₂:Eu³⁺ nanorods possess the strongest luminescence intensity among the three nanostructured samples.     

Water-soluble Ln-doped calcium fluoride nanocrystals: Controlled synthesis and luminescence properties

Water-soluble CaF₂ nanocrystals doped with different lanthanide ions (Eu³⁺, Tb³⁺) have been synthesized via a novel method using methanol as solvent. These nanocrystals can well disperse in water, forming a stable and transparent colloidal solution. The colloids of the Eu³⁺ and Tb³⁺ doped nanocrystals display intense red and green luminescence under ultraviolet excitation, respectively. The phase structures, morphology, surface structure and luminescence properties of CaF₂:Ln³⁺ nanocrystals were explored in detail. All of the results showed that these nanocrystals own powerful potentials as Down-conversion fluorescent label materials.     

Formation Process of Empty and Metal-Containing Fullerenes—Molecular Dynamics and FT-ICR Studies

Abstract

The formation mechanism of empty and metal-containing fullerene was studied through MD (molecular dynamics) simulations and FT-ICR (Fourier transform ion cyclotron resonance) mass spectroscopy of laser vaporized carbon cluster. Multi-body classical potential functions for metal-carbon and metal-metal interactions were constructed based on DFT (density functional theory) calculations of various forms of small clusters MC_n and M_n (M = La, Sc, Ni). Using the modified Brenner potential for carbon-carbon interaction, the clustering process starting from 500 isolated carbon atoms and 5 metal atoms in gas phase was simulated under the controlled temperature condition at 3000K. The difference of clustering process of La@C_n, Sc@C_n and NiC_n were compared with empty fullerene formation simulation.

FT-ICR mass spectrometer directly connected to the laser vaporization cluster beam source was implemented in order to experimentally study the clustering process. The increase of cluster nozzle pressure roughly corresponded to the later stage of the molecular dynamics simulation. The FT-ICR mass spectra of metal-carbon composite clusters were compared for various sample materials used for arc-discharge generation of metal-containing fullerene and SWNT (single-wall carbon nanotube); La, Y., Sc, Gd, Ce, Ca, and Ni-Y. Positive La-C, Y-C, Sc-C, Gd-C, Ce-C binary clusters commonly showed strong MC_2n+ signal in the range of 36 < 2n with intense magic numbers at MC₄₄ ⁺, MC₅₀ ⁺ and MC₆₀ ⁺. It was speculated that the even-numbered clusters corresponded to the annealed random caged clusters observed in the MD simulation.     

Analysis of metallofullerenes using a mass reflectron

A high-resolution mass reflectron has been used to analyze an extract of a fullerene mixture containing the metallofullerene Gd@C₈₂. It is shown that various metallofullerenes can be analyzed by means of thermal desorption followed by electron impact ionization. The C₆₀, C₈₂, and Gd@C₈₂ ion currents are obtained as functions of the evaporation temperature. Doubly charged (Gd@C₈₂)²⁺ metallofullerene ions are identified in the mass spectra. Pis’ma Zh. Tekh. Fiz. 24, 1–5 (March 12, 1998)     

An experimental design approach for hydrothermal synthesis of NaYF4: Yb3+, Tm3+ upconversion microcrystal: UV emission optimization

Ultraviolet (UV) emissions of hydrothermally synthesized NaYF₄: Yb³⁺, Tm³⁺ upconversion crystals were optimized using the response surface methodology experimental design. In these experimental designs, 9 runs, two factors namely (1) Tm³⁺ ion concentration, and (2) pH value were investigated using 3 different ligands. Introducing UV upconversion emissions as responses, their intensity were separately maximized. Analytical methods such as XRD, SEM, and FTIR could be used to study crystal structure, morphology, and fluorescent spectroscopy in order to obtain luminescence properties. From the photo-luminescence spectra, emissions centered at 347, 364, 452, 478, 648 and 803 nm were observed. Some results show that increasing each DOE factor up to an optimum value resulted in an increase in emission intensity, followed by reduction. To optimize UV emission, as a final result to the UV emission optimization, each design had a suggestion.     

Structural phase and morphology control of tetragonal and hexagonal YPO4:Eu nanoflakes for tunable luminescence properties

Eu³⁺-doped tetragonal and hexagonal YPO₄ nanocrystals with different phase structures and morphologies were successfully synthesized by a solvothermal method. It was found that the pH value is a crucial factor in determining the phase structures and their morphologies of YPO₄:Eu nanocrystals. The crystal structure and the properties of the Eu³⁺-doped YPO₄ nanocrystals were characterized by XRD, SEM, TEM, UV–Vis spectroscopy.     

Synthesis and luminescent properties of Tb3+ activated AWO4 based (A = Ca and Sr) efficient green emitting phosphors

Optically efficient terbium activated alkaline earth metal tungstate nano phosphors (AWO₄ [A = Ca, Sr]) with different doping concentrations have been prepared by mechanochemically assisted solid state metathesis reaction at room temperature for the first time. The prepared phosphors were characterized by the X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM), Fourier transform Raman (FT-Raman) spectroscopy, photoluminescence and diffuse reflectance spectroscopy measurements. The XRD and Raman spectra results showed that the prepared powders present a scheelite-type tetragonal structure. FTIR spectra exhibited a high absorption band situated at around 850 cm^?1, which was ascribed to the W–O antisymmetric stretching vibrations into the [WO₄]^2? tetrahedron groups and the SEM images reveal that the particle sizes were in the range of 20–60 nm. The excitation and the emission spectra were measured to characterize the luminescent properties of the phosphors. The excitation spectrum exhibits a charge transfer broad band along with some sharp peaks from the typical 4f–4f transitions of Tb³⁺. Under excitation of UV light, these AWO₄:xTb³⁺ (A = Ca, Sr) phosphors showed a strong emission band centered at 545 nm (green) which corresponds to ⁵ D ₄ → ⁷ F ₅ transition of Tb³⁺. Analysis of the emission spectra with different Tb³⁺ concentrations revealed that the optimum dopant concentration for CaWO₄:xTb³⁺ and SrWO₄:xTb³⁺ phosphors are about 8 and 6 mol% of Tb³⁺. The green emission intensity of the solid state meta-thesis prepared CaWO₄:0.08Tb³⁺ and SrWO₄:0.06Tb³⁺ phosphors are 1.5 and 1.2 times greater than that of the commercial LaPO₄:Ce, Tb green phosphor. All properties show that AWO₄:Tb³⁺ (A = Ca, Sr) is a very appropriate green-emitting phosphor for fluorescent lamp applications.     

A reddish La2O2S-based long-afterglow phosphor with effective absorption in the visible light region

Sm³⁺-activated La₂O₂S phosphors with good crystallinity were prepared by solid-state reaction. The formation mechanism of La₂O₂S formation was assumed and the phase change with different temperatures was discussed. The luminescence properties of phosphors with different sintering temperatures and different doping concentrations of Sm³⁺were investigated. The emission peak at 605 nm showed a well intensity can be attributed to the ⁴G_5/2 → ⁶H_7/2 transition of Sm³⁺. The optical absorption of La₂O₂S phosphors showed a stronger intensity in UV-vis region comparing with the Y₂O₂S phosphors. The long afterglow properties were investigated after the phosphors were excited with a fluorescent lamp. Phosphorescence lasted for about 3 min in the limit of light perception of the dark-adapted human eye (0.32 mcdm⁻²).     

EDTA-assisted phase conversion synthesis of (Gd0.95RE0.05)PO4 nanowires (RE = Eu,Tb) and investigation of photoluminescence

Abstract

Hexagonal (Gd_0.95RE_0.05)PO₄·nH₂O nanowires ~300 nm in length and ~10 nm in diameter have been converted from (Gd_0.95RE_0.05)₂(OH)₅NO₃·nH₂O nanosheets (RE = Eu, Tb) in the presence of monoammonium phosphate (NH₄H₂PO₄) and ethylene diamine tetraacetic acid (EDTA). They were characterized by X-ray diffraction, thermogravimetry, electron microscopy, and Fourier transform infrared and photoluminescence spectroscopies. It is shown that EDTA played an essential role in the morphology development of the nanowires. The hydrothermal products obtained up to 180 °C are of a pure hexagonal phase, while monoclinic phosphate evolved as an impurity at 200 °C. The nanowires undergo hexagonal→monoclinic phase transformation upon calcination at ≥600 °C to yield a pure monoclinic phase at ~900 °C. The effects of calcination on morphology, excitation/emission, and fluorescence decay kinetics were investigated in detail with (Gd_0.95Eu_0.05)PO₄ as example. The abnormally strong ⁵D₀→⁷F₄ electric dipole Eu³⁺ emission in the hexagonal phosphates was ascribed to site distortion. The process of energy migration was also discussed for the optically active Gd³⁺ and Eu³⁺/Tb³⁺ ions.     

Luminescence properties for the high-pressure polymorphs of CaSiO3:Pb2+ and SrSiO3:Pb2+

High-pressure phases of CaSiO₃:Pb²⁺ and SrSiO₃:Pb²⁺ phosphors were synthesized at 40–55 kbar and 1000°C, $\text{viz}$. δ-CaSiO₃:Pb²⁺, δ-SrSiO₃:Pb²⁺, and δ′-SrSiO₃:Pb²⁺, and their luminescence properties were investigated. Among them, δ-CaSiO₃:Pb²⁺ was found to give a strong violet-blue emission ($\text{ca}$. 341 nm) as well as β-CaSiO₃:Pb²⁺ (an atmospheric phase), and the emission intensity of SrSiO₃:Pb²⁺ drastically increased when the host lattice transformed into high-pressure phases (δ and δ′ forms). These results were discussed by considering their structures and quenching temperatures of luminescences.     

Effect of Al3+ on the photoluminescence properties of Ce3+-doped Zn3(BO3)2 nanoparticles

Zn₃(BO₃)₂ nanoparticles doped with Ce³⁺ and Al³⁺ have been prepared by co-precipitation method. The study on the XRD pattern and Fourier transform infrared spectroscopy (FT-IR) shows that the diffraction lines are in good agreement with monoclinic crystalline phase of Zn₃(BO₃)₂. Ce³⁺-doped Zn₃(BO₃)₂ nanoparticles show a broader emission band at 405 nm, which is attributed to the d–f transition 5d–4f¹ of Ce³⁺. The effect of Al³⁺ on luminescence properties of Ce³⁺ has been studied. The results show that the fluorescence intensity of Ce³⁺ is enhanced greatly.     

Formation of Nickel Silicide Films from Nickel Acetylacetonate and Organosilicon Compounds

Nickel films were deposited from nickel acetylacetonate vapor on silicon, gallium arsenide, and germanium wafers and SiO₂/Si structures, and their composition and properties were studied. Annealing in dimethyldichlorosilane or hexamethyldisilazane vapor exerts a considerable effect on the composition and properties of Ni/Si structures. Films deposited from the gas phase containing nickel acetylacetonate and an organosilicon compound (OSC) were examined. As found by Auger electron spectroscopy with Ar⁺ion profiling of the surface, nickel silicide films can be obtained by Ni(AcAc)₂vapor deposition followed by annealing the resulting nickel film in OSC vapor and by OSC + Ni(AcAc)₂vapor deposition.     

Optical properties of Eu<Superscript>3+</Superscript> activated SrLa<Subscript>2</Subscript>O<Subscript>4</Subscript> red-emitting phosphors for WLED applications

The SrLa_2?xO₄:xEu³⁺ phosphors are synthesized through high-temperature solid-state reaction method at 1473 K with various doping concentration. Their phase structures, absorption spectra, and luminescence properties are investigated by X-ray diffraction (XRD), UV–Vis spectrophotometer and photoluminescence spectrometry. The intense absorption of SrLa_2?xO₄:xEu³⁺ phosphors have occurred around 400 nm. The prominent luminescence spectra of the prepared phosphors exhibited bright red emission at 626 nm. The doping concentration 0.12 mol% of Eu³⁺ is shown to be optimal for prominent red emission and chromaticity coordinates are x?=?0.692, y?=?0.3072. Considering the high colour purity and appropriate emission intensity of Eu³⁺ doped SrLa₂O₄ can be used as red phosphors for white light emitting diodes (WLEDs).     

Photocatalytic degradation of formaldehyde by nanostructured TiO2 composite films

Interest in the photocatalytic oxidation of formaldehyde from contaminated wastewater is growing rapidly. The photocatalytic activity of the nanocrystalline Fe³⁺/F^? co-doped TiO₂–SiO₂ composite film for the degradation of formaldehyde solution under visible light was discussed in this study. The films were characterised by field emission scanning electron microscopy (FE-SEM) equipped with energy-dispersive spectroscopy, X-ray diffraction (XRD), BET surface area, UV–Vis absorption spectroscopy, and photoluminescence spectroscopy. The FE-SEM results revealed that the Fe³⁺/F^? co-doped TiO₂–SiO₂ film was composed of uniform round-like nanoparticles or aggregates with the size range of 5–10 nm. The XRD results indicated that only the anatase phase was observed in the film. Compared with a pure TiO₂ film and a singly modified TiO₂ film, the Fe³⁺/F^? co-doped TiO₂–SiO₂ composite film showed the best photocatalytic properties due to its strong visible light adsorption and diminished electrons-holes recombination.     

Luminescent properties of YAl3(BO3)4:Eu3+ phosphors

YAL₃(BO₃)₄:Eu³⁺ phosphors were fabricated by the sol-gel method. The structure properties were measured by x-ray diffraction (XRD) and infrared spectra (IR). Doping concentration of Eu³⁺ ions in YAL₃(BO₃)₄:Eu³⁺ phosphors of 0, 1, 3, 4, and 5 mol% were studied. The excitation spectra and emission spectra of YAL₃(BO₃)₄:Eu³⁺ phosphors were examined by fluorescent divide spectroscopy (FDS). The luminescent properties of YAL₃(BO₃)₄:Eu³⁺ phosphors are discussion. The optimal doping concentration of Eu³⁺ ions in YAL₃(BO₃)₄:Eu³⁺ phosphors was found to be approximately 3 mol%.     

Luminescence properties of Dy-doped Li2SrSiO4 for NUV-excited white LEDs

A series of single-phase full color phosphors, Dy³⁺-doped Li₂SrSiO₄ was synthesized by a solid-state reaction method. The phase of the as-prepared powders was measured by X-ray diffraction pattern (XRD) and the chemical composition was characterized using energy dispersive spectroscopy (EDS). The luminescent properties of Li₂SrSiO₄:Dy³⁺ were systematically investigated by concentration quenching, decay behavior and thermal stability measurements. The results suggested that the emission intensity of the Li₂SrSiO₄:Dy³⁺ was much stronger than that of Li₂SrSiO₄:Eu²⁺. It was worth to mention that Li₂SrSiO₄:Dy³⁺ phosphor possessed excellent thermal stability for use in light-emitting diodes (LEDs) and the emission intensity measured at 300 °C was only decreased 8% comparing with that measured at room temperature. Furthermore, the Commission International del’Eclairage (CIE) chromaticity coordinates of Li₂SrSiO₄:Dy³⁺ moved toward the ideal white light coordinates (0.33, 0.33). All results demonstrated that Li₂SrSiO₄:Dy³⁺ might be a potential phosphor for NUV-based white light-emitting diodes.