Biao Dong

Microstructure and optical properties of Eu3+ activated YV1−xPxO4 phosphors

Microstructure and spectroscopic properties of YV1−xPxO4:2u2002molu2009% Eu3+ (x=0, 0.05, 0.5, 0.95, and 1) powders derived from solid state reaction method were systematically reinvestigated by various spectroscopic techniques such as x-ray diffraction, Fourier transform infrared, excitation and emission spectra, and particularly by frequency-selective excitation techniques. The present results further show the evolutions of local environment surrounding both cations and anion groups with composition, which yielded systematic changes in spectroscopic properties. At least three symmetry sites were identified by laser-selective excitation to be present in the mixed yttrium vanadate/phosphate compounds due to chemical disorder in microstructure based on the random distribution of VO4 and PO4 tetrahedrons. Luminescence dynamics under site-selective excitation indicates that luminescence lifetime of D50 level of Eu3+ ions decreased in going from YPO4 to YVO4 host mainly due to the enhanced electronic dipole transitio...

Photochemical preparation of silver nanoparticles supported on zeolite crystals

A facile and rapid photochemical method for preparing supported silver nanoparticles (Ag-NPs) in a suspension of faujasite type (FAU) zeolite nanocrystals is described. Silver cations are introduced by ion exchange into the zeolite and subsequently irradiated with a Xe-Hg lamp (200 W) in the presence of a photoactive reducing agent (2-hydroxy-2-methylpropiophenone). UV-vis characterization indicates that irradiation time and intensity (I0) influence significantly the amount of silver cations reduced. The full reduction of silver cations takes place after 60 s of a polychromatic irradiation, and a plasmon band of Ag-NPs appears at 380 nm. Transmission electron microscopy combined with theoretical calculation of the plasmon absorbance band using Mie theory shows that the Ag-NPs, stabilized in the micropores and on the external surface of the FAU zeolite nanocrystals, have an almost spheroidal shape with diameters of 0.75 and 1.12 nm, respectively. Ag-NPs, with a homogeneous distribution of size and morphology, embedded in a suspension of FAU zeolites are very stable (∼8 months), even without stabilizers or capping agents.

Origin of luminescence enhancement and quenching of europium complex in solution phase containing Ag nanoparticles.

Luminescence enhancement and quenching of Eu(TTA)(3) x 2 H(2)O complex in DMF (N,N-dimethylformamide) solution containing silver nanoparticles were observed, which depended on the concentrations of both europium complex and silver nanoparticles. Their origins were discussed based on absorption spectra, excitation and emission spectra, and luminescent decay dynamics. The results indicated that when the concentration of Eu complex was high enough, strong interaction among complex molecules occurred. The presence of Ag nanoparticles definitely decreased the interaction among complex molecules. In the solution containing Ag nanoparticles the electronic-dipole transition rate of (5)D(0)-(7)F(2) increased due to enhanced local field surrounding Eu(3+) ions, while the nonradiative transition rate from (5)D(0) decreased owing to decreased resonant energy transfer among europium complex molecules. These two factors lead to the luminescence enhancement of europium complex. As to the luminescent quenching, was attributed to absorption competition between Ag nanoparticles and europium complex at excited wavelength.

Downconversion from visible to near infrared through multi-wavelength excitation in Er3+/Yb3+ co-doped NaYF4 nanocrystals

Homogeneous NaYF4:Yb3+/Er3+ nanoparticles (NPs) with average diameters of ∼10u2009nm and ∼200u2009nm and various doping concentrations (Yb3+:0%−20%, Er3+:2%) were prepared by the thermal decomposition of trifluoroacetate precursors. The visible and infrared (IR) emission spectra range of 500–2200u2009nm and luminescent dynamics were studied through the pumping of multi-wavelengths, 443u2009nm, 488u2009nm, and 520u2009nm. Strong and sufficient IR emissions were observed, including the transitions of 4I11/2−4I15/2 at ∼980u2009nm, 2H11/2−4I11/2 at ∼1112u2009nm, 4S3/2−4I11/2 at ∼1217u2009nm, 4I13/2−4I15/2 at ∼1540u2009nm, 4I9/2−4I13/2 at ∼1680u2009nm, and 4F9/2−,4I11/2 at ∼1955u2009nm. It is the first observation of 2H11/2−4I11/2 and 4F9/2−4I11/2 emissions to our knowledge. Through the IR emissions, several novel channels of quantum cutting (QC) were evidenced, including: (1) 2H11/2−4I11/2 and 4I11/2−4I15/2, (2) 4S3/2−4I11/2 and 4I11/2−4I15/2, (3) 4F9/2−4I11/2 and 4I11/2−4I15/2, and (4) 4I9/2−4I13/2 and 4I13/2−4I15/2. For the IR QC emissions, the overall e...

Observation of Lamb shift and modified spontaneous emission dynamics in the YBO3:Eu3+ inverse opal.

The study of Lamb shift plays a unique role in quantum electrodynamics because it provides an excellent test of the theory on photonic crystals (PCs). In this Letter, we present the first observation of large Lamb shift in the YBO(3):Eu(3+) inverse opals fabricated by the polystyrene templating method. In addition, it is very interesting to observe that the luminescent dynamics of Eu(3+) decayed with a faster power law (t(-3)), followed by a slower exponential process due to the coexistence of the diffusion field and the propagating field in the PCs.

Modified optical properties in a samarium doped titania inverse opal

The TiO(2):Sm(3+) inverse opal has been prepared by a template-assisted method, and its modification on photoluminescent (PL) properties of Sm(3+) is studied. Transmittance spectra show a dip within the photonic bandgap, whose location shifts a little to red and then to blue with an increasing detection angle between the incident light and the surface normal; such an irregular shift is attributed to uneven shrinkage of lattices. Steady-state PL spectra indicate a spatial redistribution of emission lines. Decay kinetics demonstrate that the spontaneous emission rates of Sm(3+) ions in the inverse opal decrease to varied extent depending on the emission wavelength and detection angle. All the facts are examined to be consistent with the photonic bandgap effect.

A strategy for calibrating the actual quantum efficiency of quantum cutting in YVO4:Bi3+(Nd3+), Yb3+

Recently, much attention has been paid to the quantum cutting (QC) through the energy transfer (ET) between Yb3+ and other RE ions and the theoretical quantum efficiency (QE) of QC was reported as high as 140%–195%. However, the practical measurement was rather rare. In this paper, we studied the ET and QC properties of YVO4: Bi3+u2009(5%)/Nd3+u2009(1%), Yb3+u2009(0%–20%) synthesized by the solvothermal method. And more, a strategy for calibrating the actual QE of QC was established. Through measurement, the highest QE of QC was determined to be 12.3% for YVO4: Bi3+,Yb3+, and 25.8% for YVO4: Nd3+,Yb3+, which was much lower than the prediction by luminescent dynamics. This work helps us to forecast the feasibility of potential application in enhancing the efficiency of Si-based solar cell via the Bi3+/RE3+ codoped with Yb3+ phosphors.

CdS/Cyclohexylamine inorganic-organic hybrid semiconductor nanofibers with strong quantum confinement effect.

Inorganic-organic hybrid semiconductor nanofibers of CdS/CHA (CHA = cyclohexylamine) were successfully synthesized by a simple solvothermal method. The fibers obtained had average diameter of 20 nm and length of several micrometers. In these fibers, periodic layer-like sub-nanometer structures with thickness of approximately 3 nm were identified by high-resolution transmission electron microscope (HR-TEM). The absorption of the hybrids exhibited a large blue-shift in contrast to the bulk, which was attributed to strong quantum confinement effect (QCE) induced by internal sub-nanometer structures. Pure hexagonal wurtzite CdS (H-CdS) nanorods were also obtained by extracting the CdS/CHA hybrids with dimethyl formamide (DMF). The rods obtained had average diameter of 20 nm and length of 200 nm. A CdS/CHA/polyvinyl alcohol (PVA) composite film emitting white light was prepared by spin coating.

Acute Toxicity of Silver Free and Encapsulated in Nanosized Zeolite for Eukaryotic Cells

The potential toxicity of encapsulated silver in EMT-type nanosized zeolites on prokaryotic cells, human tumor cell lines from various origins, and primary cultures of neurons and astrocytes was investigated. Silver in cationic form (Ag+) was encapsulated in EMT-type nanosized zeolites via an ion exchange process (Ag+-EMT) and compared with the reduced silver (Ag0) in the zeolite (Ag0-EMT). As reference samples for the toxicity measurements, pure EMT-type zeolite and silver perchlorate were used. Cells were exposed to silver-containing zeolites (50, 100, and 400 μg/mL) for 24 and 48 h. After exposure to Ag+-EMT (50 μg/mL) for 24 h, a loss in cell viability independent of the cell type was observed, ranging from -34.37 ± 23.90% for astrocytes to -99.5 ± 0.24% for U87-MG cells. These results were comparable with the toxicity for silver perchlorate. The Ag0-EMT sample showed lower toxicity on human cell lines in comparison to that of Ag+-EMT. A decrease in cell viability, i.e., -73.46 ± 20.78% and -62.3 ± 17.96% for U87-MG and HEK 293 cells, respectively, under exposure only to high concentration of Ag0-EMT (400 μg/mL) for 24 h was measured. However, the Ag0-EMT was as toxic as the Ag+-EMT for astrocytes and neurons (-97.95 ± 3.31% and -100 ± 1.11%, respectively, after exposure to 50 μg/mL for 24 h). No decrease in cell viability exposed to pure EMT zeolite was found. The results demonstrate the severe toxicity of silver cations, either free or encapsulated, in comparison to reduced silver encapsulated in zeolite nanocrystals. Therefore, silver cations, either free or encapsulated, must be used with great caution regarding their toxicity on eukaryotic cells.

In-fiber integrated chemiluminiscence online optical fiber sensor

We report an in-fiber integrated chemiluminiscence (CL) sensor based on a kind of hollow optical fiber with a suspended inner core. The path of microfluid is realized by etching microholes for inlets and outlets on the surface of the optical fiber without damaging the inner core and then constructing a melted point beside the microhole of the outlet. When samples are injected into the fiber, the liquids can be fully mixed and form steady microflows. Simultaneously, the photon emitted from the CL reaction is efficiently coupled into the core and can be detected at the end of the optical fiber. In this Letter, the concentration of H2O2 samples is analyzed through the emission intensity of the CL reaction among H2O2, luminol, K3Fe(CN)6, and NaOH in the optical fiber. The linear sensing range of 0.1-4.0 mmol/L of H2O2 concentration is obtained. The emission intensity can be determined within 400 ms at a total flow rate of 150 μL/min. Significantly, this work presents the information of developing in-fiber integrated online analyzing devices based on optical methods.