Biomedical subjects

Xu-rong Xu

Publications and source records attributed to Xu-rong Xu.

8 recordsLinked to original sources

PubMed2006

[Spectral properties of energy transfer in doubly doped polymer electroluminescence].

The authors report a cascade energy transfer based on the long-range dipole-dipole Förster energy transfer between polymer and two fluorescent dyes in solid thin films. The authors studied the fabrication and emission characteristics of a new doubly doped system for color purity and energy transfer efficiency, in which two fluorescent dyes, i. e. TPB and Rubrene were doped into PVK. In the blend film, PVK acted as the energy donor, Rubrene as the fluorescent dye, and the assistant dopant TPB was used to facilitate the energy transfer from PVK to the dye Rubrene. Orange emission comes from Rubrene via a cascade energy transfer from PVK toTPB and then from TPB to Rubrene.

English Abstract↗

PubMed2006

[The influence of holes buffer layer doped with different one-dimensional nanomaterials on the performance of polymer light-emitting diodes].

The effect of holes buffer layer PEDOT doped with one-dimensional nanomaterials on the performance of polymer light-emitting diodes was investigated. The photoluminescence efficiency of double layer sample PEDOT/MEH-PPV was enhanced by doping one-dimensional nanomaterials (TiO2 nanotube and ZnO nanorod) into PEDOT layer. Stronger interaction of one-dimensional nanomaterials and PEDOT suppressed the creation of defect states which can quench radiative recombination of excitons. The electroluminescence efficiency of device was improved by 2 and 2.5 folds by doping TiO2 nanotubes and ZnO nanorods into holes buffer layer PEDOT respectively.

English Abstract↗

PubMed2006

[The influence of frequency on solid state cathodoluminescence].

Solid state cathodoluminescence (SSCL) is a new mechanism of light emission in organic-inorganic system. In the present article, we get SSCL under sinusoidal alternating-current voltage with a structure of ITO/SiO2/MEH-PPV/SiO2/Al. The spectra have two peaks: 410 and 580 nm, which obey molecular theory and band model, respectively. The temporal behaviors of both peaks in SSCL are studied with a new method of estimating lifetime in frequency domain. The intensity of the peak at 410 nm decreases as the frequency of the driving voltage increases, and the intensity of the peak at 580 nm increases as the frequency of the driving voltage increases. The difference in the dependence of light intensity on the frequency of excitation comes from the difference in the lifetime of the two peaks. The lifetime of short wavelength emission is found to be less than 5 ms while that of long wavelength emission is more than 0.05 ms.

English Abstract↗

PubMed2005

[Studies on photoluminescence spectra of polyfluorene under modulation of electric field].

The photoluminescence of polyfluorene thin film modulated by an electric field are studied. The results show that the photoluminescence from polyfluorene film can obviously quenched by the extra electric field, which is attributed to the electric field-induced dissociation of photogeneration excitons. The dependence of the exciton dissociation rate constant on the intensity of electric filed is fitted. The average hopping distance of element charge is 0.68 nm in PFO. This volume is comparable with the reported results in Alq3 and polymers. The spectral dependence of the factor of EFIQP is given. The dissociation of hot-exciton is deduced, which influences on the spectral dependence of the EFIQP factor slightly.

Algorithms↗

PubMed2005

[Simultaneous determination of rate ratio of recombination to capture and trap depth from thermo-luminescence of ZnS:Cu, Co].

The recombination luminescence is in nature a bimolecular process but, the decay rule may be changing from that of mono-molecular to bimolecular rule, i.e., from exponential to hyperbolic rule, depending on the behavior of conduction electrons. This behavior is represented by relative rate of recombination with ionized centers to that of capture by traps. This relative rate depends partly on the intrinsic parameters of the specified materials, and partly on the concentration of conduction electrons supplied by traps. Each point of the TL curve is related to the material parameters and the release of electrons from traps. The ratio of relative rate of recombination to that of capture gamma(epsilon) = sigma0(n0)/sigma(nu - n) involves the parameter epsilon. They are inseparable and must be determined at the same time. In the present report, starting from the same sample ZnS:Cu, Co which has only one peak in its TL(i. e., only one kind of luminescent center and only one kind of traps), and the experimental value of sigma/sigma0 = 0.005, the authors use thermo-luminescence kinetics models and some mathematic tools to exactly estimate the ratio sigma0(n0)/sigma(nu) and the trap depth epsilon simultaneously from the glow curve. The authors found that sigma0(n0)/sigma(nu) = -2.6 and epsilon = 0.86 eV.

Cobalt↗

PubMed2004

[The influence of thickness of SiO2 on the electron acceleration in cathodluminescence-like emission].

The authors investigated the property of cathodluminescence-like (CL-like) emission in the device of MEH-PPV sandwiched between two SiO2 layers. The authors observed in addition to the inherent electroluminescence of MEH-PPV, a shorter emission peak which is considered to be corresponding to HOMO-LUMO transition. From the relative change of these two peaks with the variation of the thickness of SiO2, The authors studied the electron acceleration ability of SiO2.

English Abstract↗

PubMed2003

[Properties of the stimulated emission in the ZnO thin film].

ZnO thin film is a promising material for short-wave laser and LED etc, due to its high excition binding energy, intense stimulated emission, low lasing threshold, and high working temperature. ZnO thin films were prepared by laser molecular beam epitaxy (L-MBE) in our work. At room-temperature we reported the measurements of absorption spectra and emission spectra of ZnO thin films excited by various optical pumping intensities. High structural perfection of our sample was shown in these figures. We studied the properties and mechanism of stimulated emission in ZnO thin films. The relation between emission intensity and pumping intensity was obtained. Time behaviors of the stimulated emission under relatively high pumping intensity, spontaneous emission, and laser pulses were compared, and hence the stimulated emission of ZnO thin films was proved.

Lasers↗

PubMed2002

[Spectral characteristics of CdSe/CdS nanocrystals].

Semiconductor nanocrystals appear different optical properties from their bulk analogous due to quantum confinement effects. It is well known that optical absorption of nanocrystals shift to higher energy as the sizes decrease, while the emission at the absorption band edge is always too weak to be investigated in details due to much nonradiative recombination at nanoparticle surface. To eliminate the surface defects, some kinds of materials such as organic molecules, polymers and inorganic compounds are used to overcoat the nanoparticles. It has been found that nanocrystals overcoated with high band gap inorganic materials maned core/shell type nanocrystals exhibit high photoluminescence intensity at band edge due to effective elimination of surface nonradiative recombination. In this article we report the characteristics of CdSe/CdS core/shell nanocrystals synthesized with mercapto acid as stabilizer. The effect of CdS shell on the electronic characteristics and the luminescence of CdSe core were investigated by using optical absorption, photoluminescence and photoluminescence excitation spectra. Large band edge luminescence enhancement was found in CdSe nanoparticles overcoated with the CdS shell with a thickness of 0.3 nm due to passivation of nonradiative recombination sites on CdSe surfaces. Such bandadge emission also appeared redshift from the absorption maximum. This Stokes shift of the emission peak from the absorption edge was explained by a model of formation of excimer among the small nanoparticles based on the optical experimental results and the theoretical calculation on fine structures of bandadge excitons.

Cadmium Compounds↗