[Preparation and transmissivity of ZnS nanocolumn thin films with glancing angle deposition technology].

Nanocrystalline ZnS thin films were fabricated by glancing angle deposition (GLAD) technology in an electron beam evaporation system. Deposition was carried out in the custom vacuum chamber at a base pressure 3 x 10(-4) Pa, and the deposition rate was fixed at 0.2 nm x s(-1). ZnS films were deposited on pieces of indium tin oxide (ITO) substrates when the oblique angle of the substrate relative to the incoming molecular flux was set to 0 degrees, 80 degrees and 85 degrees off the substrate normal respectively. X-ray diffraction (XRD) spectra and scanning electron microscope (SEM) images showed that ZnS nanocrystalline films were formed on the substrates at different oblique angle, but the nanocolumn structure was only formed under the situation of alpha = 80 degrees and 85 degrees. The dynamics during the deposition process of the ZnS films at alpha = 0 degrees, 80 degrees and 85 degrees was analyzed. The transmitted spectra of ZnS thin films deposited on ITO substrates showed that the ZnS nanocolumn thin films could enhance the transmissivity in visible range. The ZnS nanocolumn could be used into electroluminescence device, and it would enhance the luminous efficiency of the device.

[Properties of energy transfer in two host materials doped with Ir(ppy)3 and Rubrene].

The devices with phosphorescent material tris(2-phenylpyridine)iridium [Ir(ppy)3] and fluorescent material 5,6,11, 12-tetraphenylnaphthacene [Rubrene] as dopants in two kinds of host were constructed in the present study. Respectively, the two kinds of host are polyvinylcarbazole [PVK] and 4,4'-N,N-dicarbazole-biphenyl [CBP]. We studied the properties of energy transfer between host materials and dopants. Firstly, the absorption and photoluminescence spectra of PVK, CBP, Ir(ppy)3 and Rubrene were measured. The spectral overlap between the photoluminescence of PVK and the absorption spectrum of Ir(ppy)3 is larger than that of Rubrene. The result of the spectral overlap for CBP is the same as PVK. It was shown that the energy transfer from the two host materials to Ir(ppy)3 is stronger than that to Rubrene. In addition, the energy transfer from Ir(ppy)3 to Rubrene is possible according to their absorption and photoluminescence spectra. We compared the electroluminescence properties of different devices. In devicel of ITO/PVK : Rubrene : Ir(ppy)3 (100 : 5 : x)/BCP(10 nm)/Alq3 (20 nm)/Al and device 2 ITO/CBP : Rubrene : Ir(ppy)3 (100 : 5 : x)/BCP(10 nm)/Alq3 (20 nm)/Al(x = 0, 3), under the same DC bias, the electroluminescence results show that energy transfer from host to Rubrene through Ir(ppy)3 is the main mechanism. And energy transfer is much more efficient in CBP as host than in PVK. In addition, at the same voltage, the light power of the device doped with Ir(ppy)3 and Rubrene is obviously stronger than that of the device doped with Rubrene only. When the concentration of Ir(ppy)3 increases, the light power decreases at the same voltage, and the effect of concentration quenching is enhanced.

[Evaluating acceleration ability of electrons of different acceleration layers in solid state cathodoluminescence].

Solid state cathodoluminescence is a brand-new excitation mode. In the device, electron acceleration layer plays a very important role in obtaining high energy hot electrons to excite organic luminescent materials in solid state cathodoluminescence. Two kinds of structural devices (A: ITO/MEH-PPV/SiO2/Al, B: ITO/MEH-PPV/ZnO/Al) were fabricated. The theoretical calculation and analysis show that the tunnel current and electric field was higher in SiO2 layer than that in ZnO layer under the same applied driving voltage. The experimental results show that the intensity of device A with SiO2 as electrons acceleration layer is stronger than that of device B with ZnO as electrons acceleration layer under the same driving voltage. And the result demonstrated that electrons in the conduction band of SiO2 can be heated to higher energy than that in ZnO.

[Study on growth mechanism and crystallization phase state of pentacene thin films on p-Si wafer].

The growth mechanism and crystallization phase state were investigated by the methods of atomic force microscopy (AFM) and X-ray diffraction (XRD). The pentacene films were deposited with a self-assembling monolayer by thermal evaporation on p(+)-Si wafer substrates at room temperature and annealed at a constant temperature (80 degrees C) for 120 min. The experimental results show that pentacene films were grown with terraces island structure with the diameter of island of about 100 nm and constituted a layer consisting of faceted grains with a average step height between terraces of 1.54 nm x s(-1), which were accord with the long axis length of pentacene molecule, and the film were vertically grown on the substrate surface. The crystallization of pentacene thin films is shown in XRD pattern. The increase in the thin film thickness introduced a second set of diffraction peaks, which were attributed to the pentacene triclinic bulk phase. The critical thickness of both phases is 150 and 80 nm, respectively. At a film thickness of 150 nm, the triclinic phase diffraction peaks become the dominant phase. This is contrast to the XRD spectrum of very thin film of 80 thickness, where the thin film phase is the only contribution.

[The preparation and characterization of 1-D orderly ZnO nanorod arrarys].

Improving on the sealing and high pressure conditions of traditional hydrothermal method, vertical ZnO nanorod arrays were synthesized on indium tin oxide substrate by employing Zn(NO3)2 x 6H2O, (CH2)4N6 as the starting materials in the presence of polyethylenimine(PEI) at ambient pressure and low temperature (92 degrees). Between the substrate and the nanorods, a layer of ZnO flim was prepared as buffer layer and seed layer. The ZnO film was gained by spin-coating zinc acetate solution on indium tin oxide substrate, then annealed at 350 degrees C for 20 min, which can make zinc acetate decompose into zinc oxide. The zinc acetate spin-coating and decomposition procedure was carried out twice to ensure a complete and uniform coverage of ZnO seeds. The second layer was annealed at 500 degrees C for 30 mini Different spin-coating speeds were adopted, one was 2500 r x min(-1), and the other was 5000 r x min(-1). XRD result indicated that the seed layer with 5000 r x min(-1) has better alignment than the layer with 2500 r x min(-1). The aligned seeds with 5000 r x min(-1) show only a (002) reflection, indicating their complete c-axis texturing, whereas the spin-coated seeds give a powder pattern because they rest at all angles on the substrate. SEM result shows that the layer is made up of grains with an the average size of about 30 nm. Well-aligned ZnO nanorod arrays were synthesized by putting the substrate with ZnO seeds into the precursor solutions vertically for one hour. The nanorod arrays were taken out and rinsed with clean ethanol and pure-water for several times, blown dry with a stream of nitrogen, then annealed at 400 degrees C for 30 min in order to wipe off the organic solvent. At room-temperature, the SEM and XRD were measured. SEM results indicate that the crystal structure of most of ZnO nanorods is hexagonal wurtzite crystallographic phase structure, mainly vertical to the substrate. ZnO nanorods have good crystallization, the diameter of the rods is around 40 nm, and the length is above micrometer. The XRD results showed the nanorod arrays have (002) and (004) angles, and the (002) is quite strong. Absorption spectra of the nanorod arrays shows ZnO essence absorption and strong ultraviolet absorption, indicating that ZnO has good quality. Optical properties were studied, and the excitation spectra of the nonorod arrays showed a strong and narrow peak at 387 nm with FWHM smaller than 30 nm and a weak blue peak.

[The photoluminescence characteristics of organic multilayer quantum wells].

By the use of multi-source high-vaccum organic beam deposition system, the authors prepared organic multilayer quantum well structures, which consist of alternate organic small molecule materials PBD and Alq3. Based on 4-period organic quantum wells, different samples with different thickness barriers and wells were prepared. The authors measured the lowest unoccupied molecular orbit (LUMO) and the highest occupied molecular orbit (HOMO) by electrochemistry cyclic voltammetry and optical absorption. From the energy diagrams, it seems like type-I quantum well structures of the inorganic semiconductor, in which PBD is used as a barrier layer and Alq3 as a well layer and emitter. From small angle X-ray diffraction measurements, the results indicate that these structures have high interface quality and uniformity. The photoluminescence characteristics of organic multilayer quantum wells were investigated. The PL peak has a blue-shift with the decrease of the well layer thickness. Meanwhile as the barrier thickness decreases the PL peaks of PBD disappear gradually. And the energy may be effectively transferred from PBD to Alq3, inducing an enhancement of the luminescence of Alq3.

[Optical and morphological investigation on the interaction of dual dopants in poly (N-vinylcarzole)].

The effect of optical and electrical properties of poly(N-vinylcarzole) (PVK) doped with two dyes, i. e. 8-tris-hydroxyquinoline (Alq3) and 4-(dicyanomethylene)-2-tert-butyl-6 (1, 1, 7, 7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB), on the energy transfer and charge trapping processes was investigated. The phase separation in blends film at different doping concentration was also studied. More homogeneous dispersion of dyes in PVK with increasing doping concentration was showed. The results indicate that there is a certain interaction of Alq3 and DCJTB in this dual-doped system. It is the incorporation of DCJTB that untangled the aggregation of Alq3 owing to the interaction of DCJTB and Alq3. But for higher doping concentration, DCJTB results in an isolated charge transport channel that decreases the electroluminescence (EL) operating voltage.

[Fabrication and spectral analysis of a novel panel full color device].

It is demonstrated that a new solid-state cathodoluminescence device based on accelerated electron in SiO2 can be fabricated using organic light emitting materials as a fluorescent film. This device (the device of sandwiched structure) is composed of a glass substrate, an ITO layer, a double SiO2 films, and an organic fluorescent film. When a bias voltage is applied to the devices, they can uniformly emit red, green, and blue light. To some extent, when the voltage is low, the red (green) emission is obtained; and when the voltage is high, the blue emission is acquired. These emissions belong to the solid-state cathodoluminescence, they originate from the accelerated electrons in SiO2, which bombard the organic layers. Their devices have achieved full color (RGB) lighting and improved blue emitting.

[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.

[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.

[The emission of organic-inorganic single quantum well with organic heterojunction].

Organic-inorganic single quantum well with organic heterojunction ITO\SiO2 (60 nm)\MEH-PPV(40 nm)\Alq3 (40 nm)\SiO2 (60 nm)\Al has been fabricated. With the detailed investigation of photoluminescence and electroluminescence of this novel device, the authors found that the permittivity confinement effect and the quantum size effect have obviously an effect on the optical and electrical properties of organic-inorganic quantum well with organic heterojunction. The electroluminescence of organic-inorganic quantum well with organic heterojunction included three different emissions under alternative-current voltages: 410, 510 and 590 nm, which originated from radiative recombination of MEH-PPV, recombination of Alq3 excitons and MEH-PPV excitons respectively.

[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.

[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.

[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.

[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.

[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.

[Photoexcitation mechanism of photoconductive device by organic/inorganic thin-film heteropairing].

Photoconductive devices with organic (polyvinylcarbazole-PVK)/inorganic (zinc-sulfide--ZnS) thin-film heteropairing were fabricated. In external field, the excitation profile of the steady-state photoconductivity and the primary photoexcitation process of hybrid devices were presented and discussed. Comparison of photoconductivity of the devices and absorption spectra of PVK and ZnS implied that both layers absorption contributes to the photocurrent, but the effective part is at the interface of PVK and ZnS. The dependence of maximum photocurrent on the applied voltage and the dark and illuminated current spectra indicates the ultrafast charge transfer at the interface.

[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.