Xu Xurong

Optical properties of strongly luminescing mercaptoacetic-acid-capped ZnS nanoparticles

We synthesized zinc sulfide nanoparticles with mercaptoacetic acid as capping agent and obtained nanoparticles of different sizes. The optical properties of ZnS nanoclusters were studied by optical absorption and photoluminescence. High sample quality is reflected in sharp absorption features and strong band edge emission, which is tunable with particle size. The selectively excited luminescence properties and the coupling between electronic and vibrational excitation in ZnS nanoparticles are discussed.

Effect of aging on CdSe nanocrystals

Abstract The effect of aging on surface stabilized CdSe nanocrystals samples has been studied through UV-vis absorption and PL measurements. The UV-vis absorption showed that the absorption maximum shifted to lower energy and the optical density became stronger with aging time. The PL measurements showed that the luminescence intensity increases with aging. The emissions associated with the band edge and shallower trap shifted to lower energy with aging time, whereas that associated with deep traps does not.

Preliminary trial of third generation electroluminescence (EL)

Abstract A preliminary trial involving the enhancement of the brightness of an EL cell is presented. Based on the experimental facts that the most important and inevitable process in EL is impact excitation or ionization, we attempt at enlarging the brightness by widening the impact excitation cross-section. By calculation, this cross-section is found to be dependent on the energy distribution and incident direction of the impinging electrons. In this calculation we take into account the conduction band structure. In order to overcome the loss in the initial acceleration phase, we preheat carriers and inject them into the high field acceleration zone, in which the production of streaming carriers is expected. In this way, we vary the energy distribution toward higher energy and really observe a several-fold enhancement of brightness.

Anisotropy of the cross-section of impact excitation in electroluminescence☆

Abstract Taking into account the structure of conduction band, we deduced a formula which showed the anisotropy of the impact cross-section. We carried out the numerical calculations for that of the luminescent centers in ZnS and found the favourable orientation, along which the probability of excitation would be greatly increased.

Multiplication of carriers by impact ionization

We have successfully transferred the acceleration of carriers in a ZnS-based electroluminescent cell of novel design to the SiO2 layer and obtained carriers of higher energy. In this paper, it is shown that the ionization coefficient in the SiO2 layer is also significantly increased and varies with electric field E as α α α0 exp(- b / E), where b = 4.4×107 V/cm. The process of ionization is discussed.

Doping effects on the polymer-chain structure of poly(3-methythiophene)

Abstract The C=C stretching Raman shifts and photoluminescense (PL) for poly(3-methylthiophene) (P3MT) are measured at various doping levels by in situ electrochemical Raman and PL spectroscopic techniques. It is found that the doping for P3MT induces the nonlinear excitations (soliton, polaron, bipolaron), but also affects the polymer-chain structure, including the conjugated length and the interchain distance.

The dispersion of BED° in unintentional doped GaN crystals

Abstract The polarization and the wavelength of the photoluminescence of BED° in not intentionaly doped GaN crystal wafers are observed to be dependent on the excitation intensity (I-exc). When I-exc increases from 1 KW/CM2 to 1000 KW/CM2, they vary at first quadratically, and then, appear saturated. This phenomenon is resulted from dispersion effect of BED° in GaN crystal wafers, which is proposed earlier (1).

Effect of TPD films as electron blocking layer on EL spectrum

In an organic thin film electroluminescence (OTFEL) device with an ITO/PPV/Alq:DCM1/A1 structure, a TPD layer was inserted between the PPV and Alq:DCM1 layers. A device without the TPD layer or with a 5-nm thick TPD layer operating at higher DC voltage (≥8 V) exhibited EL emission from both the PPV (513 nm) and Alq:DCM1 (591 nm) layers, however, a device with a 5-nm thick TPD layer operating at lower voltage (<7 V) or with a 10-nm thick TPD layer had an EL emission peak at 591 nm, implying that the TPD layer can effectively block electron transportation. Hence we can spatially control the carrier recombination zone and obtain different EL emissions by adjusting the thickness of the carrier blocking layer and the driven voltage.

Carrier transport behaviour of molecular doped poly (N-vinylcarbozole) in polymer light-emitting diodes

Single-layer polymer light-emitting diodes are prepared from blends of poly(N-vinylcarbozole) (PVK) doped with tris(8-hydroxy-quinoline) aluminium (Alq3) of 2 wt% (sample a) and 0.2 wt% (sample b). The onset of PVK transient electroluminescence (EL) is delayed with respect to that of Alq3 in sample a under pulsed excitation, while the EL onsets of Alq3 and PVK in sample b are simultaneous. The total carrier mobility of the Alq3-rich regions in sample a is larger than that of the PVK-rich regions. However, the total carrier mobility is homogeneous in sample b. The phase image of atomic force microscopy and photoluminescence spectra of samples a and b indicate that the separated phase of samples a and b exists in the PVK-rich and Alq3-rich regions. The variance of the doping concentration and separated phase in blends results in the different carrier transport mobility of Alq3-rich and PVK-rich regions.

The electroluminescence of Pr ions in ZnS thin films

Abstract ZnS thin films doped with different compounds of Pr3+ ions are prepared and their electroluminescent characteristics are studied. The experiment shows that the electroluminescence emission spectra of Pr3+ ions in ZnS thin films change with their chemical environment and the introduction of fluorine ions is advantageous for increasing blue light emission.