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Authors: Y.H. Chen, X.L. Ye, Bo Xu, Yi Ping Zeng, Z.G. Wang
Abstract: The in-plane optical anisotropy of three groups of GaAs/AlGaAs quantum well structures has been studied by reflectance-difference spectroscopy (RDS). For GaAs/Al0.36Ga0.64As single QW structures, it is found that the optical anisotropy increases quickly as the well width is decreased. For an Al0.02Ga0.98As/AlAs multiple QW with a well width of 20nm, the optical anisotropy is observed not only for the transitions between ground states but also for those between the excited states with transition index n up to 5. An increase of the anisotropy with the transition energy, or equivalently the transition index n, is clearly observed. The detailed analysis shows that the observed anisotropy arises from the interface asymmetry of QWs, which is introduced by atomic segregation or anisotropic interface roughness formed during the growth of the structures. More, when the 1 ML InAs is inserted at one interface of GaAs/AlGaAs QW, the optical anisotropy of the QW can be increased by a factor of 8 due to the enhanced asymmetry of the QW. These results demonstrate clearly that the RDS is a sensitive and powerful tool for the characterization of semiconductor interfaces.
Authors: Bo Xu, Z.G. Wang, Y.H. Chen, P. Jin, X.L. Ye, Feng Qi Liu
Abstract: This paper reviews our work on controlled growth of self-assembled semiconductor nanostructures, and their application in light-emission devices. High-power, long-life quantum dots (QD) lasers emitting at ~1 µm, red-emitting QD lasers, and long-wavelength QD lasers on GaAs substrates have successfully been achieved by optimizing the growth conditions of QDs.
Authors: J. Lu, B. Shen, N.J. Tang, D.J. Chen, Y.D. Zheng
Abstract: The weak-localization of the two-dimensional electron gas (2DEG) in a modulation-doped Al0.22Ga0.78N/GaN single quantum well has been investigated through the magnetoresistance measurements. The elastic scattering time τε, dephasing time τφ and spin-orbit(s-o) scattering time τso at various temperatures are obtained. The fitting parameters indicate that the inelastic scatterings to the 2DEG are mainly due to the piezoelectric field and the alloy disorder in the AlxGa1-xN barrier. When the second subband in the triangular quantum well at the heterointerface is occupied by the 2DEG, the anti-weak localization is observed clearly, which is due to the strong spin-orbit interaction. The spin-orbit effect dominates the quantum correction of the conductivity in the upper subband. The intersubband scattering becomes stronger with increasing temperature.
Authors: G.X. Shi, Bo Xu, P. Jin, X.L. Ye, C.X. Cui, C.L. Zhang, J. Wu, Z.G. Wang
Abstract: The structural and photoluminescence (PL) properties of the InAs quantum dots (QDs) grown on a combined InAlAs and GaAs strained buffer layer have been investigated by AFM and PL measurements. The dependence of the critical thickness for the transition from 2D to 3D on the thickness of GaAs layer is demonstrated directly by RHEED. The effects of the introduced-InAlAs layer on the density and the aspect ratio of QDs have been discussed.
Authors: W.Q. Peng, S.C. Qu, G.W. Cong, Z.G. Wang
Abstract: Using a solution-based chemical method, we have prepared ZnS nanocrystals doped with high concentration of Mn2+. The X-ray diffraction analysis confirmed a zinc blende structure. The average size was about 3 nm. Photoluminescence spectrum showed room temperature emission in the visible spectrum, which consisted of the defect-related emission and the 4 T1-6 A1 emission of Mn2+ ions. Compared with the undoped sample, the luminescence of the ZnS:Mn sample is enhanced by more than an order of magnitude, which indicated that the Mn2+ ions can efficiently boost the luminescence of ZnS nanocrystals.
Authors: Wenfa Xie, Shi Yong Liu
Abstract: Non-doped type white organic electroluminescent (EL) devices have the following structure ITO/m-MTDATA (30nm) /NPB (20-dnm) /rubrene (0.1nm) /NPB (dnm) /DPVBi (20nm) /TPBi (20nm) /Alq (10nm) /LiF/Al were fabricated. The EL spectrum of the devices are dependent on the d and when d=3, the CIE coordinates of the device were well within the white region for voltage raging from 3V to 15V. This device has a luminance of 18950cd/m2 at 15V and maximum power efficiency of 5.65cd/A at 6V.
Authors: Gang Cheng, Zengqi Xie, Ying Fang Zhang, Yuguang Ma, Shi Yong Liu
Abstract: A novel derivative of oligo(phenylenvinylene) (OPV), 2,5-diphenyl -1, 4-distyrylbenzene with two trans-double bonds (trans-DPDSB), is used as a blue emitting material in blue and white organic light-emitting devices (OLEDs). Blue devices with a configuration of indium-tin oxide (ITO)/N,N´-diphenyl-N,N´-bis(1-naphthyl)-(1,1´-biphenyl)-4,4´-diamine (NPB)/ trans-DPDSB / tris (8-hydroxyquinoline) aluminum (Alq3)/LiF/Al are constructed, where NPB, Alq3 and trans-DPDSB are used as hole-transporting, electron-transporting and light-emitting layers, respectively. The color of emission is changed from blue-green to pure blue when the trans-DPDSB layer is thicker. By inserting an ultrathin 5,6,11,12-tetraphenylnaphthacene (rubrene) yellow light-emitting layer between the Alq3 and trans-DPDSB layers, white OLEDs are obtained. The maximum efficiency and luminance of the blue and white devices are 1.2, 3.0 cd/A, and 1400, 7000 cd/m2, respectively.
Authors: Chuan Qi Feng, Keli Zhang, Jutang Sun
Abstract: A nonstoichiometric spinel phase (Li1.02Mn1.90Y0.02O4-yF0.08) was synthesized using natural polymer net method. It was characterized by XRD and XPS. The particle size and shape of the expected compounds were observed by Transmission Electron Microscopy technique. The composition of new spinel phase was checked by ICP. The electrochemical properties of the new spinel phase (Li1.02Mn1.90Y0.02O4-yF0.08) were also investigated. The results showed that the Li1.02Mn1.90Y0.02O4-yF0.08 behaved excellent recharge ability to compare with stoichiometric LiMn2O4. The initial discharge capacity of the battery was 128.5 mAh/g when current density was 1 mA·cm-2 over voltage range of 4.4 to 3.0V. The discharge capacity could retain about 96% after 100 cycles when metallic lithium was anode. The outstanding electrochemical properties of Li1.02Mn1.90Y0.02O4-yF0.08 make it possible as a promising cathode material. The novel synthesis method provides a simple and effective route for inorganic material synthesis.
Authors: Hui Shan Yang, Shu Fen Chen, Zhi Jun Wu, Yi Zhao, Jingying Hou, Shi Yong Liu
Abstract: We have fabricated an organic light-emitting devices with high efficiency and brightness utilizing thick layer of a starburst amine compound 4,4’, 4’’-tris{N,-(3-methylphenyl)-Nphenylamin} triphenylamine (m-MTDATA) as hole injection buffer layer. The brightness and the current efficiency were comparatively improved compared with those of the device without the buffer layer. The device with 10nm m-MTDATA act as buffer layer has max brightness was 18590cd/m2 at 17 V, and the highest luminous efficiency was achieved 4.30cd/A, at 7V, which is nearly three times than that of the device without it.
Authors: Q.G. Zeng, Z.J. Ding, Biao Chen, Qing Jie Zhang
Abstract: The photoluminescence and Raman spectra of the tris(dibenzoylmethane) europium(III) dihydrate (Eu(DBM)3•2H2O) are investigated at high pressures with a diamond anvil cell. For pressures lower than 3 GPa, the luminescent intensities of the Eu3+ ion 5D0→7FJ (J=0, 1, 2, 3, 4) characteristic peaks increase with the pressure. However, above 3 GPa the intensities decrease. The phenomena indicate that there is energy transition between the Eu3+ ion and the DBM ligand. With the increasing pressure, the intensity for the vibration bands becomes more obvious compared with that of the Eu3+ ion characteristic peaks, as the result of the crystal distortion at high pressures. The Raman bands at low wavenumbers have not shown significant changes with pressure, which manifests that the Eu3+ ion site symmetries are not varied but that the crystal is distorted at high pressures.

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