The storage of charges and its optical application in organic light-emitting diodes measured by a transient electroluminescence method

Organic light-emitting diodes (OLEDs) device capable of stored charges with poly (methyl methacrylate) (PMMA) layer is studied by transient electroluminescence measurements. The mechanism and optical application of stored carriers are elucidated. A spike after a driven pulse is found in the device with PMMA layer, which is attributed to the drifting back of accumulated electrons and trapped ones in shallow states, and the detrapping of latter may result in a long decay tail. A reversed post-pulse is applied to release the electrons in deep traps as they are immobile unless under a strong reversed field. Since the stored charges can lead to a great loss of carriers and weaken the performance of device, we find a way to use them in the form of light emitting with an enhanced intensity more than 3 times as against steady-state. So we have a good reason to believe if in a proper way, we can make full use of the stored charges in optical application.     

Characteristics of pulse excited electroluminescence from ZnS films containing rare earth fluroide

The transient behavior of the electrical and the optical properties under pulse excitation has been studied and analyzed in detail on the electroluminescent devices made of Au-ZnS: NdF3- Ta2O5-Ta composite films. The ZnS-Ta2O5interface is capable of accommodating a large number of trapped electrons, up to 10¹³cm^-2, with the majority of the interfacial states located at a fixed energy below the conduction band of ZnS. Carrier injection is achieved by electrons tunneling through the Au-ZnS Schottky barrier at a field of 2.6×10⁶V/cm. The threshold field of impact excitation for 1 percent NdF3in ZnS was found to be 1.5×10⁶V/cm; while the coefficient of impact excitation at 2.6×10⁶V/cm was estimated to be 1750 cm^-1. In addition, the emission time constants of several rare earth fluorides were also studied.     

2-Mercaptobenzothiazolate complexes of rare earth metals and their electroluminescent properties

We have demonstrated the electroluminescent (EL) properties of 2-mercaptobenzothiazolate complexes of rare earth metals [Ln(mbt)₃, Ln = Y, Sm, Eu, Gd, Tb, Dy, Tm] using simple non-doped two-layer organic light emitting diode with the configuration of indium tin oxide/N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine/Ln(mbt)₃/Yb. It was found that 2-mercaptobenzothiazolate complexes have highly efficient intra-energy transfer from the singlet to the triplet state of the ligand, and then to the excited state of the central lanthanide ions. Thus Y(mbt)₃ and Gd(mbt)₃ exhibit the broad ligand-centered emission with maximum near 600 nm and Dy(mbt)₃, Tb(mbt)₃ and Tm(mbt)₃ complexes exhibit pure sharp emission bands from the intra f–f transitions of lanthanide ions Tb³⁺: ⁵D₄ → ⁷F₆ (492 nm), ⁵D₄ → ⁷F₅ (547 nm), ⁵D₄ → ⁷F₄ (589 nm), ⁵D₄ → ⁷F₃ (624 nm); Dy³⁺: ⁴F_9/2 → ⁶H_13/2 (575 nm) and Tm³⁺: ³H₄–³H₆ (795 нм).     

Electron mobility measurement in short-channel FET's using thecutoff frequency method

The cutoff frequency (FT) method is presented to measure electron mobility in short-channel field-effect transistors (FETs). This technique was used to study the electron mobilities in AlGaAs-GaAs self-aligned heterostructure insulated-gate field-effect transistors (HIGFETs), with both undoped and doped channels (E and D mode). The structures were molecular-beam-epitaxy (MBE) grown on 〈100〉-oriented semi-insulating GaAs substrates. All layers were undoped during the growth. The D-mode HIGFETs were implemented on the same wafer through selective implantation of silicon ions into the channel. Computer simulations indicate that all the channels are in the GaAs layers. The data from the FT method are slightly higher than those from the previously proposed method, owing to the fact that the parasitic capacitance effects have not been excluded in the latter     

Efficient computational method for transient EM response of large-loop source over layered earth

Calculations of the ElectroMagnetic （EM） response produced by a large horizontal loop placed over layered medium are rather complex because its integral expression contains the product of two Bessel functions and has a divergent term. In this paper, an improved fast Hankel and Gaver-Stehfest transforms are introduced to solve the strong-oscillation and slow-decay properties of the integrand, where one Bessel function in the product is substituted by a carefully chosen polynomial of high accuracy and the other used as the digital filter coefficients in the convolution integral. Comparisons prove the validity and the efficiency of the proposed method.     

A mechanistic study of exciplex formation and efficient red light-emitting devices based on rare earth complexes

The mechanisms of exciplex formation between hole-transporting material N,N^′-diphenyl-N,N^′-bis(3-methylphenyl)-1,1^′-diphenyl-4,4^′-diamine (TPD) and electron-transporting materials tris(dibenzoylmethanato)-mono(bathophenanthroline)-rare earth (RE(DBM)₃bath) in TPD/RE(DBM)₃bath bilayer electroluminescence (EL) devices were studied. The formation process was identified by using fluorescent dye as dopant. It was found that interaction between the excited states of RE(DBM)₃bath and the ground state of TPD molecules resulted in the exciplex. The recombination zone of the TPD/RE(DBM)₃bath device was proved to be mainly in the RE(DBM)₃bath layer near the organic interface. On the other hand, by using dopant as efficient energy acceptor in RE-complex hosts, we found that exciplex emission was quenched thoroughly and efficient red light emission was observed, proving that RE(DBM)₃bath may act as an efficient energy donor in EL devices. In the case of Eu³⁺ as the central ion, maximum EL efficiency and highest brightness of red light emission reached 2.6% and 2000 cd/m², respectively.     

纳米结构稀土元素氢氧化物的微结构分析

利用水热合成法成功地合成了Tb(OH)3纳米管、Sm(OH)3和Eu(OH)3纳米棒.Tb(OH)3纳米管外径80nm～150 nm,内径20 nm～90 nm,长度可达几个微米;Sm(OH)3和Eu(OH)3纳米棒直径28 nm～35 m,长度只有100nm～500 nm.使用X射线衍射、透射电子显微术及选区电子衍射等分析技术,对这些样品的物相纯度、形貌、晶体结构完整性以及晶体生长方向等进行了详细的表征.在部分Tb(OH)3样品端口处可以发现c轴加倍的超晶格结构.这种结构的形成可由在纳米管的生长过程中铽离子的局域耗尽机理来解释.     

Enhanced photoluminescence from porous silicon microcavities by rare earth doping

The photoluminescence (PL) properties of porous silicon microcavities (PSMs) in the visible range at room temperature are improved by doping the rare earth ytterbium (Yb) into PSMs prepared by the electrochemical etching method. It is observed that PSMs doped with the rare earth have an emission band around 630 nm. Compared with the single-layer porous silicon (PS) film, the PSMs doped with Yb have narrower and stronger PL spectrum.     

Electron and hole mobility enhancement in strained SOI by waferbonding

N- and p-MOSFETs have been fabricated in strained Si-on-SiGe-on-insulator (SSOI) with high (15-25%) Ge content. Wafer bonding and H-induced layer transfer techniques enabled the fabrication of the high Ge content SiGe-on-insulator (SGOI) substrates. Mobility enhancement of 50% for electrons (with 15% Ge) and 15-20% for holes (with 20-25% Ge) has been demonstrated in SSOI MOSFETs. These mobility enhancements are commensurate with those reported for FETs fabricated on strained silicon on bulk SiGe substrates     

稀土Er掺杂的MoSe2纳米线的制备及发光特性研究

本文研究了稀土掺杂硒化钼(MoSe₂)垂直纳米线 的制备及光学特性。以分析纯硒化钼 粉末为原料,采用热蒸发方法在Si衬底上沉积硒化钼垂直纳米线,并在其生长过程中利用硝 酸鉺进行原位掺杂。利用原子力显微镜(AFM)、X射线衍射仪(XRD)、紫外-可见分光光度计 和 荧光光谱仪研究了掺杂硒化钼薄膜的表面形貌﹑晶体结构﹑光吸收和特性。发现掺杂后MoSe ₂纳米线的结晶性更强,长度增加2倍以上。同时,掺杂后纳米线的可见光吸收和光致发光 强 度明显增强,760 nm处MoSe₂纳米线的带间跃迁的本征发射增强4倍 以上。另外,Er³⁺掺杂后 ,在590 nm和650 nm处增加了2个来自Er³⁺离子的发射,说明稀土掺杂后发光峰增加,使 光谱谱线更加丰富。以上结果表明,稀土掺杂可显著增强硒化钼的结晶性、光吸收和发光效 率,使其可用于制备超薄、高效率的太阳能电池、光探测器等光电子器件。     

Electrical properties of rare earth silicides produced by channeled ion beam synthesis

Electrical measurements have been performed on ErSi_1.7, YSi_1.7 and Er_0.5Y_0.5Si_1.7, produced by channeled ion beam synthesis. The results have been compared with thin films of the same rare earth silicides produced by other methods. The room temperature resistivities of the ErSi_1.7, YSi_1.7 and Er_0.5Y_0.5Si_1.7 are 52, 69 and 87 μΩ cm, respectively, significantly higher than the reported values for MBE synthesised layers. The ErSi_1.7 shows evidence of magnetic ordering, but this is not observed in either the YSi_1.7 or the Er_0.5Y_0.5Si_1.7 down to 3 K.     

Electron scattering profiles in SOS films measured by temperature-dependent Hall effect

The electron scattering mechanisms at every depth in heteroepitaxial SOS films have been investigated by measuring the temperature dependence of Hall mobility. It appears that, above the `critical? temperature Tc=120 K, lattice scattering prevails only in the proximity of 1/SiO, while ionised impurity scattering becomes dominant near the substrate (2000 ? from Si/Al2O3) even at room temperature.     

Effect of surface passivation by SiN/SiO2 of AlGaN/GaN high-electron mobility transistors on Si substrate by deep level transient spectroscopy method

Device performance and defects in AlGaN/GaN high-electron mobility transistors have been correlated. The effect of SiN/SiO₂ passivation of the surface of AlGaN/GaN high-electron mobility transistors on Si substrates is reported on DC characteristics. Deep level transient spectroscopy (DLTS) measurements were performed on the device after the passivation by a (50/100 nm) SiN/SiO₂ film. The DLTS spectra from these measurements showed the existence of the same electron trap on the surface of the device.     

稀土元素掺杂材料的非线性光学特性

在材料中引入稀土元素,从而提高材料的三阶光学非线性。介绍了国内外专家利用不同的稀土元素,不同的浓度混合,以及不同的基质材料等来提高材料的三阶光学非线性,以提高材料的激光防护性能。     

Electron mobility and electron scattering by polar optical phonons in heterostructure quantum wells

Basic features of confined electron scattering in quantum wells (QWs) by confined polar optical (PO) phonons are analyzed. The dependence of electron mobility in Al_0.25Ga_0.75As/GaAs/Al_0.25Ga_0.75As QWs on the well width is calculated. It is demonstrated that increases and decreases in electron mobility (relative to the bulk value) as a function of the QW width occur due to resonance intersubband scattering. The dependence of electron mobility limited by PO phonon scattering on the electron density n _s in the QW is calculated. It is shown that anomalous behavior of electrical conductivity, which in certain cases decreases with increasing electron density, can take place in Al_0.25Ga_0.75As/GaAs/Al_0.25Ga_0.75As QWs for n _s >10¹⁶ m^?2.     

Superresolution of multipath delay profiles measured by PNcorrelation method

Time resolution of multipath delay profiles measured by using the autocorrelation of a pseudonoise (PN) code sequence is generally limited by the chip interval of the PN code sequence. A superresolution PN correlation method (SPM) is proposed which improves the time resolution of delay profiles measured by the conventional PN correlation method. The SPM is based on a decomposition of the eigenvector space of the correlation matrix of the delay profile data vector and gives the number of paths and their delay times with higher resolution. It is verified by computer simulations and experiments using coaxial delay lines that the SPM can resolve two paths with a delay difference of a few tenths of the chip interval. The applicability of the SPM to the analysis of an indoor multipath environment in which many delayed waves arrive with short delay differences is demonstrated by an indoor radio propagation experiment at 2.3 GHz     

大气压电晕放电离子迁移谱测量溴代烷烃的电子吸附速率常数

常温大气压下,在电子能量为0.35～0.65 eV的范围内,使用氮气负电晕放电-电子吸附-离子迁移谱,测量了CH2Br2,CH2BrCl,CHBr3的电子吸附速率常数,得到电子吸附速率常数的大小关系为k(CH2Br2)＞k(CH2BrCl),k(CH2Br2)＞k(CHBr3),并根据电子亲和势对CH2Br2和CH2BrCl的大小关系进行理论分析.首次对CHBr3的电子吸附过程进行了定性分析,发现样品蒸汽在迁移区通入迁移管时,溴离子会与CHBr3分子络合成团簇离子Br-(H2O)n(CHBr3)m.     

稀土铕、钕、镧配合物的激光激发荧光特性

对三种稀土离子（Eu^3 ,Nd^3 ,La^3 )的配合物,以可见激光作为激发光进行了荧光光谱测量,比较了它们的荧光光谱特性,讨论了Eu^3 配合物的荧光光谱所提供的丰富的光谱信息。     

Synthesis,photoluminescence and electroluminescence properties of iridium complexes with bulky carbazole dendrons

We synthesized solution-processable iridium complexes having bulky carbazole dendrons, fac-tris[2-{3-(3,5-bis(3,6-di-n-butylcarbazol-9-yl)phenyl)Phenyl)pyridine]iridium (III) (mCP)₃Ir and fac-bis[2-{3-(3,5-bis(3,6-di-n-butylcarbazol-9-yl)phenyl)phenyl}pyridine][2-{3-(3,5-di(4-pyridyl)phenyl)phenyl}pyridine]iridium (III) (mCP)₂(bpp)Ir. Photoluminescence quantum efficiencies (PLQEs) of (mCP)₃Ir and (mCP)₂(bpp)Ir in their diluted solutions were 91% and 84%, respectively. They showed high PLQEs of 49% for (mCP)₃Ir and 29% for (mCP)₂(bpp)Ir even in a neat film. The triplet exciton energy level of the dendronized ligand (2.8 eV), 2-[3-{3,5-bis(3,6-di-n-butylcarbazol-9-yl)phenyl}]pyridine 10, and the dendron (2.9 eV), 3,5-bis(3,6-di-n-butylcarbazol-9-yl)benzene 7, are enough higher than that of the core complex Ir(ppy)₃ (2.6 eV). External quantum efficiency (EQE) of single layer light-emitting device with (mCP)₂(bpp)Ir was much higher than that of (mCP)₃Ir because of better affinity of (mCP)₂(bpp)Ir to cathode metal. When an electron transporting and hole-blocking material was used, the EQEs of double layer devices were dramatically improved to 8.3% for (mCP)₃Ir and 5.4% for (mCP)₂(bpp)Ir at 100 cd/m².     

Simplified transient space-charge-limited current measurements of mobility using transimpedance amplifier

Transient space-charge-limited current measurement (also called time resolved dark injection) is a well known technique for mobility and contact ohmicity characterization in organic thin films. We demonstrate the feasibility of performing space-charge-limited transient current measurements using a transimpedance amplifier instead of the typically used bridge circuit. The use of a transimpedance amplifier significantly simplifies the experiment, particularly because it removes the requirements for bridge symmetry and per sample adjustment. Furthermore the experimental bandwidth and current sensitivity are increased. We detail the experiment design and verify the compatibility of measurements on a [6,6]-phenyl-C60-butyric acid methyl ester (60PCBM) blend thin film.