Enhanced Electroluminescence from Organic Light‐Emitting Diodes with an Organic–Inorganic Perovskite Host Layer

The development of host materials with high performance is essential for fabrication of efficient and stable organic light‐emitting diodes (OLEDs). Although host materials used in OLEDs are typically organics, in this study, it is shown that the organic–inorganic perovskite CH₃NH₃PbCl₃ (MAPbCl₃) can be used as a host layer for OLEDs. Vacuum‐evaporated MAPbCl₃ films have a wide band gap of about 3 eV and very high and relatively balanced hole and electron mobilities, which are suitable for the host material. Photoluminescence and electroluminescence take place through energy transfer from MAPbCl₃ to an organic emitter in films. Incorporation of an MAPbCl₃ host layer into OLEDs leads to a reduction of driving voltage and enhancement of external quantum efficiency as compared to devices with a conventional organic host layer. Additionally, OLEDs with an MAPbCl₃ host layer demonstrate very good operational stability under continuous current operation. These results can be extensively applied to organic‐ and perovskite‐based optoelectronics.     

Homocoupling Defects in a Conjugated Polymer Limit Exciton Diffusion

Copolymers such as PCDTBT (poly(N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole))) are commonly employed as donor material in bulk heterojunction solar cells. Recently, chemical defects such as homocouplings have been shown to form at the material synthesis stage, strongly reducing the short circuit current in organic photovoltaics. Here it is shown that both low molecular weight and homocoupling defects reduce the short circuit current of solar cells because of limited exciton diffusion. A model that unites and explains the influence of both chemical parameters with the distribution of conjugation lengths is proposed. The connection between limited exciton diffusion and short circuit current is revealed via kinetic Monte Carlo simulation of bulk heterojunctions. The findings are likely applicable for copolymers in general.     

激光器线宽对空间相干光通信系统性能的影响

空间相干光通信系统的信噪比受激光器线宽的影响很大。对比分析了两光束到达平衡探测器光敏面的时间差τ_d和探测器特性参数不同时,激光器线宽对外差探测输出信噪比的影响。理论分析和实验结果表明,激光器线宽展宽引起差频信号带宽增大与τ_d无关。当差频信号带宽增大2.673倍时,输出信噪比减小0.369 2倍,约等于1/2.673。增大探测器的内增益、响应度和响应带宽,可以减缓信噪比随激光器线宽增大而减小的速度,但内增益和响应带宽过大,相应的噪声信号也越强,反而不利于信噪比的提高。     

一种新颖的自反馈光注入单频窄线宽光纤激光器

报道一种基于自反馈光注入的单频窄线宽光纤激光器。激光器采用线形腔结构,用高掺杂Er3+光纤作为增益介质,利用输出信号光分束反馈与腔内振荡激光干涉,形成折射率光栅与增益光栅共同作用选择纵模,获得稳定的1 549.85 nm单频窄线宽激光输出。在975 nm单模激光二极管(LD)抽运下,激光器的抽运阈值光功率为13 mW。当抽运光功率为112 mW时,最大输出信号光功率为30.6 mW,对应的光-光转换效率为27.3%,斜率效率为30.2%,信噪比大于50 dB。采用延时自外差方法测量线宽,当使用30 km单模光纤延迟线时,测量得到激光器的3 dB线宽为4.0 kHz。     

半导体激光器线宽展宽因数的估计方法

描述了一种利用光反馈自混合效应估计半导体激光器的线宽展宽因数α和光反馈水平因子C的方法,该方法采用一个弱光反馈机制下的自混合效应模型去最佳拟合所观测的自混合信号数据,拟合算法基于非线性最小二乘法。针对不同的情况,做了大量计算机仿真。给出了仿真结果,结果表明该算法参数估计精度较高,不受参数初值选取的影响,且抗噪性能较好。     

Sol-Gel法低温共烧LiZn铁氧体研究

用溶胶-凝胶(sol-gel)法制备了Li0.5-0.5xZnxMnaFe2.5-0.5x-aO4(0.1≤x≤0.6)铁氧体纳米粉.比较了分别以柠檬酸和聚乙烯醇(PVA)为络合剂时粉料的X射线衍射(XRD)谱.XRD分析表明,以柠檬酸为络合剂制备的粉料粒度为6～22 nm,生成尖晶石的固相反应从400℃开始,到600℃完成;以PVA为络合剂的粉料的XRD谱为复杂双相结构.SEM形貌照片和烧结收缩曲线表明,不同活性粉料对烧结致密化和晶粒生长过程有明显影响.在纳米粉的低温烧结过程中发生了晶粒异常生长.选择较少(0.25 mol%)的Bi2O3添加量和适当工艺参数便可以实现Ts≤900℃的低温烧结.给出了880±20℃烧结样品的铁磁共振线宽△H和饱和磁化强度Ms随Zn含量的变化.     

Reaction of N-Acetylcysteine with Cu2+: Appearance of Intermediates with High Free Radical Scavenging Activity: Implications for Anti-/Pro-Oxidant Properties of Thiols

We studied the kinetics of the reaction of N-acetyl-l-cysteine (NAC or RSH) with cupric ions at an equimolar ratio of the reactants in aqueous acid solution (pH 1.4–2) using UV/Vis absorption and circular dichroism (CD) spectroscopies. Cu²⁺ showed a strong catalytic effect on the 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) radical (ABTSr) consumption and autoxidation of NAC. Difference spectra revealed the formation of intermediates with absorption maxima at 233 and 302 nm (ε₃₀₂/Cu > 8 × 10³ M⁻¹ cm⁻¹) and two positive Cotton effects centered at 284 and 302 nm. These intermediates accumulate during the first, O₂-independent, phase of the NAC autoxidation. The autocatalytic production of another chiral intermediate, characterized by two positive Cotton effects at 280 and 333 nm and an intense negative one at 305 nm, was observed in the second reaction phase. The intermediates are rapidly oxidized by added ABTSr; otherwise, they are stable for hours in the reaction solution, undergoing a slow pH- and O₂-dependent photosensitive decay. The kinetic and spectral data are consistent with proposed structures of the intermediates as disulfide-bridged dicopper(I) complexes of types cis-/trans-Cu^I₂(RS)₂(RSSR) and Cu^I₂(RSSR)₂. The electronic transitions observed in the UV/Vis and CD spectra are tentatively attributed to Cu(I) → disulfide charge transfer with an interaction of the transition dipole moments (exciton coupling). The catalytic activity of the intermediates as potential O₂ activators via Cu(II) peroxo-complexes is discussed. A mechanism for autocatalytic oxidation of Cu(I)–thiolates promoted by a growing electronically coupled –[Cu^I₂(RSSR)]_n– polymer is suggested. The obtained results are in line with other reported observations regarding copper-catalyzed autoxidation of thiols and provide new insight into these complicated, not yet fully understood systems. The proposed hypotheses point to the importance of the Cu(I)–disulfide interaction, which may have a profound impact on biological systems.     

影响Fizeau干涉仪测风激光雷达测量精度因素分析

基于Fizeau干涉仪测风激光雷达是利用线列探测器来测量Fizeau条纹的中心移动,以确定由于多普勒效应产生的激光频率变化的。系统噪声及激光本身的发射频率的线宽、光束发散角、发射光及回波信号光在通过干涉仪之前的光强不均匀性,以及探测器的内部结构等因素都会影响到风速的测量精度。本文对这些因素做了较为详细的分析,为提高系统测量精度提供了参考。     

基于CPM-FBG的单频窄线宽DFB光纤激光器

利用电弧放电对光纤Bragg光栅(FBG)折射率的调制作用,提出了基于折射率周期调制(CPM)FBG的单频窄线宽分布反馈(DFB)光纤激光器方案。建立了CPM-FBG的数学模型并进行了仿真,验证了CPM-FBG的相移光栅特性;在掺铒光纤(EDF)上制作出CPM-FBG,形成了DFB单频窄线宽光纤激光器,激光器阈值功率为25.4mW,3dB线宽为805Hz,边摸抑制比大于48.8dB。