CdSe/ZnS量子点掺杂聚合物光纤放大器增益特性分析

提出了一种半导体量子点CdSe/ZnS掺杂聚合物光纤放大器。测量了CdSe/ZnS量子点吸收和发射光谱,采用二能级结构和速率方程的方法,全面描述了CdSe/ZnS量子点掺杂聚合物光纤放大器的增益性能。计算了放大器增益随量子点掺杂光纤长度、量子点掺杂浓度和信号光强度的变化,给出了不同泵浦光强条件下的增益谱线及半高全宽。结果表明,在mW量级的泵浦条件下,CdSe/ZnS量子点掺杂聚合物光纤放大器可获得35dB以上的增益,获得相同增益所需泵浦光强度只有同类型染料掺杂聚合物光纤放大器的万分之一。泵浦光强与量子点掺杂浓度之间存在最佳对应关系,单位泵浦功率激发的最佳量子点数为6.33×107/mW。在室温下,CdSe/ZnS量子点掺杂聚合物光纤放大器具有550nm～610nm的带宽,含盖了聚合物光纤的低损窗口。     

CdSe/ZnS量子点光纤纤芯基底的研究

量子点光纤正逐渐成为光通信领域的研究热点。首先介绍了CdSe/ZnS量子点掺杂光纤的发展历史,随后给出两种不同纤芯基底材料的CdSe/ZnS量子点掺杂光纤的制备方法,并对它们的光谱特性及发射峰值增益进行了分析比较,最后分析得出适合CdSe/ZnS量子点掺杂光纤的纤芯基底材料。CdSe/ZnS量子点掺杂光纤基底材料的研究对其他量子点光纤的研制具有一定的借鉴作用。     

纳米晶体PbSe的吸收光谱特性及光纤掺杂工艺

测量了直径为5.5nm的人工纳米晶体(量子点)PbSe的近红外吸收光谱.根据量子点浓度、量子点粒度以及Beer-Lambert定律,确定了其吸收截面的峰值.研究了实验室量子点光纤样品制备的掺杂工艺,初步探索出抽真空法、注射法、毛细渗透法几种较为可行的掺杂方案.研究了适合于用作量子点光纤纤芯的材料,得到了一种与普通石英光纤折射率非常接近的硅酸溶胶.     

纳米晶体PbSe的吸收光谱特性及光纤掺杂工艺

测量了直径为5.5nm的人工纳米晶体(量子点)PbSe的近红外吸收光谱.根据量子点浓度、量子点粒度以及Beer-Lambert定律,确定了其吸收截面的峰值.研究了实验室量子点光纤样品制备的掺杂工艺,初步探索出抽真空法、注射法、毛细渗透法几种较为可行的掺杂方案.研究了适合于用作量子点光纤纤芯的材料,得到了一种与普通石英光纤折射率非常接近的硅酸溶胶.     

中红外宽带荧光PbSe量子点掺杂玻璃光纤研究

宽带可调谐中红外光源在光谱传感器以及医疗、环境监测等实际应用方面备受关注。目前,发光玻璃主要通过稀土离子掺杂来实现中红外波段发光,但其可调范围较小。PbSe量子点具有较窄的带隙、较大的玻尔半径,因而易实现量子限域效应。在低声子能量的锗酸盐玻璃中原位析出PbSe量子点,有望产生近中红外宽带可调谐荧光发射。本课题组利用管内熔融法成功制备了全固态PbSe量子点掺杂玻璃光纤,获得了覆盖1.8～2.8μm的宽带可调谐发射,有望用于宽带可调谐中红外光源。     

渐逝波耦合半导体量子点光纤放大器

基于半导体量子点的特性,结合光纤渐逝波耦合器,提出了一种新型的光纤放大器件,它将以溶液形式的硫化铅(PbS)半导体量子点材料沉积于耦合器熔锥区,信号光和抽运光通过渐逝波共同与半导体量子点材料相互作用,实现光的放大作用。PbS量子点材料是采用工艺容易控制的反胶束法制备的,通过透射电镜(TEM)测量得到其粒子尺寸小于10 nm。利用工作波长为980 nm,功率为30 mW的半导体激光器抽运光源对该光纤放大器抽运,在1310 nm波段得到了大于4 dB的增益,这是半导体量子点尺寸效应引起的光谱蓝移现象的体现。因此,这种有源区短、器件结构紧凑的光纤放大器在高速、宽带光纤接入等领域具有重要的实际意义和应用价值。     

PbSe量子点光纤激光器的数值模拟

提出了一种新型的光纤激光器--掺量子点的光纤激光器(QDFL).在QDFL中,利用PbSe量子点具有大发射截面的特点,将PbSe量子点作为激光器的激活介质,对QDFL进行了计算机数值模拟.数值计算了掺PbSe量子点光纤激光器的激光功率及饱和长度,并给出了不同输出镜反射率对激光功率的影响.结果表明:与传统的掺镱离子的光纤激光器相比,QDFL的输出激光功率更高,增益系数更大,光纤的饱和长度较短.QDFL的激光功率与光纤长度密切相关,饱和功率与掺杂浓度无关.改变谐振腔出射镜的反射率,可以改变激光功率.这些结果有待于实验的证实和检验.     

三基色量子点的制备与白光的实现

采用化学溶液方法,以乙基黄原酸盐作为壳层前驱体,制备了红绿蓝三色发光的CdSe/ZnS核壳量子点.以乙基黄原酸锌为前驱体形成ZnS壳层包覆CdSe核量子点,通过调节反应温度与反应气氛等条件获得了发绿光(542nm)及蓝光(483nm)的核壳量子点.以乙基黄原酸镉和乙基黄原酸锌分别作为壳层CdS及ZnS的前驱体制备了发红光(612nm)CdSe/CdS/ZnS核/多壳结构量子点.紫外-可见吸收光谱、荧光光谱及透射电镜研究结果表明,通过条件调节,温度较低时(约230℃)注入乙基黄原酸锌后量子点发光峰出现红移,而温度较高时(约260℃)则发生蓝移.通过不同发光颜色的量子点的混合实现了三基色白光.     

光纤放大器中孤子的量子效应

利用含时Hartree近似法得到光孤子在含光纤损耗、双光子吸收、三阶色散效应的光纤放大器中传输时的量子非线性薛定谔方程,在一定条件下,有量子态的孤子解,并由此方程讨论了经典和量子效应对孤子在光纤放大器中传输时的影响,由此进一步发现,光场算符的量子力学平均值是一系列修正的经典孤子的叠加。     

PbSe量子点的制备与近红外波段光学性质研究

通过化学溶液体系中反应温度与原料配比的控制获得了尺寸分布均匀的窄带隙半导体PbSe量子点。利用吸收光谱、X射线衍射（XRD）、透射电子显微镜（TEM）和高分辨透射电子显微镜（HRTEM）等手段研究了化学溶液法制备的PbSe量子点形貌、尺寸分布及红外吸收等特性。结果表明,所获得的量子点尺寸分布均匀,结晶性良好,并实现了第一吸收峰在885 nm～2 200 nm范围内可调的PbSe量子点。     

PbSe量子点掺杂玻璃的制备及表征

采用高温熔融法,经过两步热处理,成功制备了PbSe量子点(QD)掺杂的硅酸盐玻璃.当热处理温度为550℃、热处理时间为1～10 h时,X射线衍射(XRD)和透射电镜(TEM)测量表明,玻璃中,生成的PbSe QD平均尺寸为5～6 nm.随着热处理时间的延长(3～8 h),玻璃中生成的PbSe QD尺寸增大.近红外荧光(...     

Improving the Power Conversion Efficiency of Organic Solar Cell by Blending with CdSe/ZnS Core–Shell Quantum Dots

We have blended poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) with CdSe/ZnS core–shell quantum dots (QDs) as the active layer to produce organic solar cells (OSC). The size of the CdSe/ZnS core–shell QDs was determined to be about 4 nm using transmission electron microscopy. The OSC were characterized by measuring the absorption spectra, current–voltage characteristics, and external quantum efficiency (EQE) spectra. The samples doped with 0.5 wt.% CdSe/ZnS core–shell QDs exhibited higher power conversion efficiency (PCE) than samples doped with other concentrations of QDs. The PCE of the OSC increases from 2.10% to 2.38% due to an increase of the short circuit current density (J _sc) from 6.00 mA/cm² to 6.25 mA/cm². The open circuit voltage (V _oc) was kept constant when comparing OSC that were undoped and doped with 0.5 wt.% CdSe/ZnS core–shell QDs. These CdSe/ZnS core–shell QDs can increase optical absorption as well as provide extra exciton dissociation and additional electric pathways in hybrid OSC.     

Highly Efficient Quantum‐Dot‐Sensitized Solar Cell Based on Co‐Sensitization of CdS/CdSe

Cadmium sulfide (CdS) and cadmium selenide (CdSe) quantum dots (QDs) are sequentially assembled onto a nanocrystalline TiO₂ film to prepare a CdS/CdSe co‐sensitized photoelectrode for QD‐sensitized solar cell application. The results show that CdS and CdSe QDs have a complementary effect in the light harvest and the performance of a QDs co‐sensitized solar cell is strongly dependent on the order of CdS and CdSe respected to the TiO₂. In the cascade structure of TiO₂/CdS/CdSe electrode, the re‐organization of energy levels between CdS and CdSe forms a stepwise structure of band‐edge levels which is advantageous to the electron injection and hole‐recovery of CdS and CdSe QDs. An energy conversion efficiency of 4.22% is achieved using a TiO₂/CdS/CdSe/ZnS electrode, under the illumination of one sun (AM1.5,100 mW cm^?2). This efficiency is relatively higher than other QD‐sensitized solar cells previously reported in the literature.     

Improved performance of CdSe/ZnS quantum dot light-emitting diodes through doping with small molecule CBP

The poor film formation of CdSe/ZnS quantum dots (QDs) during spin-coating makes a substantial impact on the device performance of quantum dot light-emitting diodes (QLEDs). This work proposes a method to improve the morphology of the quantum dot light-emitting layer (EML) by adding small organic molecular 4,4''-Bis(9H-carbazol-9-yl) biphenyl (CBP) into the layer. Its surface roughness reduces from 6.21 nm to 2.71 nm, which guarantees a good contact between hole transport layer (HTL) and EML. Consequently, the CdSe/ZnS QDs:CBP based QLED achieves maximum external quantum efficiency (EQE) of 5.86%, and maximum brightness of 10 363 cd/m2. It is demonstrated that the additive of small organic molecules could be an effective way to improve the brightness and the efficiency of QLEDs.     

Carrier transport and memory mechanisms of multilevel resistive memory devices with an intermediate state based on double-stacked organic/inorganic nanocomposites

Multilevel resistive memory devices with an intermediate state were fabricated utilizing a poly(methylmethacrylate) (PMMA) layer sandwiched between double-stacked PMMA layers containing CdSe/ZnS core–shell quantum dots (QDs). The current–voltage (I–V) curves on a Al/[PMMA:CdSe/ZnS QD]/PMMA/[PMMA:CdSe/ZnS QD]/indium-tin-oxide/glass device at low applied voltages showed current bistabilities with three states, indicative of multilevel characteristics. A reliable intermediate state was realized under positive and negative applied voltages. The carrier transport and the memory mechanisms of the devices were described on the basis of the I–V curves and energy band diagrams, respectively. The write-read-erase-read-erase-read sequence of the devices showed rewritable, nonvolatile, multilevel, and memory behaviors. The currents as functions of the retention time showed that three current states were maintained for retention times larger than 1 × 10⁴ s, indicative of the good stability of the devices.     

Formation and characterization of self-organized CdSe quantum dots

We have investigated the formation and characteristic of self-organized CdSe quantum dots (QDs) on ZnSe(001) surfaces with the use of photoluminescence (PL) and transmission electron microscopy (TEM). Coherent CdSe QDs are naturally formed on ZnSe surfaces, when the thickness of CdSe layers is around 2 ML. The plan-view TEM images exhibit that CdSe QDs have a relatively narrow distribution of QD size, and that the density of CdSe QDs is about 10¹⁰ cm⁻². The base structure of the CdSe dot is rhombic, which has the long axis of about 20 nm in length along direction. The temperature dependence of macro-PL spectra reveals that the behavior of self-organized CdSe QDs is quite different from that of ZnCdSe quantum well (QW), resulting from characteristic features of zero-dimensional structures of QDs. Moreover, the macro-PL results suggest the existence of QW-like continuous state lying over QD states. Micro-PL measurements show several numbers of high-resolved sharp lines from individual CdSe QDs. The linewidth broadening with temperature depends on peak energy position of the QDs. The linewidths of lower energy lines, corresponding to larger size QDs, are more temperature dependent.     

Interaction of CdSe/ZnS quantum dots: Among themselves and with matrices

Photoluminescence (PL) of CdSe/ZnS quantum dots (QDs) deposited on Si, fused silica, Au film, shows red-shift; and blue-shift whenever two peaks are present, particularly on silica nanospheres. The red-shift with increasing density of QDs is attributed to interaction between QDs with PL emerging from the lower bonding state, and the second peak is attributed to molecular complexes on the surface of QD interacting with its surrounding matrices. The second peak is too weak to be detected on Si wafer with native oxide. The couplings between QD/QD and QDs/silica spheres via the molecular complexes are explained with a simple model. We also demonstrate that the band-gap of photonic crystals consisting of silica spheres can be stabilized by dehydration, annealing at high temperatures up to 1000 °C.     

Effect of CdSe/ZnS quantum dots on color purity and electrical properties of polyfluorene based hybrid light emitting diode

We report enhanced color purity of hybrid organic-inorganic light emitting diode based on polyfluorene-CdSe/ZnS quanum dot (QD) blend as emissive layer. Effect on structural, optical and electrical properties of different doping concentration (0–100 wt.%) of QD in polyfluorene (PFO) was studied. Photoluminescence and electroluminescence spectra confirm the β-formation of PFO by incorporation of CdSe/ZnS QD. Photoluminescence (PL) of blend film was also compared with another method based on one dimensional photonic band gap (1D-PBG) structure that has been used for color purity. In both the cases, that is, QD doped device and 1D-PBG based structures the narrowing of PL spectra was observed. But the fabrication of QD-doped device for color purity is easier than fabricating 1D-PBG structure using multilayer dielectric coating. The present study might find application for QD based color displays, where color purity is an important requirement.     

Characteristics of pH sensors fabricated by using protein-mediated CdSe/ZnS quantum dots

The pH sensors using protein-mediated CdSe/ZnS quantum dots in an electrolyte-insulator-semiconductor (EIS) structure have been investigated. The hydrophobic cylindrical cavity of the chaperonin (GroEL) protein template was used to trap CdSe/ZnS quantum dots on hydrophobically treated SiO₂ surface. The CdSe/ZnS quantum dot with a small diameter of 3.98 nm is observed by atomic force microscope. A fair pH response with a sensitivity of 39 mV/pH and a linearity of 99.48% are obtained by using CdSe/ZnS quantum dot based EIS sensor, while those values are found to be 53 mV/pH and 99.95% for bare SiO₂ based EIS pH sensors. The pH response and linearity of CdSe/ZnS based quantum dot sensors are inferior (slightly) as compared to the bare SiO₂ sensors owing to the initial negative charges of CdSe quantum dots membrane, which has been explained by energy band diagrams. It is expected that this kind of quantum dot membrane can be useful in future bio-molecule detections.     

Luminescent high temperature sensor based on the CdSe/ZnS quantum dot thin film

A high temperature sensor based on the multi-parameter temperature dependent characteristic of photoluminescence （PL） of quantum dot （QD） thin film is demonstrated by depositing the CdSe/ZnS core/shell QDs on the SiO2 glass substrates. The variations of the intensity, the peak wavelength and the full width at half maximum （FWHM） of PL spectra with temperature are studied experimentally and theoretically. The results indicate that the peak wavelength of the PL spectra changes linearly with temperature, while the PL intensity and FWHM vary exponentially for the tem- perature range from 30 ℃ to 180 ℃. Using the obtained temperature dependent optical parameters, the resolution of the designed sensor can reach 0.1 nm/℃.