PbSe量子点荧光匹配气体吸收光谱方法研究

PbSe量子点(PbSe-QDs)是红外波段的典型纳米材料,其具有大的玻尔半径、小的体材料禁带宽度(玻尔半径是46 nm,体材料禁带宽度是0.28 eV),因此,在近红外区域,PbSe-QDs具有强大的尺寸受限效应和较高的量子产出率。本文对不同尺寸的PbSe量子点的荧光光谱特性进行了研究,提出了一种通过调节PbSe量子点的量子尺寸匹配气体吸收光谱的方法。采用配位溶剂的方法制备了尺寸为4.6和6.1 nm的PbSe量子点,将该PbSe量子点沉积到GaN发光芯片上并经过紫外光照处理和固化后制成了光致发光的近红外光源,其中4.6 nm的PbSe-QDs的沉积厚度为671.5 μm,而6.1 nm的PbSe-QDs的沉积厚度为48 μm。将制成的近红外光源应用到C₂H₂气体和NH₃气体的检测实验中,实验结果表明,通过改变PbSe量子点的尺寸可以调节光源光致发光峰的位置,从而覆盖目标气体在近红外波段的吸收谱线。4.6 nm的光源发射光谱包含了1 500～1 550 nm之间的C₂H₂气体的全部的吸收谱;6.1 nm的光源发射光谱包含了1 900～2 060 nm之间的NH₃气体的全部的吸收谱。这种利用PbSe量子点尺寸的可调性匹配对应气体吸收谱的方法是可行和有效的,具有广阔的应用前景。     

PbSe胶质纳米晶温度依赖的光谱特性研究

在研究中,制备了3.8和5.8nm两种尺寸的PbSe胶质纳米晶,并对PbSe胶质纳米晶温度依赖的光学特性进行了研究。实验数据表明:在室温情况下,随着温度和尺寸的变化,PbSe胶质纳米晶的禁带宽度、发光峰值波长、发光强度及全波半宽度等都会发生改变。在纳米晶尺寸是3.8nm时,PbSe胶质纳米晶的禁带宽度随温度升高产生红移;但是当尺寸是5.8nm时,禁带宽度随温度升高产生蓝移。随温度的升高,PbSe胶质纳米晶的发光强度将下降、全波半宽度会增加。     

PbSe量子点在太阳能荧光聚集器中的应用研究

将PbSe量子点成功引入到了太阳能荧光聚集器(LSC)的应用中,利用光子追踪的方法,成功建立了一种基于Monte Carlo模拟方法的模型,通过实验测量,得到PbSe量子点相关数据, 在这些数据基础上,对PbSe量子点LSC的各个参数进行模拟优化,并在优化的条件下,对基于PbSe量子点LSC对太阳能电池单位输出能量造价进行考察,发现通过PbSe量子点LSC的引入,太阳能电池的造价可以降低49.2%,说明PbSe量子点非常适用于LSC体系。     

InAs/GaAs量子点的静压光谱压力系数研究

采用有效质量模型和非线性弹性理论计算了不同尺寸InAs/GaAs量子点的静压光谱发光峰的 压力系数(PC).量子点峰位随压力的变化主要来自禁带宽度和电子束缚能随压力变化两方面 的贡献.由于InAs/GaAs量子点是一个应变体系，体系的晶格常数，失配应变和弹性系数均随 外加压力变化，使得加压后量子点的禁带宽度相对于非应变体系略有减小，同时势垒高度增 加，电子束缚程度增加.两者共同作用引起的InAs应变层的禁带宽度压力系数减小是导致量 子点的压力系数小于InAs体材料的主要原因.同时计算结果表明，电子束缚能随压力变化对 不同尺寸量子点的压力系数的影响不同，量子点尺寸越小，受其影响越大，压力系数也越大 . 关键词： 量子点 压力系数 应变     

集成电路芯片温度依赖的PbSe量子点PL光谱研究

制备了3.6,5.1和6.0 nm三种尺寸的胶体PbSe量子点,并对其光学特性进行实验研究。在室温条件下,实验发现小尺寸胶体PbSe量子点的光致发光光谱随温度升高发生红移; 大尺寸胶体PbSe量子点的光致发光光谱随温度升高发生蓝移。以PbSe量子点温度依赖的光致发光光谱特性为基础,提出一种新型的集成电路芯片温度检测方法。这种新型的温度检测方法是将胶体PbSe量子点沉积在集成电路板表面,使用激光器发射出平行激光束,使芯片表面的胶体PbSe量子点层光致发光,通过红外光谱仪接收光致发光光谱,实现温度的检测;利用图像采集系统对芯片表面特定微小区域成像,实现微米尺度区域的温度检测。实验结果表明,测量精度为±3 ℃,其相对误差不大于5％。     

PbSe量子点调控的聚合物太阳能电池性能

为提升聚合物太阳能电池的光电转换效率,在有源层中掺杂PbSe量子点,研究对电池性能的影响。首先采用热化学法制备PbSe量子点,通过改变油酸的添加量及反应时间,调控PbSe量子点的尺寸及结晶性。通过透射电子显微镜和X射线衍射,对量子点进行表征,确定最佳反应条件。然后将不同质量分数的PbSe量子点掺杂至结构为ITO/ZnO/PTB7∶PC_(71)BM/MoO_3/Ag的聚合物太阳能电池中,通过J-V性能测试和紫外吸收光谱测试,分析了PbSe量子点对电池的影响机理。实验结果表明,当PbO与OA的量比为1∶2、反应时间为3 min时,可得到尺寸均匀分布在3～7 nm之间、结晶性较好的量子点,掺杂量子点质量分数为3%时,短路电流密度提升了8.37%,光电转换效率提升了37.41%,有效提升了聚合物太阳能电池的性能。     

硒化铅核壳量子点的合成与应用研究进展

硒化铅(PbSe)量子点具有宽红外光谱调控范围、高荧光量子产率和可溶液加工等特点,成为一类重要的红外材料体系。与广泛研究的PbS量子点相比,PbSe量子点在空气中容易氧化,从而严重破坏其光电特性,制约了其应用的发展。壳层的包覆是有效提升PbSe量子点光学特性和化学稳定性的策略之一,是推动PbSe量子点应用发展的材料研究方向。本文综述了PbSe核壳量子点的合成及其在光电探测、太阳能电池、激光器和光催化等领域的应用研究进展,希望能够为国内研究者开展相关研究提供参考。     

环形腔PbSe量子点单模光纤激光的计算机数值模拟

在PbSe/UV胶量子点光纤环形腔激光器实验的基础上,通过建立并数值求解粒子数速率方程和光功率传播方程等,对1550nm的激光输出特性进行了数值模拟。计算的抽运阈值功率、单/多模激光输出功率随抽运功率的变化、合适的PbSe掺杂浓度、单模激光功率随输出耦合比的变化等,与实验结果基本吻合。通过对PbSe量子点光纤中激光功率分布的研究,给出了粒子数密度的反转条件:N2/N1≥0.45,该条件可由1550nm波长处粒子数反转的吸收截面与辐射截面之比得到。研究了掺杂浓度对激光功率的影响,给出了合适的掺杂浓度范围。     

较高浓度PbSe量子点硅酸盐玻璃的制备及光学表征

采用高温熔融-热处理法,以ZnSe作为PbSe量子点的硒源,成功制备了较高浓度的PbSe量子点硅酸盐玻璃。透射电子显微镜(TEM)测试表明,量子点在玻璃基质中的体积比高达2%～4%,高于采用Se作为硒源时的掺杂体积比。X射线衍射(XRD)测试表明,PbSe量子点呈立方晶体结构。光致发光(PL)光谱测试表明,量子点有强烈的荧光发射,发光波长半峰全宽(FWHM)覆盖1400～2600nm,其PL峰值强度和FWHM均大于以Se为硒源时的情形。以ZnSe代替Se作为PbSe量子点的硒源,可有效避免Se组分的高温挥发,同时,残余Zn形成的ZnO有利于玻璃中PbSe量子点的析晶,从而提高了PbSe量子点在玻璃中的含量。该PbSe量子点玻璃,可用来进一步制备成超带宽、高增益的红外光纤放大器。     

X光CCD响应特性研究

 在北京同步辐射源上建立了X光CCD(Charge-Coupled Device)量子效率实验标定方法，获得了150eV至1500eV能区范围多个X光能点的量子效率实验结果，发展了X光CCD量子效率简化计算模型，并对X光CCD表面油沾污对量子效率的影响进行了实验研究和修正。结果表明经过油沾污修正后的简化理论模型计算结果与实验标定结果符合较好。     

Thickness effect on the band gap of magnetron sputtered Pb45Se45O10 thin films on Si

Oxygen doped PbSe thin films with different thickness were grown on the Si (100) substrates by magnetron sputtering, and characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and physical properties measurement system. As the film thickness increased, the intensity of the (200) PbSe prominent diffraction peak increased, while the (220) peak almost vanished, indicating the primary growth direction. The change rate between the light and dark resistance increased with the film thickness, and the maximum of 64.76% was obtained. According to the density functional theory calculations and the experimental results, the band gap of the PbSe thin films decreased from 0.278 eV to 0.21 eV when doped with oxygen. Doping with oxygen during the deposition process is a viable way to prepare PbSe thin films with a tunable band gap. The band gap increased almost linearly with the lattice constant, confirmed by the calculated and experimental results.     

自组织量子点光致荧光的温度依赖性

自组织量子点光致荧光的温度依赖性研究,对于实现室温下高效的量子点光电器件有着非常重要的意义。而量子点中的载流子动力学过程将决定其光致荧光的温度依赖性。采用稳态速率方程模型模拟了自组织量子点中载流子动力学过程,并且考虑了量子点材料带隙随温度的变化;模拟了不同温度下自组织量子点的光致荧光光谱,并获得了光谱的积分强度、峰值能量及半峰全宽随温度的变化曲线。研究表明:模拟结果与已报道的实验数据符合得很好。由此可知,所采用的模型能够很好地反映自组织量子点中的载流子动力学过程。     

Blueshifts of emission energy from InAs quantum dots in GaAs matrix due to narrowed interdot spacing: a token of the integrity of a nanostructure

The shifts of emission energy from InAs quantum dots (QDs) in the GaAs matrix due to change in the QD stacking period have been numerically analyzed by investigating the strain modified shifts of band edges. Narrower stacking results in a blueshift of emission energy from direct band gap transition provided the QD spacing is wide enough to avoid electronic coupling. Through a comparison with existing experimental results in the literature, processing methods and variables that have benefits in achieving a blueshift have been inferred. A blueshift through decreased QD spacing has been proposed as a token of the integrity of a processed QD nanostructure . PACS 68.65.+g; 78.66.Fd     

Electronic energy alignment at the PbSe quantum dots/ZnO(101̅0) interface

A number of solar energy conversion strategies depend on exciton dissociation across interfaces between semiconductor quantum dots (QDs) and other electron or hole conducting materials. A critical factor governing exciton dissociation and charge transfer in these systems is the alignment of electronic energy levels across the interface. We probe interfacial electronic energy alignment in a model system, sub-monolayer films of PbSe QDs adsorbed on single crystal ZnO(101?0) surfaces using ultraviolet photoemission spectroscopy. We establish electronic energy alignment as a function of quantum dot size and surface chemistry. We find that replacing insulating oleic-acid capping molecules on the QDs by the short hydrazine or ethanedithiol molecules results in pinning of the valence band maximum (VBM) of QDs to ZnO substrate states, independent of QD size. This is in contrast to similar measurements on TiO₂(110) where the alignment of the PbSe QD VBM to that of the TiO₂ substrate depends on QD size. We interpret these findings as indicative of strong electronic coupling of QDs with the ZnO surface but less with the TiO₂ surface. Based on the measured energy alignment, we predict that electron injection from the 1s_e level in photo-excited PbSe QDs to ZnO can occur with small QDs (diameter ? = 3.4 nm), but energetically unfavorably for larger dots (? = 6.7 nm). In the latter, hot electrons above the 1s_e level are necessary for interfacial electron injection.     

Decay lifetime and evolution of semiconductor quantum dots in photonic crystals

Spontaneous emission from GaAs/AlGaAs quantum dots (QDs) embedded in photonic crystals with a narrow photonic band gap is studied theoretically. The results show that the decay lifetime is very sensitive to the sizes of QDs, and both inhibited and accelerated emission can occur, which had been indicated in a previous experiment. The Weisskopf–Wigner approximation, good for atoms and molecules, may be incorrect for QDs. A damped Rabi oscillation of the excited state with the transition frequency outside the photonic band gap may appear, which is impossible for atoms and molecules.     

Energy of excitons and acceptor-exciton complexes to explain the origin of ultraviolet photoluminescence in ZnO quantum dots embedded in a SiO2 matrix

Assuming finite depth and within the effective mass approximation, the energies of exciton states and of the acceptor-exciton complexes confined in spherical ZnO quantum dots (QDs) embedded in a SiO₂ matrix are calculated using a matrix procedure, including a three-dimensional confinement of carrier in the QDs. This theoretical model has been designed to illustrate the two emission bands in the UV region observed in our experimental Photoluminescence spectrum (PL), with the first emission band observed at 3.04 eV and attributed to the bound ionized acceptor-exciton complexes, and the second one located at 3.5 and assigned to the free exciton. Our calculations have revealed a good agreement between the matrix element calculation method and the experimental results.     

立方氮化硼单晶紫外吸收光谱的研究

对于在高温、高压下合成的人工立方氮化硼(cBN)片状单晶进行了紫外吸收光谱和第一性原理的能带结构研究。实验中采用了UV WINLAB光谱分析仪,数据分析由MOLECULAR SPECTROSCOPY软件进行拟合运算,通过特殊的石英夹具对样品的测试表明cBN的紫外吸收波长限为198 nm,带隙为6.26 eV。结合第一性原理计算的cBN的能带结构和电子态密度的计算,可以证实导致紫外光吸收的过程是价带电子吸收光子到导带的间接跃迁。文章实验结果与目前报道的cBN能带结构中禁带宽度的吻合较好,表明cBN具有良好的紫外特性,是一种具有发展前景的紫外光电和高温半导体器件材料。     

Resonant Raman scattering from CdTe/ZnTe self-assembled quantum dot structures

We report resonant Raman scattering results of CdTe/ZnTe self-assembled quantum dot (QD) structures. Photoluminescence spectra reveal that the band gap energies of the CdTe QDs decrease with the increase of CdTe thickness from 2.0 to 3.5 monolayers, which indicates that the size of the QDs increases. When the CdTe/ZnTe QD structures are excited by non-resonant excitation, a longitudinal optical (LO) phonon response from the ZnTe barrier material is observed at 206 cm⁻¹. In contrast, when the CdTe/ZnTe QD structures are resonantly excited near the band gap energy of the QDs, additional phonon modes emerge at 167 and 200 cm⁻¹, while the ZnTe LO phonon response completely disappears. The 167 cm⁻¹ mode corresponds to the LO phonon of the CdTe QDs. A spatially resolved Raman scattering from the cleaved edge of the QD sample reveals that the 200 cm⁻¹ mode is strongly localized at the interface between the CdTe QDs and ZnTe cap layer. This phonon mode is attributed to the interface optical (IO) phonon. The analytically calculated value of the IO phonon energy using a dielectric continuum approach, assuming a spherical dot boundary, agrees well with the experimental value.