磁控溅射Ge/Si多层膜的发光特性研究

采用磁控溅射技术,在Si(100)衬底上制备了一系列不同周期、不同Ge层厚度的Ge/Si多层膜样品.用室温光致发光(PL)、Raman散射和AFM图谱对样品进行表征.结果表明:Ge/Si多层膜中的PL发光峰主要来自于Ge晶粒,并且Ge晶粒生长的均匀性对PL发光影响较大,生长均匀的Ge晶粒中量子限域效应明显,随着晶粒的减小,PL发光主峰发生蓝移;在Ge晶粒均匀性较差时,PL发光峰强度较弱,量子限域效应不明显.     

InAs/GaAs量子点光致发光光谱多峰结构发光本质

研究了InAs/GaAs量子点光致发光光谱中出现的多峰结构. 观察到随着激发功率的增加光谱中发光峰的数目逐渐增多并且部分发光峰的峰位随激发功率的增加向高能量方向移动. 解释了各发光峰的来源并结合量子点能级结构的特点,计算了量子点中电子和空穴各子带间的能级间距.     

InAs/GaAs量子点光致发光光谱多峰结构发光本质

研究了InAs/GaAs量子点光致发光光谱中出现的多峰结构.观察到随着激发功率的增加光谱中发光峰的数目逐渐增多并且部分发光峰的峰位随激发功率的增加向高能量方向移动.解释了各发光峰的来源并结合量子点能级结构的特点,计算了量子点中电子和空穴各子带间的能级间距.     

基于量子点的白光二极管的研究进展

量子点又称为纳米晶,是一种由Ⅱ-Ⅵ族或Ⅲ-Ⅴ族元素组成的纳米颗粒(粒径1～10nm),由于电子和空穴的量子限域效应,连续的能带结构变成分立的能级结构,受激后可以发射荧光。量子点的发光光谱可以通过量子点的粒径大小来调节。文章基于量子点的电致发光和光致发光的机理,主要介绍了近年来基于量子点的白光发光二极管的研究进展。     

InGaN/GaN多量子阱的变温发光特性研究

采用低压金属有机化学沉积方法制备了InGaN/GaN多量子阱.变温PL测量发现,量子阱发光强度具有良好的温度稳定性,随着温度升高(10～300K),发光强度只减小到1/3左右.分析认为,InGaN/GaN多量子阱的多峰发光结构是由多量子阱的组分及阱宽的不均匀引起的.随着温度升高,GaN带边及量子阱的光致发光均向低能方向移动,但与GaN带边不同,量子阱发光峰值变化并不与通过内插法得到的Varshni经验公式相吻合,而是与InN带边红移趋势一致,分析了导致这种现象的可能因素.还分析了量子阱发光寿命随温度升高而减小的原因.     

热丝法制备硅纳晶颗粒及其发光性质

利用热丝化学气相沉积法,在真空腔中通过选择设定不同加热功率的热丝热解硅烷制备出一系列不同颗粒尺寸的硅纳米颗粒样品。透射电镜分析表明硅纳米颗粒具有结晶良好的纳晶结构。通过自然氧化钝化硅纳米颗粒表面,消除表面悬键的影响,使得硅颗粒具有高效的光致发光特性,发光范围在红光到近红外区,发光特性与量子限域效应相吻合。发光寿命测量表明所制备的硅颗粒的发光寿命在微秒量级,并且通过比较不同硅颗粒分布样品中相同发光波长衰减寿命的差异,揭示了所制备样品中硅纳米颗粒之间存在耦合作用。     

微乳状液中CdS超微粒制备与光学特性研究

采用微乳状液法合成了不同粒径的CdS超微粒子,其粒径在纳米范围内。光谱结果表明,CdS有明显的量子尺寸效应。首次发现室温下CdS超微粒的激发与发射光谱的分立峰结构,并且还发现,表面包覆活性剂分子后的CdS超微粒,表面态发光被显著地减弱,空间限域激子态发射增强,这可能有助于提高三阶非线性光学响应。     

HVPE生长GaN厚膜光致发光特性研究

利用吸收光谱和光致发光(PL)光谱研究了氢化物气相外延(HVPE)法生长的GaN厚膜材料发光特性。研究发现当激发脉冲光源的重复频率较低时,PL光谱中仅能观察到带边发光峰,当重复频率增加时,PL光谱中不仅出现带边发光峰,还可观察到蓝带发光峰和黄带发光峰;随着光源重复频率的增加,带边发光峰与黄带发光峰、蓝带发光峰的光强之比也随着增大。分析认为蓝带发光起源于材料中碳杂质缺陷而黄带发光可能与位错等结构缺陷有关。     

MO-PPV/ZnSe量子点复合材料的制备及光致发光特性研究

采用水相法制备了颗粒尺寸为3.75nm的硒化锌(ZnSe)量子点,采用表面活性剂将ZnSe量子点转移到有机相聚(2-甲氧基-5-辛氧基)对苯乙炔(MO-PPV)中,获得了MO-PPV/ZnSe复合材料。通过对MO-PPV和ZnSe量子点的吸收光谱(ABS)和光致发光(PL)光谱的研究发现,随着ZnSe量子点掺杂浓度的提高,复合材料的发光强度明显增强,发光峰位置出现了蓝移。当ZnSe∶MO-PPV的质量比为1∶0.181时,发光峰位置蓝移10nm。结果表明,MO-PPV与ZnSe量子点之间存在着能量传递,这是导致MO-PPV/ZnSe量子点复合材料具有PL增强的重要原因。     

宽带隙半导体材料光电性能的测试

主要通过光致发光的实验手段,研究分析了在自支撑GaN衬底上生长的InGaN/GaN多量子阱(InGaN/GaN MQW)有源层中的载流子复合机制,实验中发现多量子阱的光致发光光谱中有一个与有源区中的深能级相关的额外的发光峰。在任何温度大功率激发条件下,自由激子的带边复合占主导地位,并且带边复合的强度随温度或激发功率的下降而减弱;在室温以下小功率激发条件下,局域化能级引入的束缚激子复合占主导地位,其复合强度随温度的下降而单调上升,随激发功率的下降而上升。带边复合在样品温度上升或者激发功率变大时发生蓝移,而局域的束缚激子复合辐射的峰值波长,随样品温度和激发功率的变化没有明显变化。     

Level crossing of nanometer sized InAs islands in GaAs

We used polarization spectroscopy to detect level crossings in the fine structure of excitons in strained InAs islands grown on [001] GaAs. The crossings gave rise to quasi-resonant peaks, when monitoring the circularly polarized photoluminescence (PL) as a function of magnetic field. The peaks could also be detected as increases of the PL intensity. The resonant magnetic field was strongly dependent on detection energy within the PL emission peak. This energy selection is equivalent to monitoring a specific size or small interval within the broader size and shape distribution inherent to the growth process. The resonance was observed to shift to a higher magnetic field, when increasing the angle between field and sample growth direction. Basic arguments based on quantum confinement and the exciton fine structure can qualitatively account for the observations. Together with hole effective g-values the level crossing fields can be used to calculate the zero magnetic field splitting of the exciton fine structure.     

Effect of Ligand Exchange on the Photoluminescence Properties of Cu-Doped Zn-In-Se Quantum Dots

The surface-bound ligands of a semiconductor nanocrystal can affect its electron transition behavior. We investigate the photoluminescence (PL) properties of Cu-doped Zn-In-Se quantum dots (QDs) through the exchange of oleylamine with 6-mercaptohexanol (MCH). Fourier transform infrared and ¹H nuclear magnetic resonance spectroscopies, and mass spectrometry reveal that the short-chain MCH molecules are bound to the QD surface. The emission peaks remain unchanged after ligand exchange, and the PL quantum yield is reduced from 49% to 38%. The effects of particle size and defect type on the change in PL behavior upon ligand substitution are excluded through high-resolution transmission electron microscopy, UV–Vis absorption, and PL spectroscopies. The origin of the decreased PL intensity is associated with increased ligand density and the stronger ligand electron-donating abilities of MCH-capped QDs that induce an increase in the nonradiative transition probability. A lower PL quenching transition temperature is observed for MCH-capped QDs and is associated with increasing electron-acoustic phonon coupling due to the lower melting temperature of MCH.     

Tunable properties of cadmium substituted ZnS nanocrystals

Tailored Zn_1−xCd_xS (x = 0, 0.25, 0.5, 0.75 and 1) nanoparticles, synthesized by co-precipitation method under ultrasonic irradiation, were studied by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), UV–Vis and photoluminescence (PL) spectroscopy measurements. According to the XRD results, substitution of Zn²⁺ by Cd²⁺ ion leads to an increase in the lattice parameters and the average size of zinc blended nanoparticles are in the range of 3–4 nm. Transmission electron microscopy image revealed the formation of nano-sized particles with dimension of 5 nm confirming that the samples are quantum dots. The shift observed in the absorption edges by increasing Cd²⁺ ion substitution is ascribed by the alloying effect but the enhancement of band gap energy compared to that of the corresponding bulk value is attributed to the nanometric grain size and quantum confinement effects. The position and intensity of PL emission peaks are tuned with Cd²⁺/Zn²⁺ ion content.     

CoTe2量子点的制备、结构及光学性质研究（特邀）

近年来,过渡金属碲化物（TMTs）以其独特的晶体结构和优异的物化特性引起了科学界的广泛关注和研究。本文采用超声法制备CoTe₂量子点（QDs）,通过TEM、AFM、EDS、XPS、XRD、FTIR等技术手段对制备的CoTe₂ QDs进行了形貌和结构的表征,同时使用分光光度计(UV-Vis)、光致发光谱(PL)和光致发光激发光谱(PLE)研究了CoTe₂ QDs的光学性质。结果表明,制备得到的CoTe₂ QDs分散性良好、粒径均匀、呈现球形形貌,晶粒的平均直径约为3.1 nm,平均高度约为2.9 nm;CoTe₂ QDs在红外波段存在明显的吸收,吸收值随稀释浓度的增加而降低;当激发光波长和发射光波长依次增加时,PL和PLE峰出现红移,具有明显的Stokes位移效应,表明CoTe₂ QDs的光致发光具有激发波长依赖性;CoTe₂ QDs具有光致多色发光特性,不同激发光波长可发出不同颜色的光;荧光量子产率可达62.6%。CoTe₂ QDs优异的光学特性尤其是在红外波段的吸收和发光特性,表明其在红外探测、激光防护涂层、荧光成像、多色发光和纳米光子器件等研究领域中具有重要的潜在应用价值,有望成为一种新型红外探测材料。     

Light emission from crystalline silicon and amorphous silicon oxide (SiOx) nanoparticles

Bright orange-red light emission was observed from single crystal silicon nanoparticles and silicon oxide (SiO_x) nanoparticles. The emission peak was recorded at about 1.5 eV both at room temperature and 77K. Varying the mean silicon particle size, we observed no effect of particle diameter on the emission wavelength. Amorphous silicon oxide (SiO_x) nanoparticles also showed essentially the same emission spectrum as the crystalline particles. The absence of change in the photoluminescence (PL) spectrum with variations in particle size and crystallinity indicates that quantum confinement is not the controlling PL mechanism. An examination of the hydrogen content with relation to the PL intensity showed no direct correlation; however, all samples did contain some hydrogen, so its effect on PL cannot be ruled out. To test for the presence of photoluminescent siloxene on the surface of the particles, nitric acid was applied; a violent reaction occurred with the silicon particles, while the SiO_x particles showed no reaction. Taken in conjunction with the emission data, these experiments demonstrate that the PL of the SiO_x is also not dependant on siloxene. Evidence points to an amorphous coating as the source of photoluminescence.     

Sb2Te3量子点的制备、结构及红外性质研究

碲化锑（Sb₂Te₃）是一种新型二维层状材料,采用“自上而下”的超声剥离法,以碲化锑粉末为原料,以N-甲基吡咯烷酮（NMP）为分散剂,首次成功制备出碲化锑量子点（Sb₂Te₃ QDs）,并采用多种手段（SEM,TEM,AFM,XPS,XRD等）对所制备Sb₂Te₃ QDs的形貌和结构进行了表征,同时还采用UV-Vis、PL及PLE探究了Sb₂Te₃ QDs的光学性质。研究表明:所制备的Sb₂Te₃ QDs平均粒径为2.3 nm,平均高度为1.9 nm,颗粒大小均匀、具有良好的分散性,PL与PLE峰位有明显的红移现象,研究还发现Sb₂Te₃ QDs在红外波段有明显的吸收与光致发光。研究表明:超声剥离法制备Sb₂Te₃ QDs是切实可行的,该量子点的PL与PLE对波长具有依赖性,其在红外波段的特性表明:它有望成为一种新型的红外探测材料。     

激光诱导生成锗纳米晶体量子点

采用氧化和析出的方法在氧化硅中凝聚生成锗纳米晶体量子点结构.其形成的锗晶体团簇没有突出的棱角和支晶结构,锗晶体团簇的轮廓较圆混,故可以用球形量子点模型来模拟实际的锗晶体团簇.对比了在高温(800℃～1000℃)条件下和在低温(200℃～500℃)用激光照射条件下所生成的锗纳米晶体结构的PL光谱和对应的锗纳米晶体团簇的尺寸分布.低温用激光照射条件下所生成的锗纳米晶体较小,其PL光谱出现蓝移.用量子点受限模型计算了锗纳米晶体团簇的能隙结构,用Monte Carlo方法模拟了PL光谱和对应的锗纳米晶体团簇的尺寸分布,分别与实验结果吻合较好.     

Investigation of luminescence properties of ZnO nanowires at room temperature

The controllable growth processes of ZnO nanowires by evaporation of metal zinc with high purity and its luminescence properties have been investigated in detail. Firstly, the power of ZnO nanowires with high yield and homogeneous dimension was synthesized using the special quartz boat at 600 °C. Then, the oriented ZnO nanowires with about 20 nm diameter were synthesized by using a 90 nm-thick layer of ZnO nanocrystals on the Si substrate as the seed layer. Both fabrication processes are repeatable and no catalysts are necessary. Finally, photoluminescence (PL) spectroscopy for ZnO nanowires using an He-Cd laser line of 325 nm as the excitation source were measured at room temperature and both samples showed a sharp strong ultraviolet (UV) near-band edge emission. However, different UV peak positions (385 nm for ZnO nanowire powder, 377 nm for ZnO nanowire array) can be observed. The size confinement effect for excitons and carriers is proposed to explain the blue shift of the near-band edge emission with decreasing size and the native defects are responsible for the green emission.     

纳米硅薄膜的发光特性研究

研究了 nc- Si:H薄膜的光致发光 ( PL) ,分析了晶粒尺寸、温度对发光特性的影响。对发光样品 ,晶粒尺寸有一上限 ,其值在 4～ 5nm之间。在 10～ 77K,nc- Si:H薄膜的发光强度几乎没有变化 ;当温度高于 77K,发光强度指数式下降。随温度升高 ,发光峰位有少许红移。讨论了nc- Si:H光致发光机理 ,用量子限制 -发光中心模型对实验现象进行了解释。从载流子的激发、复合两方面讨论了发光过程 ,认为载流子在晶粒内部激发后 ,弛豫到晶粒界面的发光中心复合发光。