Highly efficient yellow organic light-emitting diodes based on a hole-dominant host layer co-doped with yellow emitting and electron transporting guests

We fabricated high efficiency yellow-color organic light-emitting diodes (OLEDs) by co-doping 2,8-di(t-butyl)-5,11-di[4-(t-butyl)phenyl]-6,12-diphenylnaphthacene (TBRb) and tris(8-hydroxyquinolinato)aluminum (Alq₃) guests in a N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) host. Co-doping of electron-transporting Alq₃ with yellow dopant TBRb in hole-dominant NPB layers resulted in substantial luminance-yield improvement compared to TBRb-only counterparts without color contamination from Alq₃ green emission. The luminance yield of 11.4 cd/A, corresponding to the co-doping of 8% TBRb and 2% Alq₃, is larger than previously reported luminance-yield values of conventional TBRb-based yellow OLEDs. Another advantage of the TBRb-Alq₃ co-doped OLEDs is an insignificant roll-off of efficiency at high current-density and/or brightness levels.     

Optical properties of alumina membranes prepared by anodic oxidation process

The luminescence property of anodic alumina membranes (AAMs) with ordered nanopore arrays prepared by electrochemically anodizing aluminum in oxalic acid solutions have been investigated. Photoluminescence emission (PL) measurement shows that a blue PL band occurs in the wavelength ranges of 300-600 nm. The PL intensity and peak position of AAMs depend markedly on the excitation wavelength. A new peak located at 518 nm can be observed under a monitoring wavelength at 429 nm in the photoluminescence excitation (PLE) spectra. Convincing evidences have been presented that the PLE would be associated with the residual aluminum ions in the membrane. The PLE and PL of AAMs, as a function of anodizing times, have been discussed. It is found that the oxalic impurities incorporated in the AAMs would have important influences on the optical properties of AAMs in the initial stage of anodization. The PL and PLE spectra obtained show that there are three optical centers, of which the first is originated from the F⁺ centers in AAMs, the second is correlated with the oxalic impurities incorporated in the AAMs, and the third is associated with the excess aluminum ions in the membrane.     

溶胶-凝胶法制备MgxZn1-xO薄膜的结构及光学特性

用溶胶-凝胶法制备了一系列的Mg_xZn_1-xO(0≤x≤0.3)薄膜,并用X射线衍射(XRD)和光致发光(PL)研究了不同的退火温度和Mg的掺杂含量对Mg_xZn_1-xO薄膜的结构和光学性质的影响.研究表明:Mg_xZn_1-xO薄膜为单相六角纤锌矿结构,并且具有沿c轴的择优取向;发现了中间热处理温度为350℃的Mg_xZn_1-xO薄膜退火温度的转折点为700℃,低于这个温度时随退火温度的升高,(002)衍射峰强度增强且掺Mg的薄膜既有紫外光又有绿光发射;800℃退火时,薄膜的(002)衍射峰强度减小,出现了(100)和(101)衍射峰,且掺Mg的薄膜只有紫外发光峰.不同的掺杂浓度对于发光也有影响,低于700℃退火时,ZnO薄膜只出现紫外发光峰,掺Mg的薄膜却出现了紫外和绿光两个发光峰.     

Photoluminescence and optical characterization of CdS nanoparticles prepared by solid-state method at low temperature

The photoluminescence (PL) and optical properties of CdS nanoparticles prepared by the solid-state method at low temperature have been discussed. The effects of NaCl and anionic surfactant SDBS (sodium dodecylbenzene sulfonate) on the luminescent properties of CdS nanophosphors prepared using this method, without the inert gas or the H₂S environment, were studied separately. The synthesized products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscope (FESEM), and energy dispersive X-ray spectroscopy (EDAX). UV–VIS absorption and PL spectra were also studied. XRD studies confirmed the single-phase formation of CdS nanoparticles. TEM micrograph revealed the formation of nearly spherical nanoparticles with a diameter of 2.5 nm. The PL emission for the CdS shows the main peak at 560 nm with a shoulder at 624 nm, with an increase in the PL intensity after the addition of SDBS. The effect of Mn doping on PL intensity has also been investigated. The PL spectra show that the emission intensity decreases as the dopant concentration increases.     

Controlled rotation and orientation of rubrene particles and Escherichia coli using optical tweezers

Optical trapping and rotating of suspended micro-sized rubrene particles were performed using optical tweezers with circularly polarized light. The experimental results show that the rotation speed of the rubrene particles is proportional to the laser power, and the orientation of the rubrene particles can be controlled by the optical tweezers with linearly polarized light. Interestingly, by combining with the rubrene particle, the Escherichia coli (E. coli) can be rotated and oriented by optical tweezers. However, the rotating and orientating are mainly determined by the characteristics of rubrene particles. Our experiment provides a simple and convenient way to orient biological particles even if they are not sensitive to the polarization of the laser beam. Moreover, the rubrene can emit strong fluorescence when excited by the laser at the wavelength of 532 nm, and which can be potential applied to manipulate other particles with the fluorescence characteristics.     

氢对GaAs薄膜的钝化作用

报导了射频磁控溅射与沉积气氛掺氢相结合制备单层(13~20 nm厚)高质量GaAs多晶态纳米薄膜的方法,研究了氢钝化对薄膜微观结构及光学性质的影响.对GaAs薄膜进行了X射线衍射、原子力显微镜、吸收光谱、光致荧光谱的研究分析.结果表明,衬底温度500℃的掺氢薄膜和520℃的薄膜呈面心立方闪锌矿结构,薄膜的晶团尺寸较大,微观表面较为粗糙,其吸收光谱出现了吸收边蓝移和明显的激子峰,带隙光致荧光峰强明显增加,说明氢在衬底温度500℃~520℃下对薄膜有重要的钝化作用.     

Au纳米颗粒和CdTe量子点复合体系发光增强和猝灭效应

利用金属蒸发真空多弧离子源注入机, 将Au离子注入到高纯石英玻璃来制备镶嵌有Au 纳米颗粒的衬底材料, 随后将化学方法合成的CdTe量子点旋涂在玻璃衬底上制备了Au纳米颗粒和CdTe量子点复合体系. 通过对镶嵌有Au纳米颗粒的衬底进行热退火处理来控制Au纳米颗粒的生长和分布, 系统研究了Au纳米颗粒的局域表面等离子体共振对CdTe量子点光致发光性能的影响. 利用光学吸收谱、原子力显微镜、透射电子显微镜和光致发光谱对样品进行了表征和测试. 光致发光谱表明, Au纳米颗粒的局域表面等离子体对CdTe量子点的发光有增强效应也有猝灭效应. 深入分析了Au纳米颗粒和CdTe量子点之间的相互作用过程, 提出了关于Au-CdTe 纳米复合体系中CdTe 发光增强和猝灭的新机理. 该实验结果为利用金属纳米颗粒表面等离子体技术制备高发光性能的光电子器件提供了较好的参考.     

Initial study on the structure and photoluminescence properties of SiC films doped with Al

SiC films doped with aluminum (Al) were prepared by the rf-magnetron sputtering technique on p-Si substrates with a composite target of a single crystalline SiC containing several Al pieces on the surface. The as-deposited films were annealed in the temperature range of 400-800 °C under nitrogen ambient. The thin films have been characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The results show that the introduction of Al into films hinders crystalline formation process. And with the increase of annealing temperature, more Si particles are formed in the films, which strongly affect the optical absorption properties. The photoluminescence (PL) spectra of the samples show two peaks at 370 nm and 412 nm. The intensities of the PL peaks are evidently improved after Al doped. We attribute the origin of the two PL peaks to a kind of Si-related defect centres. The obtained results are expected to have important applications in modern optoelectronic devices.     

In插入层对硅衬底外延InN晶体质量和光学特性的影响

在Si（111）衬底上分别预沉积0,0.1,0.5,1 nm厚度的In插入层后,采用等离子辅助分子束外延法制备了纤锌矿结构的InN材料,结合X射线衍射（XRD）、扫描电子显微镜（SEM）、吸收谱及光致发光谱研究了不同厚度的In插入层对外延InN晶体质量和光学特性的影响。XRD和SEM的测试结果表明,在Si衬底上预沉积0.5 nm厚的In插入层有利于改善外延InN材料的形貌,提高材料的晶体质量。吸收谱和光致发光谱测试表明,0.5 nm厚In插入层对应的InN样品吸收边蓝移程度最小,光致发射谱半峰宽最窄,并且有最高的带边辐射复合发光效率。可见,引入适当厚度的InN插入层可以改善Si衬底上外延InN材料的晶体质量和光学特性。     

Influence of Al doping on microstructure,morphology, optical and photoluminescence properties of pyrolytic ZnO thin films prepared in an ambient atmosphere

Zinc oxide (ZnO) and aluminium (Al) doped zinc oxide (AZO) thin films have been fabricated by spray pyrolysis technique in normal atmospheric condition. Samples of different Al-concentrations (0–5% Al) were deposited at 350 °C onto glass substrate to study the structural, morphological, optical and photoluminescence properties. X-ray diffraction study confirms that the films are polycrystalline having hexagonal structure. SEM images show that the films have rope and tube like morphology. Optical properties, such as transmittance, optical band gap, extinction coefficient, refractive index, optical conductivity, dielectric constants and electron energy loss functions were analyzed and discussed. Results show that the optical parameters have been changed significantly with Al-doping concentration. The photoluminescence spectra indicate that the PL peaks originated from deep level emissions (DLE) with different intensities for ZnO and Al-doped ZnO films.     

MOVPE 生长GaN薄膜的 光致黄带发光与激发光源的相关性

用四种不同光源作为激发光源,研究了蓝宝石衬底金属有机物汽相外延方法生长的氮化镓薄膜的光致发光特性。结果发现用连续光作为激发光源时,光致发光谱中除出现365 nm的带边发射峰外,同时观察到中心波长位于约550 nm 的较宽黄带发光;而用脉冲光作为激发光源时其发光光谱主要是365 nm附近的带边发光峰,未观察到黄带发光。氮化镓薄膜的光致发光特性依赖于所用的激发光源性质。     

LiGaO2衬底上ZnO外延膜的结构与光学特性

采用磁控溅射法在(001),(100)及(010)LiGaO2衬底上制备了ZnO薄膜,通过X射线衍射(XRD)、原子力显微镜(AFM)、透过光谱以及光致发光谱(PL)对薄膜的结构、形貌及光学性质进行了表征.结果表明LiGaO2衬底不同晶面上制备的ZnO薄膜具有不同的择优取向,在(001)、(100)及(010)LiGaO2上分别获得了[001]、[1100]及[1120]取向的ZnO薄膜;不同取向的ZnO薄膜表面形貌差异较大;薄膜在可见光波段具有较高的透过率;在ZnO薄膜的光致发光谱中只观察到了位于378 nm的紫外发射峰,而深能级发射几乎观察不到,(1100)取向的薄膜紫外发射峰强度最大,半高宽也最小,薄膜光致发光件质的差异丰要和晶粒尺寸有关.     

Optical properties investigation of [nc-Si:SiO2/SiO2]30 periodic multilayer films

The optical properties of 30-layer [nc-Si:SiO₂/SiO₂]₃₀ periodic films have been studied. The films were prepared by alternately evaporating SiO and SiO₂ onto Si(100) substrates, followed by annealing at 1100?^°C. Spectroscopic ellipsometry spectrum analysis was used to determine the optical constants of the samples via the Forouhi?CBloomer model. The optical bandgap of a single periodic film is calculated. The photoluminescence (PL) spectra of three samples with different thicknesses clearly show that there are two physical origins of the PL process.     

Preparation and characterization of Mg-doped ZnO thin films by sol-gel method

Undoped and Mg-doped ZnO thin films were deposited on Si(1 0 0) and quartz substrates by the sol-gel method. The thin films were annealed at 873 K for 60 min. Microstructure, surface topography and optical properties of the thin films have been measured by X-ray diffraction (XRD), atomic force microscope (AFM), UV-vis spectrophotometer, and fluorophotometer (FL), respectively. The XRD results show that the polycrystalline with hexagonal wurtzite structure are observed for the ZnO thin film with Mg:Zn = 0.0, 0.02, and 0.04, while a secondary phase of MgO is evolved for the thin film with Mg:Zn = 0.08. The ZnO:Mg-2% thin film exhibits high c-axis preferred orientation. AFM studies reveal that rms roughness of the thin films changes from 7.89 nm to 16.9 nm with increasing Mg concentrations. PL spectra show that the UV-violet emission band around 386-402 nm and the blue emission peak about 460 nm are observed. The optical band gap calculated from absorption spectra and the resistivity of the ZnO thin films increase with increasing Mg concentration. In addition, the effects of Mg concentrations on microstructure, surface topography, PL spectra and electrical properties are discussed.     

有机电致发光器件中Rubrene掺杂剂的荧光光谱性质

通过改变黄色荧光染料5,6,11,12-tetraphenylnaphthacene(Rubrene)的溶液浓度,研究了溶液的浓度改变对荧光小分子染料的发光光谱的影响.采用测试不同浓度Rubrene溶液光致发光(PL)的光谱强度手段,确定了溶液中染料的最佳浓度,即最大程度避免或减弱浓度效应(浓度猝灭)且光致发光强度最大时的溶液浓度.首先确定极限浓度的范围,然后通过测试范围内的不同浓度的PL光谱强度判断精确的极限浓度位置.结果表明,在Rubrene浓度为2×10-3 mol·L-1时,PL光谱强度最大,并且随着溶液浓度的继续增加,PL光谱强度的降低仅为11%,进而确定Rubrene分子的极限浓度应该在2×10-3 mol.L-1左右.通过对比不同掺杂比例的Rubrene:N,N'-Bis(naphthalen-l-y)-N,N'-bis(phenyl)benzidine(NPB)在溶液中的混合体系的PL光谱发现,NPB与Rubrene分子之间存在小完全的能鞋传递过程,有利于实现NPB分子和Rubrene分子共同的蓝光和黄光发射,从而得到色纯度较高的白色荧光.     

The structure and photoluminescence properties of Cr-doped SiC films

Cr-doped SiC films are prepared by the RF-magnetron sputtering technique on Si substrates with a composite target of a single-crystalline SiC containing several Cr pieces on the surface. The as-deposited films are annealed in the temperature of 1000 °C under nitrogen ambient. The structure of the samples has been characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and Raman scattering measurement. The results show that the SiC crystal is formed and that majority of Cr doped in the SiC resulted in the formation of the C clusters. Then the photoluminescence (PL) spectra of the samples are observed in the visible range at room temperature. The optical properties of the samples have also been discussed briefly. We attribute the origin of the 412-nm PL band to a kind of C cluster center.     

Effect of Fe-doping on the structural,morphological and optical properties of ZnO nanoparticles synthesized by solution combustion process

The effect of Fe-doping on the structural, morphological and optical properties of ZnO nanoparticles synthesized by simple solution combustion process are reported. The powder XRD pattern indicates that the Fe-doped ZnO samples exhibit primary and secondary phases. The primary phase indicates the hexagonal wurtzite structure with the average crystalline size of around 25–50 nm and the secondary phase is associated with the face centered cubic structure of magnetite iron oxide. The elemental composition of pure and Fe-doped samples are evaluvated by EDX. The results of FE-SEM and HR-TEM cleary show that particles morphology have changed with respect to the incorporation of doping agent and particles are in aggregating nature. The vibrational properties of the synthesized ZnO nanoparticles are investigated by Raman scattering technique and it exhibits that the influence of Fe-doping significantly modify the lattice vibrational characteristics in ZnO sites. The optical properties of the Fe-doped ZnO nanoparticles are carried out by UV–vis absorption and PL spectra. The results of PL spectra show the near-band edge related emission as well as strong blue emissions in the Fe-doped ZnO nanoparticles.     

溶液法制备PVP为界面修饰层的红荧烯结晶性薄膜

为了获得低成本、高结晶度的红荧烯薄膜,采用溶液加工的方法和聚合物界面修饰层研究了红荧烯薄膜的性质。首先,通过旋涂方法在Si/SiO₂衬底上先沉积一层聚乙烯吡咯烷酮（PVP）作为界面修饰层,利用偏光显微镜（POM）、原子力显微镜（AFM）研究了PVP层表面形貌及粗糙度。接着在PVP上滴涂红荧烯溶液后固化烘干,制备红荧烯晶体薄膜,研究了不同PVP浓度和不同成膜温度下界面修饰层对红荧烯表面形貌的影响。然后,利用X射线衍射（XRD）表征对比研究了薄膜的微观结构。最后,分析了红荧烯晶体薄膜的生长机制。实验结果表明：80~140℃及低浓度的PVP条件下能得到结晶度高、连续的红荧烯球晶,并且温度升高时,球晶尺寸变大。PVP作为界面修饰层有利于改善红荧烯的成膜性,制备高结晶度的晶体薄膜。     

The optical properties and energy transition process in nanocomposite of polyvinyl-pyrrolidone polymer and Mn-doped ZnS

This study has been carried out on the optical properties of polyvinyl-pyrrolidone (PVP), the energy transition process in nanocomposite of PVP capped ZnS:Mn nanocrystalline and the influence of the PVP concentration on the optical properties of the PVP capped ZnS:Mn nanocrystalline thin films synthesized by the wet chemical method. The microstructures of the samples were investigated by X-ray diffraction, the atomic absorption spectroscopy, and transmission electron microscopy. The results showed that the prepared samples belonged to the sphalerite structure with the average particle size of about 2–3 nm. The optical properties of samples are studied by measuring absorption, photoluminescence (PL) spectra and time-resolved PL spectra in the wavelength range from 200 to 700 nm at 300 K. From data of the absorption spectra, the absorption edge of PVP polymer was found about of 230 nm. The absorption edge of PVP capped ZnS:Mn nanoparticles shifted from 322 to 305 nm when the PVP concentration increases. The luminescence spectra of PVP showed a blue emission with peak maximum at 394 nm. The luminescence spectra of ZnS:Mn–PVP exhibits a blue emission with peak maximum at 437 nm and an orange–yellow emission of ion Mn²⁺ with peak maximum at 600 nm. While the PVP coating did not affect the microstructure of ZnS:Mn nanomaterial, the PL spectra of the PVP capped ZnS:Mn samples were found to be affected strongly by the PVP concentration.     

Photoluminescence and optical absorption properties of silicon quantum dots embedded in Si-rich silicon nitride matrices

Silicon nitride (SiN_x) films were prepared with a gas mixture of SiH₄ and NH₃ on Si wafers using the plasma-enhanced chemical vapor deposition (PECVD) method. High-resolution transmission electron microscopy and infrared absorption have been used to reveal the existence of the Si quantum dots (Si QDs) and to determine the chemical composition of the silicon nitride layers. The optical properties of these structures were studied by photoluminescence (PL) spectroscopy and indicate that emission mechanisms are dominated by confined excitons within Si QDs. The peak position of PL could be controlled in the wavelength range from 1.5 to 2.2 eV by adjusting the flow rates of ammonia and silane gases. Absorbance spectra obtained in the transmission mode reveal optical absorption from Si QDs, which is in good correlation with PL properties. These results have implications for future nanomaterial deposition controlling and device applications.