不同激发波长下多壁碳纳米管光致发光特性

用化学气相沉积法(CVD)制备了多壁碳纳米管(MWNTs),并用扫描电镜(SEM)测量了纳米管的形貌。在室温条件下,测量了样品的拉曼光谱和吸收光谱:拉曼光谱表明样品含有较多缺陷,吸收光谱说明了该样品有光致发光的通道。测量了在不同波长光的激发下样品的光致发光光谱:当用550 nm的光激发多壁碳纳米管时,观察到峰值强度弱、峰值波长约为820 nm的带状光谱;当激发波长增加到580 nm时,发射光谱变为峰值波长约为868 nm、峰值强度较强、形状相似的光谱;当激发光波长增加到600 nm时,观察到峰值强度强、峰值波长约为900 nm的带状光谱。     

大气压液体阴极等离子体中O原子和OH自由基的特性

为更好地理解液体阴极放电等离子体的性质,建立了一种基于液体阴极放电的大气压等离子体的发生装置。测量了200~900 nm光谱范围内的发射光谱,观察到了强度较高的波长为656.8 nm的Hα谱线、波长在309 nm附近的OH(A-X)谱带、在337 nm附近的N2(C-B)谱带,以及强度较弱的波长为777.2 nm和844.6 nm的O原子谱线。并对这些激发物种的激发过程进行了说明,分析了等离子体光谱中含氧活性粒子(OH和O)的空间分布,计算了放电空间中不同位置的电子激发温度。研究表明,含氧活性粒子数目在液体阴极和金属阳极附近均有1个峰值;单一O谱线的2个峰值强度和单一峰值的2条O谱线的谱线强度均呈现交替变化的现象;OH谱线的谱线强度远大于2条O谱线,2者最大值相差2个数量级;靠近阴极区区域的电子激发温度较低,而正柱区区域的电子激发温度较高。     

缺陷对多壁碳纳米管光致发光特性的影响

采用化学气相沉积法,在反应温度分别为980℃和1040℃时制备了多壁碳纳米管（MWNTs）样品,并采用扫描电镜和拉曼光谱对样品进行了表征;结果表明,当反应温度为9800C时,制备的碳纳米管结构缺陷更多。使用波长为350nm的光激发2种样品并测量它们的光致发光光谱。发射峰值约在550nm处,反应温度为980℃时制备的碳纳米管的发射光谱的光强较强。     

蓝粉光谱特征对三基色荧光灯光色影响的色度学模拟计算

用计算机模拟的方法计算分析了三基色荧光灯中蓝色荧光粉光谱位置和带宽变化对三基色荧光灯光效和显色指数的影响。计算结果表明 :当蓝粉的峰值波长为 4 5 5nm时 ,三基色荧光灯的发光效率为最大 ,而峰值波长为 4 70nm时 ,其荧光灯的显色指数为最佳。综合两者考虑 ,要得到高效率和高显色性的三基色荧光灯 ,蓝色荧光粉发光峰的峰值波长应处在 4 5 5～ 4 70nm之间。当蓝色荧光粉发光峰强度和带宽不变 ,峰值波长从 4 5 5nm向长波移动 ,虽然蓝粉本身的亮度在增加 ,而模拟的三基色荧光灯光效却有所下降 ,但显色指数有一定的提高。蓝粉带宽的增加不利于荧光灯总亮度的提高 ,但对显色指数的提高有帮助。总之 ,若蓝粉的发光峰峰值波长已处在 4 5 5nm附近 ,提高三基色荧光灯光效的根本途径是提高蓝粉的量子效率 ,而不是移动其发光峰位置。     

电晕放电中光谱特性的分析及实验程序设计

为了解电晕放电中光的光谱特性和通过光辐射光谱的测量分析电晕放电的规律,介绍了利用光栅单色仪、锁相放大器等设备检测交流电晕放电光谱特性的实现方法和软件设计并分析了光谱特性。所测光谱范围190.0～900.0nm,光谱峰值波长集中在200.0～400.0nm,主要有297.9、316.8、338.0、367.8、380.0nm等,属紫外光谱,分析得出特征波长上光谱峰值的大小可作为判断电晕放电强度的参考量,工程上可利用200.0～320.0nm波段内紫外光避开日光紫外线对电晕放电紫外线的干扰。     

基于ZnO/Graphene纳米复合材料紫外光探测器的制备与实现

利用化学气相沉积法制备氧化锌（ZnO）纳米线,通过微加工工艺获得了基于 ZnO 纳米线与ZnO石墨烯量子点纳米复合材料的紫外光探测器。ZnO 石墨烯纳米复合材料的结构和表面形貌通过 X 射线电子衍射和扫描电镜来表征,结果表明,ZnO 纳米线的直径约为33 nm,与石墨烯量子点很好地复合在了一起。利用紫外可见吸收谱对样品的光吸收进行了记录,实验表明,基于ZnO复合石墨烯量子点纳米复合材料的紫外探测器在 UV 照射下显示出良好的光响应行为,该类型基于ZnO复合石墨烯量子点探测器可能在ZnO紫外探测的应用方面具有潜在的意义。     

基于瞳孔光响应的光谱灵敏度模型研究初探

本文综述了现有的非视觉生物效应光谱灵敏度研究,设计了一套新的实验装置和流程研究瞳孔光响应。根据稳定瞳孔收缩率和最大瞳孔收缩率数据,基于数据拟合和归一化处理,获得了两个基于瞳孔光响应的光谱灵敏度曲线,其峰值波长分别为482.8 nm和495.6 nm,对应的曲线半峰值宽度为95.1 nm和62.9 nm。     

白光与钠光的对比

1　前言当由黄昏转向夜晚 ,照明等级的降低使人眼的视网膜在响应不同波长的光线时发生变化。光谱 ,或称色彩 ,当照明等级较高时 ,人眼响应的峰值为 5 5 5nm ,在黄色区域。这可由图 1中的实线表示 ,记作V(λ)。在计算灯的流量输出时 ,使用该人眼光谱响应曲线对钠灯光源特别有利 ,这是因为高压钠灯输出的主要光谱落入了接近人眼峰值的感应区域 ,使钠灯光源具有较高的流明输出。图 1　明视光V(λ)曲线 (实线 )及暗视光曲线V′(λ) (虚线 )　 然而 ,在照明等级较低时 ,典型情况为照度低于3cd m2 时 ,人眼所响应的光谱改变了。视网膜灵敏度相对…     

LED峰值波长对多光谱组合白光色参数的影响

多光谱组合的LED在动态照明、光环境、医疗、健康等领域具有广泛的应用前景,但是其光度和色度的一致性和稳定性极大影响着这类技术方案的应用前景。采用6种单色LED使用光谱组合的方式构建了典型色温5500 K和2700 K的白光器件,并对组成白光的单色LED的光谱稳定性进行了分析,仿真实验研究了多种单色LED峰值波长的漂移对色温、显色指数和色坐标的影响。实验表明,红色630 nm和橙色590 nm附近的峰值波长漂移对于色温的影响最大,漂移2 nm左右即可导致色温100 K左右的变化;橙色590 nm的峰值波长漂移对于显色指数的影响最大,在漂移2 nm左右即可导致显色指数的变化大于2;在5500 K附近x坐标的最大变化量0.016出现在红光631 nm的波长变化中,y坐标的最大变化量0.015出现在宝蓝色480 nm的波长变化中;在2700 K附近,x坐标的最大变化量0.016出现在橙色590 nm和红色631 nm的波长变化中,y坐标的最大变化量0.017出现在橙色590 nm的波长变化中。     

黄疸光疗仪LED光源光学参数的动态可调研究

为进一步增强新生儿黄疸光疗仪LED光源降解胆红素的效果,设计了一种能够实现多通道控制的黄疸光疗仪LED驱动电路,对四种不同峰值波长的单色LED灯进行独立脉宽调制调光(PWM调光),达到光照度可调、光谱可调的目的。提出以MAX16823驱动芯片及NE555定时器为核心元件组成的脉宽调制LED驱动电路,并分析了PWM调光的优势,通过Multisim10对该驱动电路进行仿真确保方案的可行性,再制作电路板驱动新生儿黄疸光疗仪LED光源,在距离光源中心55 cm处测量不同占空比下光照度和光谱变化。实验结果表明四种不同峰值波长的单色LED光照度调节范围分别为0~35 lx、0~61 lx、0~215 lx、0~337 lx,且在四种峰值波长单色LED同时发光的情况下,峰值波长变化范围在20 nm左右,半高宽变化范围在50 nm左右。     

Light Emission From Silicon in Photonic Crystal Nanocavity

We have introduced a photonic crystal into a single-crystal silicon slab in order to manipulate the light emission. When the lattice constant of a defect-free photonic crystal matches the wavelength of light in the medium, the light emitted from the silicon is resonantly extracted at the photonic band edge within the escape light cone. When the lattice constant is larger than the wavelength, Brillouin zone folding of the photonic band also allows the light to be extracted; we achieved an intensity that was enhanced by a factor of ~ 20 due to the diffraction of internal light into the light cone. We have also created a point defect in photonic crystals with smaller lattice constants that functions as a nanocavity and strongly interacts with the silicon emitter. Four cavity modes were observed, with different Q -factors and emission patterns. The mode orders were assigned using the resonant wavelengths and polarizations. The observed emission at room temperature was enhanced by a factor of ~ 30 in comparison to that of an unprocessed area of silicon-on-insulator. Our study demonstrates that employing a photonic crystal nanocavity in silicon can greatly improve the light extraction efficiency, the characteristics of the radiation pattern, and the internal quantum efficiency.     

Investigating up-conversion fluorescence of Phloxine B

The steady-state and time-resolved emission of Phloxine B was examined when excited with 90 fs pulses from a mode-locked Ti:sapphire laser. Above the excitation wavelength (775 nm), Phloxine B was found to display two-photon excitation fluorescence with estimated cross-section for excitation of 0.87×10^-49 cm⁴ s/photon, and fluorescence spectrum consistent with one-photon excitation. Over the excitation wavelength range from 590 to 650 nm, Phloxine B was found to display one-photon excitation up-conversion fluorescence. The up-conversion fluorescence of Phloxine B was confirmed by frequency-domain measurements. The intensity decays revealed different double-exponential intensity decays for one-photon excitation at 390 nm and 633 nm. The longer fluorescence lifetimes were observed with 633 nm excitation. Hence, anti-Stokes excitation of Phloxine B causes delay emission at shorter wavelengths. Time-resolved anisotropy decay measurements revealed similar correlation times, but different amplitudes, as has been observed previously for two- versus one-photon excitation     

Synthesis and Luminescence Properties of Eu3+ Doped Sr2SiO4 Phosphor

Abstract

The europium doped Sr₂SiO₄ phosphors were prepared by the combustion synthesis technique. The prepared samples of europium doped Sr₂SiO₄ phosphors were characterized by the X-Ray Diffraction (XRD), Ultraviolet Visible spectroscopy (UV), Fourier Transform Infrared Spectroscopy (FT-IR), Field Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive Spectra (EDS) and Photoluminescence Technique (PL). The orthorhombic crystal structure of the prepared sample was confirmed by using XRD. The formation of fiber like nano structured nature was confirmed by the images captured using the FE-SEM technique. The band gap energies were calculated using the UV-Visible spectra of the samples and these band gap energies were observed as 4.5826?eV for Sr₂SiO₄ and 4.1748?eV for Eu (5?m%) doped Sr₂SiO₄. The two different PL emission peaks were observed for two different excitation wavelengths. One peak was observed at the 590?nm under 393?nm excitation and another peak was observed at the 615?nm under 408?nm excitation. The CIE color coordinates of the Eu³⁺ doped Sr₂SiO₄ phosphors are x?≈?0.6615, y?≈?0.3382 (red color) observed for 408?nm excitation and x?≈?0.5636, y?≈?0.4356 (orange) observed for 393?nm excitation calculated using the color calculator program radiant imaging.     

Synthesis and luminescence of ceria decorated graphene quantum dots (GQDs): Evolution of band gap

ABSTRACT

Graphene quantum dots (GQDs) and CeO₂-GQDs were synthesized by using a facile hydrothermal method at 140°C. All the synthesized materials were characterized by TEM, UV-Vis Spectroscopy, FT-IR, Raman Spectroscopy and PL. Ceria decorated GQDs show different emission peaks with different excitation of wavelengths. The discrete change in dominant luminescence features of the GQDs and their composites indicate that the variation in PL occurs because of alteration in its shape, size and bandgap. Based on the experimental results of PL peak wavelength, the emission is attributed to quasi-molecular PL from the fragments composed of a few aromatic rings with oxygen containing functional groups.     

Visible Light Emission From Dye Molecular Grains via Infrared Excitation Based on the Nonadiabatic Transition Induced by the Optical Near Field

We observed light emission in the visible wavelength range (lambda = 600-690 nm) from aggregated 4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM) dye molecule grains excited by infrared light (lambda_ex = 805 nm). The domains of visible light emission were localized at the surface and edges of the dye grains, where the optical near field was strengthened. The emitted visible light intensity decayed exponentially according to the time constants tau₁ = 0.45 ns and tau² = 1.37 ns, which were equivalent to those of conventional fluorescence excited by visible light at lambda_ex = 402 nm. The emitted light intensity increased with the infrared excitation intensity, in agreement with the theoretical results of the exciton-phonon polariton model. This confirmed that the visible light emission originated from the nonadiabatic transition process due to optical near-field features. The frequency upconversion efficiency for excitation from infrared (lambda_ex = 805 nm) to visible (lambda = 600-690 nm) in the film of the DCM molecular grains was experimentally estimated to be higher than that of the second harmonic generation (SHG) from a potassium dihydrogen phosphate (KDP) crystal. In particular, it was higher when the fundamental light power density was lower than 100 W/cm². Visible light emission from the grains of the rhodamine 6G (N-{2-[2-(2-aminoethoxy)ethoxy]ethyl} rhodamine 6G-amide bis[trifluoroacetate]) dye molecule was also observed in the infrared light (lambda_ex = 805 nm). Our results demonstrated the universality of the nonadiabatic transition process.     

Efficient superfluorescent light sources with broad bandwidth

We demonstrate various efficient broad band light sources at ~1-μm wavelength with a 3-dB bandwidth of up to 65 nm at 108-mW output power, based on rare-earth doped silica fibers and a simple adjustable spectral filter     

Growth of InGaN self-assembled quantum dots and their applicationto lasers

We have successfully grown InGaN self assembled quantum dots (QD's) on a GaN layer, using atmospheric-pressure metalorganic chemical vapor deposition (MOCVD). The average diameter of the QD's was as small as 8.4 nm, and strong emission from the QD's was observed at room temperature. Next, we have investigated a structure in which InGaN QD's were stacked to increase the total QD density. InGaN QD's were formed even when the number of stacked layers was ten. As the number of layers increased, the photoluminescence (PL) intensity increased drastically. Moreover, we have fabricated a laser structure with InGaN QD's embedded into the active layer. A clear threshold of 6.0 mJ/cm² was observed in the dependence of the emission intensity on the excitation energy at room temperature under optical excitation. Above the threshold, the emission was strongly polarized in the transverse electric (TE) mode, and the linewidth of the emission spectra was reduced to below 0.1 nm (resolution limit). The peak wavelength was around 405 nm. These results indicate lasing action at room temperature     

Photoluminescence in Polyamide/mica and Polyethylene/ MgO Nanocomposites Induced by Ultraviolet Photons

Nature of electronic states in the energy band is investigated by means of optical absorption and photoluminescence induced by vacuum ultraviolet photons for polyamide-6/mica and low-density polyethylene/MgO nanocomposites. The nanofiller loading does not affect the absorption spectra of polyamide samples. Contrary to this, two absorption bands are induced at around 5.0 and 6.2 eV by the nanofiller loading in polyethylene samples, but they are due to absorption by the fillers. A luminescence band is observed at around 3.0 eV in polyamide samples, whereas three luminescence bands are observed at around 4.3, 3.7, and 2.9 eV in polyethylene samples. However, for all the luminescence bands, neither emission nor excitation energies change by the addition of nanofillers. Decay profiles of all the luminescence bands are essentially unchanged by the nanofiller loading. Moreover, no new PL bands are induced in the observed wavelength range. These results indicate that localized states, at least as far as the ones that can emit luminescence photons with intensities more than the sensitivity of the present research, are not induced by the nanofiller loading.     

Spectroscopic imaging and the characterization of the autofluorescence properties of human bronchus tissues using UV laser diodes

Ultraviolet laser diodes (UV-LD) were used for the excitation source of autofluorescence (AF) measurements and spectroscopic imaging of the AF originating from the human bronchus was obtained. The AF spectra from normal bronchus tissues were measured and a clear AF spectrum was obtained by using a short wavelength (400 nm) laser diode; the overlap of the AF signal and excitation source could be substantially eliminated. In order to study the origin of AF intensity deterioration from bronchus tissue due to the formation of tumor tissues, the fluorescence spectrum was measured for various AF substances under various conditions. The blue AF signal of elastin and NADH solutions, which could not be easily studied by conventional excitation light sources, as well as the green AF became weak by adding lactic acid. The AF spectrum was measured for 512/spl times/512 pixels and the intensity mapping as a function of emission wavelength was obtained. Two-dimensional information of the AF signal intensity distribution for a certain wavelength component was measured. The feature originating from a region as small as about 100 /spl mu/m could be recognized. Numerical calculations of the data were performed and precise features of the AF were revealed.