近紫外非相干宽带腔增强吸收光谱应用于Cl原子启动的光化学反应过程中OClO及CH2O的探 (cited: 3)

OClO是Cl原子活性的一个重要的指示剂,对OClO的检测有利于更好的理解Cl原子的化学反应过程及其对沿海及工业污染地区空气质量的影响. 本工作建立了一套基于氙灯的近紫外(335～375 nm)非相干宽带腔增强吸收光谱系统,并将其应用于烟雾箱中OClO的定量测量研究,同时测量了反应过程中重要的中间产物CH₂O及大气中重要的痕量气体NO₂. 结果表明,非相干宽带腔增强吸收光谱可应用于实验室大气卤素化学方面的研究.     

Spectral studies on erbium doped potassium lithium tantalate niobate single crystal grown by the step-cooling technique

An erbium doped K_0.603Li_0.397Ta_0.428Nb_0.572O₃ single crystal was grown by the step-cooling technique. The crystal has a tetragonal tungsten bronze-type structure at room temperature with a Curie temperature of 303°C. There are Er ions characteristic absorption bands around 449, 485, 521, 550, and 652 nm in the visible absorption spectrum. Upconversion fluorescence spectra and power dependence centered at 527 nm, 548 nm, and 660 nm under 975 nm excitation were measured at room temperature. Decay lifetimes of the 548 nm and 660 nm emission bands are 281 μs and 420 μs, respectively. The lifetime of the 548 nm emission corresponding to the transition of ?⁴ S _3/2→⁴ I _15/2 is ten times the lifetime of the same transition of Er³⁺ in LiNbO₃ crystal and twice in KYb(WO₄)₂ crystal. The crystal might become a promising upconversion laser material. The upconversion mechanism of Er³⁺ in the sample was discussed based on decay curves and pump power dependence analyses in this work.     

Optical Analysis of Er3+:Boro-Fluoro-Phosphate Glasses

This paper deals with the preparation and optical analysis of Er³⁺ (0.2 mol%) boro-fluoro-phosphate glasses in the following glass compositions:

• Series A: 69.8 B₂O₃–10 P₂O₅–10(ZnO/CdO/TeO₂)–10 AlF₃

• Series B: 69.8 B₂O₃–10 P₂O₅–10(ZnO/CdO/TeO₂)–10 LiF

Measured Vis-NIR absorption spectra of Er³⁺:boro-fluoro-phosphate glasses have revealed nine absorption bands at 377 nm, 405 nm, 450 nm, 486 nm, 519 nm, 543 nm, 649 nm, 973 nm and 1529 nm, which correspond with the transitions of ⁴I_15/2 → ⁴G_11/2, (²G_9/2,⁴H_9/2), ⁴F_5/2, ⁴F_7/2, ²H_11/2, ⁴S_3/2, ⁴F_9/2, ⁴I_11/2, and ⁴I_13/2, respectively. With an excitation at λ _exci = 375 nm, a bright green emission (⁴S_3/2 → ⁴I_15/2) at 547 nm has been observed from these erbium glasses. Judd–Ofelt characteristic intensity Ω_λ (λ = 2, 4, 6) parameters are obtained from the absorption spectra, and these results were used to compute the radiative properties of Er³⁺:boro-fluoro-phosphate glasses. The NIR emission (⁴I_13/2 → ⁴I_15/2) at 1547 nm from these glasses was measured with an Ar⁺ laser (514.5 nm) as an excitation source.     

An investigation on the variations in properties of Ni+ irradiated ZnO thin films

ZnO thin films, irradiated by 80 MeV Ni⁺ ions, were analysed with the help of different characterization techniques like X-ray diffraction, optical absorption, transmission, photoluminescence (PL), electrical resistivity, photosensitivity (PS) and thermally stimulated current (TSC) measurements. Crystallinity and absorption edge were hardly affected by irradiation. PL spectrum of pristine sample showed a broad peak at 517 nm, whereas irradiated film had two emissions at 517 and 590 nm. Intensity ratio between these two emissions (I₅₁₇/I₅₉₀) decreased with the fluence, and finally at a fluence of 3×10¹³ ions/cm², the emission at 517 nm completely disappeared. Electrical resistivity of the sample irradiated with a fluence of 1×10¹³ ions/cm² drastically increased. However, on increasing the fluence to 3×10¹³ ions/cm², resistivity decreased, probably due the onset of hopping conduction through defects. PS also decreased due to irradiation. TSC measurements on pristine sample could reveal only one defect level at 0.6 eV, due to interstitia1 zinc (Zn_I). But, irradiation at a fluence of 1×10¹² ions/cm², resulted in three different defect levels as per TSC studies. Interestingly, the sample irradiated at a fluence of 3×10¹³ ions/cm² had only one defect level corresponding to a deep donor. The possible origin of these defect levels is also discussed in the paper.     

Structural and Upconversion Studies of Er3+ Codoped with CdS Nanoparticles in Sol-Gel Glasses

The Er³⁺ codoped with CdS nanoparticles in sol-gel glass with an average particle size of about 10 nm have been synthesized by sol-gel method. The green and red up-conversion emissions centered at about 534, 560 and 680 nm, corresponding to the ²H_11/2→⁴I_15/2, ⁴S_3/2→⁴I_15/2 and ⁴F_9/2→⁴I_15/2 transitions of Er³⁺, respectively; were detected by a 800 nm excitation. The two-photon absorption process is involved in the green and red up-conversion emissions.     

Spectroscopic characterisation of Er-doped LuVO4 single crystals

The LuVO₄:Er single crystals were grown by the Czochralski technique. The crystal-field split energy levels of Er³⁺ ion were derived experimentally employing absorption and emission spectra measured at T=10 K. The Judd–Ofelt phenomenological method was used to estimate intensity parameters, radiative lifetimes and branching ratios of luminescence. The excited state dynamics of the LuVO₄:Er systems was investigated and experimental lifetimes of emitting levels were measured. The emission cross section of the ⁴I_13/2→⁴I_15/2 transition in the infrared was calculated by the Füchtbauer–Ladenburg method. The gain cross section, estimated for several inverse-population parameters, allowed us to evaluate a potential laser activity of the LuVO₄:Er system at 1.6 μm. Also, the potential range of the optical pumping was assessed based on absorption spectra achieved at the room temperature. The optical losses related to the green up-converted emission, encountered under the 978 nm excitation between 300 and 670 K were indicated and discussed. Spectroscopic peculiarities of the Er³⁺-doped LuVO₄ crystal were discussed in relation to optical properties of the YVO₄:Er and GdVO₄:Er crystals. Taking into account the high quantum efficiency of the ⁴I_13/2 level, and satisfactory absorption and emission features, the LuVO₄:Er crystal can be considered as a promising active material for laser operation near 1.6 μm.     

Picosecond nonlinearity of GeO2–Bi2O3–PbO–TiO2 glasses at 532 and 1,064 nm

The third-order optical properties of GeO₂–Bi₂O₃–PbO–TiO₂ glasses at 532 nm and 1,064 nm were studied to evaluate their potential for optical limiting and all-optical switching. The Z-scan technique was used to determine the nonlinear (NL) refractive index, n ₂, and the NL absorption coefficient, α ₂, of samples with different amounts of the constituent oxides. Values of n ₂ ≈ + 0.7 × 10^?14 cm²/W at 1,064 nm and ≈+1.5 × 10^?14 cm²/W at 532 nm were measured. The NL absorption coefficient, α ₂, was smaller than the minimum that our apparatus can measure (α ₂ < 0.01 cm/GW) in the near-infrared (1,064 nm); in the visible region (532 nm), we obtained α ₂ ≈ 4.4 cm/GW. The set of NL parameters measured indicates the potential usefulness of the GeO₂–Bi₂O₃–PbO–TiO₂ glasses for all-optical switching at 1,064 nm and for optical limiting at 532 nm.     

Mössbauer and XRD study of pulse plated Fe–P and Fe–Ni thin layers

⁵⁷Fe conversion electron Mössbauer spectroscopy, X-ray diffraction, electrochemical and magnetic measurements were used to study pulse electroplated Fe–P and Ni–Fe coatings. XRD and ⁵⁷Fe CEMS measurements revealed the amorphous character of the novel pulse plated Fe–P alloys. CEM spectra indicated significant differences in the short range order and in the magnetic anisotropy between the Fe–P deposits pulse plated at medium long deposition time (t _on?=?2 ms), with short relaxation time (t _off?=?9 ms) and low current density (I _p?=?0.05 Acm^?2) or at short deposition time (t _on?=?1 ms) with long relaxation time (t _off?=?250 ms) and high current density (I _p?=?1.0 Acm^?2). The broad peaks centred around the fcc reflections in XRD of the pulse plated Ni-22 wt.% Fe deposit reflected a microcrystalline Ni–Fe alloy with a very fine, 5–8 nm, grain size. The CEM spectrum of the pulse plated Ni-22 wt.% Fe coating corresponded to a highly disordered solid solution alloy containing a minute amount of ferrihydrite. Extreme favourable soft magnetic properties were observed with these Ni–Fe and Fe–P pulse plated thin layers.     

开放光路非相干宽带腔增强吸收光谱技术测量大气NO2

采用蓝色发光二极管(LED)作为非相干宽带腔增强吸收光谱技术(IBBCEAS)系统光源,测量了436～470nm波段内NO2样气的吸收,验证IBBCEAS的高探测灵敏度。通过氮气和氦气两者瑞利散射截面的差异标定了镜片在430～490nm波段内的反射率,并利用纯氧中氧气二聚体(O2-O2)在477nm处的吸收验证了镜片反射率标定的准确性。镜片反射率在461nm处最大且为0.99937,光学腔长度为73.5cm时的最大有效光程为1.17km。当光谱采集时间为20s时,NO2的探测灵敏度(1σ)达到了0.25×10-9。进行了开放光路下环境大气中NO2和O2-O2在454～486nm波段内的吸收测量,结果表明大气中气溶胶等颗粒物的Mie散射消光降低了IBBCEAS仪器的探测灵敏度(1.04×10-9)。大气中O2-O2的测量为IBBCEAS吸收光程的在线标定提供了一种可行的途径。     

Solvent and surfactant effect on the self-assembly and luminescence properties of ZrO2:Eu3+ nanoparticles

ZrO₂:Eu³⁺ nanocrystals ranging from 17 to 43 nm were prepared by the facile precipitation method with a hydrothermal process. The crystallite size was strongly influenced by the solvent composition and enhanced with the presence of surfactant. The use of ethanol combined with surfactant stabilizes 50 wt% of the monoclinic phase, while the use of water only results in 100 wt% tetragonal phase. 80% of nanobelts were obtained preparing the sample with ethanol and surfactant as a results of the self-assembly of nanoparticles. The photoluminescence emission peak centered at 606 nm dominates the emission band for nanobelts, while for nanoparticles it is dominated by a peak centered at 612 nm. Such differences were explained in terms of the site symmetry occupying Eu³⁺ in the host that in turn depends on the crystalline phase. Changes in the intensity ratio I(612 nm)/I(606 nm) is proposed as a tool to analyzing changes in the monoclinic/tetragonal phase composition. The calculated asymmetry ratio R=⁷F₂/⁷F₁～1.2 suggest a high degree of crystallinity of the prepared samples.     

A trace methane gas sensor using mid-infrared quantum cascaded laser at 7.5 μm

Presented is a compact instrument developed for in situ high-stable and sensitive continuous measurement of trace gases in air, with results shown for ambient methane (CH₄) concentration. This instrument takes advantage of recent technology in thermoelectrically cooled pulsed Fabry–Perot (FP) quantum cascaded (QC) laser driving in a pulse mode operating at 7.5 μm to monitor a well-isolated spectral line near the ν4 fundamental band of CH₄. A high-quality liquid nitrogen cooled mercury cadmium telluride mid-infrared detector with time discriminating electronics is used along with a total reflection coated gold ellipsoid mirror offering 20 cm single pass optical absorption in an open-path cell to achieve stability of 5.2 × 10^?3 under experimental condition of 200 ppm measured ambient CH₄. The instrument operates continuously, and integrated software for laser control using direct absorption provides quantitative trace gas measurements without calibration. One may substitute a QC laser operating at a different wavelength to measure other gases. The instrument can be applied to field measurements of gases of environmental concern.     

Quantitative Radar REMPI measurements of methyl radicals in flames at atmospheric pressure

Spatially resolved quantitative measurements of methyl radicals (CH₃) in CH₄/air flames at atmospheric pressure have been achieved using coherent microwave Rayleigh scattering from Resonance enhanced multi-photon ionization, Radar REMPI. Relative direct measurements of the methyl radicals were conducted by Radar REMPI via the two-photon resonance of the $ 3p^{2} A_{2}^{\prime \prime } 0_{0}^{0} $ state and subsequent one-photon ionization. Due to the proximity of the argon resonance state of 2s ²2p ⁵4f [7/2, J = 4](4+1 REMPI by 332.5 nm) with the CH₃ state of $ 3p^{2} A_{2}^{\prime \prime } 0_{0}^{0} $ (2+1 REMPI by 333.6 nm), in situ calibration with argon was performed to quantify the absolute concentration of CH₃. The REMPI cross sections of CH₃ and argon were calculated based on time-dependent quantum perturbation theory. The measured CH₃ concentration in CH₄/air flames was in good agreement with numerical simulations performed using detailed chemical kinetics. The Radar REMPI method has shown great flexibility for spatial scanning, large signal-to-noise ratio for measurements at atmospheric pressures, and significant potential to be straightforwardly generalized for the quantitative measurements of other radicals and intermediate species in practical and relevant combustion environments.     

Optical Spectroscopy of YPO4 Single Crystals Doped with Ho3+

ABSTRACT

Crystal field absorption and emission spectra originated by ⁵I₈ ? ⁵F₅ transitions, due to Ho³⁺ (1% molar fraction) in a YPO₄ single crystal, were investigated in the 15000 to 16000 cm^?1 range. Fourier Transform high resolution absorption measurements, performed in the 9 to 300 K range, and photoluminescence, monitored at 10 K upon 540 nm excitation, supplied the sublevel separations within both ⁵I₈ and ⁵F₅ manifolds. The sublevel positions were compared to those calculated by diagonalization of the full 4f-configuration matrix in the framework of a single-ion model. The results are discussed also in relation with experimental data previously reported for similar systems containing Ho³⁺.     

Multi-species laser absorption sensors for in situ monitoring of syngas composition

Tunable diode laser absorption spectroscopy sensors for detection of CO, CO₂, CH₄ and H₂O at elevated pressures in mixtures of synthesis gas (syngas: products of coal and/or biomass gasification) were developed and tested. Wavelength modulation spectroscopy (WMS) with 1f-normalized 2f detection was employed. Fiber-coupled DFB diode lasers operating at 2325, 2017, 2290 and 1352 nm were used for simultaneously measuring CO, CO₂, CH₄ and H₂O, respectively. Criteria for the selection of transitions were developed, and transitions were selected to optimize the signal and minimize interference from other species. For quantitative WMS measurements, the collision-broadening coefficients of the selected transitions were determined for collisions with possible syngas components, namely CO, CO₂, CH₄, H₂O, N₂ and H₂. Sample measurements were performed for each species in gas cells at a temperature of 25 °C up to pressures of 20 atm. To validate the sensor performance, the composition of synthetic syngas was determined by the absorption sensor and compared with the known values. A method of estimating the lower heating value and Wobbe index of the syngas mixture from these measurements was also demonstrated.     

A Novel Ratiometric Fluorescent Mercury Probe Based on Deprotonation-ICT Mechanism

A new NBD-rhodamine dye (1) was developed as a colorimetric and ratiometric fluorescent chemosensor for Hg²⁺ with good selectivity in aqueous ethanol solutions under neutral to basic conditions. Sensor 1 showed absorption at 468 nm and a weak emission at 529 nm (? _F ?=?0.063) in ethanol/aqueous tris buffer (9:1, v/v) of pH 9.17 solution. Bathochromic shifts in both absorption (492 nm) and fluorescence spectra (569 nm, ? _F ?=?0.129), respectively upon addition of 2 equiv. of Hg²⁺ were observed. The ring-opening reaction of the spirolactam form to the corresponding xanthene form was not found. The interaction of Hg²⁺ with chemosensor 1 resulted in the deprotonation of the secondary amine conjugated to the NBD component so that the electron-donating ability of the N atom was enhanced. Deprotonation-ICT mechanism of secondary amines was suggested for the ratiometric fluorescent chemosensing for Hg²⁺.     

宽带腔增强吸收光谱法测量大气NO2定标方法研究

非相干宽带腔增强吸收光谱法定量探测大气痕量气体浓度需要准确定标。以定量探测大气NO₂为目的,建立了基于蓝色发光二极管光源的非相干宽带腔增强吸收光谱测量系统,研究了(1)仅使用浓度已知的NO₂吸收光谱、(2)同时使用浓度已知的NO₂和纯氧气中氧气二聚体O₂-O₂吸收光谱、(3)利用纯氮气和纯氦气的瑞利散射消光差异等三种方法,分别获取非相干宽带腔增强吸收光谱在430～490 nm波段的镜片反射率定标曲线。三种方法得到的镜片反射率最大值对应波长均约为460 nm,但这些最大值存在一定差异,分别为0.999 25,0.999 33和0.999 37。利用NO₂样气吸收测量对比了三种定标方法,发现方法(1)与另外两种方法的测量结果不一致性分别约为14%和19%,而后两种方法所测结果的不一致性仅为4%。测量结果表明,NO₂标准气体浓度的不准确性以及壁损耗等因素恶化了方法(1)的定标精度,应尽量避免使用该定标方法。通过对实际大气中NO₂和O₂-O₂在440～485 nm波段内的同时测量,进一步验证了非相干宽带腔增强吸收光谱法的高灵敏度以及所用标定方法的有效性。     

基于O2-O2吸收的非相干宽带腔增强吸收光谱浓度反演方法研究

针对传统非相干宽带腔增强吸收光谱浓度反演方法的定量结果易受镜片反射率标定误差的影响问题, 提出了一种基于测量大气O₂-O₂吸收的浓度反演方法. 该方法是将非相干宽带腔增强吸收光谱技术的光学增强腔等效成吸收光程不随波长变化的多次反射池, 首先根据测得的宽带腔增强大气吸收谱和参考谱计算出光学厚度, 并应用差分光学吸收光谱算法拟合修正后的气体吸收截面到光学厚度, 反演得到大气中O₂-O₂以及被测气体的柱浓度, 然后根据O₂-O₂在大气中的含量已知且相对稳定这一特性, 确定出等效多次反射池的吸收光程, 最后从被测气体的柱浓度中扣除吸收光程信息得到被测气体的浓度值. 以监测大气中NO₂实验为例, 应用该方法在454-487 nm波段反演得到了大气NO₂的浓度(1-30 ppbv范围内), 并将反演结果与传统浓度反演方法的结果进行了对比, 发现两者的不一致性在7%以内. 实验结果表明, 非相干宽带腔增强吸收光谱技术可以利用大气O₂-O₂的吸收来定量其他被测气体的浓度, 而且定量结果对镜片反射率的标定误差不敏感.     

Native Fluorescence and Time Resolved Fluorescence Spectroscopic Characterization of Normal and Malignant Oral Tissues Under UV Excitation—an In Vitro Study

The present work aims to investigates the native fluorescence and time resolved fluorescence spectroscopic characterization of oral tissues under UV excitation. The fluorescence emission spectra of oral tissues at 280 nm excitation were obtained. From the spectra, it was observed that the alteration in the biochemical and morphological changes present in tissues. Subsequently, the Full width at Half Maximum (FWHM) of every individual spectra of 20 normal and 40 malignant subjects were calculated. The student’s t-test analysis reveals that the data were statistically significant (p?=?0.001). The fluorescence excitation spectra at 350 nm emission of malignant tissues confirms the alteration in protein fluorescence with respect to normal counterpart. To quantify the observed spectral differences, the two ratio variables R₁?=?I₂₇₅/I₃₁₀ and R₂?=?I₃₁₀/I₃₂₈ were introduced in the excitation spectra. Among them, the Linear Discriminant Analysis (LDA) of R₁ reveals better classification with 86.4 % specificity and 82.5 % sensitivity. The fluorescence decay kinetics of oral tissues was obtained at 350 nm emission and it was found that the decay kinetics was triple exponential. Then the ROC analysis of fractional amplitudes and component lifetime reveals that the average lifetime shows 77 % sensitivity and 70 % specificity with the cut off value 4.85 ns. Briefly, the average lifetime exhibits better statistical significance when compared to fractional amplitudes and component lifetimes.     

Representation of type I heterostructure junctionless tunnel field effect transistor for high-performance logic application

In this paper, a gate-all-around junctionless tunnel field effect transistor (JLTFET) based on heterostructure of compound and group III–V semiconductors is introduced and simulated. In order to blend the high tunneling efficiency of narrow band gap material JLTFETs and the high electron mobility of III–V JLTFETs, a type I heterostructure junctionless TFET adopting Ge–Al _x Ga_1?x As–Ge system has been optimized by numerical simulation in terms of aluminum (Al) composition. To improve device performance, we considered a nanowire structure, and it was illustrated that high-performance logic technology can be achieved by the proposed device. The optimal Al composition founded to be around 20 % (x = 0.2). The numerical simulation results demonstrate that the proposed device has low leakage current I _OFF of ~1.9 × 10^?17, I _ON of 4 µA/µm, I _ON/I _OFF current ratio of 1.7 × 10¹¹ and subthreshold swing SS of 12.6 mV/decade at the 40 nm gate length and temperature of 300 K.