共查询到20条相似文献,搜索用时 93 毫秒
1.
Kui Han Juanjuan WangYifeng Sheng Faliang JuXiaopeng Sheng Yuxi WuGang Tang 《Physics letters. A》2012
In this work, we study temporal evolution of multi-photon-pumped stimulated emission from ZnO nanowires. In addition to second harmonic generation, ultraviolet stimulated emission is observed in ZnO nanowires under femtosecond pulse excitation at 800 nm. Sharp emission peaks appear when excitation flux reaches a threshold of 80 mJ/cm2, which can be interpreted as lasing action in self-formed nanowire microcavities. Temporal evolution of the emission captured by Kerr shutter technique shows strong excitation-power dependence. The dynamic trace of stimulated emission exhibits a fast decay with a lifetime about 4.5 ps at intermediate excitation (∼100 mJ/cm2) and a lifetime about 2 ps at high excitation (>160 mJ/cm2). The difference in the lifetime can be attributed to different gain mechanisms related to excitonic interaction and electron-hole plasma, respectively. 相似文献
2.
R.Q. Guo J. Nishimura M. Matsumoto M. Higashihata D. Nakamura J. Suehiro T. Okada 《Applied physics. B, Lasers and optics》2008,90(3-4):539-542
Ordered ZnO nanowire arrays have been fabricated in N2 background gas by catalyst-free nanoparticle-assisted pulsed-laser deposition. A single ZnO nanowire was collected in an
electrode gap by dielectrophoresis. Under the optical pumping above an exciting laser (λ= 355 nm) threshold of ∼ 334 kW/cm2, ultraviolet lasing action in a single ZnO nanowire was observed at room temperature, indicating that the as-synthesized
nanowires in pure N2 background gas are of high quality. The crystalline facets of both ends of the nanowire acted to form an optical cavity.
Therefore, the mode spacings corresponding to cavity lengths of the respective nanowires were observed in photoluminescence
spectra.
PACS 78.66.Hf; 81.07.Bc; 78.67.-n; 81.16.Mk 相似文献
3.
V. V. Zalamai V. V. Ursaki C. Klingshirn H. Kalt G. A. Emelchenko A. N. Redkin 《Applied physics. B, Lasers and optics》2009,97(4):817-823
A vertically arranged nearly parallel array of ZnO nanorods and randomly oriented nanowires has been grown by low pressure
chemical vapor deposition (CVD) on silica substrates and on stainless steel gauze woven from a wire with a diameter of 40 μm,
respectively. The quality of the produced material is high enough to act as a gain medium for stimulated emission in the ultraviolet
spectral region. Multiple sharp lasing peaks were realized from single hexagonal nanorods and arrays of hexagonal ZnO nanorods.
The lasing peaks display successive onset and saturation with increasing excitation power density and fit well the expected
resonance spectrum of guided modes in hexagonal nanorods. The behavior of lasing spectra from shot to shot of pumping in randomly
oriented nanowires along with the independence of the lasing threshold on the excitation spot area suggest that the emission
spectrum results from the superposition of lasing modes in individual nanowires, rather than from random lasing due to photon
coherent scattering. 相似文献
4.
Cuicui Wang Ke Yu Lijun Li Qiong Li Ziqiang Zhu 《Applied Physics A: Materials Science & Processing》2008,90(4):739-743
Two kinds of ZnO nanotubes, including taper-like and flat-roofed tubes, have been successfully fabricated using a simple aqueous
solution route by changing the experimental conditions. All the obtained nanotubes have a uniform size of 500 nm in diameter,
10–50 nm in wall thickness, and 2–5 μm in length. The growth mechanism of two kinds of ZnO nanotubes was investigated. Field
emission measurements showed that tapering nanotubes have the good field emission performance with a low turn-on field of
∼ 2.1 V μm-1 and a low threshold field of ∼ 3.8 V μm-1, which suggests the possible applications of the ZnO tubular structures in field emission microelectronic devices.
PACS 73.61.Ga; 73.63. Fg; 85.45.Db 相似文献
5.
Distributed feedback (DFB) lasing in permanent volume transmission gratings formed in a laser dye-doped organic–inorganic
nanocomposite has been investigated. DFB laser cavities were fabricated using one-step two-beam holographic exposure of Pyrromethene
567 (PM567) doped photopolymerizable acrylate monomers containing inorganic (LaPO4) nanoparticles. Compared to the formulation previously utilized, the material composition presented provides longer lifetime
of the laser. Spectral and polarization properties, input–output and stability characteristics of the laser output have been
investigated by varying the material composition and the patterning parameters. DFB lasing emission of the second and the
third diffraction orders has been demonstrated. The spectral linewidth of ∼0.08 nm has been observed at a pump energy threshold
of about 0.2 μJ/pulse for the second-order DFB lasing when pumped with 532 nm 500 ps laser pulses. Spectral tuning of the
lasing output over ∼56 and ∼7 nm was obtained by varying the grating period and the content of inorganic nanoparticles in
the polymer matrix, respectively. 相似文献
6.
Guoping Wang Sheng Chu Ning Zhan Huimei Zhou Jianlin Liu 《Applied Physics A: Materials Science & Processing》2011,103(4):951-954
P-type ZnO nanowires with silver (Ag) doping were synthesized via a chemical vapor deposition process. The incorporation of
Ag was confirmed by selected-area energy-dispersive x-ray spectroscopy. The formation of acceptor states was demonstrated
by temperature and excitation power-dependent photoluminescence measurements. Characterization of field-effect transistors
using Ag-doped ZnO nanowires as channels showed p-type conductivity of the nanowires with a hole concentration of 4.9×1017 cm−3 and a carrier mobility of approximately 0.18 cm2 V−1 s−1. 相似文献
7.
Jesús Alvarez Marien Lopez-Arias Rebeca de Nalda Margarita Martín 《Applied Physics A: Materials Science & Processing》2008,92(4):831-836
The neutral species present in CdS ablation plumes upon nanosecond 532 nm laser irradiation at a moderate fluence of 0.5–0.75 J cm−2 have been studied. Neutral Cd
n
S
m
clusters have been identified, some as large as (CdS)33−34 (1–2 nm in diameter). The analysis of the dynamics of neutral species shows an expansion with two components that differ
both in composition and dynamics. A fast, high kinetic energy component, dominated by S2 which acquires free-flow conditions at short distances from the target, is followed by a slower component characterized by
similar speeds for all species. This slower component shows dynamic features that are expected to favor aggregation processes
leading to effective cluster formation. 相似文献
8.
M. A. Gondal M. A. Dastageer A. Khalil K. Hayat Z. H. Yamani 《Journal of nanoparticle research》2011,13(8):3423-3430
Nanostructured ZnO photo catalyst was synthesized by precipitation method and was applied in conjunction with 355 nm pulsed
laser irradiation for effective disinfection of the water contaminated with Escherichia coli micro organism. The morphological studies using X-Ray Diffractometer (XRD) and Transmission Electron Microscope (TEM) were
carried out on the synthesized nano-ZnO, and these studies indicated that the catalyst has the crystallographic structure
of hexagonal wurtzite and has the grain size of around 20–40 nm. The bacteria decay rate constants were estimated for nine
different concentrations of nano-ZnO in infected water. The parametric optimization was carried out, and we could reach the
decay rate constant as high as 0.24 min,−1 which is higher than micro-structured ZnO and the familiar TiO2 photo catalysts under similar experimental condition. 相似文献
9.
M. Bryushinin V. Golubev Y. Kumzerov D. Kurdyukov I. Sokolov 《Applied physics. B, Lasers and optics》2009,95(3):489-495
We report an experimental investigation of the non-steady-state photoelectromotive force in nanostructured GaN within porous
glass and polypyrrole within chrysotile asbestos. The samples are illuminated by an oscillating interference pattern created
by two coherent light beams and the alternating current is detected as a response of the material. Dependences of the signal
amplitude versus temporal and spatial frequencies, light intensity, and temperature are studied for two wavelengths λ=442 and 532 nm. The conductivity of the GaN composite is measured: σ=(1.1–1.6)×10−10 Ω−1 cm−1 (λ=442 nm, I
0=0.045–0.19 W/cm2, T=293 K) and σ=(3.5–4.6)×10−10 Ω−1 cm−1 (λ=532 nm, I
0=2.3 W/cm2, T=249–388 K). The diffusion length of photocarriers in polypyrrole nanowires is also estimated: L
D=0.18 μm. 相似文献
10.
M. Santos L. Díaz J. J. Camacho J. M. L. Poyato J. Pola T. Krenek 《Applied Physics A: Materials Science & Processing》2010,99(4):811-821
Laser-induced breakdown spectroscopy (LIBS) in germane (GeH4), initially at room temperature and pressures ranging from 2 to 10 kPa, was studied using a high-power transverse excitation
atmospheric (TEA) CO2 laser (λ=10.653 μm, τ
FWHM=64 ns and power densities ranging from 0.28 to 5.52 GW cm−2). The strong emission spectrum of the generated plasma is mainly due to electronic relaxation of excited Ge, H and ionic
fragments Ge+, Ge2+ and Ge3+. The weak emission is due to molecular bands of H2. Excitation temperatures of 8100±300 K and 23,500±2500 K were estimated by Ge atomic and Ge+ singly ionized lines, respectively. Electron number densities of the order of (0.7–6.2)×1017 cm−3 were deduced from the Stark broadening of several atomic Ge lines. The characteristics of the spectral emission intensities
from different species have been investigated as functions of the germane pressure and laser irradiance. Optical breakdown
threshold intensities in germane at 10.653 μm have been determined. The mechanism of initiation of the laser-induced plasma
in germane has been analyzed. 相似文献
11.
A new spectrofluorimetric method has been developed and validated for the quantification of ceftriaxone in bulk powder, pharmaceutical
formulations and spiked human plasma. The developed method is reproducible, accurate, sensitive and cost effective. In this
method, ceftriaxone was converted into a fluorescent compound by reacting with 0.8 M ethyl acetoacetate and 25% formaldehyde
in a buffered medium (pH = 4.2) at 90 °C. The excitation and emission wavelengths of the fluorescent reaction product are
316 nm and 388 nm respectively. Optimization of the experimental conditions affecting the condensation reaction were carefully
carried out and the optimum experimental conditions were incorporated in the procedure. The developed method has a broad linear
range (0.2–20 μg mL−1) with a correlation coefficient of 0.9992. The limit of detection (LOD) and limit of quantification (LOQ) was found to be
1.94 × 10−2 μg mL−1 and 6.47 × 10−2 μg mL−1 respectively. The common excipients and co-administered drugs were investigated for their interferences effect in the assay.
The developed method was validated statistically through recovery studies and successfully applied to ceftriaxone determination
in bulk powder, pharmaceutical formulations and spiked human plasma samples. The percent recoveries were found to be in the
range of 99.04–100.26% for bulk powder, 98.88–99.92% for pharmaceutical formulations and 94.22–98.48% for spiked human plasma.
The results were verified by comparing with reference literature HPLC method and were found in good agreement. 相似文献
12.
Enhanced field emission from pulsed laser deposited nanocrystalline ZnO thin films on Re and W 总被引:1,自引:0,他引:1
Dattatray J. Late Pankaj Misra B. N. Singh Lalit M. Kukreja Dilip S. Joag Mahendra A. More 《Applied Physics A: Materials Science & Processing》2009,95(2):613-620
Nanocrystalline ZnO thin films have been deposited on rhenium and tungsten pointed and flat substrates by pulsed laser deposition
method. An emission current of 1 nA with an onset voltage of 120 V was observed repeatedly and maximum current density ∼1.3 A/cm2 and 9.3 mA/cm2 has been drawn from ZnO/Re and ZnO/W pointed emitters at an applied voltage of 12.8 and 14 kV, respectively. In case of planar
emitters (ZnO deposited on flat substrates), the onset field required to draw 1 nA emission current is observed to be 0.87
and 1.2 V/μm for ZnO/Re and ZnO/W planar emitters, respectively. The Fowler–Nordheim plots of both the emitters show nonlinear
behaviour, typical for a semiconducting field emitter. The field enhancement factor β is estimated to be ∼2.15×105 cm−1 and 2.16×105 cm−1 for pointed and 3.2×104 and 1.74×104 for planar ZnO/Re and ZnO/W emitters, respectively. The high value of β factor suggests that the emission is from the nanometric features of the emitter surface. The emission current–time plots
exhibit good stability of emission current over a period of more than three hours. The post field emission surface morphology
studies show no significant deterioration of the emitter surface indicating that the ZnO thin film has a very strong adherence
to both the substrates and exhibits a remarkable structural stability against high-field-induced mechanical stresses and ion
bombardment. The results reveal that PLD offers unprecedented advantages in fabricating the ZnO field emitters for practical
applications in field-emission-based electron sources. 相似文献
13.
R. Guo J. Nishimura M. Matsumoto M. Higashihata D. Nakamura T. Okada 《Applied physics. B, Lasers and optics》2009,94(1):33-38
Vertically aligned ZnO nanowires were successfully grown on the sapphire substrate by nanoparticle-assisted pulsed laser deposition
(NAPLD), which were employed in fabricating the ZnO nanowire-based heterojunction structures. p-GaN/n-ZnO heterojunction light-emitting diodes (LEDs) with embedded ZnO nanowires were obtained by fabricating p-GaN:Mg film/ZnO nanowire/n-ZnO film structures. The current–voltage measurements showed a typical diode characteristic with a threshold voltage of about
2.5 V. Electroluminescence (EL) emission having the wavelength of about 380 nm was observed under forward bias in the heterojunction
diodes and was intensified by increasing the applied voltage up to 30 V. 相似文献
14.
The ZnO filler has been introduced into a solid polymeric electrolyte of polyvinyl chloride (PVC)–ZnO–LiClO4, replacing costly organic filler for conductivity improvement. Ionic conductivity of PVC–ZnO–LiClO4 as a function of ZnO concentration and temperature has been studied. The electrolyte samples were prepared by solution casting
technique. The ionic conductivity was measured using impedance spectroscopy technique. It was observed that the conductivity
of the electrolyte varies with ZnO concentration and temperature. The temperature dependence on the conductivity of electrolyte
was modelled by Arrhenius and Vogel–Tammann–Fulcher equations, respectively. The temperature dependence on the conductivity
does not fit in both models. The highest room temperature conductivity of the electrolyte of 3.7 × 10−7 Scm−1 was obtained at 20% by weight of ZnO and that without ZnO filler was found to be 8.8 × 10−10 Scm−1. The conductivity has been improved by 420 times when the ZnO filler was introduced into the PVC–LiClO4 electrolyte system. It was also found that the glass transition temperature of the electrolyte PVC–ZnO–LiClO4 is about the same as PVC–LiClO4. The increase in conductivity of the electrolyte with the ZnO filler was explained in terms of its surface morphology. 相似文献
15.
S.?Sujecki L.?Sójka E.?Bere?-Pawlik Z.?Tang D.?Furniss A.?B.?Seddon T.?M.?Benson 《Optical and Quantum Electronics》2010,42(2):69-79
A simple Dy3+-doped chalcogenide glass fibre laser design for mid-infrared light generation is studied using a one dimensional rate equation
model. The fibre laser design employs the concept of cascade lasing. The results obtained demonstrate that efficient cascade
lasing may be achieved in practice without the need for fibre grating fabrication, as a sufficient level of feedback for laser
action is provided by Fresnel light reflection at chalcogenide glass fibre–air interfaces. Further enhancement of the laser
efficiency can be achieved by terminating one of the fibre ends with a mirror. A numerical analysis of the effect of the Dy3+ doping concentration and fibre loss on the laser operation shows that with 5 W of pump power, at 1.71 μm wavelength, output
powers above 100 mW at ∼ 4.5 μm wavelength can be achieved with Dy3+ ion concentrations as low as 3 × 1019 cm−3, when fibre loss is of the order 1dB/m. 相似文献
16.
Karim MM Jeon CW Lee HS Alam SM Lee SH Choi JH Jin SO Das AK 《Journal of fluorescence》2006,16(5):713-721
A sensitive, rapid, and specific assay has been developed for the simultaneous determination of acetylsalicylic acid and caffeine in commercial tablets based on their natural fluorescence. The mixture of these drugs was resolved by first derivative synchronous fluorimetric technique using two scans. At Δλ=106 nm, using first derivative synchronous scanning, only acetylsalicylic acid yields a detectable signal at 316 nm (peak to zero method) which is unaffected by caffeine. At Δλ=30 nm, the signal of caffeine at 288 nm (peak to zero method) is not affected by acetylsalicylic acid. The range of application is between 0.021 and 41.62 μg ml−1 (correlation coefficient, R=0.9995) for acetylsalicylic acid and between 0.4486 and 44.86 μg ml−1 (correlation coefficient, R=0.99786) for caffeine. The recovery range of 98.40–102% for acetylsalicylic acid and 90–100.5% for caffeine from their synthetic mixture was reported. Overall recovery of both compounds about 97–99% for acetylsalicylic acid and 97–98% for caffeine was obtained from real sample analysis. The detection limits are 0.0013 μg ml−1 and 0.0306 μg ml−1 for acetylsalicylic acid and caffeine, respectively. The relative standard deviation (n=10) for 20 μg ml−1 of acetylsalicylic acid is 2.75% and for 2.2 μg ml−1of caffeine is 1.7%. 相似文献
17.
M. V. Bogdanovich V. V. Kabanov Y. V. Lebiadok A. A. Ramanenka A. G. Ryabtsev G. I. Ryabtsev M. A. Shchemelev S. K. Mehta 《Journal of Applied Spectroscopy》2012,78(6):811-816
The development of amplified luminescence fluxes in powerful InGaAs/AlGaAs laser diode arrays (lasing wavelength 940–960 nm)
has been studied experimentally and theoretically at pump levels above the threshold value. Flux density values for amplified
luminescence propagation along (1.88⋅109 W/m2) and across (1.21⋅109 W/m2) the laser diode array cavity axis have been evaluated for the threshold pump level at room temperature (293 K). The contribution
of the recombination rate induced by the amplified luminescence to the threshold current generation of the laser diode array
reaches 7%. It has been shown that the amplified luminescence flux density is increased by 49% as the pump level rises from
one to three threshold values. 相似文献
18.
Performances of a distributed feedback (DFB) organic dye laser were enhanced by introducing an intermediate high refractive
index layer of poly(N-vinylcarbazole) (PVCz) laminated between a glass substrate and a laser dye doped active polymer layer.
The active layer is consisted of rhodamine 6G and cellulose acetate (CA). Introduction of an intermediate layer allows a single
mode lasing. Slope efficiencies of 2.2 and 4.7% and thresholds of 0.3 and 0.14 mJ/cm2/pulse were measured for the waveguides with 1.7 and 3.4 μm active layers, respectively. Furthermore, permanent relief grating
on an intermediate layer gave rise to the reduction of the threshold. With increasing in amplitude of the relief grating from
20 to 45 nm, lasing threshold was reduced from 0.18 to 0.04 mJ/cm2/pulse for the waveguide with 1.7 μm active layer. The slope efficiency increased from 3.5 to 4.2%. 相似文献
19.
Zhuming Wang Xijuan Tan Donghua Chen Qiaoli Yue Zhenghua Song 《Journal of fluorescence》2009,19(5):801-808
It was first found that the intrinsic fluorescence of lysozyme at 340 nm can be quenched by cephalosporin analogues through
the static quenching and non-radiative energy transferring procedure. In the acetate buffer solution with pH 7.0 and 298 K,
the quenching fluorescence intensity was in a good linearity over the concentration of drugs in the range of 1–100 μmol L−1, 0.1–100 μmol L−1, 0.5–100 μmol L−1 and 0.05–100 μmol L−1 for cefradine, cefuroxime, cefotaxime and ceftriaxone, respectively. The quenching ability or the binding ability of the
studied drugs followed the pattern: ceftriaxone > cefotaxime > cefuroxime > cefradine, which was close to the order of their
antibacterial ability. The binding parameters including the association constant and the number of binding potential point
were calculated at different temperatures (288, 298 and 308 K), and thermodynamic parameters ΔH°, ΔS° and ΔG° were given. The binding mode of lysozyme with cephalosporins showed that the hydrophobic effect might play a major role.
The binding distance between cephalosporin and tryptophan residue in lysozyme was obtained. The results provided the quantitative
information for the binding of cephalosporin to lysozyme, and it was suggested that the drugs probably bound to the active
site near Trp62 in lysozyme. 相似文献
20.
Deok Kyu Kim Kyeong Min Kim Choon Bae Park 《Applied Physics A: Materials Science & Processing》2010,98(4):913-917
A p-type ZnO thin film was prepared using arsenic diffusion via the ampoule-tube method. This was followed by fabrication
of a ZnO p–n homojunction using n-type ZnO and characterization of the device properties. The ZnO thin film exhibited p-type
characteristics, with a resistivity of 2.19×10−3 Ω cm, a carrier concentration of 1.73×1020/cm3, and a mobility of 26.7 cm2/V s. Secondary ion mass spectrometer analysis confirmed that in- and out-diffusion occurred simultaneously from the external
As source and the GaAs substrate. The device exhibited the rectification characteristics of a typical p–n junction; the forward
voltage at 20 mA was approximately 5.5 V. The reverse-bias leakage current was very low—0.1 mA for −10 V; the breakdown voltage
was −11 V. The ampoule-tube method for fabricating p-type ZnO thin films may be useful in producing ultraviolet ZnO LEDs and
other ZnO-based devices. 相似文献