共查询到20条相似文献,搜索用时 109 毫秒
1.
O. V. Yaroshchuk Yu. P. Piryatinskiĭ L. A. Dolgov T. V. Bidna D. Enke 《Optics and Spectroscopy》2006,100(3):394-399
The fluorescence spectra of the nematic liquid crystal n-pentyl-n′-cyanobiphenyl (5CB) in porous glasses with pores from 1 to 44 nm in diameter are investigated. A decrease in the pore diameter leads to suppression of some long-wavelength spectral components corresponding to H-type predimer and dimer pairs (the molecular sieve effect). The spectrum of 5CB in small pores (smaller than 4 nm in diameter) can be explained by the superposition of the monomer fluorescence and the fluorescence of J-type dimer pairs of 5CB molecules, as well as associates of 5CB molecules and surface groups on pore walls. Exposure of samples to UV light enhances the molecular interaction in associates, possibly, due to the formation of strong chemical bonds. 相似文献
2.
N. V. Gaponenko G. K. Malyarevich A. V. Mudryi O. B. Gusev M. V. Stepikhova M. Yu. Tsvetkov S. M. Kleshcheva M. I. Samoilovich A. P. Stupak 《Journal of Applied Spectroscopy》2007,74(5):687-691
We have studied the luminescence and luminescence excitation spectra of erbium in the 1.54 μm region in titanium oxide and
silicon oxide xerogels, formed in the mesoscopic pores of three-dimensional synthetic opals and two-dimensional porous aluminum
oxide structures. For erbium-doped titanium oxide films formed in opal, in contrast to analogous films on porous aluminum
oxide, in the luminescence excitation spectra we observe an intense broad band with a maximum in the ∼360 nm region. We discuss
the possible nature of this band.
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Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 622–626, September–October, 2007. 相似文献
3.
Suspensions of oligophenylenevinylene (nPV) nanoparticles withn = 2 vinylene units are doped with nPVs of longer chainlengths,n = 3–5. Absorption and fluorescence spectroscopy and steady-state and time-resolved fluorescence anisotropy measurements
are used to determine the photo-physical properties of the suspensions. Undoped nanoparticles form highly oriented H-aggregates
with low fluorescence quantum yields (ΦF ≈ 0.1). Introduction of bulky substituents into the particle constituting molecules perturbs the intermolecular orientation.
Upon doping, efficient energy transfer to the dopants is found, changing the color and leading to enhancement of the fluorescence
quantum yields up to ΦF = 0.6. The intermolecular orientation is not changed upon doping. 相似文献
4.
The influence of electron irradiation on the light-emitting properties of p-and n-type porous silicon prepared by electrochemical etching is investigated. The dose and energy dependences of the electron-stimulated
quenching of the photoluminescence (PL) are determined. It is shown that electron treatment of a porous silicon surface followed
by prolonged storage in air can be used to stabilize the PL. The excitation of photoluminescence by a UV laser acting on sections
of porous silicon samples subjected to preliminary electron treatment is discovered for the first time. The influence of the
electron energy and the power of the laser beam on this process is investigated. The results presented are attributed to variation
in the number of radiative recombination centers as a result of the dissociation and restoration of hydrogen-containing groups
on the pore surface.
Zh. Tekh. Fiz. 68, 58–63 (March 1998) 相似文献
5.
S. Aravamudhan K. Luongo P. Poddar H. Srikanth S. Bhansali 《Applied Physics A: Materials Science & Processing》2007,87(4):773-780
We report the fabrication and characterization of porous silicon templates for electrodeposition of high aspect ratio one-dimensional
metallic nanostructures (nanowires/nanoparticles) in them. Even though nanostructures/nanowires in the past have been fabricated
in alumina, polymer or silica templates, the advantages of this approach are the possibility for seamless integration of nanostructures
with other silicon components, and silicon based sensors because of better physical and electrical interconnection between
the nanostructure and the silicon substrate. In this work, fabrication and characterization of nanowires/nanostructures such
as single-segment Ni–Fe and Au and two-segment Ni–Fe/Au electrodeposited in the porous silicon template are presented. The
templates with ordered and controlled nanometer-sized pores, 40 nm and 290 nm in diameter, were created through porous Si
etching. The morphology, composition and structural characteristics of the template and of the single-segment Ni–Fe and Au
and two-segment Ni–Fe/Au nanostructures of diameter 275±25 nm, length up to 100 μm and pitch of 1 μm were analyzed using scanning
electron microscopy and X-ray diffraction techniques. The micrographs confirm that the plating parameters have a strong influence
on morphology and composition of the structures. Further, the Ni–Fe images show the formation of both vertical and branched
nanowires along with nanoparticles, from breakage/discontinuous growth of nanowires. Ni–Fe nanostructures were further analyzed
for temperature-dependent magnetization and magnetization vs. magnetic field measurements using a commercial physical property
measurement system. They reveal no magnetic anisotropy of the nanostructures probably due to a balance between ‘reduced’ shape
anisotropy from branched and rough pore surfaces and magnetocrystalline anisotropy.
PACS 61.46.+w; 75.75.+a; 81.07.-b; 81.16.Be 相似文献
6.
V. I. Tomin 《Optics and Spectroscopy》2010,108(4):544-552
The dual fluorescence spectra of 3-hydroxyflavone molecules excited by electromagnetic radiation in the region of the S
1 and S
2 absorption bands in the temperature region of 20–80°C are studied using the dynamic quenching of the excited state. An analysis
of the fluorescence parameters shows that heating the solution from room temperature to 60°C increases the proton transfer
rate by a factor of 1.24 in the case of standard excitation into the main absorption band and even stronger (by a factor of
6.9) in the case of excitation into the second absorption band. The presence of a quencher reduces the yield of the two emission
bands and noticeably increases the proton transfer rate, by a factor of 1.16 at room temperature and by a factor of 1.25 at
80°C. Upon excitation into the second singlet band, the transfer rate increases even more (especially at higher temperatures),
by a factors of 1.24 and 3.5 for the same temperatures. The temperature dependences of the transfer rate constant allowed
us to estimate the activation energies of the proton transfer reaction under different physical conditions and reach conclusions
about the mechanism by which this reaction proceeds. It is found that the proton transfer activation energy decreases from
500 to 360 cm−1 when measured in temperature ranges of 20–40 and 20–60°C. The introduction of a quencher with a concentration of 5 × 10−3 M increases the activation barrier to 534 and 471 cm−1 in the same temperature ranges. 相似文献
7.
T. D. Ibragimov N. J. Ismailov E. A. Allahverdiyev I. S. Hasanov 《Journal of Applied Spectroscopy》2008,75(6):766-770
The possibility for homogeneous orientation of liquid-crystal (LC) molecules was studied after argon-ion bombardment of substrates
(Si, Ge) transparent in the infrared (IR) spectral region. The orientation of the LC molecules was monitored by IR spectroscopy.
Nematic LC 4-methoxybenzylidene-4′-butylaniline (MBBA) was used to study the molecular orientation. Absorption spectra were
analyzed near the band with maximum at 1630 cm−1 corresponding to − CH=N-group vibrations along the long axis of the MBBA molecule. The type and degree of initial orientation
of the LC molecules were determined from the correlation of the integrated absorptions of this band without and with an applied
electric field (above the threshold voltage for the Fredericksz effect). It has been established that an increased ion fluence
results in a planar orientation of the LC molecules and in a gradual transformation of the planar orientation of the molecules
to a homeotropic one with preliminary argon-ion bombardment of substrates at energies of 250 eV and 1.25 keV, respectively.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 763–767, November–December, 2008. 相似文献
8.
A replacement of the adsorbate in porous silicon is carried out in ultra-high vacuum. The photoluminescence line is shifted
and quenched as the products of anodization of silicon — silicon hydrides and atomic and molecular hydrogen — undergo thermal
decomposition and desorption. Adsorption of molecular chlorine restores the 560 nm photoluminescence band, which we identified
as radiation from graphite nanoparticles.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 2, 106–111 (25 January 1996) 相似文献
9.
Photoluminescence spectra of porous silicon filled by luminescent liquid crystals 5CB and H109 were investigated. It was observed that there were photoluminescence bands corresponding to both porous silicon and liquid crystal in experimental spectra. In addition, the band corresponding to porous silicon increases in comparison with photoluminescence of porous silicon without the filler. Experimental results are explained by the radiating and nonradiating energy transfer from liquid crystal to porous silicon. 相似文献
10.
The spectral characteristics of acetonitrile solutions of 4′-(diethylamino)-3-hydroxyflavone dye with dual fluorescence are
studied under selective excitation. This dye is a structural analog of 3-hydroxyflavone and exhibits excited-state proton
transfer, which, in contrast to 3-hydroxyflavone, has a thermodynamic rather than a kinetic character. The fluorescence spectra
at different excitation photon energies and the excitation spectra of different fluorescence bands are studied. It is found
that the intensity ratio of the normal and tautomeric fluorescence bands lying near 507 and 570 nm, respectively, depends
on the excitation wavelength, namely, this ratio is 1.45 and almost does not change in the region of the main absorption band
(370–420 nm), while, in the region of the second singlet band (near 280 nm), it decreases to 1.15. This can be explained by
an increase in the probability of proton transfer with formation of a tautomeric form in the case of excitation into the second
band. Another interesting feature is the existence of a latent third emission band peaked at 535 nm, which was found and reliably
recorded upon excitation at wavelengths of 470–500 nm. Addition of water quenches this emission, which indicates that it belongs
to the anionic form of the dye. 相似文献
11.
R. Vivek Sabaapathy N. Sankara Subramanian S. Vinoth Kumar S. Naveen Chandran G. Vimal Kumar 《Ionics》2007,13(5):311-317
The present work deals with the design, development, and implementation of an angle detector using n-ATO/p-PSi photovoltaic
sensor. Nanoporous structures have been developed over p-type porous silicon wafers by anodization technique under optimized
conditions. Photoluminescence studies of porous silicon show emission between 700 and 702 nm for the constant excitation at
350 nm, which illustrates that the band gap can be tuned according to the HF:H2O:C2H5OH ratio. n-ATO/p-PSi O heterojunction photovoltaic sensor has been developed by cost-effective Spray pyrolysis method. I–V
characteristics under dark and different illumination intensities have been investigated, and the results are discussed. The
fabricated sensor is employed for sensitive angle detection of a light source. The sensor is attached to a DC motor, which
rotates at 30 rpm. When the light is from the source incident on the light sensor, a dc voltage has been produced, which in
turn is amplified, and the signal has been used to stop the motor. The motor is coupled to a rotary transducer, which is calibrated
to read or display 0–3.60 V for 0–360°.
Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006. 相似文献
12.
It is found that the magnetoresistance of manganese-doped porous amorphous silicon in fields 0–5 T is negative and depends
on the orientation of the magnetic field. The experimental curves of the magnetic-field dependence are described well by the
theory of quantum corrections to the conductivity in the one-dimensional case. The phase coherence length in the material
is ≈25 nm at T=4.2 K.
Pis’ma Zh. éksp. Teor. Fiz. 69, No. 3, 189–193 (10 February 1999) 相似文献
13.
V. A. Lapina P. P. Pershukevich A. E. Dontsov M. V. Bel’kov 《Journal of Applied Spectroscopy》2008,75(1):53-63
The spectra and kinetics of fluorescence of two-component solutions of the chlortetracycline (CHTC)-DOPA-melanin (melanin
or ME) system in water have been investigated. The data obtained have been compared to similar data for solutions of CHTC-melanosome
from bull eye (MB), which contains natural melanin, in K-phosphate buffer at pH 7.4. The overall results indicate the occurrence
of complexation between molecules of CHTC and ME as they are being excited. The studies of complexation in the solution of
CHTC-MB in the buffer are complicated by the formation of a CHTC-buffer complex. The effect of optical radiation in the range
330–750 nm on the CHTC-ME complex shows selectivity: the greatest change in the spectrum occurs when the wavelength of the
exciting radiation coincides with the long-wavelength band maximum of the fluorescence excitation spectrum of the CHTC-ME
complex in aqueous solution. In this range, CHTC and especially ME show high photochemical stability. The nature of the radiation
effect on the studied compounds in the hard UV range (λ < 330 nm) differs greatly from that in the range 330–750 nm. It is
apparently accompanied by significant photochemical transmutations of all system components. By comparing the characteristics
of the CHTC-ME systems with those of the related drug doxycycline (DC-ME), the conclusion has been made that the chlorine
atom plays a vital role in formation of the short-wavelength band in the fluorescence spectrum of the CHTC-ME complex.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 1, pp. 52–62, January–February, 2008. 相似文献
14.
Hoffmann K Mix R Friedrich JF Buschmann HJ Resch-Genger U 《Journal of fluorescence》2009,19(2):229-237
Polypropylene supports were functionalized by plasma-deposition of polymeric allylamine layers. The surface amino groups generated
were wet-chemically reacted with xanthene dyes resulting in fluorescent polymer films. The effect of polymer-attachment of
the dyes on their emission features was studied fluorometrically and different methods were tested to improve the fluorescence
properties of the films. Modification with cucurbit[6]uril (CB6) yields a moderately enhanced fluorescence as well as an improved
photostability. The observed effect is most likely due to CB6-induced rigidization of the linker molecules which seems to
reduce fluorescence quenching dye–dye and fluorophore–surface interactions. 相似文献
15.
A. I. Yakimov N. P. Stepina A. V. Dvurechenskii L. A. Shcherbakova 《Journal of Experimental and Theoretical Physics》1997,85(3):501-506
The temperature dependence of the hopping conductivity and the relaxation kinetics of the transient current in porous amorphous
silicon are investigated after treatment in a hydrogen plasma at 200 °C. It is discovered that posthydrogenation of the material
increases the dimension of the conducting channel from 2.5 to 3, while suppressing and slowing the relaxation of the transient
current. The results obtained are attributed to passivation of the electrically active dangling bonds on the pore surface
by hydrogen. It is concluded that electron transport in porous amorphous silicon in the temperature range T>T*, where T* lies in the range 130–270 K and depends on the density of states, takes place between superlocalized states of the internal
surface, which is enriched with dangling bonds and acts as a fractal percolation system. When the temperature is lowered below
T*, a transition to one-dimensional hopping conduction in the bulk silicon regions occurs.
Zh. éksp. Teor. Fiz. 112, 926–935 (September 1997) 相似文献
16.
The value of intrinsic chlorophyll fluorescence polarization, and the intensity in emission spectrum were investigated in
leaf segments of Alocasia macrorrhiza under several stress conditions including different temperatures (25–50°C), various concentrations of NaCl (0–250 mM), methyl
viologen (MV, 0–25 μM), SDS (0–1.0%) and NaHSO3 (0–80 μM). Fluorescence emission spectrum of leaves at wavelength regions of 500–800 nm was monitored by excitation at 436 nm.
The value of fluorescence polarization (P value), as result of energy transfer and mutual orientation between chlorophyll molecules, was determined by excitation at
436 nm and emission at 685 nm. The results showed that elevated temperature and concentrations of salt (NaCl), photooxidant
(MV), surfactant (SDS) and simulated SO2 (NaHSO3) treatments all induced a reduction of fluorescence polarization to various degrees. However, alteration of the fluorescence
spectrum and emission intensity of F685 and F731 depended on the individual treatment. Increase in temperature and concentration of NaHSO3 enhanced fluorescence intensity mainly at F685, while an increase in MV concentration led to a decrease at both F685 and F731. On the contrary, NaCl and SDS did not cause remarkable change in fluorescence spectrum. Among different treatments, the
negative correlation between polarization and fluorescence intensity was found with NaHSO3 treatments only. We concluded that P value being measured with intrinsic chlorophyll fluorescence as probe in leaves is a susceptible indicator responding to
changes in environmental conditions. The alteration of P value and fluorescence intensity might not always be shown a functional relation pattern. The possible reasons of differed
response to various treatments were discussed. 相似文献
17.
This paper describes the first investigations of how the intensities of various time-resolved components of the luminescence
from porous silicon relax with time. A paradoxical correlation is observed between the macro-and microtemporal relaxation
of luminescence from porous silicon under pulsed photoexcitation: namely, a relative increase in the rate of macrorelaxation
for the slower components of the luminescence. Spectral investigations show that the difference in the rates of fatigue relaxation
“tiredness” is maximum at the long-wavelength edge of the luminescence band. We propose a model that allows us to explain
the observed effects starting from the assumption that photoexcitations drift toward radiative recombination centers.
Fiz. Tverd. Tela (St. Petersburg) 39, 1165–1169 (July 1997) 相似文献
18.
V. N. Bagratashvili S. G. Dorofeev A. A. Ischenko V. V. Koltashev N. N. Kononov A. A. Krutikova A. O. Rybaltovskii G. V. Fetisov 《Russian Journal of Physical Chemistry B, Focus on Physics》2010,4(7):1164-1170
With the use of supercritical carbon dioxide (SC-CO2), the matrix immobilization of photoluminescent silicon nanocrystals (nc-Si) in polytetrafluoroethylene microparticles (mp-PTFE)
is performed, which leads to the formation of mp-PTFE/nc-Si photoluminescent nanocomposite containing ∼103–104 nc-Si particles per mp-PTFE particle (1–2 μm in size). This approach is based on the effect of polymer swelling in SC-CO2, efficient SC-CO2-assisted transport of nanoparticles into the internal free volume of the polymer, and contraction of the nanocomposite after
the release of CO2, an effect that prevents the subsequent agglutination of nanoparticles. Particles of nc-Si photoluminescent in the visible
spectrum were synthesized from silicon suboxide powder (SiO
x
, x ≈ 1) heated at various temperatures within 25–950°C and then etched in concentrated hydrofluoric acid. The hydrosilylation
procedure was used to graft 1-octadecene molecules to the surface of nc-Si particles. As a result, the photoluminescence intensity
of nc-Si increased substantially. According to TEM images and small angle X-ray scattering data, the maximum size of nc-Si
particles did not exceed 5 nm and 7 nm, respectively, and the core of these nanoparticles consisted of crystalline silicon.
The structure and spectral properties of the initial nc-Si particles and synthesized mp-PTFE/nc-Si photoluminescent nanocomposite
microparticles were studied. 相似文献
19.
We studied the steady-state fluorescence spectra of solutions of FET (4′-(diethylamino)-3-hydroxyflavone) in acetonitrile
that were excited at different temperatures by quanta with different energies located in the range of the main absorption
band and in its long-wavelength wing. We found that, at room temperature, the emission intensity ratio of the bands of the
normal and tautomeric forms, which are located at 505 and 570 nm, respectively, depends on the excitation wavelength. In the
range of the main absorption band 300–360 nm, this ratio remains nearly the same, i.e., 1.45, while, upon excitation in the
range of the long-wavelength wing 360–380 nm of the main band, it decreases to 1.33 at a wavelength of 460 nm. In this same
range, a long-wavelength excitation effect that is unusual for liquid inviscid solvents at room temperature, i.e., a bathochromic
shift of the entire short-wavelength emission band by 11 nm, manifests itself. We propose to explain these dependences using
energy diagrams, which take into account the dependence of free energy on the orientational polarization of the polar solvent.
The observed effect of the long-wavelength shift of the fluorescence spectrum with increasing excitation wavelength is explained
in terms of the inhomogeneous broadening of electronic spectra of polar solutions, and it should be described using the scheme
of energy states that takes into account sublevels of orientational broadening due to orientational dipole-dipole interactions
of the fluorophore with nearest molecules of the polar solvent, as well as the relation between the fluorophore lifetime in
the excited state and the dielectric relaxation time of solvent molecules in the field of the fluorophore dipole. 相似文献
20.
A. K. Shuaibov Z. T. Gomoki A. G. Kalyuzhnaya A. I. Shchedrin 《Optics and Spectroscopy》2010,109(5):669-673
The UV radiation of glow- and capacitive-discharge lamps based on mixtures of inert gases with iodine vapors are optimized
in the spectral range of 175–360 nm, in which working helium-iodine mixtures of different compositions are used. The most
intense spectral lines in the bactericidal region of the spectrum were the atomic lines of iodine (183.0, 206.2 nm), and in
the region of 320–360 nm, emission of the spectral band of an iodine molecule prevailed with a maximum at λ = 342 nm. For
a capacitive lamp with a casing opaque in the spectral range λ < 250 nm, the main part of the plasma emission power is concentrated
in the A′-D′ band of an iodine molecule with a maximum at 342 nm. The emission brightness of this lamp is optimized in iodine molecule
transitions depending on the partial helium pressure. We present the results of simulating the kinetics of processes in a
glow-discharge plasma in mixtures of He, Xe, and iodine vapors. We establish the dependence of the main part of the emission
intensity of the 206.2 nm spectral line of an iodine atom and the 342 nm band of an iodine molecule on the helium pressure
in a glow-discharge lamp operating on a He-I2 mixture. 相似文献