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1.
We have studied photoluminescence and thermoluminescence (PL and TL) in CaGa2Se4:Eu crystals in the temperature range 77–400 K. We have established that broadband photoluminescence with maximum at 571 nm
is due to intracenter transitions 4f6 5d–4f7 (8S7/2) of the Eu2+ ions. From the temperature dependence of the intensity (log I–103/T), we determined the activation energy (E
a = 0.04 eV) for thermal quenching of photoluminescence. From the thermoluminescence spectra, we determined the trap depths:
0.31, 0.44, 0.53, 0.59 eV. The lifetime of the excited state 4f6 5d of the Eu2+ ions in the CaGa2Se4 crystal found from the luminescence decay kinetics is 3.8 μsec.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 112–116, January–February, 2009. 相似文献
2.
Iron oxide films were deposited on <100> Si substrates by reactive pulsed laser deposition (RPLD) using a KrF laser (248 nm).
These films were deposited too by laser (light) chemical vapor deposition (LCVD) using continuous ultraviolet photodiode radiation
(360 nm). The deposited films demonstrated semiconducting properties. These films had large thermo-electromotive force (e.m.f.)
coefficient (S) and high photosensitivity (F). For films deposited by RPLD the S coefficient varied in the range 0.8–1.65 mV/K at 205–322 K. This coefficient depended on the band gap (E
g
) of the semiconductor films, which varied in the range 0.43–0.93 eV. The largest F value found was 44 Vc/W for white light at power density I≅0.006 W/cm2. Using LCVD, iron oxide films were deposited from iron carbonyl vapor. For these films, the S coefficient varied in the range −0.5 to 1.5 mV/K at 110–330 K. The S coefficient depended on E
g
of the semiconductor films, which varied in the range 0.44–0.51 eV. The largest F value of these films was about 40 Vc/W at the same I≅0.006 W/cm2. Our results showed that RPLD and LCVD can be used to synthesize iron oxide thin films with variable stoichiometry and, consequently,
with different values of E
g
. These films have large S coefficient and high photosensitivity F and therefore can be used as multi-parameter sensors: thermo–photo sensors. 相似文献
3.
H. Kim G. P. Kushto R. C. Y. Auyeung A. Piqué 《Applied Physics A: Materials Science & Processing》2008,93(2):521-526
Fluorine-doped tin oxide (FTO) thin films have been investigated as an alternative to indium tin oxide anodes in organic photovoltaic
devices. The structural, electrical, and optical properties of the FTO films grown by pulsed laser deposition were studied
as a function of oxygen deposition pressure. For 400 nm thick FTO films deposited at 300°C and 6.7 Pa of oxygen, an electrical
resistivity of 5×10−4 Ω-cm, sheet resistance of 12.5 Ω/□, average transmittance of 87% in the visible range, and optical band gap of 4.25 eV were obtained. Organic photovoltaic (OPV)
cells based on poly(3-hexylthiophene)/[6,6]-phenyl-C61-butyric acid methyl ester bulk heterojunctions were prepared on FTO/glass electrodes and the device performance was investigated as a function of FTO
film thickness. OPV cells fabricated on the optimum FTO anodes (∼300–600 nm thick) exhibited power conversion efficiencies
of ∼3%, which is comparable to the same device made on commercial ITO/glass electrodes (3.4%). 相似文献
4.
Photoacoustic spectroscopy (PAS) is one of the important branches of spectroscopy, which enables one to detect light-induced
heat production following the absorption of pulsed radiation by the sample. As2S3, As2Se3 and GeSe2 exhibit a wide variety of photo-induced phenomena that enable them to be used as optical imaging or storage medium and various
electronic devices, including electro-optic information storage devices and optical mass memories. Therefore, accurate measurement
of thermal properties of semiconducting films is necessary to study the memory density. The thermal conductivity of thin films
of As2S3 (thickness 100 μm and 80 μm), As2Se3 (thickness 100 μm and 80 μm) and GeSe2 (thickness 120 μm and 100 μm) has been measured using PAS technique. Our result shows that the thermal conductivity of thicker films is larger than the
thinner films. This can be explained by the thermal resistance effect between the film and the surface of the substrate.
相似文献
5.
So Yeon Bang Kyung Ju Lee Joo Hwan Koh Moon-Sung Kang Yong Soo Kang Jong Hak Kim 《Ionics》2008,14(2):143-148
In this paper, we aim to prepare polymer electrolytes consisting of NaI and I2 dissolved in poly(ethylene oxide) (PEO) and dioctyl phthalate (DOP) as an additive and apply the electrolytes to dye-sensitized
solar cells (DSSC). Upon the incorporation of salt, the phthalic-stretching C=O bands of DOP in Fourier transform infrared
spectra shifted to a lower wave number (Δf = 93 cm−1), confirming the unusual strong complex formation between sodium ions and phthalic oxygen. Coordinative interactions and
structural changes of PEO/NaI/I2/DOP electrolytes have also been characterized by wide angle X-ray scattering, presenting an almost amorphous structure of
the polymer electrolytes. The ionic conductivity of the polymer electrolytes reached ∼10–4 S/cm at room temperature at the mole ratio of [EO]:[Na]:[DOP] = 10:1:0.5, as determined by the four-probe method. DSSC using
the polymer electrolytes and conductive indium tin oxide glasses exhibited 2.9% of overall energy conversion efficiency (=P
max/P
in × 100) at one sun condition (100 mW/cm2). The good interfacial contact between the electrolytes and the dye-attached nanocrystalline TiO2 layers were verified by field-emission scanning electron microscopy. 相似文献
6.
The layered LiNi0.5Mn0.47Al0.03O2 was synthesized by wet chemical method and characterized by X-ray diffraction and analysis of magnetic measurements. The
powders adopted the α-NaFeO2 structure. This substitution of Al for Mn promotes the formation of Li(Ni0.472+Ni0.033+Mn0.474+Al0.033+)O2 structures and induces an increase in the average oxidation state of Ni, thereby leading to the shrinkage of the lattice
unit cell. The concentration of antisite defects in which Ni2+ occupies the (3a) Li lattice sites in the Wyckoff notation has been estimated from the ferromagnetic Ni2+(3a)–Mn4+(3b) pairing observed below 140 K. The substitution of 3% Al for Mn reduces the amount of antisite defects from 7% to 6.4–6.5%.
The analysis of the magnetic properties in the paramagnetic phase in the framework of the Curie–Weiss law agrees well with
the combination of Ni2+ (S = 1), Ni3+ (S = 1/2) and Mn4+ (S = 3/2) spin-only values. Delithiation has been made by the use of K2S2O8. According to this process, known to be softer than the electrochemical one, the nickel ions in the (3b) sites are converted into Ni4+ in the high spin configuration, while Ni2+(3a)–Mn4+(3b) ferromagnetic pairs remain, as the Li+(3b) ions linked to the Ni2+(3a) ions in the antisite defects are not removed. The results show that the antisite defect is surrounded by Mn4+ ions, implying the nonuniform distribution of the cations in agreement with previous NMR and neutron experiments. 相似文献
7.
A new scheme of optical film sensor is presented. The sensor is based on p-polarized reflectance, consisting of a sensing coated substrate, is easily optimized for maximum sensitivity in different applications. The resolutions of refractive index nf, extinction coefficient kf and thickness hf of the sensitive films are predicted to be 10−7, 10−5 and 10−3 nm, respectively. Experimentally, we selected the sol–gel derived SnO2 films as gas-sensitive films and conducted preliminary gas-sensing test. The results indicate that novel optical film sensor scheme has higher sensitivity, and the detection sensitivity is available to 10−1 ppm on the condition of optimum optical parameters and incident angle. 相似文献
8.
We study memoryless, discrete time, matrix channels with additive white Gaussian noise and input power constraints of the
form Y
i = ∑
j
H
ij
X
j
+ Z
i
, where Y
i
, X
j
and Z
i
are complex, i = 1… m, j = 1… n, and H is a complex m× n matrix with some degree of randomness in its entries. The additive Gaussian noise vector is assumed to have uncorrelated
entries. Let H be a full matrix (non-sparse) with pairwise correlations between matrix entries of the form E[H
ik
H
*
jl] = 1/n
C
ij
D
kl, where C, D are positive definite Hermitian matrices. Simplicities arise in the limit of large matrix sizes (the so called large-n limit) which allow us to obtain several exact expressions relating to the channel capacity. We study the probability distribution
of the quantity f(H) = log (1+PH
†
SH) . S is non-negative definite and hermitian, with TrS = n and P being the signal power per input channel. Note that the expectation E[f(H)], maximised over S, gives the capacity of the above channel with an input power constraint in the case H is known at the receiver but not at the transmitter. For arbitrary C, D exact expressions are obtained for the expectation and variance of f(H) in the large matrix size limit. For C = D = I, where I is the identity matrix, expressions are in addition obtained for the full moment generating function for arbitrary (finite)
matrix size in the large signal to noise limit. Finally, we obtain the channel capacity where the channel matrix is partly
known and partly unknown and of the form α; I+ β H, α,β being known constants and entries of H i.i.d. Gaussian with variance 1/n. Channels of the form described above are of interest for wireless transmission with multiple antennae and receivers. 相似文献
9.
Kun Yin Hui Xu Gaoyu Zhong Gang Ni Wei Huang 《Applied Physics A: Materials Science & Processing》2009,95(2):595-600
A novel europium complex Eu(TTA)3(CPPO)2 (1) (TTA=thenoyltrifluoroacetone, CPPO=9-[4-(diphenyl-phosphinoyl)-phenyl]-9H-carbazole) based on the phosphine oxide ligand
with bipolar structure was used to fabricate double-layer devices. The strong hole injection and transport ability of 1 was proved. The luminance of 414 cd m−2 was achieved with the device configuration ITO/Eu(TTA)3(CPPO)2(40 nm)/BCP (30 nm)/Mg:Ag (BCP = 2, 9-dimethyl-4, 7-diphenyl-1, 10-phenanthroline), which is favorable among double-layer
organic light emitting devices based on small molecular Eu3+ complexes. The maximum current efficiency of 2.44 cd A−1 and external quantum efficiency of 1.55% demonstrate the potential application of 1 as a promising candidate for high-efficiency, simple-structure and pure red-emitting devices. 相似文献
10.
Conductivity studies of plasticized anhydrous PEO-KOH alkaline solid polymer electrolyte 总被引:1,自引:0,他引:1
Polyethylene oxide (PEO)–potassium hydroxide (KOH)-based alkaline solid polymer electrolyte films have been prepared by using
methanol as solvent. The highest room temperature ionic conductivity of (2.1 ± 0.5) × 10−8 S cm−1 was achieved for the composition of 70 wt% PEO:30 wt% KOH. The addition of plasticizer, ethylene carbonate, propylene carbonate,
or polyethylene glycol to the highest conductivity of PEO–KOH system helps to increase the ambient ionic conductivity to the
order of 10−6–10−4 S cm−1. The log σ vs 1/T plot of PEO–KOH showed a small conductivity decrease at 50–60 °C range. The small decrease and the hysteresis that occur
during the heating–cooling cycle was overcome by the presence of the plasticizer. X-ray diffraction observation supports the
conductivity results. 相似文献
11.
Guang Yang Aiping Chen Ming Fu Hua Long Peixiang Lu 《Applied Physics A: Materials Science & Processing》2011,104(1):171-175
By controlling the oxygen pressure, single-phase CuO and Cu2O thin films have been obtained on quartz substrates using a pulsed laser deposition technique. The structure properties and
linear optical absorption of the films were characterized by X-ray diffraction and UV–VIS spectroscopy. By performing z-scan measurements using a femtosecond laser (800 nm, 50 fs), the real and imaginary parts of the third-order nonlinear susceptibility,
Re χ
(3) and Im χ
(3), of the films were determined. Both CuO and Cu2O films exhibited large optical nonlinearities, which is comparable to those in some representative semiconductor films such
as ZnO and GaN films using femtosecond laser excitation. Compared with Cu2O films, the CuO films showed larger third-order nonlinear optical effects under off-resonance excitation. Furthermore, the
mechanisms of the optical nonlinearities in CuO and Cu2O films are explained in the main text. It was suggested that the reasons of the difference in their nonlinear refractive
effects may be related to the different electronic structure in CuO and Cu2O materials. 相似文献
12.
Results of the scanning electron microscopy (SEM), X-ray diffraction (XRD), optical absorption, photoconductivity (PC), and
photoluminescence (PL) studies for the CdSSe:CdCl2,Ho films are presented in this paper. The SEM studies of different CdSSe films show a layered growth structure. A crystalline
nature of the films is observed in the XRD studies. The regions with stacking fault were also observed in the X-ray diffractograms.
The optical absorption spectra of these films show variations corresponding to the band gaps and the grain-sizes obtained
under various deposition conditions and also with annealing. The effect of flux, impurities and annealing on the saturated
photo to dark current ratio Ipc/Idc is observed in the PC rise and decay studies. The maximum value of Ipc/Idc ∼107 is obtained for the impurity doped annealed films. The PL emission spectra of CdSSe films show two emission peaks associated
with the annihilation of free excitons and the transitions between shallow donor and deep acceptor states. In CdSSe:CdCl2,Ho films, two PL emission peaks are observed at 495 nm and 545 nm corresponding to the transitions 5S2→5I8 and 5F3→5I8, respectively, in Ho. The effect of pH on PL and grain size is also included in the present studies. 相似文献
13.
Physical mechanics of fluctuation processes in advanced submicron and decananometer MOSFETs (metal-oxide-semiconductor field-effect
transistors) including the ultra-thin film SOI (siliconon-insulator) devices using strained silicon films are reviewed. The
review is substantially based on the results obtained by the authors. It is shown that the following drastic changes occur
in the nature and parameters of noise in such devices as a result of their downscaling when the gate oxide thickness and the
channel length and width are decreased, the SOI substrates are used, the silicon film thickness is reduced, the film doping
level is varied, the strained silicon films are employed, etc. Firstly, the Lorentzian components can appear in the current
noise spectra. Those components are due to (i) electron tunneling from the valence band through the gate oxide in the SOI
MOSFETs of a sufficiently thin gate oxide (LKE-Lorentzians); (ii) Nyquist fluctuations generated in the source and drain regions
near the back Si/SiO2 interface in the SOI MOSFETs (BGI Lorentzians); (iii) electron exchange between the channel and some single trap in the gate
oxide of the transistors with sufficiently small length and width of the channel (RTS Lorentzians). Secondly, the 1/f-noise level can increase due to (i) the appearance of recombination processes near the Si/SiO2 interface activated by the currents of electron tunneling from the valence band; (ii) an increase in the trap density in
the gate oxide of the devices fabricated on the biaxially tensile-strained silicon films; (iii) the contribution of the 1/f fluctuations of the current flowing through the gate oxide as a result of electron tunneling from the conduction band. At
the same time, the 1/f-noise level may decrease due to a decrease in the trap density in the gate oxide of the transistors fabricated on the uniaxially
tensile-strained silicon films. Moreover, a 1/f
1.7 component may appear in the noise spectra for the transistors of a sufficiently thin gate oxide, whose component is due to
charge fluctuations on the defects located near the interface between the gate polysilicon and the gate oxide. 相似文献
14.
Fluorophosphate glass with 4 mol. % ErF3 content was prepared. The different scanning calorimetry was conducted. Raman spectrum, infrared transmission spectrum, absorption spectrum were measured. Fluorescence spectrum and lifetime of emission around 1.53 μm were measured under 970 nm laser diode excitation. The metaphosphate content in the composition is limited, but the maximum phonon energy of glass amounts to 1290 cm-1, and is comparatively high. The full width at half maximum is about 56 nm, and is wider than for most of the materials investigated. The measured lifetime of 4
I
13/2→4
I
15/2 transition, contributed by the high phonon energy, inefficient interaction of Er3+ ions, and low water content, amounts to no less than 7.36 ms though the Er3+ concentration is high. This work might provide useful information for the development of compact optical devices. PACS 78.20.-e; 42.70.Ce; 42.70.Hj; 32.70.Cs 相似文献
15.
Thin films of ZnSe and PEO–chitosan blend polymer doped with NH4I and iodine crystals were prepared to form the two sides of a semiconductor electrolyte junction. ZnSe was electrodeposited
on indium tin oxide (ITO) conducting glass. The polymer is a blend of 50 wt% chitosan and 50 wt% polyethylene oxide. The polymer
blend was complexed with ammonium iodide (NH4I), and some iodine crystals were added to the polymer–NH4I solution to provide the I−/I3−redox couple. The room temperature ionic conductivity of the polymer electrolyte is 4.32 × 10−6 S/cm. The polymer film was sandwiched between the ZnSe semiconductor and an ITO glass to form a ZnSe/polymer electrolyte/ITO
photovoltaic cell. The open circuit voltage (V
oc) of the fabricated cells ranges between 200 to 400 mV and the short circuit current between 7 to 10 μA. 相似文献
16.
The legume lectins are a large family of homologous carbohydrate-binding proteins. Their carbohydrate specificity and quaternary
structure vary widely. The carbohydrate binding activity of legume lectins depends on the simultaneous presence of calcium
and transition-metal ions, especially the Mn2+ ion. In the present work, thermal stabilities of Mn2+ binding sites in pea, lentil, soybean and kidney-bean lectins have been studied by electron spin resonance spectroscopy in
the temperature range of 120–400 K in different atmospheres. The evolution of parameters, such as the line width, peak-to-peak
intensity associated with the hyperfine transition [m
I
(+5/2) → m′
I
(−5/2)] at the lowest magnetic field side of the central electron transition [m
S
(+1/2) → m′
S
(−1/2)] of the Mn+2 ion, g-factor and hyperfine splitting was evaluated. Annealing was also performed at high temperatures (353, 373, 383, 403 and 443
K) and the oxidation activation energy of Mn2+ ions in the indicated legumes was determined. 相似文献
17.
Solvent-free films of poly (ethylene oxide)–silver triflate (PEO–AgCF3SO3)/MgO-based nanocomposite polymer electrolytes (PEO)50AgCF3SO3–x wt.% MgO (x = 1, 3, 5, 7, and 10) obtained using solution casting technique were found to exhibit an appreciably good complexation of
MgO nanofiller within the polymer electrolyte system and non-Debye type of relaxation as revealed by Fourier transform infrared
and complex impedance analyses. Optimized filler (5 wt.% MgO) when incorporated into the polymer electrolyte resulted in a
maximum electrical conductivity of 2 × 10−6 S cm−1 in conjunction with a silver ionic transference number (t
Ag+) of 0.23 at room temperature (298 K). Detailed structural, thermal, and surface morphological investigation indicated a slight
reduction in the degree of crystallinity owing to the addition of MgO nanofiller. 相似文献
18.
N. Venkatram D. Narayana Rao L. Giribabu S. Venugopal Rao 《Applied physics. B, Lasers and optics》2008,91(1):149-156
We report our results on the nonlinear optical and optical limiting properties of two alkoxy phthalocyanines namely 2,3,9,10,16,17,23,24-octakis-(heptyloxy)
phthalocyanine and 2,3,9,10,16,17,23,24-octakis-(heptyloxy) phthalocyanine zinc(II) studied at a wavelength of 532 nm using
6 ns pulses. Using the standard Z-scan technique we observed that both the phthalocyanines exhibited negative nonlinearity
as revealed by the signature of closed aperture data. The magnitude of the nonlinear refractive index n2 evaluated from the closed aperture data was ∼ 1.61×10-11 cm2/W for the free-base phthalocyanine and ∼ 1.56×10-11 cm2/W for the metallic phthalocyanine. Open aperture Z-scan data indicates strong nonlinear absorption in both the phthalocyanines
with measured nonlinear coefficients of ∼ 1650 cm/GW and ∼ 1850 cm/GW respectively. We also report optical limiting properties
of these phthalocyanines with limiting thresholds (I1/2) of ∼ 0.5 J/cm2. Our studies suggest that these phthalocyanines are one of the best molecules for nonlinear optical applications studied
recently.
PACS 42.65.-k; 42.70.Jk, 42.65.Jx 相似文献
19.
The influence of the sample orientation on the effective value of the hydrostatic piezoelectric coefficients d
h
(i)
of Sn2P2S6 crystals has been studied. The hydrostatic piezoelectric coefficients d
h
(1)
and d′
h
(3)
, were measured, d
h
(1)
=(244±3) pC/N and d′
h
(3)
=(92±1) pC/N. The hydrostatic piezoelectric coefficient d
h
(3)
for orthogonal axis system was calculated to be d
h
(3)
=(87±2) pC/N. The, optimal orientation of the sample has been found as (Xy l)−20°-cut. Maximal value of the effective hydrostatic piezoelectric coefficient d
h
(1)
equals 260 pC/N. Double rotated samples were also studied. The orientation of the samples insensitive to the pressure has
been found. The theoretical mean value of hydrostatic piezoelectric coefficient (d
h
)
mean
corresponding to randomly oriented Sn2P2S6 grains in a poled composite has been calculated to be (d
h
)
mean
=136 pC/N. 相似文献
20.
T.J. Rinke R.B. Bergmann J.H. Werner 《Applied Physics A: Materials Science & Processing》1999,68(6):705-707
Thermal crystallization of a double layer porous Si film creates a monocrystalline Si film with a thin separation layer between
the Si film and the reusable starting wafer. The process enables transfer of thin monocrystalline Si films to foreign substrates,
whereby devices may be formed before or after separation of the film. Sub-micrometer thick films are almost compact, while
films with a thickness of several μm contain voids, and are therefore termed “quasi-monocrystalline”. Internal voids strongly
enhance optical absorption by light scattering. The hole mobility is 78 cm2 V-1 s-1 at a p-type starting wafer resistivity of 0.05 Ω cm.
Received: 24 March 1999 / Accepted: 29 March 1999 / Published online: 5 May 1999 相似文献