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1.
V. I. Pokatashkin V. V. Syt'ko A. N. Krasovskii D. S. Umreiko 《Journal of Applied Spectroscopy》1999,66(6):960-965
Using the configuration interaction model, we investigate the dependence of the shape, half-width, and position of the phononless
lines (PL) in absorption and luminescence spectra of K3UO2F5 and Rb3UO2F5 crystals in the region 4.2–40 K. It is established that a Stokes shift in combining electron states leads to a nonsymmetric
distortion in the Gauss shape of thePL. The temperature broadening of the PL is mainly associated with a change in the population of the initial states of oscillators
(of the ground state for absorption and the 1 st excited state for luminescence), while a shift in maxima of the PL is caused
by the forbidden 1 st electron transitions in complex uranyl compounds and is determined by the nonlinear electron-phonon
interaction.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 6, pp. 824–827, November–December, 1999. 相似文献
2.
Zongyou Yin Xiaohong Tang Jixuan Zhang Jinghua Zhao Sentosa Deny Hao Gong 《Journal of nanoparticle research》2009,11(8):1947-1955
The effects of the top barrier and the dot density on photoluminescence (PL) of the InAs quantum dots (QDs) sandwiched by
the graded InxGa1−xAs barriers grown by metal-organic vapor phase epitaxy (MOVPE) have been studied. Two emission peaks corresponding to the
ground state and the 1st excited state transitions of the QD structures have been observed, which matches well to the theoretical
calculation. The PL emission linewidth and intensity of the InAs QDs structure are improved by reducing the Indium/Gallium
composition variation of the graded InxGa1−xAs top barrier layer of the structure. The QDs’ ground states filling excitation power depends on the crystal quality of the
InGaAs barrier layer and the QD density. The extracted thermal activation energy for the QDs’ PL emission is sensitive to
the QD size. 相似文献
3.
Abstract Measurements of the photoluminescence (PL) of strained In0.2Ga0.8As/GaAs and In0.15Ga0.85As/GaAs quantum well structures together with the PL from bulk GaAs, in a diamond anvil cell show that the pressure coefficient of the ground confined state in the wells depends upon well width (LZ). In the thinnest wells, the coefficient is closer to that of the bulk GaAs (10.7 meV/kbar), as expected. However, in the widest wells the coefficients tend to values (9.5meV/kbar for the 15% alloy and 9.1meV/kbar for the 20% alloy) that are significantly lower than the pressure coefficient of unstrained In0.53Ga0.47As (10.9meV/kbar). It is found that the low pressure coefficients can not be explained by the change in uniaxial stress with pressure due to a difference in bulk moduli between the barrier and well. 相似文献
4.
F. Guffarth R. Heitz A. Schliwa K. Ptschke D. Bimberg 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):326
A pronounced modulation is observed in the photoluminescence (PL) spectrum of self-organized InAs/GaAs quantum dots (QDs), recorded at low excitation densities. The clearly distinguishable peaks are identified as a multimodal distribution of the ground state transition energy, originating from a discrete, stepwise variation of the structural properties of the QDs, which is associated with an increase of the QD height in monolayer (ML) steps. The observation of a ML splitting implies a flat QD shape with well-defined upper and lower interfaces as well as negligible indium segregation. The electronic properties of the InAs/GaAs QDs were investigated by PL and PL-excitation spectroscopy and are discussed based on realistic calculations for flat InAs/GaAs QDs with a truncated pyramidal shape based on an extended 8-band k·p model. The calculations predict a red shift of the ground state transition with each additional ML, which saturates for heights above 9 ML, is in good agreement with experiment. 相似文献
5.
Bani-Yaseen AD 《Journal of fluorescence》2011,21(3):1061-1067
The Fluorescence spectroscopic and solvatochromic behavior of Sulfisoxazole, a sulfa drug with antimicrobial activities, in
various pure solvents of different polarity and hydrogen bonding capability is reported. The fluorescence emission spectrum
of sulfisoxazole was found to be solvent polarity dependent, where a notable red shift in emission maximum was observed with
increasing solvent polarity as well as hydrogen bonding capability. The effects of the latter two solvent parameters were
quantitatively investigated using the methods of Lippert–Mataga and solvatochromic comparison method (SCM) that is based on
the Kamlet-Taft equation. Particularly, the Lippert–Mataga method was applied to estimate the dipole moment of the excited
state (μe) upon plotting Stokes shift versus solvent polarizability (Δf), where a value of 11.54 Debye was obtained. On the other hand, applying the multiple regression analysis to the SCM method
revealed that solvent polarizability (π*) and hydrogen-bond donor capability (α) approximately equally stabilize sulfisoxazole
in the excited state with minor destabilization contribution by the hydrogen-bond acceptor capability (β). These findings
revealed that the excited state of sulfisoxazole is stabilized by polar solvents, indicating that this drug molecules exhibit
larger dipole moment in the excited state than in the ground state, which in turn implies that a potential intramolecular
charge transfer (ICT) occurs after excitation. 相似文献
6.
M. Babamoradi M. Heidari Saani A. Ranjbar M. A. Vesaghi Y. Kawazoe 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,84(1):1-9
Using a generalized Hubbard Hamiltonian, many-electron wavefunctions of negatively
charged (NV−) and neutral nitrogen-vacancy (NV0) centers in diamond
were calculated. We report the effect of symmetric relaxation of surrounding atoms on the
spin density, calculated from the many electron wavefunctions in the ground and excited
states. We evaluated the error, that, arises in estimation of spin density when lattice
relaxation effect is neglected in Electron Paramagnetic Resonance experiment and showed
that the ground state spin density distribution is accessible in outward relaxations. The
computed oscillator strengths give a higher efficiency for the 1.945 eV photoluminescence
(PL) line of NV− with respect to 2.156 eV PL line of NV0 which
agrees well with experiment. This result is explained based on the largest the ground
state spin among available values for the NV− with respect to NV0.
The transition probability between degenerate ground and excited states slightly depends
on the S
z
value. Finally, we report on the
electronic configurations which contribute to the ground and excited states and discuss
the population variation of electronic configurations with relaxation. 相似文献
7.
Quasihydrostatic pressure resistivity experiments on a single crystal of SmS are reported up to 27.5 kbar. At low temperature, a regime change occurs at P ~ 20 kbar, between a “quasiinsulating” behavior (P < 20 kbar) and a metallic ground state (P 20 kbar). Striking similarities appear with TmSe and TmS cases. 相似文献
8.
L. Bouzaïene L. Sfaxi M. Baira H. Maaref C. Bru-Chevallier 《Journal of nanoparticle research》2011,13(1):257-262
Self-assembled InAs/GaAs (001) quantum dots (QDs) were grown by molecular beam epitaxy using ultra low-growth rate. A typical
dot diameter of around 28 ± 2 nm and a typical height of 5 ± 1 nm are observed based on atomic force microscopy image. The
photoluminescence (PL) spectra, their power and temperature dependences have been studied for ground (GS) and three excited
states (1–3ES) in InAs QDs. By changing the excitation power density, we can significantly influence the distribution of excitons
within the QD ensemble. The PL peak energy positions of GS and ES emissions bands depend on an excitation light power. With
increasing excitation power, the GS emission energy was red-shifted, while the 1–3ES emission energies were blue-shifted.
It is found that the full width at half maximum of the PL spectra has unusual relationship with increasing temperature from
9 to 300 K. The temperature dependence of QD PL spectra shown the existence of two stages of PL thermal quenching and two
distinct activation energies corresponding to the temperature ranges I (9–100 K) and II (100–300 K). 相似文献
9.
The absorption of OH∗ chemiluminescence and laser-induced fluorescence (LIF) in the exhaust gas of confined premixed laminar CH4/air flames at atmospheric pressure was investigated. One flame was used as source and a second as absorber. OH LIF was excited
in the ν″=0→ν′=1 band of the A–X electronic system around ≈283 nm and spectrally resolved detected in the (0,0) and (1,1) vibrational bands
around 305–320 nm. For OH∗ chemiluminescence, spectrally resolved detection was performed in the wavelength range 280–340 nm. For an absorption path
of 54 mm and at T≈2000 K, signal trapping on the order of 10–40% was observed. Signal trapping was most pronounced in the (0,0) band, as expected
from the thermal population distribution of OH in the electronic ground state. The spectral distribution of the signals and
the wavelength dependence of the signal trapping are addressed in this paper. Implications from the results with respect to
detection strategies and chemiluminescence-based equivalence ratio measurements are discussed. 相似文献
10.
The absorption and emission spectra of two coumarins namely 7, 8 benzo-4-azidomethyl coumarin (C1) and 6-methoxy-4-azidomethyl coumarin (C2) have been recorded at room temperature in solvents of different polarities. The ground state dipole moments (μ
g
) of two coumarins were determined experimentally by Guggenheim method. The exited state (μ
e
) dipole moments were estimated from Lippert’s, Bakhshievs and Chamma-Viallet’s equations by using the variation of Stoke’s
shift with the solvent dielectric constant and refractive index. The ground and excited state dipole moments were calculated
by means of solvatochromic shift method and also the excited state dipole moments are determined in combination with ground
state dipole moments. It was observed that dipole moments of excited state were higher than those of the ground state, indicating
a substantial redistribution of the π-electron densities in a more polar excited state for two coumarins. 相似文献
11.
In the present paper, a new two-parameter inverted equation of state (EOS) is developed which is found to be working very
well in the high-pressure region. To check its success and validity, this EOS has been applied in a number of solids. The
computed volume compression is found to be in very good agreement with the experimental data in the whole range of pressure
in all the solids. The minimum and the maximum pressure range used in the present study is 0–320 kbar and 0–3000 kbar, respectively. 相似文献
12.
T. Passerat de Silans B. Farias M. Oriá M. Chevrollier 《Applied physics. B, Lasers and optics》2006,82(3):367-371
We propose an optical technique to load neutral atoms in quantum adsorption states of a dielectric surface. Considering a
realistic atom–surface potential well, we show that free cold lithium atoms approaching a LiF surface may be transferred to
a surface bound state of the first excited atomic state. We also discuss schemes to populate adsorption energy levels of the
atomic electronic ground state, and we find that spontaneous mechanisms transfer more than 90% of the excited adsorbed atoms
into vibrational levels of the fundamental adsorption potential. The lifetime of the resulting two-dimensional waveguide is
calculated, considering the adatoms’ interaction with the crystal phonons.
PACS 34.50.Dy; 68.43.-h; 68.35.Ja; 32.80.Pj 相似文献
13.
A. V. Malakhovskii S. L. Gnatchenko I. S. Kachur V. G. Piryatinskaya A. L. Sukhachev V. L. Temerov 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,80(1):1-10
Optical absorption spectra of trigonal crystal TbFe3(BO3)4 have been studied in the region of 7F6 → 5D4 transition in Tb3+ ion depending on temperature (2–220 K) and on magnetic field (0–60 kOe). Splitting of the Tb3+ excited states, both under the influence of the external magnetic field and effective exchange field of the Fe-sublattice,
have been determined. Landé factors of the excited states have been found. Stepwise splitting of one of the
absorption lines has been discovered in the region of the Fe-sublattice magnetic ordering temperature. This is shown to be
due to the abrupt change of equilibrium geometry of the local Tb3+ ion environment only in the excited state of the Tb3+ ion. In general, the magnetic ordering is accompanied by temperature variations of the Tb3+ local environment in the excited states. The crystal field splitting components have been identified. In particular, it has
been shown that the ground state (in D
3 symmetry approximation) consists of two close singlet states of A
1 and A
2 type, which are split and magnetized by effective exchange field of the Fe-sublattice. Orientations of magnetic moments of
the excited electronic states relative to that of the ground state have been
experimentally determined in the magnetically ordered state of the crystal. A pronounced shift of one of absorption lines
has been observed in the vicinity of the TbFe3(BO3)4 structural phase transition. The temperature interval of coexistence of the phases is about 3 K. 相似文献
14.
The pressure dependence of optical transitions in Ga0.64In0.36As/GaAs and Ga0.64In0.36N0.01As0.99/GaAs single quantum well (SQW) structures were studied in photoreflectance (PR) spectroscopy. In order to apply high hydrostatic pressure, up to ∼11 kbar, the liquid-filled clamp-pressure cell with a sapphire window for optical access has been adopted in the PR set-up with the so called ‘bright configuration’. It has been found that the linear hydrostatic pressure coefficient for the ground state transition are equal to 8.6 and 7.3 meV/kbar for the GaInAs/GaAs and GaInNAs/GaAs SQWs, respectively. This result shows that the incorporation of only 1% of N atoms into GaInAs/GaAs leads to ∼15% decrease in the pressure coefficient. In addition, a non-linearity in the pressure dependence of the ground state transition has been resolved for the GaInNAs/GaAs SQW. 相似文献
15.
G. Gerasimov B. Krylov A. Loginov G. Zvereva R. Hallin A. Arnesen F. Heijkenskjöld 《Applied physics. B, Lasers and optics》1998,66(1):81-90
u , 0u
+ and the weakly bound ground state 0g
+. A semiempirical method was suggested and applied to describe the experimental spectra and to estimate the temperature of
the radiating plasma volume. Electron impact, transferring dimers from the ground state to the excited states, is shown to
be an efficient excitation mechanism in the 100–850 hPa and the 10–50 mA pressure and discharge current ranges. The spectra
obtained as well as the results of calculations corroborate the high rate of this mechanism.
Received: 31 July 1996/Revised version: 17 March 1997 相似文献
16.
S. M. Stishov A. E. Petrova S. Khasanov G. Kh. Panova A. A. Shikov J. C. Lashley D. Wu T. A. Lograsso 《Journal of Experimental and Theoretical Physics》2008,106(5):888-896
Magnetic susceptibility, heat capacity, thermal expansion, and resistivity of a high-quality single crystal of MnSi were carefully
studied at ambient pressure. The calculated change in magnetic entropy in the temperature range 0–30 K is less than 0.1R, a low value that emphasizes the itinerant nature of magnetism in MnSi. A linear temperature term dominates the behavior
of the thermal expansion coefficient in the range 30–150 K, which correlates to a large enhancement of the linear electronic
term in the heat capacity. A surprising similarity between variation of the heat capacity, the thermal expansion coefficient,
and the temperature derivative of resistivity through the phase transition in MnSi is observed. Specific forms of the heat
capacity, thermal expansion coefficient, and temperature derivative of resistivity at the phase transition to a helical magnetic
state near 29 K are interpreted as a combination of sharp first-order features and broad peaks or shallow valleys of yet unknown
origin. The appearance of these broad satellites probably hints at a frustrated magnetic state in MnSi slightly above the
transition temperature. Present experimental findings bring the current views on the phase diagram of MnSi into question.
The text was submitted by the authors in English. 相似文献
17.
C. Sciascia J. Crochet T. Hertel G. Lanzani 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,75(2):115-120
We study the photo-induced transmission change (ΔT/T) upon
quasi-continuum laser excitation, for different modulation frequency and
excitation intensity in films of (6, 5) enriched CoMoCat single wall
nanotubes (SWNTs) embedded in a polymeric matrix. This technique probes
long-lived excited species, with lifetime in the 1 ms–1 s domain. The
observed line-shape of ΔT/T spectra that can be assigned to a
superposition of ground state bleaching and absorption modulation. We
speculate that photo-excitation creates charges which get trapped in the
sample, acquiring ms lifetime. This causes bleaching of the ground state
absorption due to state filling and possibly a tube diameter expansion, with
consequent blue shift of the optical transition. 相似文献
18.
The pressure dependence of the vibrational modes in ZnP2 has been investigated by Raman Spectroscopy using a diamond anvil cell, up to 150 kbar pressure. The intrachain phosphorus
modes exhibit a strong pressure dependence whereas the low frequency Zn-P modes soften very slightly under pressure. For a
crystal which is treated as a molecular crystal this is an unexpected result. It is suggested that the behaviour may be due
to a buckling of the phosphorus chain, or due to a double bond promotion between P atoms, or a charge transfer under pressure.
The shift in the energy gap has also been measured to 100 kbar hydrostatic pressure. There is a small initial blue shift which
gradually changes over to a red shift. However the whole shift in 100 kbar is quite small. Combining the (dEg/dP)
T
with the published (dEg/dT)
P
the thermal expansion contribution and the electron-phonon interaction contribution were evaluated. The latter dominates
the total (dEg/dT)
P
of ZnP2.
The authors felicitate Prof. D S Kothari on his eightieth birthday and dedicate this paper to him on this occasion. 相似文献
19.
Z.Y. Zhang C.L. YangY.Q. Wei X.L. YeP. Jin Ch.M. LiX.Q. Meng B. XuZ.G. Wang 《Solid State Communications》2003,126(7):391-394
In this report we have investigated the temperature dependence of photoluminescence (PL) from self-assembled InAs quantum dots (QDs) covered by an InAlAs/InGaAs combination layer. The ground state experiences an abnormal variation of PL linewidth from 15 K up to room temperature. Meanwhile, the PL integrated intensity ratio of the first excited state to the ground state for InAs QDs unexpectedly decreases with increasing temperature, which we attribute to the phonon bottleneck effect. We believe that these experimental results are closely related to the partially coupled quantum dots system and the large energy separation between the ground and the first excited states. 相似文献
20.
Photoinduced electron transfer (PET) was studied in toluene solutions of the Pd-porphyrin-quinone (Pd-PQ) dyad by flash photolysis
in the picosecond time range and by a luminescence method. It is found that Pd-PQ has a high rate of intercombination conversion
Kisc=(7.7±0.2)·1010 sec−1. Competing intramolecular PET occurs from the lower excited singlet state of the dyad with the rate constant K
et
s
=(2.7 ±0.3)·1010 sec−1. Therefore, ∼74% of excited molecules from the dyad make a transition to the triplet T1 state and 26% take part in intramolecular PET resulting in formation of radical products. The radical products relax to the
ground state with the rate constant K=(7.4±0.2)·109 sec−1.
Institute of Molecular and Atomic Physics of the National Academy of Sciences of Belarus, 70, F. Skorina St., Minsk, 220072,
Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 1, pp. 11–18, January–February, 1999. 相似文献