The magnetic-dipole interaction constant A and the electric-quadrupole interaction constant B in the the 9^{2}D_{3/2} state of ^{85}Rb were measured using the quantum beat method. The results are |A| = 0.561(11) MHz, |B| = 0.20(3) MHz and B/A > 0.
All-experimental self-quenching cross-sections σ_ nf ^q are reported for K(nf) states (n=5, 6, 7, 8). The experiment was performed at varied temperatures of K vapour in a spectral cell. Time-resolved fluorescence was observed following pulsed step-wise excitation with dipole and quadrupole transitions K(4s) K(4p) K(nf). The values: σ _ 5f ^q=2.4±1.7, σ_ 6f ^q=4.5±1.4, σ_ 7f ^q=8.1±1.8, and σ_ 8f ^q=18.2±3.0 (in units of 10^ -13 cm^ -1 ) were obtained from Stern-Volmer-type plots.
The resonance fluorescence spectrum of an ensemble of two-level atoms driven by two classical, frequency degenerate and noncollinear laser beams is investigated. It has been found that the spatially-averaged resonance fluorescence spectra differ significantly from the spectra of two-level atoms calculated for the single-beam excitation. The differences were noticed in the number of peaks, their positions and shapes and in their dependences on an angle between wave vectors of the incident beams.
In the present work we explored the possibility of obtaining Y_2O_3:Eu^{3+} μm-size particles by an ultrasonic spray pyrolysis method. As-prepared sample constitutes of spherical, hollow particles with an average size of 1 to 2 μm. Pure, well crystalline, cubic Y_2O_3 is formed after additional thermal treatment at 800°C for 2 h. A detailed optical investigation has been done with photoluminescence measurements in the energy and time domains. Experimental intensity parameters, transition rates and quantum efficiency of the ^{5}D_0 emission are evaluated on the basis of Judd-Ofelt theory.
Laser induced fluorescence is a powerful spectroscopic technique commonly used to study the structure and internal state distributions in molecules of biological interest. Betanin (C_{24}H_{26}N_{2}O_{13}) is a specific violet betacyanin and the most prominent pigment in the red beet root where it contributes to 75-95% of the total visible color. Our method of excitation of the beet root extract is based on the tunable (320 nm to 475 nm) Nd:YAG laser system. Fluorescence images of beet root extract excited at 320, 340, 360 and 400 nm were obtained. The fluorescence is observed in range from 580 nm to 660 nm. The influence of the solution concentrations on the fluorescence intensity is also analyzed.
L X-ray fluorescence cross-sections of some elements in the atomic number range 50 ≤ Z ≤ 59 have been calculated theoretically according to subshell excitation energies of elements. The Coster-Kronig transitions (f₁₂, f₂₃, and f₁₃) are non-radiative transitions. The Coster-Kronig enhancement factors due to the effect of the Coster-Kronig transitions on L X-ray fluorescence cross-sections have been calculated theoretically. The calculated values have been compared with other earlier experimental and theoretical values.
Fluorescence excitation spectra of spatially resolved single terrylene molecules in a naphthalene crystal were studied at 5 K as a function of exciting laser light intensity. The fully saturated fluorescence detection rate for purely electronic transition (0,0) was found to be about twice smaller than that for the two main vibronic components located 239 and 251 cm^{-1} above. This relation is fulfilled when the triplet population rate k_{23} is much weaker than the depopulation rate k_{31}. We propose that the weak fluorescence excitation lines observed at the frequencies of 38, 67, 97, and 145 cm^{-1} correspond to nontotally symmetric low-frequency vibration modes of terrylene.
The L_{3l}, L_{3α}, L_{3β}, L_{2β}, L_{2γ}, L_{2η}, L_{1β} and L_{1γ} X-ray production cross-sections and L shell average fluorescence yields were measured for the elements from Re to U using excitation energy of 123.6 keV. Measurements were performed using an ^{57}Co annular radioactive source and a Si(Li) detector. The theoretical values of the cross-sections were calculated using theoretically tabulated values of subshell photoionization cross-sections;the Coster-Kronig transition probabilities were based on the Dirac-Hartree-Slater theory and radiative emission rates. Experimental results were compared with the theoretically calculated values of L shell X-ray cross-sections. The present experimental results are in agreement with theoretical values.
In any complex system at temperature T the absorption cross-section and fluorescent power at a given photon energy are connected by a simple relation if the system is in thermal equilibrium while occupying one particular electronic excited state. Although this situation is impossible in principle because of finite excited-state lifetimes, it is often approximated to the extent that the simple relation, which is expressed as a linear function of energy with slope -1/k_{B}T, holds in a variety of cases. (The usual symbols for Boltzmann's constant and absolute temperature are used.) Observed deviations are of two principal kinds: a slope characteristic of some temperature T* other than ambient, and departures from a single pure straight line. The latter may include seemingly random variations and in some cases multiple regions of straight-line behavior. We have recently introduced an effective temperature T*(E), derived from the actual local slope of the putative straight line at energy E, which turns out to be a very sensitive detector of deviations from the ideal and, we believe, from equilibrium in the excited state. Plots of T*(E) display a variety of features. An anomaly in the T*(E) spectrum of chlorophyll a can be analyzed on this model, indicating a second weakly fluorescent state about 70 meV below the well-known Q_{y} band. The cases of chlorophyll and many others are included in a selective review of applications of the universal relation to fluorescent systems.
We present a rate-equation theoretical model describing the optical pumping processes on the K D_{1} line and we then discuss their influence on the electromagnetically induced transparency resonance parameters. We present also a comparison with the results of an experiment performed in cells containing pure alkali metal or added with a few torrs of buffer gas. The model shows that, in the last case, the complete Maxwellisation of the atomic population velocity distribution, along with the overlapping Doppler profiles of the transitions from the ground-states typical of K, leads to a partial compensation of optical pumping and a significant increase of the amplitude of the electromagnetically induced transparency resonances.
The enhancing properties of silver nanoparticles in surface-enhanced Raman scattering (SERS) and metal-enhanced fluorescence (MEF) are studied in this work. The obtained results confirm that the partial aggregation of nanoparticles leads to a great increase of Raman scattering cross-section but there are significant differences in SERS-activity of colloidal silver treated with various aggregating compounds. The differences are interpreted through the analysis of both experimental and computational results. The same silver colloid covered with silica shell preventing the fluorescence quenching makes possible a several-fold increase in fluorescence emission. The effect strongly depends on thickness of the outer layer of nanoparticles. Geometrical parameters of nanoparticles (radius or radius and thickness of the adsorption layer in core-shell systems) are determined on the basis of the dynamic light scattering (DLS) data and extinction spectra analysis.
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