The effect of intermediate catalysis with Ag on structural and near-band-edge-emission properties of ZnO was studied. It was found that the regrowth of ZnO on top of (110)-oriented ZnO structure coated with Ag results in the change of ZnO crystallographic characteristics and appearance of stimulated emission, which was observed under nanosecond photoexcitation. It was assumed that the excitation of lasing became possible due to formation of c-axis oriented ZnO crystals, which can serve as laser microcavities.
The effect of the magnetic field on the exciton radiation of ZnO films formed by randomly packed nanorods and covered with Ag nanoparticles has been discovered and studied at room temperature. Photoexcitation was performed by third and fourth harmonics of Nd:YAG laser. The radiation of the investigated samples consisted of exciton luminescence and random lasing in the near UV range. Several percent enhancement of the exciton radiation intensity was observed at some areas of the films subjected to the magnetic field H ∼ 1 T. The enhancement depends slightly on the excitation level. At the same time, in some other areas of the same films, the effect was negligible or absent. It is supposed that the observed effect is related to magnetoexcitons, which are possibly formed due to increasing of the exciton momentum nearby the Ag nanoparticles. The probability of magnetoexciton recombination increases significantly even in a weak magnetic field due to strong stretching of its wave function.
The influence of a weak magnetic field (H ~ 1 T) on the exciton radiation of the ZnO films covered with Ag island film was investigated at room temperature. It was found that there are some areas on these films where the several-percent enhancement of the exciton radiation intensity can be observed. The value of the enhancement slightly depends on the excitation level. At the same time there are other areas on the same films where the effect is negligible or absent. It is supposed that in the first case, magnetoexcitons are possibly formed due to the increase of the exciton momentum nearby an Ag nanoparticle. The probability of magnetoexciton recombination significantly increases even in a weak magnetic field due to the strong stretch of its wave function.
Amplitude modulation of backscattered light caused by blood volume fluctuations was studied in Laser Doppler Flowmetry. It was shown that the amplitude-modulated signal significantly contributes to the power spectral density of photocurrent and calculated perfusion.
Using multidetector computed tomography, thicknesses of bone squame and soft tissues
of human head were assessed. MC simulation revealed impropriety of source-detector separation
distances for 3 oximeters, which can cause extracerebral contamination.
For the analysis of ZnO luminescence and the influence of surface plasmon resonance (SPR) on it the simplified
approach is proposed. This approach is based on the set of rate equations (SRE), which describes processes taking part in
the luminescence. The SRE includes the set of parameters that describe processes determining luminescence of an
investigated sample. The proposed approach gives an opportunity for modeling the dependence of radiation intensity on
pumping level and to estimate the values of parameters in SRE. As a result it is possible to make conclusions about
peculiarities of samples and investigated processes. A number of experimental facts can be explained using this SRE, in
particular the proposed approach was applied to consideration of insulating spacer role in ZnO/Ag system. It was shown
that it is possible to interpret experimental results using SRE where values of some parameters depend on the spacer
thickness. The proposed approach can be applied not only to ZnO-based structures but also to other emitters.
For the analysis of ZnO luminescence, a set of rate equations (SRE) is proposed. It contains a set of parameters that characterize processes participating in luminescence: zone–zone excitation, excitons formation and recombination, formation and disappearance of photons, surface plasmons (SP), and phonons. It is shown that experimental ZnO microstructure radiation intensity dependence on photoexcitation levels can be approximated by using SRE. This approach was applied for the analysis of ZnO microfilm radiation with different thicknesses of Ag island film covering. It was revealed that the increase of cover thickness leads to an increase of losses and a decrease of the probability of photon-to-SP conversion. In order to take into account visible emission, rate equations for level populations in the bandgap and for corresponding photons and SPs were added to the SRE. By using such an SRE, it is demonstrated that the form of visible luminescence intensity dependence on excitation level (P) like P1/3, as obtained elsewhere, is possible only if donor–acceptor pairs exist. The proposed approach was also applied for consideration of experimental results obtained in several papers taking into account the interpretation of these results based on assumptions about the transfer of electrons from the defect level in the ZnO bandgap to metal and then to the conduction band.
For the analysis of ZnO luminescence the system of rate equations (SRE) was proposed. It contains a set of parameters that characterizes processes participating in luminescence: zone-zone excitation, excitons formation and recombination, formation and disappearance of photons and surface plasmons (SP). It is shown that experimental ZnO microstructure radiation intensity dependence on photoexcitation level can be approximated by using SRE. Thus, the values of these parameters can be estimated and used for luminescence analysis. This approach was applied for the analysis of ZnO microfilms radiation with different thickness of Ag island film covering. It was revealed that the increase of cover thickness leads to the increase of losses and decrease of probability of photons to SP conversion. In order to take into account visible emission, rate equations for levels populations in band-gap and for corresponding photons and SP were added to SRE. By using such SRE it is demonstrated that the form of visible luminescence intensity dependence on excitation level (P) like P1/3, as obtained elsewhere [1], is possible only in case of donor-acceptor pairs existence. The proposed approach was applied for consideration of experimental results obtained in [5-8] taking into account their interpretation of these results based on assumption about transfer of electrons from defect level in ZnO band-gap to metal and then to conduction band in ZnO. Results of performed calculations using modified SRE revealed that effects observed in these papers can exist under only low pumping level. This result will be experimentally checked later.
In luminescence spectra of certain ZnO films there is a second band in the near-ultraviolet region alongside with an
exciton band. With the increasing of pumping this band intensity increases much faster than the intensity of the exciton
band. It is shown that the above second band is not the so called P-line. It is rather connected with shallow level in ZnO
structures. We suggest interpreting the observed effect with a due account of Burstein-Moss effect. For approximate
modeling of the observed process rate equation system has been formulated. It is demonstrated that it is possible to find
such parameters so that the relevant numerical solution gives a dependence of bands emission intensity ratio on pumping
power that simulates quality wise experimental results.
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