Functionalized nanoparticles are important analytical tool for biomedical applications. Pulsed laser ablation of bulk targets in an aqueous media is the one-step method for the fabrication, size manipulation and biofunctionalization of nanoparticles. We performed kHz laser ablation of a silver target by nanosecond pulses in tetramethylammonium hydroxide (TMAH) and sodium dodecyl sulfate (SDS) aqueous solutions to prepare silver nanoparticles. It was shown that the formation efficiency was increased by addition of TMAH and SDS as well as the stability of nanoparticles. The size decrease of the nanoparticles by addition of SDS was more remarkable than in the laser ablation in TMAH aqueous solutions. Emitted nanoparticles interact with TMAH and SDS in the secondary laser irradiation process leads to the nanoparticles stabilization in aqueous solutions.
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.
Two series of MgxZn1-xO/ZnO multiple quantum wells with 18 at.% and 27 at.% of magnesium content in barrier layers and well width Lw from 1 nm to 20 have been grown by pulsed laser deposition method. The stimulated emission is observed in photoluminescence spectra excited by pulsed laser (λexc=248 nm). The pump density threshold of stimulated emission nonmonotonously depends on the well width that is associated with an increase of the internal quantum efficiency of two-dimensional structures caused by a reduction of radiative lifetime of excitons at decreasing of the well width as it has been shown by the time-resolved photoluminescence spectra analysis. The minimum value of a lifetime τr=355 ps was obtained for the Mg0.27Zn0.73O/ZnO MQW with the well width Lw=2.6 nm.
The Mg0.27Zn0.73O/ZnO multiple quantum wells with different well width Lw have been grown by pulsed laser
deposition method. The interface roughness of quantum wells was inherited from the bottom one and did not exceed 1
nm. The quantum confinement effect has been observed. The exciton binding energy of the two-dimensional
Mg0.27Zn0.73O/ZnO structures was two times higher in comparison with the bulk ZnO. A sharp increase of exciton peak
intensity in the photoluminescence spectra at well width reduction was observed. The optical excited stimulated
emission in quantum wells Mg 0.27Zn0.73O/ZnO with an excitation threshold ~210 kW/cm2 has been demonstrated.
The formation of laser-induced structures on the multicrystalline silicon surface has been investigated. Optimum
performances of the surface structurization have been explored. A cardinal decrease in reflectance from modified
surface has been discovered in a wide spectral range in comparison with the samples of chemically texturized
monocrystalline silicon. The influence of subsequent chemical etching on the reflection spectra of the texturized
samples surface has been analyzed.
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