Search results for "electromagnetic"
showing 10 items of 1595 documents
Energy transport in silica to oxygen-deficient luminescence centers. Comparison with other luminescence centers in silica and α-quartz
2004
Abstract The transport of energy absorbed by silica glass to oxygen-deficient luminescence centers in was studied in the range of intrinsic absorption from 8.2 up to 35 eV. The low efficiency of exciting those luminescence centers by transport of energy could not be ascribed merely to carrier scattering by the disordered structure. Other centers (Cu + , for example) could be excited in such process with sufficiently high efficiency, albeit lower than that in crystals. The low efficiency of interaction of oxygen deficient centers with quasi-particles is attributed to isolation of these centers in clusters and the non-radiative annihilation of the quasi-particles on the boundaries of these cl…
Absorption and luminescence in amorphous silica synthesized by low-pressure plasmachemical technology
2007
A comparison study of as-deposited by the hydrogen-free SPCVD process silicon dioxide with and without fluorine as well as the one in the form of fused materials is performed to define whether glass forming processing affects its optical properties. Raman scattering, optical absorption in the vacuum ultraviolet region as well as luminescence at different temperatures and various excitation conditions are measured. A difference in Urbach rule parameters and intrinsic defect concentrations for different samples is revealed. No significant impact on the structure responsible for Raman scattering is observed.
Controlling the oxidation processes of Zn nanoparticles produced by pulsed laser ablation in aqueous solution
2016
We used online UV-VIS optical absorption and photoluminescence spectra, acquired during and after pulsed laser ablation of a Zinc plate in aqueous solution, to investigate the effect of the laser repetition rate and liquid environment on the oxidation processes of the produced nanoparticles. A transient Zn/ZnO core-shell structure was revealed by the coexistence of an absorption peak around 5.0 eV due to Zn surface plasmon resonance and of an edge at 3.4 eV coming from wurtzite ZnO. The growth kinetics of ZnO at the various repetition rates, selectively probed by the excitonic emission at 3.3 eV, began immediately at the onset of laser ablation and was largely independent of the repetition …
Single-molecule spectroscopy of molecular aggregates at low temperature
2004
We have conducted single-molecule spectroscopy of a fluorescent polyphenylene dendrimer consisting of four peripheral perylenemonoimides which serve as energy donors and a central terrylenediimide which is the energy acceptor. After selective excitation of the donors the low-temperature emission spectra of single dendrimers show the purely electronic zero-phonon line as the most prominent feature of the acceptor. These sharp emission lines are subjected to appreciable spectral shifts. Fluorescence excitation spectroscopy of individual dendrimers in the spectral region of the donor absorption allows to extract energy transfer rates for single donors within the dendrimer. Although the energy …
Photoluminescence in silicon-doped n-indium selenide
1994
Photoluminescence results on silicon-doped indium selenide are reported. The effect of temperature and excitation intensity is studied. At low temperature, free and neutral donor bound exciton peaks are observed. Above 100 K only free exciton and band-to-band photoluminescence is detected. In order to give account of the full lineshape as a function of the absorption coefficient, the Urbach absorption tail of InSe is measured. Transmission and reflection photoluminescence spectra are also compared in order to study the effect of carrier diffusion. The shape of the photoluminescence spectrum can be accounted for through a direct gap model.
Optical transitions and excitonic recombination in InAs/InP self-assembled quantum wires
2001
InAs self-assembled quantum wire structures have been grown on InP substrates and studied by means of photoluminescence and polarized-light absorption measurements. According to our calculations, the observed optical transitions in each sample are consistent with wires of different heights, namely from 6 to 13 monolayers. The nonradiative mechanism limiting the emission intensity at room temperature is related to thermal escape of carriers out of the wires.
Conformational heterogeneity of the point defects in silica: The lifetime of the phosphorescence band at 2.7 eV
2008
We have measured the excitation and emission energy dependence of the lifetimes of the 2.7 eV photoluminescence band associated to oxygen deficient centers in silica glasses. The non-exponential behavior of this time decay is consistent with intrinsic conformational heterogeneity of these point defects in the amorphous matrix. Accordingly, we have analyzed the data in terms of a radiative rates distribution. Moreover, both surface and bulk typologies of these point defects have been studied. The mean value of the lifetime distribution of the surface defects increases from 12 to 15 ms varying the excitation energy from 4.6 to 5.2 eV, and it increases from 14 to 15 ms in the emission energy i…
Luminescence properties of LiGaO2 crystal
2017
The study was supported by the Latvia-Lithuania-Taiwan research project “Nonpolar ZnO thin films: growth-related structural and optical properties” (Latvia: LV-LT-TW/2016/5 , Lithuania: TAP LLT 02/2014 , Taiwan: MOST 103-2923-M-110-001-MY3 ).
Photoluminescence in ZnO:Co2+ (0.01%–5%) Nanoparticles, Nanowires, Thin Films, and Single Crystals as a Function of Pressure and Temperature: Explori…
2014
This work investigates the electronic structure and photoluminescence properties of Co2+-doped ZnO and their pressure and temperature dependences through high-resolution absorption and emission spe...
The effect of quantum size confinement on the optical properties of PbSe nanocrystals as a function of temperature and hydrostatic pressure
2013
A study based on photoluminescence and absorption measurements as a function of temperature and pressure for PbSe nanocrystals with sizes in the range 3–13 nm reveals the influence of size quantum confinement on the observed variation. In the case of the temperature variation, the effective bandgap changes from showing a positive rate of change to showing a negative one (for a quantum dot 3 nm in diameter), which can be accounted for by incorporating a linear variation of the carrier effective masses into a simple calculation of the exciton ground state in the quantum dot. In the case of the pressure variation, we observe a clear inverse correlation between the absolute value of the pressur…