Search results for "electromagnetic"
showing 10 items of 1595 documents
Luminescence of unfused 95%SiO2–5%GeO2 amorphous films with fluorine additive: No evidence for presence of GeODC(I) defects found
2013
Abstract Photoluminescence (PL) of unfused amorphous germanosilicate films with fluorine additive is studied in 2–8.5 eV spectral range. Experiments are based on films deposited on silica substrates by means of the surface-plasma chemical vapor deposition (SPCVD). Films of about 100 μm in thickness with “high F” (~ 4.2 wt.%) and “low F” (~ 0.5 wt.%) fluorine content have been fabricated for the experiments. KrF (248 nm), ArF (193 nm) and F2 (157 nm) excimer lasers are used to pump PL. It is found that absorption and luminescence associated with germanium oxygen deficient centers (GeODCs) in “high F” and “low F” films differ. In the “high F” unfused film absorption coefficient of the band at…
Optical properties of ZnMgO films grown by spray pyrolysis and their application to UV photodetection
2015
This work presents a comprehensive optical characterization of Zn1−xMgxO thin films grown by spray pyrolysis (SP). Absorption measurements show the high potential of this technique to tune the bandgap from 3.30 to 4.11 eV by changing the Mg acetate content in the precursor solution, leading to a change of the Mg-content ranging from 0 up to 35%, as measured by transmission electron microscopy-energy dispersive x-ray spectroscopy. The optical emission of the films obtained by cathodoluminescence and photoluminescence spectroscopy shows a blue shift of the peak position from 3.26 to 3.89 eV with increasing Mg incorporation, with a clear excitonic contribution even at high Mg contents. The lin…
Optical absorption, luminescence, and ESR spectral properties of point defects in silica
2001
Publisher Summary This chapter is divided into two parts: (1) In the introductory part, it describes the problems of point defects in a-SiO2, and (2) in the second part it discusses the experimental results. This chapter focuses on the Oxygen-Deficient Centers (ODCs) species in silica. This chapter investigates the ODC defects in a-SiO2 through their optical absorption, photoluminescence, and electron spin resonance activities. The effects of γ-ray irradiation are also investigated to evidence their ability to generate or transform structural defects. The aim of this chapter is to understand the optical activity of such defects to help in the characterization of their structure. The propert…
Absorption and luminescence in amorphous SixGe1-xO2 films fabricated by SPCVD
2012
Abstract Optical absorption and photoluminescence of Ge-doped silica films fabricated by the surface-plasma chemical vapor deposition (SPCVD) are studied in the 2–8 eV spectral band. The deposited on silica substrate films of about 10 μm in thickness are composed as x·GeO2-(1-x)·SiO2 with x ranging from 0.02 to 1. It is found that all as‐deposited films do not luminesce under the excitation by a KrF (5 eV) excimer laser, thus indicating lack of oxygen deficient centers (ODCs) in them. After subsequent fusion of silicon containing (x
Synthesis of multi-color luminescent ZnO nanoparticles by ultra-short pulsed laser ablation
2020
Abstract Crystalline ZnO nanoparticles (NPs) are synthesized by ultra-short femtosecond (fs) pulsed laser ablation (PLA) of a zinc plate in deionized water, and are investigated by optical absorption and time resolved luminescence spectra in combination with the morphology and structure analysis. The comparison with previous experiments based on short nanosecond (ns) PLA highlights that pulse duration is a crucial parameter to determine the size and the optical properties of ZnO NPs. While short PLA generates NPs with average size S ‾ of ~ 30 nm, ultrashort PLA allows to achieve much smaller NPs, S ‾ ⩽ 10 nm, that evidence weak quantum confinement effects on both the absorption edge and th…
Detailed photoluminescence study of vapor deposited Bi2S3 films of different surface morphology
2014
authorenWe present a temperature- and intensity-dependent photoluminescence (PL) study of the binary semiconductor on the mm-scale and a laterally resolved PL measurement with a resolution of nm. The films can show a rather rough surface with needles and flakes of with different orientations as well as very flat and smooth surface morphology. Despite a band gap of eV the films show a splitting of quasi-Fermi levels (QFL) of meV at room temperature. By means of temperature-dependent PL we have located several radiative and non-radiative defect states in the band gap. For a better understanding of this thin film semiconductor a full analysis of the laterally resolved PL measurement including …
Role of Self-Absorption in the Photoluminescence Waveguided along CsPbBr3 Perovskite Nanocrystals Thin Films
2020
During the last years, perovskite nanocrystals (PNCs) have been intensively studied as nanomaterials with excellent light absorption/emission properties. For example, PNCs have been successfully applied in solar cells, where the high absorption coefficient above the band gap increases the conversion efficiencies; or in optical sources, where the high quantum yield of emission at room temperature allows a low threshold of stimulated emission. In this scenario, an optical waveguide represents a suitable platform to enhance their electrooptical properties and to integrate different photonic functionalities. However, propagation of light along close packed films of PNCs is usually restricted to…
<title>PLZT ceramics as optical phantom for simulation of light scattering in eye segments and other biological tissues</title>
1999
ABSTRACT Coefficients of light absorption ta and scattering for biological tissues lie within a broad range - minimum ones forhealthy eye tissues up to higher values (fe. t a 0.3 cm and i = 40 cm' at 633 nm for muscle tissues ) for other andmainly turbid tissues. The specific feature of the transparent PLZT ceramics (having absorption t a > 0. 1 cm in the visible and in the near infrared spectrum range) is electrically controlled light scattering. The present work reports onexperimental results of the light transport and backscattering for PLZT 9/65/35 (Pb091La009Zr065Ti035O3). We proposePLZT ceramics with fast and continuously controllable light scattering as an optical phantom for photon …
Reflection-refraction effects on light distribution inside tubular photobioreactors
2017
One of the main parameters affecting autotrophic algae cultures is photon absorption distribution inside the photobioreactor. This clearly depends on the geometry of both the radiation source and the photobioreactor, as well as on algae suspension optical properties. In this work the local volumetric rate of photon absorption LVRPA in a cross-section of a horizontal-pipe photobioreactor was investigated by means of simplified Monte Carlo simulations. In particular, the fate of a number of photons perpendicularly hitting the photobioreactor circular section was simulated in relation to different values of algae concentration. The model takes into account refraction/reflection phenomena at th…
Strong optical nonlinearities in gallium and indium selenides related to inter-valence-band transitions induced by light pulses
1997
A nonlinear optical effect is shown to occur in gallium and indium selenides at photon energies of the order of 1.5 eV. It corresponds to transitions from a lower-energy valence band to the uppermost one when a nonequilibrium degenerate hole gas is created in the latter by a laser pulse. This inter-valence-band transition is allowed by crystal symmetry. Its oscillator strength is estimated through the $f$-sum rule and turns out to be about two orders of magnitude higher than that of the fundamental transition. The intensity of this effect is stronger when the pump pulse photon energy is close to that of the inter-valence-band transition; a condition that can be fulfilled only in indium sele…