Search results for "SPECTRA"
showing 10 items of 3542 documents
Peculiarities of photoluminescence excited by 157nm wavelength F2 excimer laser in fused and unfused silicon dioxide
2009
Abstract Photoluminescence (PL) spectra and kinetics of high purity amorphous silicon dioxide with ultra low hydroxyl content is studied under the excitation by F 2 excimer laser (157 nm wavelength) pulses. Materials synthesized in the SPCVD plasma chemical process are studied before and after fusion. Two bands are found in the PL spectra: one centered at 2.6–2.9 eV (a blue band) and the other at 4.4 eV (a UV band). Luminescence intensity of unfused material is found to increase significantly with exposure time starting from a very small level, whereas in fused counterpart it does not depend on irradiation time. Both bands show complicated decay kinetics, to which add exponential and hyperb…
Thienylpyridine-based cyclometallated iridium(III) complexes and their use in solid state light-emitting electrochemical cells
2013
The synthesis and characterization of four iridium(iii) complexes [Ir(thpy)2(N^N)][PF6] where Hthpy = 2-(2'-thienyl)pyridine and N^N are 6-phenyl-2,2'-bipyridine (1), 4,4'-di-(t)butyl-2,2'-bipyridine (2), 4,4'-di-(t)butyl-6-phenyl-2,2'-bipyridine (3) or 4,4'-dimethylthio-2,2'-bipyridine (4) are described. The single crystal structures of ligand 4 and the complexes containing the [Ir(thpy)2(1)](+) and [Ir(thpy)2(4)](+) cations have been determined. In [Ir(thpy)2(1)](+), the pendant phenyl ring engages in an intra-cation π-stacking interaction with one of the thienyl rings in the solid state, and undergoes hindered rotation on the NMR timescale in [Ir(thpy)2(1)](+) and [Ir(thpy)2(3)](+). The …
Luminescence properties of Eu, RE3+ (RE = Dy, Sm, Tb) co-doped oxyfluoride glasses and glass–ceramics
2017
Abstract Eu, RE3+ (RE = Dy, Sm, Tb) co-doped SiO2–CaF2–Al2O3–CaO oxyfluoride glasses have been prepared by the melt quenching method. By heating the precursor glasses at 670 °C for 1 h, glass–ceramics containing CaF2 nanocrystallites were obtained. DTA and XRD measurements were performed. Excitation spectra of the prepared samples as well as photoluminescence spectra at the excitation of 355 nm and 450 nm were measured, CIE colour coordinates and colour rendering indexes were found. In the glass–ceramics the presence of Eu2+ ions was observed by a broad emission band in the 400–500 nm spectral range. The most promising doping combinations for white light luminophores within our research are…
Excitation and photoluminescence spectra of single- and non-single-phased phosphors based on LaInO3 doped with Dy3+, Ho3+ activators and Sb3+ probabl…
2017
Abstract Single-phased La 0.95 Ln 0.05 InO 3 ( Ln – Dy, Ho), La 0.90 Dy 0.05 Ho 0.05 InO 3 , LaInO 3 ceramic samples as well as the La 0.95 Ln 0.05 In 0.98 Sb 0.02 O 3 ( Ln – Dy, Ho), La 0.90 Dy 0.05 Ho 0.05 In 0.98 Sb 0.02 O 3 , LaIn 0.98 Sb 0.02 O 3 samples with additional impurity LaSbO 3 phase were prepared by solid-state reactions method. Their excitation and photoluminescence (PL) spectra were measured at room temperature. It was established that PL bands intensity of spectra obtained for samples of nominal composition La 0.95 Dy 0.05 In 0.98 Sb 0.02 O 3 , La 0.95 Ho 0.05 In 0.98 Sb 0.02 O 3 , La 0.90 Dy 0.05 Ho 0.05 In 0.98 Sb 0.02 O 3 is much higher than that of single-phase La 0.95…
Optical characterization of Mg-doped GaN films grown by metalorganic chemical vapor phase deposition
2000
Scanning electron microscopy, micro-Raman, and photoluminescence (PL) measurements are reported for Mg-doped GaN films grown on (0001) sapphire substrates by low-pressure metalorganic chemical vapor phase deposition. The surface morphology, structural, and optical properties of GaN samples with Mg concentrations ranging from 1019 to 1021 cm−3 have been studied. In the scanning micrographs large triangular pyramids are observed, probably due to stacking fault formation and three-dimensional growth. The density and size of these structures increase with the amount of magnesium incorporated in the samples. In the photoluminescence spectra, intense lines were found at 3.36 and 3.31 eV on the tr…
Growth and optical characterization of indirect-gap AlxGa1−xAs alloys
1999
Nonintentionally doped AlxGa1−xAs layers with 0.38 x 0.84 were grown on (100) GaAs substrates by liquid phase epitaxy (LPE) under near-equilibrium conditions. The crystalline quality of the samples was studied by photoluminescence at 2 K and room temperature Raman spectroscopy. The peculiar behavior in the photoluminescence intensities of the indirect bound exciton line and the donor–acceptor pair transition is explained from the evolution of the silicon donor binding energy according to the aluminum composition. It was also possible to observe the excitonic transition corresponding to the AlxGa1−xAs/GaAs interface, despite the disorder and other factors which are normally involved when gro…
Spectral properties of AIN ceramics
1997
Spectral properties of oxygen-related defects are studied in AIN ceramics at room temperatures. Original results concerning the photoluminescence under ultraviolet irradiation are obtained; they include the excitation spectrum and irradiation dose effects. The ultraviolet light energy storage and its release under irradiation with visible or infrared light in the form of the photostimulated luminescence has been observed in AIN ceramics. The properties of the photostimulated luminescence such as creation, emission and stimulation spectra are reported. For the explanation of the experimental results the mechanism of the recombination luminescence involving the oxygen-related defect is propos…
Valence-band splitting energies in wurtzite InP nanowires : Photoluminescence spectroscopy and ab initio calculations
2010
We investigated experimentally and theoretically the valence-band structure of wurtzite InP nanowires. The wurtzite phase, which usually is not stable for III-V phosphide compounds, has been observed in InP nanowires. We present results on the electronic properties of these nanowires using the photoluminescence excitation technique. Spectra from an ensemble of nanowires show three clear absorption edges separated by 44 meV and 143 meV, respectively. The band edges are attributed to excitonic absorptions involving three distinct valence-bands labeled: A, B, and C. Theoretical results based on “ab initio” calculation gives corresponding valence-band energy separations of 50 meV and 200 meV, r…
Isoelectronic series of oxygen deficient centers in silica: experimental estimation of homogeneous and inhomogeneous spectral widths
2008
We report nanosecond time-resolved photoluminescence measurements on the isoelectronic series of oxygen deficient centers in amorphous silica related to silicon, germanium and tin atoms, which are responsible of fluorescence activities at approximately 4 eV under excitation at approximately 5 eV. The dependence of the first moment of their emission band on time and that of the radiative decay lifetime on emission energy are analyzed within a theoretical model able to describe the effects introduced by disorder on the optical properties of the defects. We obtain separate estimates of the homogeneous and inhomogeneous contributions to the measured emission line width, and we derive homogeneou…
Raman spectroscopy and photoluminescence of ZnTe thin films grown on GaAs
2002
5 páginas, 4 figuras, 1 tabla.