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Luminescence Bands (luminescence + bands)
Selected AbstractsGrowth and characterization of Nd, Yb , yttrium oxide nanopowders obtained by sol-gel methodCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2007A. Rzepka Abstract Nanopowders of Y2O3 pure, doped and codoped by Nd3+, Yb3+ were obtained by sol-gel method. Solution with ethylene glycol was choosed as the proper solution where crystallites of powder with Nd and Yb dopants had the same size. Finally the one-phased compounds of Y2O3 doped 0.5 at% Nd and 1, 2 or 4 at% Yb were obtained. Grain growth and their morphology were investigated in various temperature and time of heating. The changes of crystallite sizes and lattice constants in relation to the heating time and temperature for the composition Y2O3 doped 0.5 at% Nd and 2 at% Yb are presented. Y2O3 containing 0,5 at% of Nd exhibits intense luminescence bands centered at 920 nm, 1100 nm and 1360 nm whereas a single band at about 1020 nm appears in samples co-doped with neodymium and ytterbium. Luminescence spectra recorded did not depend on the sample preparation procedure and size of grains. OH impurity affects critically the relaxation dynamics of luminescent ion in nanopowders. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Radiative properties of dislocations generated around oxygen precipitates in SiPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2007E. A. Steinman Abstract Generation of dislocations during the growth of oxygen precipitates has been used as an alternative way of introduction of dislocation-related luminescence centers. For this purpose a multistep annealing of Cz Si samples with different initial concentrations of oxygen has been carried out. The analysis of defect density and structure was performed by optical microscopy (OM) and transmission electron microscopy (TEM). The dislocation-related luminescence (DRL) appeared only after a growth stage, while its intensity strongly depended on the duration of the preliminary nucleation treatment. The duration of growth annealing had a strong influence on the spectral distribution of the DRL intensity. No correlation has been found between a particular defect density, defined by TEM, and the shape of luminescence bands. Therefore, it was concluded that the cause of the gradual DRL transformation is redistribution of oxygen, collected near dislocations. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photoluminescence and Hall studies of GaN:Fe and (Ga,Fe)N:Mg layersPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2007M. Wegscheider Abstract Temperature dependent photoluminescence (PL) in the ultraviolet (UV) regime and Hall measurements at room temperature have been performed on Metal-Organic-Chemical-Vapour-Deposition (MOCVD) grown GaN:Fe and (Ga,Fe)N:Mg layers. PL measurements were employed in order to study the dopants' influence on the near-band edge excitonic emission and their tendency to provoke the formation and suppression of defects or incorporation of impurities. For their identification and for the understanding of the PL spectra the evaluation of the free carrier concentrations via Hall measurements were necessary. Depending on the iron concentration of the (Ga,Fe)N layers, the near-band edge emission goes through two different stages: at low Fe-concentration no excitonic emission can be seen whereas with higher doping levels, excitonic features develop. The (Ga,Fe)N films exhibit n-type behaviour. The Mg codoped samples show strong Mg and defect related luminescence bands, whose occurrence and intensity also strongly depends on whether high or low Fe concentration is present. The (Ga,Fe)N:Mg layers were semi insulating. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] 1.5 µm luminescence of silicon nanowires fabricated by thermal evaporation of SiOPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2006G. Jia Abstract Silicon nanowires (NWs) fabricated by thermal evaporation of SiO were studied by cathodoluminescence. A band around 1550 nm (0.8 eV) was observed. It appears above 225 K and its intensity increases with increasing temperature. The broad band consists of the defect-related D1 and D2 lines and is supposed to be formed by extended defects within the NWs that are decorated with oxygen. Moreover, luminescence bands are found that are related to Si oxide and/or the interface between Si and Si oxide. In addition, the Si band-to-band line and the G center are observed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Discrete luminescence bands in AlGaN-based quantum wellsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009Hideaki Murotani Abstract The excitation-power-density dependent photoluminescence (PL) spectra have been studied for AlGaN-based quantum wells (QWs) with a well-layer thickness of 2, 4, and 6 nm. With increasing excitation-power density, an additional luminescence line was observed at the higher energy side of an initial luminescence line for the QWs with the well-layer thickness of 4 and 6 nm. The additional line also shifted toward higher energy side with further increasing excitation-power density. It was found from a theoretical calculation of the transition energy under applied electric field that an energy difference between the additional and the initial lines agreed with an energy separation for a well-layer-thickness variation of 2 monolayer for each QW. Therefore, these observations indicated that in the QWs with the well-layer thickness of 4 and 6 nm, the screening of the internal electric field occurred effectively after the saturation of localized states caused by the interface disorder. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Excitons in AgI,oxide particle composites: AgI,SrTiO3PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2006Fumito Fujishiro Abstract We fabricated (x)AgI,(1,x)SrTiO3 fine particle composites over a wide composition range of 0,100 mol% AgI. It is found that the dispersion of SrTiO3 fine particles enhances the ionic conductivity and (0.6)AgI,(0.4)SrTiO3 has the highest ionic conductivity (1.68 × 10,4 S/cm which is two hundreds times in comparison with that of pristine AgI), for the first time. In order to clarify such ionic conductivity enhanced by dispersing SrTiO3 fine particles into AgI, the photoluminescence measurements were carried out at different temperatures between 10 K and room temperature under different photoexcitation intensities, together with the structural and morphological studies (X-ray diffractometry, scanning electron microscopy and energy dispersive X-ray fluorescence spectroscopy). The spectra consist of free exciton luminescence band and several broad luminescence bands due to the excitons trapped at crystal defects and residual impurities. The free exciton luminescence band almost disappears at x = 0.6, which may suggest the existence of considerable number of non-radiative traps (crystal defects) at the AgI/SrTiO3 particle interfaces. Such crystal defects may act as ionic pathways. The structural and morphological studies confirm the randomly-stacked ,AgI/,AgI heterostructures at the AgI/SrTiO3 particle interfaces. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Recombination mechanism of luminescence excitation of self-trapped excitons in BeOPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2005S.V. Gorbunov Abstract Time-resolved spectra, polarization of the luminescence and transient optical absorption (TOA) induced by irradiation of beryllium oxide crystals with electron pulses have been studied. Exponential stages with decay time , = 6.5 ms in luminescence bands at 4.0, 5.0 and 6.7 eV coinciding in spectral and polarized properties with the luminescence of two different types of self-trapped excitons (STE) have been found. Efficiency of formation of centers with decay time 6.5 ms appeared to be comparable with that of formation of triplet STE. The electron fluence increase does not change the exponential character and relaxation of TOA decaying with time 6.5 ms and results in a linear growth of optical density. These data are typical of monomolecular recombination processes. Similarity of TOA spectra of centers with decay time 6.5 ms with those of V-type hole centers and hole component of STE shows that the stage 6.5 ms is due to the recombination of cation Frenkel defects. The recombination of close spatially correlated Frenkel pairs Be+ V, manifests itself in a form of exponential components with decay time 6.5 ms in the luminescence of two types of STE in BeO. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||