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PL Efficiency (pl + efficiency)
Selected AbstractsShallow and deep excited states of mesoscopic structure in AgI,,Al2O3 compositesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2003Shosuke Mochizuki Abstract The photoluminescence (PL) and PL excitation (PLE) spectra of superionic conducting AgI,,Al2O3 composites have been measured at different temperatures between 7 K and room temperature. The X-ray diffraction patterns of these composites have also been measured at room temperature. The PL intensity peak observed at 426 nm is closely connected with radiative decay of free excitons in AgI, while other emission bands are connected with shallow excited states in AgI and deep excited states at the AgI/,Al2O3 interface. With increasing excitation light intensity, the PL efficiencies of several emission bands become saturated, except for the free exciton band. These results may give important information about the origins of the high ionic motion in these composites. [source] Shallow- and deep-luminescence centers in AgI-based superionic conductor glassPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2003Shosuke Mochizuki Abstract The photoluminescence (PL), time-resolved photoluminescence (TRPL) and PL-excitation (PLE) spectra of superionic conductor glass (AgI)0.85(Ag2WO4)0.15 have been measured at different temperatures between 8 K and room temperature. The PL intensity peak is observed at 426 nm which corresponds to free exciton wavelength of pristine AgI. There are also different PL bands well related to the internal and interface states of mesoscopic AgI particles in Ag2WO4 glass matrix. This may give important information about the origins of superionic conduction. With increasing excitation light intensity, the PL efficiencies of several emission bands become saturated, except for the free exciton band. [source] Preparation-Condition Dependence of Hybrid SiO2 -Coated CdTe Nanocrystals with Intense and Tunable PhotoluminescenceADVANCED FUNCTIONAL MATERIALS, Issue 8 2010Ping Yang Abstract When aqueously prepared CdTe nanocrystals (NCs) are coated with a SiO2 shell containing Cd ions and a sulfur source, they show a drastic increase in photoluminescence (PL) efficiency with a significant red shift and spectral narrowing after reflux. This is ascribed to the creation of a hybrid structure characterized by the formation of CdS-like clusters in the vicinity of the NCs in the SiO2 shell. Since these clusters are close to the NCs, their effective size increases to reduce the quantum size effect. The dependences of the PL properties on the preparation conditions are systematically investigated. The PL efficiency increases from 28% to 80% in the best case with a red shift of 80,nm. The PL behaviors differ from those of normal CdTe NCs and include less temperature quenching and longer PL lifetime. The SiO2 coating enables bioconjugation with IgG without deterioration of PL efficiency, making hybrid NCs amenable for bioapplication. [source] Photophysics and Photocurrent Generation in Polythiophene/Polyfluorene Copolymer BlendsADVANCED FUNCTIONAL MATERIALS, Issue 19 2009Christopher R. McNeill Abstract Here, studies on the evolution of photophysics and device performance with annealing of blends of poly(3-hexylthiophene) with the two polyfluorene copolymers poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2,,2,,-diyl) (F8TBT) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) are reported. In blends with F8TBT, P3HT is found to reorganize at low annealing temperatures (100,°C or below), evidenced by a redshift of both absorption and photoluminescence (PL), and by a decrease in PL lifetime. Annealing to 140,°C, however, is found to optimize device performance, accompanied by an increase in PL efficiency and lifetime. Grazing-incidence small-angle X-ray scattering is also performed to study the evolution in film nanomorphology with annealing, with the 140,°C-annealed film showing enhanced phase separation. It is concluded that reorganization of P3HT alone is not sufficient to optimize device performance but must also be accompanied by a coarsening of the morphology to promote charge separation. The shape of the photocurrent action spectra of P3HT:F8TBT devices is also studied, aided by optical modeling of the absorption spectrum of the blend in a device structure. Changes in the shape of the photocurrent action spectra with annealing are observed, and these are attributed to changes in the relative contribution of each polymer to photocurrent as morphology and polymer conformation evolve. In particular, in as-spun films from xylene, photocurrent is preferentially generated from ordered P3HT segments attributed to the increased charge separation efficiency in ordered P3HT compared to disordered P3HT. For optimized devices, photocurrent is efficiently generated from both P3HT and F8TBT. In contrast to blends with F8TBT, P3HT is only found to reorganize in blends with F8BT at annealing temperatures of over 200,°C. The low efficiency of the P3HT:F8BT system can then be attributed to poor charge generation and separation efficiencies that result from the failure of P3HT to reorganize. [source] Design and Synthesis of Phosphorescent Iridium Containing Dendrimers for Potential Applications in Organic Light-Emitting Diodes,MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 18 2008Qin-De Liu Abstract Three phosphorescent dendrimers (IrC1, IrC3, and IrF2) with an iridium complex core and oligocarbazole or oligofluorene substituted ligands were synthesized and characterized. The structures of the oligocarbazole were designed to maintain high triplet energy of the ligands so that phosphorescence quenching in the resulting dendrimers can be prevented, while the oligofluorene in IrF2 resulted in undesired phosphorescence quenching. Best performance was obtained from an IrC3 based electrophosphorescent light-emitting device with a maximum luminance of 13,060 cd,·,m,2 at a driving voltage of 11.5 V and a peak current-efficiency of 4.3 cd,·,A,1 at a luminance of 3,400 cd,·,m,2, owing to its high PL efficiency, and efficient energy transfer between the iridium complex core and the ligands. [source] Singlet oxygen inhibits nonradiative defects in porous siliconPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2009V. B. Pikulev Abstract Experimental evidences are presented for the first time that singlet oxygen generated ex situ acts as an inhibitor of nonradiative recombination in porous silicon (PSi). This effect is observed on a pristine PSi as well as on degraded porous layers quenched by ozone adsorption. A photoluminescence (PL) enhancement produced by singlet oxygen is accompanied with only slight oxidation of a PSi. We assume that the observed effect on PL efficiency is due to gentle selective oxidation of single defects on silicon nanocrystal surface. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Hydrogenation of strain engineered InAs/InxGa1,x As quantum dotsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2004D. Ochoa Abstract InxGa1,xAs/InAs/InxGa1,xAs structures have been grown by atomic layer molecular beam epitaxy on top of a GaAs buffer and substrate. In these structures, the thickness d and/or the In composition x of the lower InxGa1,xAs confining layer control the strain in self-assembled quantum dots. This strain engineering has allowed achieving emission energies as low as 1.5 ,m at low T, with a rapid quenching of the photoluminescence (PL) signal at high T. Hydrogen irradiation of these structures leads to an increase in the PL efficiency, higher in samples with higher x, with a blue shift in the peak energy. A higher concentration of non radiative defects in confining layers richer in indium is responsible for the observed PL quenching, more than an increased thermal escape of carriers toward the InxGa1,xAs barriers. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||