Search results for "quantum yield"
showing 10 items of 163 documents
Efficient orange light-emitting electrochemical cells
2012
We report the first bis-cyclometalated cationic iridium(III) complex with N-aryl-substituted 1H-imidazo [4,5-f][1,10]phenanthroline. The complex emits yellow-orange phosphorescence with a maximum at 583 nm, a quantum yield of 43%, and an excited-state lifetime of 910 ns in argon-saturated dichloromethane. Optimized orange light-emitting electrochemical cells with the new Ir(III) complex exhibit fast turn-on, a peak luminance of 684 cd m(-2) and a peak efficacy of 6.5 cd A(-1); in 850 h of continuous operation their luminance and efficacy decrease only by 20%.
Special needs and characteristic features of (photo)catalytic reactors with a review of the proposed Solutions
2019
Abstract In the present chapter, the analogies between photocatalytic systems and the systems where the more common thermally activated reactions take place are highlighted. The objective is to propose a unified approach for the analysis and the design, which, however, must take into account how and why photocatalytic reactors differ from reactors with thermal reactions. The necessity of absorbing photons to activate the photocatalytic process adds complexity to the system, but some approaches are presented to simplify the problems and make easier their solution.
Changes of the Quantum Yield of Oxygen Evolution and the Electron Transport Capacity of Isolated Spinach Thylakoids during Photoinhibition
1992
Summary Isolated spinach thylakoids can be protected from photoinhibitory loss of electron transport capacity by the radical defense system composed of the enzymes SOD and catalase, as well as the antioxidants glutathione and ascorbate. With these compounds present at saturating concentrations, thylakoids not only retain a high photochemical capacity but also do not suffer D1-protein degradation during photoinhibition. However, a strong decrease in the quantum yield of oxygen evolution, Φ O 2 , occurs with the same thylakoids. These results support the view that the photochemical capacity and the quantum yield of oxygen evolution decline due to different mechanisms during photoinhibition. T…
Pyrene-benzoylthiophene Bichromophores as Selective Triplet Photosensitizers.
2006
Combination of the pyrene and benzoylthiophene units constitutes an interesting approach to design bichromophoric photosensitizers with increased intersystem crossing quantum yield and enhanced selectivity. The potential of this strategy has been illustrated in the present work by using a model photoisomerization reaction.
Carborane-stilbene dyads: influence of substituents and cluster isomers on the photoluminescence properties
2017
Two novel styrene-containing meta-carborane derivatives substituted at the second carbon cluster atom (Cc) with either a methyl (Me), or a phenyl (Ph) group, are introduced herein alongside with a new set of stilbene-containing ortho- (o-) and meta- (m-) carborane dyads. The latter set of compounds has been prepared from styrenecontaining carborane derivatives via Heck coupling reaction. High regioselectivity has been achieved for these compounds by using a combination of palladium complexes [Pd2(dba)3]/[Pd(t-Bu3P)2] as a catalytic system, yielding exclusively E isomers. All compounds have been fully characterized and the crystal structures of seven of them analyzed by X-ray diffraction. Th…
Ultrafast Relaxation Dynamics of Osmium−Polypyridine Complexes in Solution
2013
We present steady-state absorption and emission spectroscopy and femtosecond broadband photoluminescence up-conversion spectroscopy studies of the electronic relaxation of Os(dmbp)(3) (Os1) and Os(bpy)(2)(dpp) (Os2) in ethanol, where dmbp is 4,4'-dimethyl-2,2'-biypridine, bpy is 2,2'-biypridine, and dpp is 2,3-dipyridyl pyrazine. In both cases, the steady-state phosphorescence is due to the lowest (MLCT)-M-3 state, whose quantum yield we estimate to be <= 5.0 x 10(-3). For Os1, the steady-state phosphorescence lifetime is 25 ns. In both complexes, the photoluminescence excitation spectra map the absorption spectrum, pointing to an excitation wavelength-independent quantum yield. The ultrafa…
Thiphenylmethane based structural fragments as building blocks towards solution-processable heteroleptic iridium(iii) complexes for OLED use
2019
A novel structural approach to solution-processable heteroleptic iridium(III) complexes is presented. On the basis of 2-arylbenzo[d]thiazole cyclometalating main ligands and picolinic acid (pic) and acetylacetone (acac) ancillary ligands six new yellow or orange emitting materials were obtained using attached 1,1,1-triphenylmethylpentane substituents as aggregation preventing and solubility enhancing functional fragments. The obtained compounds show high photoluminescence quantum yield values in the range of 0.64 to 0.90. OLEDs with a spin-coated emissive layer were successfully prepared, with the highest achieved external quantum efficiency of 7.9%, current efficiency of 12.4 cd A−1 and po…
Luminescence properties of nonbridging oxygen hole centers at the silica surface
2009
Abstract Two variants of the surface-nonbridging oxygen hole center, ( Si–O)3Si–O• and ( Si–O)2(H–O)Si–O•, stabilized in porous films of silica nano-particles were investigated by time resolved luminescence excited in the visible and UV spectral range by a tunable laser system. Both defects emit a photoluminescence around 2.0 eV with an excitation spectrum evidencing two maxima at 2.0 and 4.8 eV, this emission decreases by a factor ∼2 on increasing the temperature from 8 up to 290 K. However, the different local structure influences the emission lineshape, the quantum yield and the decay lifetime. Such peculiarities are discussed on the basis of the symmetry properties of these defects.
Delayed Luminescence in Lead Halide Perovskite Nanocrystals
2017
The mechanism responsible for the extremely long photoluminescence (PL) lifetimes observed in many lead halide perovskites is still under debate. While the presence of trap states is widely accepted, the process of electron detrapping back to the emissive state has been mostly ignored, especially from deep traps as these are typically associated with nonradiative recombination. Here, we study the photophysics of methylammonium lead bromide perovskite nanocrystals (PNCs) with a photoluminescence quantum yield close to unity. We show that the lifetime of the spontaneous radiative recombination in PNCs is as short as 2 ns, which is expected considering the direct bandgap character of perovskit…
Near-Quantitative Internal Quantum Efficiency in a Light-Emitting Electrochemical Cell
2008
A green-light-emitting iridium(III) complex was prepared that has a photoluminescence quantum yield in a thin-film configuration of almost unity. When used in a simple solid-state single-layer light-emitting electrochemical cell, it yielded an external quantum efficiency of nearly 15% and a power efficiency of 38 Lm/W. We argue that these high external efficiencies are only possible if near-quantitative internal electron-to-photon conversion occurs. This shows that the limiting factor for the efficiency of these devices is the photoluminescence quantum yield in a solid film configuration. The observed efficiencies show the prospect of these simple electroluminescent devices for lighting and…