Overall luminescence efficiency

Both the absolute quantum yield (determined with respect to zinc tctraphcny 1 porphvrin in ethanol) and the product of the molar absorption coefficient at the excitation wavelength with the quantum yield, e Q, which represents the overall luminescence efficiency follow the... 

As has been described in [ Basics of Lanthanide Photophysics , BiinzU, Eliseeva] and in [ Stable Luminescent Chelates and MacrocyclicCompounds , Mathis, Bazin], luminescent lanthanide complexes contain an antenna chromophore that serves to efficiently absorb excitation light and transfer this energy to the incorporated lanthanide ion that can then exhibit its photoluminescence. In this case, the overall luminescence quantum yield,, ot, is given by the product of the photosensitisation efficiency Tjsens, which gives the overall antenna-to-lanthanide energy transfer efficiency, and the intrinsic photoluminescence quantum yield of the lanthanide ion, [Pg.137]

In the optimisation of every class of luminescent materials, it is crucial to have quantitative data on the luminescence brightness of each member of the class. This quantitative brightness, in molecular terms, is the product of the extinctimi coefficient and the overall luminescence quantum yield (see Chap. 2). More detailed information on the photophysical performance of luminescent lanthanide complexes may be obtained by dissecting this brightness into the individual contributions of extinction coefficient, energy transfer efficiency and intrinsic lanthanide luminescence yield. 

The measurement of the absolute quantum yield has to be completed by the determination of the hfetimes tobs and the radiative lifetimes trad, giving access to the intrinsic d>Ln quantum yields, and overall sensitization efficiency jjsens-These values are sometimes neglected however, they allow a better understanding of the electronic structure of the ligand and therefore of the influence of the ligand for sensitizing the lanthanide ion. They can allow a better prediction of the properties of the complexes. For a better definition of each of these values, the reader is referred to Luminescence, and for a discussion of the influence of these parameters within the heUcate famihes, to the article of Biinzli et al ... 

Tables Comparative photophysical data for the Ln -centered luminescence of the [Ln2(L / 03] helicates with Eu " and Tb , at room temperature, pH 7.4 (Tris buffer 0.1 M solution), [L]t = 10 M Ln" lifetimes tohs, absolute and intrinsic quantum yields, radiative lifetimes trad and overall sensitization efficiency Vsens...

ZnS, an SC with large of 3.68 eV at 25°C (Table 1), possesses a direct-band gap, which makes optical transitions very probable. Pure ZnS is characterized byn-type conductivity. ZnS is chemically more stable and thus technologically easier to manipulate than other compound SC materials [69]. ZnS is a luminescent material well known for its PL, EL, and cathodoluminescence. ZnS-based phosphors exhibit excellent conversion efficiencies for fast electrons into electron-hole pairs and are, therefore, among materials with the highest overall cathodoluminescence efficiency [70]. Because of its wide-band gap, ZnS has become one of the most applied active layers in TEEL devices [26]. 

An interesting alternative cathode, ZrC was explored by Sheats et al.. [31] ZrC has a low work function (between Ca and Al) and is unreactive. For example, it is highly stable in air for long times. Like many other transition-metal carbides, it has a good electrical conductivity. These factors make it appear a nearly ideal contact material. Indeed, good electrical results were obtained for ZrC cathode contacts to MEH-PPV. Unfortunately, the devices showed low luminescence efficiency, possibly because of defect formation near the contact in the organic layer. Likewise, the Hfetimes of the ZrC based devices were relatively poor. Overall, this has led to the abandonment of ZrC as a contact material. Further research might find a solution to the observed problems. 

An alternative path includes oxidation, in the absence of light, of the diazaquinone with weak chemiluminescence (154). The effect of iron(II) on the luminescent intensity was interpreted by considering that it can efficiently generate the O - radical in a reaction with 02 and, as a consequence, increase the importance of reaction (108) in the overall process (155). 

MLCT) state occurs with an efficiency < es approaching 100%. Consequently, the overall, actinometrically determined ECL efficiency ( ci expressed in emitted photons produced per annihilation event) is close to the luminescence quantum... 

The intensity (I) of chemiluminescence will depend on the rate of the luminescent reaction (R), the overall efficiency of the formation and emission of excited species (O) and a geometrical factor (G), which is a product of the fraction of emitted photons that are detected and the detection efficiency [24] ... 

It should also be noted that, although the main interest in antennas comes from the search for an effective artificial photosynthesis, antennas may be relevant for any kind of application involving light-induced processes, such as luminescent sensors, photochemical reactions, and so on. The efficiency of any photoinduced process may actually be significantly enhanced by using suitable antennas, when the overall light energy incident on the system is considered. 

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