Exciton quenching

The triplet exciton quenching by doublet species is well established. Annihilation of triplet excitons has been observed on... 

Kanazawa, A. and Kramer, D.M. 2002. In vivo modulation of nonphotochemical exciton quenching (NPQ) by regulation of the chloroplast ATP synthase. Proc. Natl. Acad. Sci. USA 99. 12789-12794. 

Use of wide-gap transport layers to carry charges to the electrodes from the lower-gap active layers without risk of exciton quenching at the electrodes (Penmans et al, 2000 Drechsel et al, 2005). 

Figure 8-15. Field-induced exciton breaking rate y(f), calculated from Eq. (8.2). The inset shows the experimental field-induced SE quenching at 2.53 eV (circles) and the exciton quenching AA smf (0 calculated using Eq. (8.2) (solid line) (from Ref. [40] with permission).

Results in time-resolved PL measurements were reported (Dittmer et al., 2000). It is seen that time evolution of PL intensity of poIy[2-methoxy-5-(2 -ethyI-hexyIoxy)-l,4-phenyIene vinylene] (MEH-PPV) on quartz shows mono-exponential decrease due to natural decay of excitons with a characteristic time constant 300 ps. PL intensity of MEH-PPV on Ti02 decreases at initial time much quicker than that for MEH-PPV on quartz due to exciton quenching at the interface with Ti02 substrate (Figure 2). 

The other alternative for exciton quenching due to doping is Forster-type energy transfer towards a chromophore with bathochromatically shifted absorption spectrum so that the spectral overlap between the donor and acceptor absorption is larger. An example is fluorescence quenching in a film of poly(phenyl-pheny-lene-vinylene) (PPPV) blended with polycarbonate (PC) at a PPPV PC ratio of 20 80 per weight and doped by the 4-dicyanomethylenc-2-methyl-6-p-dimcthyla-... 

Another interesting finding based on the thermodynamic data is the low A fH0A (-28.9 kcal/mol or -121.0 kj/mol) of the Ca/CsF system. The combined used of Ca and CsF should conceptually construct a novel cathode configuration in OLEDs. Our device studies in Section 5.5 have clarified this presumption. The device performances are also dependent of other factors, e. g. they may be deteriorated by exciton quenching that arise from the gap-state formation over a rather thick interface region due to the highly exothermic reaction between the Ca and CsF. 

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