Exciton trap

Yersin H (2004) Triplet Emitters for OLED Applications. Mechanisms of Exciton Trapping and Control of Emission Properties. 241 1-6 Yeung LK,see Crooks RM (2001) 212 81-135... 

O Neil, M. Marohn, J. McLendon, G. Picosecond measurements of exciton trapping in semiconductor clusters, Chem. Phys. Lett. 1990, 168, 208. 

The polymer exhibits very low dark currents (o60° = 3 x 10 19 ohm-1 cm-1). The photocurrent was reported to be proportional to the applied voltage and light intensity but its magnitude was far inferior to that of PVK. The poor photoconductivity is attributed to the high concentration of exdmer forming sites acting as exciton traps and also to poor transport characteristics. The carrier transport is expected to be slower since the ionization potential of the polymer is higher (7.88 eV) than that of PVK (7.43 eV). 

Molecules situated on either side of such interfaces, which generally function as exciton traps, can photo-dimerize to yield products that cannot be generated at unfaulted regions of the crystal. 

The determination of the triplet exciton-trapped hole overall rate constant (yxq) was initially made by measuring... 

Yersin, H. (2004)Triplet emitters for OLED apphcations mechanisms of exciton trapping and control of emission properties. Topics in Current Chemistry, 24, 1—26. 

The triplet excimer phosphorescence from liquid solutions of naphthalene and di-2-naphthylalkenes in isooctane previously reported has not been confirmed and the emission probably arose from impurities like biacetyl . Exciton trapping has been studied in doped 1,4-dibromonaphthalene . ENOOR applied to the study of triplet traps of phenanthrene-TCNB in naphthalene-TCNB , and triplet 1- and 2-naphthylphenylcarbenes produced by photolysis of diazo compounds . Conformers of triplet states of 2-naphthaldehyde at 300K , T and T2 states from dual... 

How can we interpret this parameter for excitons in J-aggregates There is a competition between two processes exciton radiative relaxation and exciton trapping and even if an exciton forms near the trap there is a possibility that it is deactivated radiatively before trapping due to a very short radiative lifetime of J-aggregates (hundreds picoseconds and less) [3,5]. 

Exciton Trapping and Self-Trapping in Molecular Crystals. 

Figure 5.13 illustrates the temporal evolution of photoinduced colour centres in colloidal TiOi following picosecond laser pulse excitation. These centres form as a result of carrier/exciton trapping by pre-existing defects (anion Va and cation Vc vacancies), and by some ions in irregular (defect) positions in the lattice, for example Ti rreg in titania (or Zr" i .eg in zirconia)—stages 16 to 21. ... 

Charge-carrier and exciton trapping by pre-existing surface defects (S) yields surface-active centres (S and S" ) for adsorption and catalysis (step 4). 

Energy transfer in polymers has been studied in the pure solid state, in heterogeneous systems (e.g. polymer blends), in liquid solutions and in solid solutions. The last case, which will be considered here, provides relatively simple and clear experimental conditions since interactions between the macromolecules can be excluded by dilution and molecular movement is severely restricted by low temperature and rigid environment. Thus, excitonic energy transfer can be studied without competing molecular movement. The luminescence of dilute, solid solutions of aromatic polymers is not dominated by excimers - in sharp contrast to the other modes of observation - so that side group fluorescence and phosphorescence can be observed. This does not mean, however, that exciton trapping processes are absent in these systems. 

A distinction between the different possibilities can be achieved by time-resolved fluorescence and quenching experiments which have not yet been performed for aromatic polymers in solid solution. A more detailed discussion on exciton trapping in pseudo one-dimensional systems is presented in the next section, since much more information la available about phosphorescence quenching and triplet excitons than about fluorescence. 

Time dependent fluorescence depolarization is influenced by the exciton annihilation which occurs in confined molecular domains . Photoemission results from singlet exciton fusion as shown by the excitation intensity dependence which occurs in anthracene crystals. Reabsorption of excitonic luminescence is an effect which has been shown to occur in pyrene crystals. The dynamics of exciton trapping in p-methylnaphthalene doped naphthalene crystals involves phonon assisted detrapping of electronic energy. Ps time resolved spectroscopy was the experimental technique used in this work. 

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