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Photoexcitation

The fluorescence spectra are subject to substantial deformation due to such a broad spatial distribution of emitting species. Two examples are shown in Fig. 56. The real fluorescence spectra (3) have been obtained from the apparent spectra (T) based on the spatial distribution of singlet excitons, S(x), from Fig. 54, using the following expression for the fluorescence intensity  [Pg.152]

p(A) is the real emission spectrum to be determined, ji(X) denotes the absorption coefficient of the fluorescent light and A stands for an apparatus factor. The experimental term exp[-/((/.)x] represents the photon (he//1) escape probability at a distance x from the observed crystal illuminated surface. The integral runs along the whole thickness d of the crystal. With a simplifying assumption S(x) = S(0) exp(—/(ax), where pa is the absorption coefficient of the exciting light Wa), the solution of Eq. (148) for q (X) on the basis of experimentally known ( .) and pa may be found and the results are shown in Fig. 56. [Pg.154]

The spatial distribution of emitting species produced in the electron-hole recombination process is one of important reasons for a difference between the PL and EL spectra, and a characteristic determining the EL quantum efficiency. The self-absorption of the short-wavelength part of the fluorescence can be utilized for determining the spatial distribution of EL. The principle of the method, as discussed in Sec. 3.1 and used for photoexcited states in Sec. 3.2, has been adapted to the recombination radiation as follows [41] the unknown spatial distribution of the EL light intensity, if/ x) from a plate-shaped emitting sample, is related to the experimentally observed EL signal, El(Zo), by the expression [Pg.156]

At first glance, the low-field spatial EL pattern apparent in Fig. 58 resembles the spatial distribution of singlet excitons [Pg.159]

The width of the recombination zone is directly related to the EL efficiency of LEDs, through its definition as a distance traversed by a carrier during the recombination time, Trec [2] [Pg.160]


Photoexcited fluorescence from spread monolayers may be studied [158,159] if the substance has both a strong absorption band and a high emission yield as in the case for chlorophyll [159]. Gaines and co-workers [160] have reported on the emission from monolayers of Ru(bipyridine)3, one of the pyridine ligands having attached C g aliphatic chains. Ruorescence depolarization provides information about the restriction of rotational diffusion of molecules in a monolayer [161], Combining pressure-area... [Pg.127]

NO , SiFq and SiF7 [34]. Interestingly, the result of photoexcitation of the latter four... [Pg.802]

According to Kramers model, for flat barrier tops associated with predominantly small barriers, the transition from the low- to the high-damping regime is expected to occur in low-density fluids. This expectation is home out by an extensively studied model reaction, the photoisomerization of tran.s-stilbene and similar compounds [70, 71] involving a small energy barrier in the first excited singlet state whose decay after photoexcitation is directly related to the rate coefficient of tran.s-c/.s-photoisomerization and can be conveniently measured by ultrafast laser spectroscopic teclmiques. [Pg.820]

Figure Bl.16.16 shows an example of RTPM in which the radical species is TEMPO (10), a stable nitroxide radical, while the triplet state is produced by photoexcitation of benzophenone (11) [45]. Figure Bl.16.16 shows an example of RTPM in which the radical species is TEMPO (10), a stable nitroxide radical, while the triplet state is produced by photoexcitation of benzophenone (11) [45].
Hwang K C and Mauzerall D C 1992 Vectorial electron transfer from an interfacial photoexcited porphyrin to ground-state Cgg and C g and from ascorbate to triplet Cgg and C g in a lipid bilayer J. Am. Chem. Soc. 114 9705-6... [Pg.2433]

Bawendi M G ef a/1990 Electronic structure and photoexcited carrier dynamics in nanometre size CdSe clusters Phys. Rev. Lett. 65 1623... [Pg.2922]

After this, Martinez and Ben-Nun applied the method to the photoexcitation of ethylene [88,247]. The lowest energy excitation is the HOMO-LUMO n n transition. These states are labeled A and Close in energy to... [Pg.309]

Worth and Cederbaum [100], propose to facilitate the search for finding a conical intersection if the two states have different symmetiies If they cross along a totally symmetric nuclear coordinate, then the crossing point is a conical intersection. Even this simplifying criterion leaves open a large number of possibilities in any real system. Therefore, Worth and Cederbaum base their search on large scale nuclear motions that have been identified experimentally to be important in the evolution of the system after photoexcitation. [Pg.385]

The preferable theoretical tools for the description of dynamical processes in systems of a few atoms are certainly quantum mechanical calculations. There is a large arsenal of powerful, well established methods for quantum mechanical computations of processes such as photoexcitation, photodissociation, inelastic scattering and reactive collisions for systems having, in the present state-of-the-art, up to three or four atoms, typically. " Both time-dependent and time-independent numerically exact algorithms are available for many of the processes, so in cases where potential surfaces of good accuracy are available, excellent quantitative agreement with experiment is generally obtained. In addition to the full quantum-mechanical methods, sophisticated semiclassical approximations have been developed that for many cases are essentially of near-quantitative accuracy and certainly at a level sufficient for the interpretation of most experiments.These methods also are com-... [Pg.365]

It turned out that the dodecylsulfate surfactants Co(DS)i Ni(DS)2, Cu(DS)2 and Zn(DS)2 containing catalytically active counterions are extremely potent catalysts for the Diels-Alder reaction between 5.1 and 5.2 (see Scheme 5.1). The physical properties of these micelles have been described in the literature and a small number of catalytic studies have been reported. The influence of Cu(DS)2 micelles on the kinetics of quenching of a photoexcited species has been investigated. Interestingly, Kobayashi recently employed surfactants in scandium triflate catalysed aldol reactions". Robinson et al. have demonshuted that the interaction between metal ions and ligand at the surface of dodecylsulfate micelles can be extremely efficient. ... [Pg.139]

The photosensitized dimerization of isoprene in the presence of henzil has been investigated. Mixtures of substituted cyclobutanes, cyclohexenes, and cyclooctadienes were formed and identified (53). The reaction is beheved to proceed by formation of a reactive triplet intermediate. The energy for this triplet state presumably is obtained by interaction with the photoexcited henzil species. Under other conditions, photolysis results in the formation of a methylcydobutene (54,55). [Pg.465]

Excited-State Relaxation. A further photophysical topic of intense interest is pathways for thermal relaxation of excited states in condensed phases. According to the Franck-Condon principle, photoexcitation occurs with no concurrent relaxation of atomic positions in space, either of the photoexcited chromophore or of the solvating medium. Subsequent to excitation, but typically on the picosecond time scale, atomic positions change to a new equihbrium position, sometimes termed the (28)- Relaxation of the solvating medium is often more dramatic than that of the chromophore... [Pg.389]

Fig. 1. Relaxation of molecule-medium system subsequent to photoexcitation where Sq is the singlet ground state the fkst excited singlet state and... Fig. 1. Relaxation of molecule-medium system subsequent to photoexcitation where Sq is the singlet ground state the fkst excited singlet state and...
This is essentially the same process responsible for deactivation of photoexcited cyanine dyes. [Pg.394]

Fig. 1. Photoexcitation modes iu a semiconductor having band gap energy, E, and impurity states, E. The photon energy must be sufficient to release an electron (° ) iato the conduction band (CB) or a hole (o) iato the valence band (VB) (a) an intrinsic detector (b) and (c) extrinsic donor and acceptor... Fig. 1. Photoexcitation modes iu a semiconductor having band gap energy, E, and impurity states, E. The photon energy must be sufficient to release an electron (° ) iato the conduction band (CB) or a hole (o) iato the valence band (VB) (a) an intrinsic detector (b) and (c) extrinsic donor and acceptor...
Another common loss process results from electron—hole recombination. In this process, the photoexcited electron in the LUMO falls back into the HOMO rather than transferring into the conduction band. This inefficiency can be mitigated by using supersensitizing molecules which donate an electron to the HOMO of the excited sensitizing dye, thereby precluding electron—hole recombination. In optimally sensitized commercial products, dyes... [Pg.450]

In perfect semiconductors, there are no mobile charges at low temperatures. Temperatures or photon energies high enough to excite electrons across the band gap, leaving mobile holes in the Fermi distribution, produce plasmas in semiconductors. Thermal or photoexcitation produces equal... [Pg.113]

Dicarbocyanine and trie arbo cyanine laser dyes such as stmcture (1) (n = 2 and n = 3, X = oxygen) and stmcture (34) (n = 3) are photoexcited in ethanol solution to produce relatively long-Hved photoisomers (lO " -10 s), and the absorption spectra are shifted to longer wavelength by several tens of nanometers (41,42). In polar media like ethanol, the excited state relaxation times for trie arbo cyanine (34) (n = 3) are independent of the anion, but in less polar solvent (dichloroethane) significant dependence on the anion occurs (43). The carbocyanine from stmcture (34) (n = 1) exists as a tight ion pair with borate anions, represented RB(CgH5 )g, in benzene solution photoexcitation of this dye—anion pair yields a new, transient species, presumably due to intra-ion pair electron transfer from the borate to yield the neutral dye radical (ie, the reduced state of the dye) (44). [Pg.398]


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Alkenes photoexcited

Alkenes photoexcited states

Anodic transfer reactions of photoexcited holes

Azobenzene photoexcitation

Binding neutral photoexcitations

Bulk photoexcitation

Charged photoexcitations

Colour centres photoexcitation

Complex photoexcited

Copper, photoexcitation

Cross section photoexcitation

Direct photoexcitation processes

Doping photoexcitation

Electric fields photoexcitation

Electron photoexcitation

Electron transfer photoexcitation combined with

Electronic photoexcitation

Energy transfer, after photoexcitation

Hopping photoexcited

Intersystem crossing after photoexcitation

Jablonski diagram describing photoexcitation process

Ketones photoexcited states

Laser photoexcitation

Laser photoexcitation and photodetection of diatomic molecules

Laser photoexcitation intramolecular

Metal photoexcitation

Neutral photoexcitations

Photoexcitated

Photoexcitation advantages

Photoexcitation and Carrier Collection Dynamic Behavior

Photoexcitation and Carrier Collection Steady-state Behavior

Photoexcitation and Relaxation Processes in Solution

Photoexcitation and ionization

Photoexcitation and subsequent

Photoexcitation center

Photoexcitation charge-transfer state recombination

Photoexcitation control process

Photoexcitation direct transition

Photoexcitation donor:acceptor materials

Photoexcitation dynamics

Photoexcitation electron transfer

Photoexcitation energy

Photoexcitation energy equivalence

Photoexcitation of Metals (Electron Photoemission into Solutions)

Photoexcitation of dye

Photoexcitation of electrons

Photoexcitation of reactants

Photoexcitation of reacting species

Photoexcitation of semiconductor electrodes

Photoexcitation photocurrent

Photoexcitation photopotential

Photoexcitation process

Photoexcitation quantum yield

Photoexcitation reaction

Photoexcitation recombination

Photoexcitation semiconductor electrode

Photoexcitation sensitization

Photoexcitation specific solutes

Photoexcitation spectral distribution

Photoexcitation spectroscopy

Photoexcitation time scale

Photoexcitation under illumination

Photoexcitation, colloidal

Photoexcitation, colloidal semiconductors

Photoexcitation, direct

Photoexcitation, electron-hole pair

Photoexcitation, electron-hole pair generation

Photoexcitation, molecular dynamics

Photoexcitation, processes following

Photoexcitation, selection rules

Photoexcitations

Photoexcitations in conjugated polymers

Photoexcitations, polydiacetylenes

Photoexcited

Photoexcited 4 capture

Photoexcited Structure of a Diplatinum Complex

Photoexcited benzaldehyde

Photoexcited benzophenone

Photoexcited catalyst

Photoexcited copper

Photoexcited electrode reaction current (Photocurrent)

Photoexcited electron acceptor reaction

Photoexcited electron donors

Photoexcited electrons

Photoexcited enones

Photoexcited fullerenes

Photoexcited intramolecular electron

Photoexcited intramolecular electron transfer

Photoexcited metal atoms

Photoexcited metal ions

Photoexcited quinone

Photoexcited semiconductors

Photoexcited singlet

Photoexcited singlet excited state

Photoexcited singlet state

Photoexcited state charge transport

Photoexcited states

Photoexcited triplet excited state

Photoexcited triplet state

Poly photoexcitation spectroscopy

Polyacetylene photoexcitation

Polymers as Photoexcited Donors

Polythiophene photoexcitation

Processes Caused by Photoexcitation of Reactants in the Solution

Recombination of photoexcited holes in anodic reactions

Spectroscopy of Photoexcitation in Conjugated Polymers

Spectroscopy of Photoexcitations in Conjugated Polymers

The Primary Photoexcitations in m-LPPP

The flat band potential of photoexcited electrodes

Thermodynamics of Photoexcitation

Time photoexcited states

Titanium oxide, photoexcitation

Transient couplings, photoexcitation

Ultrashort laser pulses, photoexcitation

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