On delayed fluorescence

Magnetic field effects on delayed fluorescence from methylene chloride solutions ... 

F. Perrin Discussion on Jean Perriris diagram for the explanation of the delayed fluorescence by the intermediate passage through a metastable state First qualitative theory of fluorescence depolarization by resonance energy transfer... 

Figure 8.7. Delayed fluorescence and diffuse reflectance transient absorption spectroscopy on scattering substrates. Example terthicnyl on silica gel excited with = 354 nm (neodymium/yttrium-aluminum-garnet) (Nd/YAG) laser pulse of 10 nsec, 20 mj), recorded with a gated diode array spectrometer.

In pure crystals, singlet excitons can be created by mutual annihilation of triplet excitons. The intensity of the singlet exciton fluorescence depends quadratically on the triplet exciton concentration and is therefore proportional to the square of the singlet-triplet extinction coefficient. It is interesting to compare such a delayed fluorescence excitation spectrum, observed by Avakian et cd. 52) on naphthalene, with a corresponding phosphorescence excitation spectrum (Fig. 22). 

Fig. 33. Dependence of the rhodamine sensitized delayed fluorescence in anthracene on the magnetic field oriented parallel to the 001 surface of anthracene. (2 x 10-7 M rhodamine and 10 1 NaHSC>3 in aqueous solution) 9°)...

Effect of Anthracene Concentration on the Intensity of Delayed Fluorescence in Ethanol° b... 

Effect of Light Intensity on the Delayed Fluorescence of Anthracene Solutions 1 ... 

Under all conditions investigated the intensity of delayed fluorescence was small compared with that of normal fluorescence. Thus, when the exciting light is switched on we can ignore triplet-triplet quenching and consider the population of excited states (P, P2 ) to be maintained only by direct excitation from P to P. The rate of formation of P2 is then equal to its rate of disappearance, i.e.,... 

C. Dependence of Intensity of Delayed Fluorescence on the Rate of Light... 

Although at high rates of light absorption the square law dependence on rate of light absorption is no longer obeyed, the intensity of P-type delayed fluorescence is still proportional to the square of the intensity of triplet-singlet emission because the latter is always proportional to... 

The delayed fluorescence efficiency of the donor will thus decrease rapidly on the addition of small concentrations of acceptor. 

A slightly different method could be used for compounds such as naphthacene, which give rise to no delayed fluorescence on their own. If it is assumed that the reason for the absence of naphthacene delayed fluorescence is that its triplet energy is less than one-half of its singlet... 

On thermal excitation to the S, state, fluorescence will occur with usual fluorescence efficiency f. Therefore, the efficiency of delayed fluorescence faa is given as... 

B) P-type delayed fluorescence is so called because it was first observed in pyrene and phenanthrene solutions. In aromatic hydrocarbons singlet-triplet splitting is large and therefore thermal activation to excited singlet state at room temperature is not possible. The mechanism was first formulated by Parker and Hatchard based on the observation that the intensity of emission of the delayed fluorescence Ipd was proportional to the square of the intensity of absorption of the exciting light Ia. 

P-type delayed fluorescence this is also known as triplet-triplet annihilation and depends on the energy transfer between two triplet excited states 3M to form an excited singlet state 1M and a ground state M... 

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