Phosphorescent energy

The results of an extensive study by Eaton38b on phosphorescence energies and lifetimes of ketones are given in Tables II-V. For purposes of this review, discussion is limited to this important class of compounds. 

Absorbance Internal conversion Fluorescence Intersystem crossing Phosphorescence Energy transfer Luminescence... 

A very interesting series has been prepared and studied by Balzani, Belser, De Cola and co-workers [82], in which Ru(bpy)3 and Os(bpy)3 end groups are connected by three, five or seven phenylene units, the metal-metal distance ranging from 24 to 42 A. Energy transfer is deduced from the observed quenching of the Ru(II) phosphorescence, with a parallel sensitization of the Os(II) phosphorescence. Energy transfer rate constants vary from 6.7 x 10 s for n = 3 to 1.3 x 10 s for = 7 at 293 K in acetonitrile, and a decay rate of —0.32 A was established for the rate constants, corresponding to -0.16 A for the matrix elements. 

The parameter is the corrected emission phosphorescence energy maximum. The parameter 4>p is the quantum yield for emission phosphorescence. 

Ruorescence and phosphorescence energy transfer and sensitized iuminescence... 

Complexation-induced Changes in Fluorescence and Phosphorescence Energy Transfer Light Harvesters Ion Sensing Conclusion... 

Various competitive routes are available for dissipation of absorbed radiant energy. These include both non-radiative transitions and radiative photophysical processes, such as fluorescence and phosphorescence. Energy can be transferred directly to other molecules by a process known as quenching dissipated through the vibrational motion of the molecule. Quenching depends on collisions between molecules internal transfer of energy as a result of which a molecule passes over into a lower-lying electronic state facilitates the vibrational process. 

Figure Bl.1.3. State energy diagram for a typical organic molecule. Solid arrows show radiative transitions A absorption, F fluorescence, P phosphorescence. Dotted arrows non-radiative transitions.

Zeng Y, Biczok L and Linschitz H 1992 External heavy atom induced phosphorescence emission of fullerenes the energy of triplet Cgg J. Phys. Chem. 96 5237-9... 

Luminescent Pigments. Luminescence is the abihty of matter to emit light after it absorbs energy (see Luminescent materials). Materials that have luminescent properties are known as phosphors, or luminescent pigments. If the light emission ceases shortly after the excitation source is removed (<10 s), the process is fluorescence. The process with longer decay times is referred to as phosphorescence. 

Show by a diagram why the energy of radiation emitted from an excited electronic state (by fluorescence or phosphorescence) is of lower energy than the exciting radiation. Would you expect the shift to lower energy to be more pronounced for fluorescence or phosphorescence Explain. 

Fluorescent and phosphorescent substances are excited into an unstable energy state by UV light. When they return to the ground state they release a part of the energy taken up in the form of radiation. The emitted radiation is less energetic than the light absorbed and usually lies in the visible part of the spectrum. Since absorption (excitation) and emission obey a linear relationship over a certain range a reduction in absorption leads to a reduction in the luminescence, too. 

Fig. 5 Schematic representation of the electronic transitions during luminescence phenomena [5]. — A absorbed energy, F fluorescence emission, P phosphorescence, S ground state. S excited singlet state, T forbidden triplet transition.

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