Phosphorescence effect

The arcades are zones of special effects where optical illusions, tricks of the light and transformations readily occur. This is why the arcades appear so magical, but it also intimates something of their propensity to deception and delusion. The very magic of the space colludes with the commodity promises on sale. Walter Benjamin mentions a phosphorescent effect in an... 

Having established that the electrical and phosphorescent effects of cathode rays could not be separated, Thomson proceeded to demolish another objection to the charged-particle theory. This was that iio deflection of the cathode ray beam had been observed when it was passed between two plates maintained at a small potential difference. Thomson argued that the passage of the rays rendered the... 

Furthermore, the ability to substitute the A site by a rare earth element allows to realize new phosphors with various colors emission [85-88] (oxide serves as host crystal for the activator ions). Several studies have been performed with substitutions such as Sm , Er , Eu , and Pr " . For the last doping element, a long-lasting phosphorescence effect was demonstrated by Chu Ming-Hui et al. [89]. 

Measurement must be performed at a very low temperature so as to suppress radiationless relaxation. Thus, some phosphorescence effects visible at room temperature are more interesting for use with chemical sensors. They are found with substances adsorbed at a soUd surface. Adsorptive bond may stabihze the triplet state. 

Sensitivity From equations 10.32 and 10.33 we can see that the sensitivity of a fluorescent or phosphorescent method is influenced by a number of parameters. The importance of quantum yield and the effect of temperature and solution composition on f and p already have been considered. Besides quantum yield, the sensitivity of an analysis can be improved by using an excitation source that has a greater... 

This effect, which can also be produced if fluorescent substances are applied to the chromatogram by spraying or dipping after development, is an absorption effect and not a quenching process in the true sense of the word. It is correct to refer to fluorescence or phosphorescence diminishing. The more absorbant sample molecules there are present in the zone the darker this will appear (Fig. 4B). 

Pawlewski s rule, 407 Peltier effect, 450, 460 Perpetuuin mobile, 51, 70 Phase, 20 rule, 169, 388, 446 Phosphorescence, 35 Physically small, 38, 69 Plait point, 244... 

Solid-surface room-temperature phosphorescence (RTF) is a relatively new technique which has been used for organic trace analysis in several fields. However, the fundamental interactions needed for RTF are only partly understood. To clarify some of the interactions required for strong RTF, organic compounds adsorbed on several surfaces are being studied. Fluorescence quantum yield values, phosphorescence quantum yield values, and phosphorescence lifetime values were obtained for model compounds adsorbed on sodiiun acetate-sodium chloride mixtures and on a-cyclodextrin-sodium chloride mixtures. With the data obtained, the triplet formation efficiency and some of the rate constants related to the luminescence processes were calculated. This information clarified several of the interactions responsible for RTF from organic compounds adsorbed on sodium acetate-sodium chloride and a-cyclodextrin-sodium chloride mixtures. Work with silica gel chromatoplates has involved studying the effects of moisture, gases, and various solvents on the fluorescence and phosphorescence intensities. The net result of the study has been to improve the experimental conditions for enhanced sensitivity and selectivity in solid-surface luminescence analysis. 

Lu, W., Li, Y, Chan, M.C.W., Che, C.-M., Cheung, K.-K and Zhu, N. (2002) Organic triplet emissions of arylacetylide moieties harnessed through coordination to [Au(PCy3)]. Effect of molecular structure upon photoluminescent properties. Journal of the American Chemical Society, 124,14696-14706 (c) Lu, W., Zhu, N. and Che, C.M. (2003) Polymorphic forms of a gold(I) arylacetylide complex with contrasting phosphorescent characteristics. Journal of the American Chemical Society, 125, 16081—16088 ... 

Most dyes and pigments owe their colour to the selective absorption of incident light. In some compounds, colour can also be observed as a result of the emission of visible light of specific wavelengths. These compounds are referred to as luminescent. The most commonly encountered luminescent effects are fluorescence and phosphorescence. The transitions which can occur in a molecule exhibiting either fluorescence... 

Thus we would expect the phosphorescence efficiency to be greater for the first case than the second. In agreement with this conclusion, Similar effects are observed for heterocycles for example, the phosphorescence quantum yield for pyrazine (lowest n, it triplet) is 0.30(119) while that for quinoline in a hydroxylic solvent (lowest 77,77 triplet) is 0.19/305... 

The results of this study show a definite quenching of the 418 nm phosphorescence emission of DMT. One would expect that the quenching effect, in a rigid glass, would fit the Perrin model (73). A plot in In 4>0/4> versus concentration of 4,4 -BPDC yielded a straight line, the slope of which was identified with NV. The radius, R, of the active volume of quenching sphere was calculated by the following equation ... 

If neither mode of energy transfer is acceptable, a different explanation of the apparent quenching of the DMT phosphorescence must be put forth. It must be recalled that both DMT and 4,4 -BPDC absorb 298 nm light, which introduces the argument that competitive absorption causes the apparent quenching effect. 

A third possible channel of S state deexcitation is the S) —> Ti transition -nonradiative intersystem crossing isc. In principle, this process is spin forbidden, however, there are different intra- and intermolecular factors (spin-orbital coupling, heavy atom effect, and some others), which favor this process. With the rates kisc = 107-109 s"1, it can compete with other channels of S) state deactivation. At normal conditions in solutions, the nonradiative deexcitation of the triplet state T , kTm, is predominant over phosphorescence, which is the radiative deactivation of the T state. This transition is also spin-forbidden and its rate, kj, is low. Therefore, normally, phosphorescence is observed at low temperatures or in rigid (polymers, crystals) matrices, and the lifetimes of triplet state xT at such conditions may be quite long, up to a few seconds. Obviously, the phosphorescence spectrum is located at wavelengths longer than the fluorescence spectrum (see the bottom of Fig. 1). 

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