Phosphorescence intensity

The total fluorescence (or phosphorescence) intensity is proportional to the quanta of light absorbed, To — T, and to the efficiency (f>, which is the ratio of quanta absorbed to quanta emitted ... 

The following data was recorded for the phosphorescence intensity for several standard solutions of benzo[a]pyrene. 

After the laser flash, one then monitors the progress of events by some rapidly responding method. Conductivity, absorption spectroscopy, and fluorescence spectroscopy are the methods most commonly used. If a reaction product has a characteristic absorption band of sufficient intensity, one can monitor its buildup with time. This might be a UV, visible, or IR band. The need for a band with a high molar absorptivity arises because the reactive transient is usually present at a relatively low concentration, KT6-lCr5 M being typical. If the species of interest is phosphorescent, then the timed decay of its phosphorescence intensity can be recorded. 

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. 

Thus a plot of t //p vs. 1/[A] should yield a straight line with intercept kf + kic + klsc)IKkisc or 1 imlsc. Thus intersystem crossing efficiency of the donor can be obtained. 

It is relatively easy to decide which vibronic bands have a common origin. This is accomplished by observing the phosphorescence intensity change of each band upon microwave saturation at a frequency that corresponds to transitions between rz and tx. This is known as phosphorescence-microwave double resonance (PMDR) spectroscopy. These frequencies for 2,3-dichloroquinoxaline are given in Table 6.3. 

The biacetyl phosphorescence intensity I is given by the following equation ... 

C, excitation at 289 nm, emission observed at 525 nm, degassed films. (l2) Measured total phosphorescence intensity of MBC (arbitrary units) ("I, X y) component of the MBC phosphorescence due to direct absorption of MBC molecules (ltenJ component of the MBC phosphorescence due to energy transfer. 

In these sensors, the intrinsic absorption of the analyte is measured directly. No indicator chemistry is involved. Thus, it is more a kind of remote spectroscopy, except that the instrument comes to the sample (rather than the sample to the instrument or cuvette). Numerous geometries have been designed for plain fiber chemical sensors, all kinds of spectroscopies (from IR to mid-IR and visible to the UV from Raman to light scatter, and from fluorescence and phosphorescence intensity to the respective decay times) have been exploited, and more sophisticated methods including evanescent wave spectroscopy and surface plasmon resonance have been applied. 

Not all the phosphorescent molecular glasses are metal complexes. For the phenoxazine 25a, it was reported that the phosphorescence intensity may exceed the fluorescence intensity, but only at low temperatures [166]. 

Dorn anus el al.(74> proposed that the ratio of phosphorescence intensity to lifetime, P/t), of tryptophan phosphorescence as a function of temperature be used to distinguish heterogeneity in emission from multitryptophan proteins. Since different tryptophans within one protein show different temperature-... 

Ti So spectra can be determined by scanning the sample with monochromatic light and by monitoring the phosphorescence intensity at a fixed wavelength... 

Figure 1. Logarithm of the phosphorescence intensity IT as a function of reciprocal temperature for films of (a) polyethylene and (b) polystyrene containing traces of carbonyl groups.

Fig. 8. Relationship between chopper phase and phosphorescence intensity.7 (Full line represents phosphorescence intensity.)...

If the phosphorescence lifetime was of the same order as the periods of illumination and darkness, the phosphorescence intensity decayed considerably during the dark period before observation by the photomultiplier and the observed phosphorescence had to be multiplied by a factor greater than te/t3 to obtain the total phosphorescence emitted in a complete cycle. The relationship between the observed phosphorescence intensity out-of-phase (PD) and the phosphorescence intensity (P) which would be observed if the second chopper were open for a complete cycle is given by the following expression ... 

When we applied ketones. J-iX to Silicalite using the inclusion technique described earlier we observed phosphorescence in only a few examples, see Table I. Elemental analysis of the samples revealed a clear correlation between their carbon content and the relative phosphorescent intensity. The behaviour observed can be adequately analyzed by separating the ketones in three main groups ... 

The intensity of emission was independent of the observation time for Silicalite and MS-10X (for at least a few hours). However, in the case of MS-13X the phosphorescence intensity decays quickly... 

Figure 3. Time dependence of the phosphorescence intensity of K-phenylpropiophenone (Aem=450 nm) with varying conditions.

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