Characteristic decay time wavelength

Sensors based on fluorescence are quite robust because the wavelength and the orthogonal detection geometry of the incident and emitted radiation results in a high signal-to-noise ratio. The sensors described here utilize quenching of fluorescence. Thus, the analyte is the quencher Q and the indicator is a fluorescing dye F, which when excited to F, emits fluorescence with a characteristic decay time. 

Lin et al. [17] studied the dynamics of copolymers adsorbed on an air-water interface. These measurements complemented the static measurements described above and in Fig. 4. The extent of the polymer films perpendicular to the surface is small compared to penetration distance and wavelength so that EWDLS is most sensitive to variation of composition in the plane of the interface. Figure 7 shows the measured normalized autocorrelation I (/) for different surface pressures. Frames a-d were taken during the first compression of the monolayer, and frames e-h were taken during the second compression. The difference between the two sets of measurements is an indication of structural changes induced by compression cycling. The frames e-g can be compared to the data in Fig. 4. The solid lines in the three frames are fits to a sum of two exponential functions, each with a characteristic decay time. The fast decay constant has a characteristic associated with diffusive motion of the disks. The slow decay constant ( several seconds) was ascribed to the dynamics of the associations of disks. 

Definition and Uses of Standards. In the context of this paper, the term "standard" denotes a well-characterized material for which a physical parameter or concentration of chemical constituent has been determined with a known precision and accuracy. These standards can be used to check or determine (a) instrumental parameters such as wavelength accuracy, detection-system spectral responsivity, and stability (b) the instrument response to specific fluorescent species and (c) the accuracy of measurements made by specific Instruments or measurement procedures (assess whether the analytical measurement process is in statistical control and whether it exhibits bias). Once the luminescence instrumentation has been calibrated, it can be used to measure the luminescence characteristics of chemical systems, including corrected excitation and emission spectra, quantum yields, decay times, emission anisotropies, energy transfer, and, with appropriate standards, the concentrations of chemical constituents in complex S2unples. 

Plastic scintillators have a density of about 10 kg/m. Their light output is lower than that of anthracene (Table 6.3). Their decay time is short, and the wavelength corresponding to the maximum intensity of their emission spectrum is between 350 and 450 nm. Trade names of commonly used plastic scintillators are Pilot B, Pilot Y, NE 102, and NE 110. The characteristics of these phosphors are discussed in Refs. 11-13. Plastic scintillators loaded with tin and lead have been tried as X-ray detectors in the 5-100 keV range. " Thin plastic scintillator films (as thin as 20 X 10 kg/m = 20 p,g/cm ) have proven to be useful detectors in time-of-flight measurements " (see Chap. 13). 

In the presence of moderate amounts of sorbic add (e.g., 0.0015 M), the triplet lifetime of I is shortened by can be readily time-resolved. Under these conditions we rind that the characteristic guaiacoxy radical long-wavelength band is mostly present immediately following the laser pulse as opposed to growing in as die triplet decays. 

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