Laser-excited delayed emission

Figure 6. Laser excited delayed emission from...

Figure 8. Laser excited delayed emission from poly(n-propyl methyl silylene) in methylcyclopentane. ...

Fig. 10-8 shows the observed CIDEP spectra for the reaction of triplet eosin Y (FlBr/ ) with duroquinone. In this figure, CIDEP spectra of the duroquinone radical anion were only observed. The spectra of Xn" were not observed because of its fast spin relaxation. As clearly shown in Fig. 10-8, the initial spectrum measured at 60 ns after the laser excitation showed an emissive polarization, which was due to the usual p-type TM. This polarization was found to change as the delay time was increased. The spectrum measured at 200 ns after the excitation showed a strong absorptive polarization, which was proposed to be due to the d-type TM. Similar polarization changes were also observed for such dyes as erthrosin B (FlLi ) and dibromofluorescein (FlBr2 ) which contain heavy atoms. On the other hand, an emissive polarization was only observed for the reaction of fluoresein (Fl ), which contain no heavy atom. From these results, Tero-Kubota et al. concluded that the strong absorptive... 

Time-resolved studies employed previously-described ( ) equipment but were improved upon as follows. Part of the excitation Nd-YAG laser beam was split off and delivered to the phototube, serving as a marker pulse to trigger our Biomation 6500 for data acquisition the sample emission signal was timed by a laser pulse delay line to arrive vl5 ns after the marker pulse. Laser jitter was thereby minimized, and computer signal averaging more precise. 

Figure 6 displays the phosphorescence spectra of three alkyl polysilylenes obtained from pulsed laser excitation of thin film samples at low temperature. For these spectra, the data was integrated over the period from 200 pseo to 0.01 sec following the laser pulse. All of the alkyl polysilylenes studied show a substantial amount of emission in the region of fluorescence which has essentially the same shape as the normal fluorescence. We interpret this emission as delayed fluorescence resulting from triplet-triplet annihilation. The delayed fluorescence provides a convenient comparison between the fluorescence shape and width and that of the phosphorescence. 

Direct observation of phosphorescence from conjugated polymers has been achieved by the application of gated detection techniques. In these techniques the detection window of an intensified CCD is delayed with respect to the excitation laser pulse. Therefore the detector is blocked during the intense prompt fluorescence caused by the conjugated polymer and able to detect the delayed emission that is usually orders of magnitude lower than prompt fluorescence. Spectrally resolved detection allows for the observation of the shape and energetic position of the delayed emission. By varying the width of the detection window... 

Fig. 23 Time-resolved gated emission images of CHO cells incubated with 47 (Y = Z = H). The images were recorded after 355 nm laser excitation at the time delays shown between 100 and 2,900 ns after the laser flash. The time gate used was 100 ns, exposure time 0.02 s, five accumulations per time delay. Scale bar. 50 pm [89]...

Luminescence lifetimes measured using pulsed laser excitation involve either direct detection of emission decays with time or a technique known as time-correlated single photon counting (TCSPC). The latter technique involves repeated measurement of the delay time between the excitation pulse and the arrival of an emitted photon packet above a given discrimination level the intensity-time decay profile accumulates over many millions of excitation pulses. The TCSPC experiment has the advantage that much better signal to noise can be obtained relative to the direct capture of the luminescence decay. 

The plasma component followed here is the dimer C2, with excitation (delayed with respect to the laser pulse initiating carbon ablation) on the (0,0) transition and LIF emission on the (0, 1) transition within the Swan-band a n -d ng- Clearly, the evolution in space and time can be traced in the snapshots of the plasma volume, with the distribution of C2 becoming more homogeneous with time. 

The luminescence of many titanium minerals was studied by steady-state luminescence spectroscopy and it was proposed that blue luminescence bands mutual for these minerals is connected with TiOe complex luminescence (Gaft et al. 1981a White 1990). Figure 4.82a presents spectral properties of the blue emission from benitoite at 300 K. Under short and middle-wave UV laser excitation, such as at 266 and 308 nm, respectively, an intensive broad blue emission band peaking at approximately 420 nm with half-width of 80 nm is detected. Spectra with different excitations, delays and gates revealed that this band consists of only one... 

The most important zirconium minerals are zircon and baddeleyite, often associated with rutile and ilmenite deposits. Zircon and baddeleyite are characterized by strong luminescence under powerful laser excitation. The main background emission is connected with organic matter sorption and sometimes with fluorite. Emission spectra of zircon and baddeleyite together with their decay times demonstrate that delay time of 200 ns and gate of 10-50 ps combined with excitation near 300 nm enable to remove background signal drastically. 

Fig. 5-8. CIDEP spectra measured in ethanol at -28 °C for photogenerated DQ " as function of time delay after laser excitation. Absorption signals point up and emission ones down. (Reproduced from Ref. [17] by permission from The American Chemical Society)...

Campbell, E. E. B. and R. D. Levine (2000). Delayed ionization and fragmentation en route to thermionic emission statistics and dynamics. Ann. Rev. Phys. Chem. 51, 65. Campbell, E. E. B., H. Schmidt, et al. (1988). Symmetry and angular momentum in collisions with laser excited polarised atoms. ylrfu Chem. Phys. 72, 37. 

---