Emission sensitized delayed

Fig. 22. Sensitized delayed fluorescence spectra of anthracene in 10 SM phenan-threne solution.38 Intensity of exciting light was approximately 2.7 X 10-8 einstein cm. 2 sec. 1 at 3.19m-1 (313 dim)- Delayed emission spectra with anthracene concentrations of (1) 10 8Af, (2) 5 X 10 W, (3) 10-W, (4) 10- M, (5) 10 9M. Curve (6) Fluorescence emission spectrum of solution 1 at 260 times less sensitivity. (Owing to variation in the shapes of the cylindrical optical cells, the relative intensities of the delayed emission are only approximately proportional to 9A/fF.)...

By using phase sensitive detection, the detector phase angle can be adjusted to be exactly out of phase with the phase-delayed emission from any single fluorophore, suppressing its contribution to the total emission signal. Phase sensitive detection, coupled with... 

The luminescence spectrum of the Canada apatite contains the yellow band, which is similar to Mn + emission in the Ca(II) site (Fig. 5.71). Nevertheless, this band has short decay time, which is not suitable for strictly forbidden d-d transitions in Mn +. It dominates in the time-resolved spectrum with a delay of 10 ps and gate of 100 ps when the shorter-lived centers are quenched, while the longer-Hved ones are not detected. A change in the lifetime may be indicative of the energy transfer from Mn + by a radiationless mechanism. A condition necessary for this mechanism is coincidence or a close distance between energy level pairs of the ion sensitizer and the ion activator. Here, the process of luminescence is of an additive nature and a longer duration and greater quantum yield of the activator luminescence accompany a reduced... 

Fig. 12. Eosin in glycerol (7 X 10 Af) and eosin in ethanol (1.5 X 10 W). (a) Fluorescence emission spectrum at +30°C. (6) delayed emission spectrum (DES) at +69°C. (c) DES at +48°C. (d) DES at + 18°C. (e) DES at -40°C. Delayed emission spectra at a sensitivity 600 times greater than that for the fluorescence emission spectrum. (/) Fluorescence emission spectrum at -J-22°C. (g) delayed emission spectrum (DES) at +71 °C. (h) DES at +43°C. (j) DES at +22°C. (Z) DES at — 7°C. (m) DES at —58°C. (s) Sensitivity of 1)558 photomultiplier with quartz monochromator (unite of quanta and frequency). Delayed emission spectra at a sensitivity 3000 times greater than that for the fluorescence emission spectrum.

Fig. 15. Delayed emission spectra of 10 W proflavine hydrochloride in glycerol (left) and ethanol (right).s [Excitation at 2.73 n l (366 m/ )]. (1) Fluorescence emission spectrum at 20°C. (2) delayed emission spectrum (DES) at 20°C. (3) DES at —18° (4) DES at —38° (5) DES at —76°. Delayed emission spectra at a sensitivity approximately 80 times greater than that for the fluorescence emission spectrum. (6) Fluorescence emission spectrum at 20° (7) DES at 20° (8) DES at 0° (9) DES at —21° (10) DES at —39° (11) DES at —74°. Delayed emission spectra at a sensitivity approximately 10,000 times greater than that for the fluorescence emission spectrum.

Fig. 16. Delayed emission spectra of 10 3M phenanthrene in ethanol.33 The left-hand sections of the spectra (delayed fluorescence) all were recorded at a sensitivity approximately 1000 times greater than that used for curve (1) (normal fluorescence). The right hand sections of the curves (phosphorescence) were recorded at the following sensitivities (2) —107° at 60X (3)...

Fig. 17. Delayed fluorescence spectrum of 5 X 10-63/ anthracene in ethanol.84 Half-bandwidth of analyzing monochromator was 0.05 ju-1 at 2.5 n K Intensity of exciting light was approximately 1.4 X 10 einstein cm. a sec.-1 at 2.73m-1 (366 mju). (1) Normal fluorescence spectrum (distorted by self-absorption). (2) Delayed emission spectrum at sensitivity 260 times greater than for curve 1. (3) Spectral sensitivity of instrument (units of quanta and frequency).

Fig. 21. Emission spectra of 3 X 10-lAf naphthalene in ethanol.46 Excitation at 313 ran with frontal illumination, (a) Normal fluorescence at — 105°C. at sensitivity IX (6) delayed fluorescence at — 105°C. at sensitivity 60X (c) delayed fluorescence at -f 22°C. at sensitivity 140X.

Parker and Williams recently reported NAND logic action in the terbium complex 16.[S8] The delayed emission of the lanthanide ion is switched off when H+ and 02 are present simultaneously. Protonation of the phenanthridine side chain causes its triplet excited state to approach theTb(m) 5D4 excited state energetically. This leads to equilibration of these two excited states and sharing of their properties. Thus, the metal-centered state displays the 02 sensitivity usually only found in organic triplets. 

The selection of the delay time and the measurement time is very important to obtain really high sensitivity. If the delay time is too long, the emission intensity decreases and the total sensitivity is lowered. If the delay time is too short, the background fluorescence still remains... 

No emission at 1269 nm was detected, which was taken to mean that no 02 was formed or that its formation quantum yield, fl>A, was lower than the sensitivity limit of the detector (5 x 10-3). In two-laser, two-color experiments, after excitation at 355 nm the merocyanine formed was excited (2-ns delay) with a green layer (532 nm), and again no 02 was detected, a clear indication that the (photo)merocyanine did not participate in the sensitized formation of singlet oxygen, the species that could induce oxidative degradation of the photochromes. The only noticeable exception was found for 11 for which fl>Awas measured to be 0.15. 

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