Photobleaching curve

Application to a CEL dye. The UV spectra of Dl in a PVP matrix before and after bleaching are shown in Figure 4. The absorption maximum of Dl lies at 376 nm. The photobleaching curve of the Dl-CEL layer consisting of Dl and PVP is shown in Figure 5. The transmittance of the unbleached layer is less than 1% and that of the completely bleached layer is about 90%. Contrast and resolution of the photoresist are expected to be greatly improved with the use of the Dl-CEL. 

Figure 5. Photobleaching curve of the Dl-CEL layer exposed at the i-line (365 nm).

FIGURE 8.6 Effect of dispersion and pulse energy on photobleaching. Photobleaching curves for GDD-only (9 mW) and MIIPS compensated (9 mW and 3 mW) pulses. Inset Phaser plot for the three considered cases. The modulation frequency, which is a free parameter in these measurements [for details, refer to (Digman et al. 2008)], is taken to be 0.03 rad/s. The counterclockwise shift of the phasor end point indicates the decrease of the decay rate. 

Table 7 lists the values of the effective rate constants of the light-induced etr decay, Vz/z, and of the radii of capture of et by acceptors, Rz, calculated from the et photobleaching curves by means of eqn. (28). The value of z = 20 s for a 10 M aqueous NaOH solution needed for such calculations, was found from the curve of etj photobleaching in the presence of CrO and from the values of ae and ve for this acceptor given in Table 2. 

Figure 1.6 Solvent accessibility and photobleaching behaviour of nanoparticle synthesis intermediates. (A-C) Excitation and emission spectra of nanoparticle intermediates ((A) TRITC (B) core (C) core-shell) in ethanol (blue) and water (red). (D) Photobleaching behaviour of nanoparticle intermediates (blue, TRITC green, core red, core-shell) and fluorescein (black). All curves in (A)-(D) are normalized by the peak values. (Reproduced from ref. 13, with permission.)...

Fig. 3. Schematic diagram of the spot photobleaching method of FRAP. (A) Darkened circles represent fluorescently labeled molecules evenly distributed over a two-dimensional surface (assumed to be an infinite plane). (B) White and light gray circles represent the initial postbleach distribution of photobleached molecules within a 1-pm diameter spot. (C) Redistribution of photobleached and unbleached molecules as a consequence of random diffusion over time. (D) Curve representing the fluorescence intensity within the l-pm diameter spot monitored over time arrows a, b, and c indicate the time-points that correspond to their respective panels. The rate of recovery from point b to point c is used to determine the diffusion constant. The magnitude of the recovery is determined by comparing the fluorescence intensity at point c with the initial intensity at point a, and is used to determine the mobile fraction.

In order to check the proposed model of et photobleaching, in refs. 40 and 62 the kinetics of et photobleaching in the presence of acceptor additives in vitreous water-alkaline and water-ethylene glycol matrices at 77 K was studied. Typical curves for photobleaching are presented in Fig. 31. The addition of acceptors is shown to result in an essential increase in the rate of e,r. photobleaching, the kinetics of e,r decay in the presence of additives being described by an exponential law in accordance with eqn. (28). 

Fig. 31. Kinetic curves for the photobleaching [40,62] of et in a vitreous 10 M aqueous NaOH solution irradiated at 77 K in the absence (O) and in the presence (solid symbols) of acceptor additives in the coordinates of eqn. (28).

Figure 7. Linear curves obtained from Figure 6 by linking together the reflectance values (Roo) from either the photoyellowing or photobleaching periods as a function of radiation time.

Fig. 2.10. Photobleaching relaxation kinetic curves at the bandedge of absorption spectrum of a CdS colloid obtained in the excess of Cd2+ ions with the particles of various sizes. [CdS] = 10 M, [DCH] = 210 3 M, [TG] = 5-10 3 M. Illumination at X < 360 nm (UFS-1), Cell length 1 is 10 cm, T = 20°C.

To study the regularities of photoexcited electron relaxation in the reaction of the electron transfer by the method of flash photolysis in microsecond timescale, we had to change the electron acceptor concentration in a liquid phase. The ability of the acceptor molecules to adsorb at the surface of the semiconductor colloidal particle was found to determine the character of changes in the photobleaching relaxation kinetic curves. 

Fig. 2.11 shows the photobleaching relaxation kinetic curves of colloidal CdS obtained in an excess of the cadmium ions (the positive surface charge of the colloid) at adding of two different electron acceptors. One may see that the addition of negatively... 

The addition of positively charged methylviologen ions, which are poorly adsorbed on the colloid under consideration, changes the kinetic dependence of the photobleaching relaxation. The kinetic curves obtained do not obey the logarithmic law (Eq. (2.9)), and are expressed by an exponential dependence on time,... 

Fig. 2.13. Photobleaching relaxation kinetic curves of colloidal CdS with an excess of Cd2+ ions at various temperatures and at the addition of various electron acceptors a) without acceptors b) MV, 1CT6 M c) PWi2, 3-10"6 M. The temperature variation along the arrows 20, 30,40, 50, 60, and 70°C. [CdS] = ltT M, [SDS] = 2-10-3 M, [TG] = 10 2 M.

To verify the effect of the ions adsorption on the regularities of photoexcitation relaxation, we studied the temperature effect on the kinetics of the ultradispersed CdS photobleaching relaxation at the addition of electron acceptors of various nature. Fig. 2.13 presents the kinetic curves of the colloidal CdS photobleaching relaxation prepared with an excess of cadmium ions at different temperatures and at the addition of different... 

Up to now, most proposals for photobleaching image enhancement have relied on linear photochemistry, in which the transmittance is a function only of total dose, and not on the rate at which that dose is delivered. The kinetics of such linear photochemistry are well understood and have been described analytically (28). The exposure depends solely on a single parameter which is the product of extinction coefficient, quantum yield, intensity, and time. No increase in contrast can be obtained by changing extinction coefficient or quantum yield, since this merely scales the dose. Contrast can be increased only by increasing the initial optical density, which increases the dose requirement. Only with nonlinear (intensity dependent) photochemistry can one obtain steeper bleaching curves at a specified optical density. 

In addition, for reasons that we cannot explain, the curve of Figure 3 is sharper than the theory of reference 13 would predict, and is sharper than would be obtained from a linear photobleaching system of the same initial optical density (28). Thus there appear to be significant advantages in this type of nonlinear transient bleaching, although more work is needed to understand it. 

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