The average thickness of tabular silver bromide grains can be calculated from the magnitude of the specific dye adsorption if some estimate of the average grain diameter is available. Using 1,1′-diethyl 2,2′-cyanine chloride as the dye, we related the calculated grain thicknesses, in the range from 30 to 150 nm, to data from atomic force microscopy. To bring these two methods into agreement, a limiting molecular area of 0.62 ± 0.01 nm² had to be assigned, which is 10% higher than the reported value for octahedral {111} faces. Dye adsorption gives a result close to the number average thickness of the grains, unless there exists a significant correlation between grain thickness and diameter.

A full understanding of the chemical sensitization of silver halide microcrystals with nanoscale silver/gold-sulfide clusters requires knowledge of both their nature and distribution on the microcrystal surface. Because direct electron microscopy studies of sensitized silver halide microcrystals are almost impossible, due to the electron-induced release of photolytic silver, one must resort to reliable preparation techniques such as carbon replication or gelatin encapsulation. In the present study different replication techniques are investigated and compared. For cubic and octahedral silver bromide microcrystals, the carbon replica technique in combination with the complexing agent 1,2,4-triazolium-thiolate is favored, because the traditional complexing agent, sodium thiosulfate, itself creates silver sulfide clusters as artifacts, which hampers the investigation of genuine silver–sulfur sensitization centers. Gelatin encapsulation, an alternative to carbon replication, shows severe reduction problems created during the hardening process of the gelatin. Tabular crystals, on the other hand, can be replicated by the latter process without the need for hardening.

Experiments were made on the anisotropic growth mechanism of tabular grains, according to which the predominance of their lateral growth rate over the vertical was ascribed by Jagannathan et al. to rapid growth of the self-generating {100} faces on their side surfaces at low pBr. This mechanism was supported by analyses of the preferential adsorption of a dye to {100} faces on the side surfaces. The lateral and vertical growth rates of tabular silver bromide grains at critical supersaturation were measured in reaction solutions with varied pBr values as functions of their equivalent circular diameter (D_c) and thickness (h). The lateral growth rate at low pBr was larger than the growth rate of cubic grains and increased with increasing D_c and decreasing h, whereas the vertical growth rate at low pBr was smaller than the growth rate of octahedral grains. This result indicates that the diffusion of solute ions through the solution from the vicinity of the main surfaces to that of the side surfaces enhanced the anisotropic growth of the grains at low pBr. At high pBr, the lateral and vertical growth rates were small, nearly equal to each other, and decreased with increasing D_c, obeying the diffusion-controlled scheme. At some intermediate pBr, the lateral growth rate decreased with increasing D_c and was still much larger than the vertical growth rate, providing the opportunity for the precipitation of monodisperse tabular grains.

The reducing agents dimethylamineborane and SnCl₂ were used to produce silver clusters chemically in an AgBr emulsion. These silver clusters were detected with diffuse reflectance spectroscopy at photographically relevant sensitizer concentrations, and their reflectance at 476 nm correlated well with the effects of these reducing agents on photographic sensitivity. Spectroscopy was used to monitor the photochemical reactions of these silver clusters. A portion of the 476-nm peak derived from the Kubelka–Munk transform of the reflectance spectra could be photobleached using band-gap excitation, indicating that some of the silver clusters were destroyed by photogenerated holes. However, some silver clusters did not react with photoholes and these clusters may be electron-trapping. The decrease in peak height upon photobleaching indicated two distinct silver clusters in terms of their ease of bleaching by photoholes. A simple reaction model was found to be consistent with the concentration dependence of the peak height, suggesting that only one size of silver cluster is being produced under most of our reaction conditions.

The correlation of photographic performance of indocarbocyanine dyes having different substituent groups on the benzene ring and the heterocyclic nitrogen atom with their electrochemical properties and aggregation behavior in solution and on emulsion grains was investigated. The experimental results indicate that the physicochemical properties of the dyes are determined by their skeletons and subtle structure features. The photographic performance of the dyed emulsion depends on the dye's photophysical and electrochemical properties and on the energy level positions of the sensitizer.

From the study of the distribution of latent images and the Sabattier effect of emulsions with internally sensitized core–shell grains having uniform iodide distribution, it is found that the surface sensitivity decreases with increase of the internal sensitivity. To show a strong Sabattier effect, an emulsion should contain grains with both surface sensitivity centers and internal sensitivity centers, and they should be well matched. The ratio of the two sensitivities and the second exposure are two important factors that decide the kinds of Sabattier reversal. The results can be explained by the behavior of photoelectrons and photoholes within the silver halide grains during the two exposures and developments. The surface latent image specks formed during the first exposure are bleached by the photoholes during the second exposure, resulting in a reversed image.

The Yule–Nielsen effect, also called optical dot gain, is a nonlinear relationship between the reflectance of a halftone image and the fractional dot area of the halftone dots. Two models of the Yule–Nielsen effect are examined. The first is an empirical model previously described in the literature, and the second is an a priori model derived for an idealized halftone line system in one spatial dimension. Both are shown to model halftone behavior well. By combining the two models we derive a semiempirical function that establishes a simple connection between the magnitude of the Yule–Nielsen effect and independently measurable scattering characteristics of the paper. The potential utility of this semiempirical model for characterizing the impact of other factors, such as the shape of halftone dots and depth of ink penetration, is discussed.

Color printing using halftoning techniques is becoming ubiquitous on the desktop. Accuracy and consistency of the color printed by these devices depends on, among other things, the optical properties of the paper. The general influence of light scattering within the paper has been known for half a century, but calculation of the effect on the color gamut is complex and depends on the details of the paper optical spread function and of the halftone pattern. Two limiting cases are analyzed, no-paper-scattering and complete-paper-scattering (optical paper spread function is much larger than the halftone cell size). Simple models are presented for the limiting cases of halftone printed color images, and the predictions are compared with measurements of single-colorant samples from a wax thermal printer. Results show that the simple models bound the single-colorant colors produced by the wax thermal printer. The simple model predicts that the major effect of the paper scatter on single-colorant images is the shifting of colors along the CIE L*a*b* locus. This can result in color differences for the two scattering extremes of 20 CIE L*a*b* units for the same fractional dot area. Two different CIE L*a*b* loci are computed for the same colorant, under the no-light-scattering versus complete-light-scattering conditions, but this is a much smaller effect.

Hole and electron mobilities have been measured in N-[p-(di-ptolylamino) phenyl]-N'-(1,2-dimethylpropyl)-1,4,5,8-naphthalenetetracarboxylic diimide (TAND)- oped polycarbonate (PC). The TAND molecule contains a naphthalene diimide acceptor functionality and a triarylamine donor functionality. Both electron and hole transport are observed in TAND-doped PC with comparable mobilities. To our knowledge, this is the first literature report of bipolar transport in a doped polymer containing a bifunctional dopant molecule. The results are described by a model based on disorder, due to Bassler and coworkers. The model is premised on the assumption that charge transport occurs by hopping through a manifold of localized states with superimposed energetic and positional disorder. The key parameters of the formalism are σ, the energy width of the hopping site manifold, and Σ, the degree of positional disorder. For TAND-doped PC, the widths are 0.130 and 0.137 eV for hole and electron transport, respectively. The corresponding values of the positional disorder are 3.7 and 3.4. The results suggest that the hole and electron transport manifolds are each independent and not influenced by the transport states of the oppositely charged carriers.