The challenges that non-impact printing technologies pose to the use of color paper today are accompanied by two major trends: the proliferation of digital imaging and the need to protect our ecology. The color paper technology industry can respond by increasing the productivity of color processing systems, continuing to minimize those systems' demands on waste disposal, as well as by dealing with the interrelationships of these two trends.

Silver bromide crystals have been precipitated by the double-jet method. The presence of polar aprotic solvents or protic solvents with a dissociation constant smaller than water increased the ratio and size of tabular crystals in the precipitate. This is explained considering that {111} surfaces are mainly composed of halide ions and therefore charged. Organic solvents reduce the solvation of the halide ions in the solution and stabilize the surface charge. A high ionic strength greatly favored the ratio of tabular crystals and enhanced tabular growth probably by helping the formation of the double electrical layer on the charged {111} faces.

Despite the continuous development of new synthetic polymers, gelatin remains as the principal component of the binder used in most silver halide photographic films and papers. The main reason for the longevity of gelatin in silver halide photographic systems is its remarkable property to play a unique role in almost every step of the manufacture as well as in the photographic processing of these products. The most important function of gelatin in the preparation of photographic emulsions is to provide colloid protection and stabilization for the AgX crystals. Colloid stability of fine AgX particles is provided through steric stabilization, facilitated by the adsorption of gelatin on the AgX surface. A critical level of gelatin is required for such stabilization. The experimentally estimated critical gelatin surface coverage required to prevent coalescence during precipitation is in good agreement with previous theoretical calculations and with equilibrium adsorption measurements. Inadequate peptization of AgX colloid particles during precipitation can cause aggregation that can lead to undesirable agglomeration and coalescence. But in some cases gelatin can attenuate flocculation and control coalescence resulting in desirable dislocations such as the formation of twinning dislocations, which is the key step in the nucleation and growth of tabular AgX crystals. This is demonstrated by a strong correlation between the degree of flocculation during nucleation and the resulting tabular grain population fraction.

Cross sections of (111) AgBrI platelets have been examined by low- and high-resolution transmission electron microscopy. They provide direct microstructural evidence for stacking fault arrangement between the internal twin boundary and the external grain surface. Their orientation relationship also provides insight into how (111) and (100) surfaces can coexist at the tabular-grain surface.

Digestion of AgBr emulsions with increasing amounts of reduction sensitizers achieved stepwise increase in sensitivity corresponding to the formation of two kinds of sensitization centers, designated R centers, acting as positive-hole traps, and P centers, acting as electron traps. It has been proposed that R and P centers are silver dimers formed at electrically neutral and positively charged surface sites on AgBr grains, respectively. The formation of P centers was depressed by addition of TAI and PMT, which are preferably adsorbed to positively charged surface sites on the grains, and enhanced by cyanine dyes, which are preferably adsorbed to negatively charged surface sites. Reduction sensitization of AgCl emulsions was less effective than that of AgBr emulsions in that the former brought about less increase in sensitivity and more increase in fog density than the latter with increasing amounts of sensitizers. Reduction sensitization of AgCl emulsions was significantly improved by digesting the emulsions for reduction sensitization in the presence of PMT and TAI. From the fact that the sensitivity increase of AgCl emulsions was not associated with a decrease in photoconductivity with photoelectrons as carriers and was not observed in the presence of hydrogen hypersensitization centers acting as positive-hole traps, it is considered that, in AgCl emulsions, reduction sensitization centers were solely R centers, while P centers acted as fog centers. The developability of P centers in AgCl emulsions was however very weak. It was found that R centers exhibited their absorption band, whose peak wavelength (420 nm) was close to that of the absorption band of Ag2 in rare gas (412 nm). This result supports the proposed model where an R center is a silver dimer at a neutral site that physically interacts with the surface of silver halide.

The combination of spectroscopic information concerning the light absorption, spectral sensitivity, and photobleaching involving the reduction sensitization centers allowed reasonable positioning of their electronic energy levels relative to the band edges of silver halides. A well-defined absorption band centered at 455 nm was observed both for the reduction sensitization centers produced by dimethylamine borane (DMAB) and for the hydrogen hypersensitization centers by using a diffuse transmittance spectroscopy method. We conclude that the common type of reduction sensitization centers, which must be predominantly hole trapping, have their HOMO (highest occupied molecular orbital) levels ∼1.9 eV below the conduction band edge. Additional centers produced at the high level of DMAB sensitization have a higher HOMO level ∼1.6 eV below the conduction band edge, which is identical with that previously ascribed to the subimage center. The dielectric polarization of the surrounding medium critically affects these energy levels. Possible limitations of the spectroscopic information as well as its advantages are also discussed.

Electron spin resonance experiments on AgCl emulsions doped with [Ru(CN)₆]⁴⁻ are performed. This transition metal complex acts as a shallow trap for electrons. The effective mass model is used to explain the electron spin resonance spectral changes, i.e., intensity and line width, after UV-illumination. Changes in line width are explained in terms of exchange and motional narrowing. These effects are studied as a function of concentration, temperature, and UV-irradiation. Finally, the concentration dependence of the stability of shallowly trapped electrons is studied using thermal anneal experiments.

Melts and coatings of a 0.3-μm octahedral AgBr emulsion were prepared with four concentrations of each of three different 4-hydroxy-1,3,3a,7-tetraazaindenes (TAIs). pAg measurements were made on the melt samples and ionic thermocurrent and radiofrequency photoconductivity measurements were made on the coated samples. The melt pAg (i.e., a measure of the Br⁻ desorbed from the grain surface) increased as the pK_sp and the concentration of the TAI added to the sample increased. The concentration of desorbed Br⁻ measured as a function of TAI concentration was consistent with the proposal that TAI anions compete with Br⁻ for adsorption to the surface of the grain. The ionic activation energy for formation of interstitial silver ions and the photoelectron lifetime increased as the pK_sp and the concentration of TAI⁻ increased. A linear correlation between desorbed Br⁻ and ionic activation energy was observed. The log of the rate constant for electron trapping decreased linearly as the ionic activation energy increased. The presence of TAI did not affect the photohole response. For TAIs with pK_a<5.0, these effects were independent of pH for pH values between 4.5 and 7.0, whereas when pK_a > 6, these effects decreased with decreasing pH.