The silver halide photographic process

The light-sensitive elements of conventional photographic materials are crystallites principally of the bromide or chloride salts of silver. Certain chemical modifications employing sulphur and gold compounds are used to maximize the response, and organic dyes are adsorbed to provide sensitivity throughout the visible spectrum. Absorption of a few photons results in the reductive formation of one or more clusters of silver or gold atoms on the surface. These clusters act as catalysts to promote further reduction of the host crystallites during photographic development. The success of the system depends upon the particular physical properties of the silver halides, such as their bonding and electron structure, the dielectric properties, the point defect structure, and the electronic transport characteristics. These are all reviewed, and the ways in which they interact to lead to the favourable photodecomposition are followed in some detail. A nucleation-and-growth mechanism operates to provide several of the favourable features of the process, and the chemical treatments used optimize the competition between these desirable steps and the unwanted recombination of electronic carriers.     

Investigation of photoelectron temporal characteristics in silver halide microcrystals using the microwave absorption technique

The free photoelectron lifetime reflects to a large extent the latent image formation efficiency and sensitivity of silver halide material. The microwave absorption dielectric-spectrum technique enables measurement of the photoelectron decay process of silver halide emulsion exposed to 35ps laser pulse. For T-grain AgBr emulsion, the relationship between exciting energy and photoelectron action has been obtained, and the influence of iodide dopants on photoelectron lifetime was measured and analysed. The photoelectron lifetime of dye-sensitized AgBr emulsion with tabular grains is shorter than that with cubic grains, and the latent image formation efficiency of the former is higher than the latter.     

Self-diffusion in polycrystalline silver

An experimental study of self-diffusion in polycrystalline silver has been carried out using the radioisotope Ag-110. The electrolytic sectioning technique was used for measuring. This method made it possible to determine the temperature range in which the self-diffusion of silver is not influenced by grain-boundary diffusion. The temperature was found where the grain-diffusion predominates over the volume diffusion so that the grain-boundary diffusion coefficient can be estimated by Fischer's treatment. Finally, it was found that the temperature range of 619°C< <718°C is the transition region where the electrolytic sectioning technique does not permit the volume or grain-boundary diffusion coefficients to be determined.     

On the formation of silver specks in silver halide crystals

This theoretical study summarizes ionic and electronic processes in AgBr crystals and the influence of its results on photographic process. It deals with the importance of surface generated interstitials which Gurney and Mott left untouched because of the non-availability of sufficient data at that time. The magnitude of various parameters,e.g., mean intra-electron-ion distance in a latent image site, the rate of neutralization of Ag⁺ ion with trapped electron and capture cross-section for combination of Ag⁺ ion with the trapped electron, etc. (as desired for understanding the theory of photographic process) are calculated at different temperatures. The results when used in our earlier papers (Singh and Sharma, 1974 and 1975, and Singh 1975) for calculating charged particle track characteristics theoretically were found to give good agreement with the published experimental data (Della Corteet al 1953 and Dyer and Hechman 1967). A model for the mechanism of latent image formation (silver speck) is discussed.     

The fractional ionic character of alkali and silver halide crystals

The fractional ionic character of alkali and silver halide crystals is defined in terms of the deviations from the additivity rule for polarizabilities of ions. The electronic polarizabilities of ions are calculated using an empirical relationship according to which the electronic polarizability of an ion can be assumed to be directly proportional to the cube of its radius. The calculated ionicities indicate that the alkali halides are nearly or more than 90% ionic and silver halides are much less ionic which is also evident from the Phillips ionicity scale.     

Ionic conductivity of mixed silver halide crystals

To evaluate the effects of mixed halides on the lattice defect parameters of the silver halides, we have measured the ionic conductivity both of the entire range of mixed AgBr-AgCl single crystals, aftd also of several iodide-doped crystals. For the AgBr-AgCl system, the intrinsic conductivity at a given temperature decreases monotonically from pure AgBr to pure AgCl. The deduced Frenkel defect formation energy varies only a little from 0 to 50 mole % AgCl, and then increases rapidly with further increase in AgCl content, closely paralleling the ratio of bulk modulus to dielectric constant. The defect formation energy in these crystals hence reflects the average macroscopic properties of the solid solution. For the iodide-doped crystals, however, the results are quite different. Small amounts-of iodide cause large increases in the conductivity of AgBr andiAgCl, especially in the latter. These results suggest that the elastic strain introduced by the oversized iodide ion exerts an appreciable local effect on the Frenkel defect formation, in contrast to the crystal-averaged response found for the AgBr-AgCl solid solutions. Furthermore, the Arrhenius plots for the conductivitiei of the AgBr: I specimens show curvature which suggests a temperature-dependent pairing of the solute.     

The far-infrared absorption spectra of some alkali halide alloys

A study has been made of the far-infrared transmission spectra of some K_xRb_1−x⁻ Cl_yBr1−y alloys with (x,y) ≈ 1 mole%. and the results are reported in this paper. An absorption band at 94.5cm⁻¹ in KBr:Cl has been observed, in agreement with the results of other workers. New bands at 99 cm⁻¹ in KBr:Rb. 99 cm⁻¹ in RbCl:K and 103 cm⁻¹ in RbCl:Br have also been found. These bands are attributed to impurity-induced modes in the gaps in the frequency distributions of KBr and RbCl. Comparison of these results with the theoretical results of Mitani and Takeno indicates that the ‘force constants’ associated with Rb and Br impurities are enhanced relative to those associated with K and Cl impurities. The relationship between the results presented here and some features in the infrared reflection spectra of non-dilute alloys is discussed.     

The absorption spectrum of beryllium

Energy terms, dipole oscillator strengths and photoionization cross-sections from the ground state are calculated. Autoionizing state transition energies and line widths for the ¹P⁰ resonances in the continuum are also obtained. The configuration interaction method for initial and final states is used, and atomic orbitals are generated through angular-momentum-dependent, scaled Thomas-Fermi-Dirac potentials.     

Defects in the silver halide photographic process

The imaging efficiency of today's photographic film and paper is influenced in a variety of ways. Among them, the incorporation of dopants is widely used to increase efficiency, control contrast or improve imaging deficiencies such as reciprocity law failure. Transition metal-organic ligand dopants are attractive because the organic ligand influences the photographic properties. Experimental studies have shown that many of these dopants incorporate well into the silver halide microcrystal even with large organic ligands. In this paper, experimental and computational results are presented on a variety of Ir-OL dopants in AgCl where OL is a small nitrogen and/or sulfur-containing heterocycle. Electron paramagnetic resonance methods provide information about the electronic structure, electron trapping properties and the stability of the electron trap state. These results are complemented by ab initio studies that give information about the optimum structure, charge compensation and the possibility of electron and hole trapping.     

Noise gratings in silver halide volume holograms

Diffraction efficiencies of 70% have been reported for planar gratings in silver halide emulsion. The main obstacle in increasing the efficiency is the granular structure of the recording material which causes scattering of the input light both at recording and at reconstruction. This study concentrates on the effect of noise gratings recorded when the incident beam interferes with its own scattered radiation. The experimental evaluation is divided into two parts. Firstly, one single beam is used for recording a holographic plate, and the transmitted intensity of the reconstructing beam illuminating the developed hologram is measured as a function of incident angle and wavelength. Dips in the measured intensity are associated with the reconstruction of a strong scattered beam. Secondly, a main grating is recorded by two incident beams, which also interfere with the field scattered by the grains and give rise to noise gratings. When a beam is incident upon the developed hologram at the same angle and wavelength as one of the recording beams then besides the desired beam the scattered radiation is also reconstructed. This may reduce the otherwise available efficiency by several percent.     

Higher-order harmonics in bleached silver halide holograms

A large number of plane wave holograms were recorded in Agfa-Gevaert 8E75HD holographic plates, at a wide range of bias exposures and fringe visibilities. The plates were processed by various combinations of developers (AAC, Pyrogallol and Catechol) and bleaching agents (R-9 and EDTA). The phase gratings were studied by phase-contrast microscopy, using a high-power immersion (100×) objective. The phase-contrast photomicrographs were Fourier analysed. Thus, first-, second-, and third-order modulations of the refractive index as a function of bias exposure and visibility of the recording interference pattern could be determined. The ratio of the amplitudes of higher-order modulations to that of the first-order can serve as a measure of the nonlinearity of the holographic recording.     

Analytical electron microscopy of silver halide photographic systems

Studies of silver halide (AgX) photographic materials and individual microcomponents by TEM/STEM/SEM/EDX, CL, EFTEM/EELS and digital image analysis techniques are reviewed. Electron-beam-AgX interactions are discussed to clarify relationships between the signals analysed in various operating AEM modes. An optimum strategy of structural and analytical diagnosis of complex silver halide photographic systems by a number of AEM methods is considered, using a number of examples (colour and black-and-white films, AgX microcrystals, and colour coupler dispersions). AEM applications to study of the main stages of the photographic process, i.e., chemical ripening, spectral sensitisation, latent image formation and development are also presented. Current trends and future directions in research of AgX-based photographic systems by AEM techniques are outlined.