Silver halide crystals

Other detection modes in bright CL or BL reactions are multichannel detectors, which provide simultaneous detection of the dispersed radiation and produce a permanent image of a wide area. Photographic films or plates are emulsions that contain silver halide crystals in which incident photons produce stable clusters of silver atoms within the crystals. Internal amplification is provided in the development process by an electron donor that reduces the remaining silver ions to silver atoms within the exposed crystals. A complexing agent is used to remove the... 

Ion exclusion chromatography, of ascorbic acid, 25 760 Ion hopping, 14 469 Ionic aggregates, 14 463—466 Ionically conducting polymers, 13 540 Ionic carbides, 4 647 Ionic compounds, rubidium, 21 822 Ionic conduction, ceramics, 5 587-589 Ionic crystals, 19 185. See also Silver halide crystals... 

Lattice defects in silver halide crystals. Philos. Mag. 40, 667 (1949). 

The suggested mechanisms differ in detail (Mott, 66, 67 Berg, 68 Anastasevich, 69 Frank-Kamenetskii, 70 Bagdasar yan, 17, 71) but all involve the idea that electrons can be transferred to silver much more readily than to a silver halide crystal. Each mechanism can be criticized on some detail (cf. Sheppard, 15 James, 72). As a general criticism, however, none of the mechanisms has explained the fact that the rate of development under simplified conditions varies with the square root of the hydroquinone and catechol concentrations, whereas the rate of reduction of silver ions from solution by the same agents varies as the first or somewhat higher power of the concentration. 

Hasse et al. [366] have used in situ AFM for the detection of silver nucleation at the three-phase junction of the type metal-silver halide-electrolyte solution. At this phase boundary, electrochemical reduction of submicrometer size silver halide crystals immobilized on the surface of gold and platinum electrodes took place. Following nucleation, the reaction advanced until the entire surface of the silver hahde crystals was covered with 20 atomic layers of silver. Then, reduction was terminated. The obtained silver layer could be oxidized and the next layer of silver halide crystals became accessible for further reduction. 

Let us finally estimate the relaxation times of homogeneous defect reactions. To this end, we analyze the equilibration course of a silver halide crystal, AX, with predominantly intrinsic cation Frenkel disorder. The Frenkel reaction is... 

The colloidal metallic silver formed in this way is opaque (it would appear black in reflected or transmitted light). The halogen atoms combine with an organic substrate mixed with the silver halide crystals to produce bromides. 

The silver halide crystals can be formed as microscopic grains suspended in a protective colloid, usually gelatin. This dispersion, the photographic emulsion, can be coated on a suitable support to obtain photographic films, plates, and papers. 

The silver halide crystals show ionic conductivity by Frenkel defects (interstitial silver ions, Ag"t). 

The silver nuclei constitute an invisible latent image, which can be converted to a visible image by chemical action. The silver halide crystals that contain latent image nuclei can be reduced completely to silver by this chemical action (development) or silver ions from solution can be reduced at these nuclei. The amplification factor... 

These forces are the result of elastic stress fields that. exist near every impurity ion or aggregate and crystal imperfection like a dislocation line or grain boundary. These forces are very strong and are mainly responsible for the creation of second phase impurity aggregates in a host of ionic crystals. If the latent image is considered as a second phase formation of Ag° atoms in the silver halide crystal, then it seems that the elastic forces are those that cause the formation of this Ag aggregate. 

In spectral sensitization, conduction electrons appear in the silver halide crystal when the dye absorbs radiation, just as when the silver halide absorbs radiation. According to the mechanism that has received the strongest support in recent years, an electron is transferred to the silver halide from the excited dye molecule, leaving behind an electron-deficient dye molecule (hole). This is analogous to the result of direct absorption of a photon by the silver halide, except that the hole remains in the dye, at least temporarily, instead of in the silver halide. 

---