Silver bromide crystal

Silver bromide crystals, formed from stoichiometric amounts of silver nitrate and potassium bromide, are characterized by a cubic stmcture having interionic distances of 0.29 nm. If, however, an excess of either ion is present, octahedral crystals tend to form. The yellow color of silver bromide has been attributed to ionic deformation, an indication of its partially covalent character. Silver bromide melts at 434°C and dissociates when heated above 500°C. 

It has been found that only a few photons, maybe as little as six, are needed to form the latent image. Photographic film is a very sensitive light detector. The final step in the photographic process, fixing, removes the unreacted silver bromide crystals from the emulsion, thus stabilizing the image (Fig. 2.4). 

When light hits a silver bromide crystal, silver cations (Ag+) accept an electron (reduction) from the bromide ions (Br ), which are oxidised. Hence, silver atoms and bromine atoms are produced in the emulsion. 

B. Emulsion, light-sensitive silver bromide crystals suspended in gelatin. The size of the crystals (granules]... 

Cyanine dyes in this series have been described as photographic sensitizers, and are strongly adsorbed on the silver bromide crystals. The sensitization maximum is at about 500-650 m/x.83... 

Figure 43. Optical absorption spectra of silver chloride and silver bromide crystals at room temperature. A is the absorption coefficient, which is defined as the fractional decrease in transmitted light intensity due to absorption, per unit thickness [154], Figure adapted from [154],...

Figure 50. Dependence of Orel on sensitizer reduction potential [187], The solid curve represents the expected dependence based on Marcus theory using a value for I of 0,05 eV. The energy obtained for the CB of the cubic silver bromide crystals used in this experiment, F red, is -1.37 V, vs. SCE. Figure adapted from [187].

Figure 1. Complexity of silver bromide crystal growth without imperfections, with a single twin plane, and with a pair of twin planes.

As an example of the lateral resolution obtainable with a ToF-SIMS instrument. Fig. 7 shows negative secondary-ion images of tabular silver bromide crystals coated with iodine. The field of view is 6 x 6 pm-, and the elemental... 

Spectral Sensitization. The intrinsic absorption, and therefore the intrinsic photographic sensitivity, of silver bromide and silver iodobromide microcrystals falls off rapidly for wavelengths greater than 500 nm (see Fig. 2). In fact, silver chloride crystals have almost no sensitivity in the visible... 

The crystal stmcture of photographic silver bromide is often octahedral. 

Fig. 3.16. High-resolution TOF SIMS images of silver bromide and silver chloride crystals.

In this section we are concerned with the properties of intrinsic Schottky and Frenkel disorder in pure ionic conducting crystals and with the same systems doped with aliovalent cations. As already remarked in Section I, the properties of uni-univalent crystals, e.g. sodium choride and silver bromide which contain Schottky and cationic Frenkel disorder respectively, doped with divalent cation impurities are of particular interest. At low concentrations the impurity is incorporated substitutionally together with an additional cation vacancy to preserve electrical neutrality. At sufficiently low temperatures the concentration of intrinsic defects in a doped crystal is negligible compared with the concentration of added defects. We shall first mention briefly the theoretical methods used for such systems and then review the use of the cluster formalism. 

The light-sensitive layer of the present-day photographic material consists essentially of a large number (e.g., 108 per square centimeter) of tiny crystals of silver halide embedded in a layer of gelatin. The tiny crystals, or grains as they are commonly called, of the most sensitive photographic materials are composed of silver bromide, a small percentage of iodide, and a very small but very important amount of silver sulfide (Sheppard, 1) or possibly silver (Carroll and Hubbard, la) or both. The halide in the less sensitive materials may be simply bromide, chloride, or mixtures of the two. 

When Berthier treated a specimen of this ore from the San Onofe Mine with an excess of hot ammonium hydroxide, he observed, mixed with the metallic silver, a green powder which had been only incompletely attacked. This was the circumstance, said he, which drew my attention to the ore from Plateros and which led me to realize that the substance which had been taken for silver chloride is pure bromide, without admixture of chloride or iodide, a substance which had not yet been met within the mineral realm and which therefore constitutes a new species (151). Berthier learned that this mineral is not rare in Mexico but is often found in beautiful cubic and octahedral crystals. He also found the same mineral at Huelgoeth, Department of Finistere, France, and discovered some of it among the Chilean silver minerals which Ignaz Domeyko, professor of chemistry at the College of Coquimbo, had sent to the School of Mines at Paris (151, 152). The mineral which Berthier analyzed was evidently bromyrite (silver bromide). 

A mixture of Re(CO)5Br dissolved in 8 mL of fluorobenzene and finely divided and freshly prepared silver fluoride (30 mg, 0.24 mmol, two-fold excess) is stirred in a glass vessel at room temperature for 2 h. The solution is filtered to remove the precipitated silver bromide and excess silver fluoride. The filtrate is heated to reflux at 90 to 100°C for 5 h, cooled to room temperature, and the solvent is removed under vacuum to give the yellow product. Yield 44 mg, 0.036 mmol (75% yield). This can be recrystallized from a diethyl ether solution into which fluorobenzene is allowed to diffuse and dried in vacuo to give needle or prismatic crystals. 

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