Photographic emulsions, sensitization

The discussion in Section II-B indicates that optical emission from 02(1E 7+) or 02(1A9) to the ground state may provide a useful method for the identification and estimation of the excited species. In laboratory studies, the (0, 0) bands, lying at about 7620 A and 1.27 [x, respectively, are likely to be the strongest. The emission at 7620 A is relatively easily detected by suitable photomultipliers, and spectra may even be recorded with photographic emulsions sensitive to the near infrared (such as the Kodak N coating). Trialkali (S20) photocathodes combine a high sensitivity with low dark current, and photomultipliers with an S20 cathode... 

The ultraviolet offers numerous opportunities for use but apparently, satellites planned up to 1980 will not carry instruments operating in these bands, with the exception of photographic emulsions sensitive to the very near ultraviolet which could be used by astronauts or personnel in the Skylab and Spacelab manned orbiting platforms, with recoverable shuttles plying to and from earth. 

Sensitizers as well as desensitizers form a reversal oxidoreduction system with silver halides, according to both pH and pAg of the photographic emulsion. But besides the specific influence of the emulsion, the efficiency of a sensitizing dye depends on many other factors such as its adsorption, its spectral absorption, the energetic transfer yield, the dye aggregate to the silver halide, and finally on its desensitizing property in... 

A solid emulsion is a suspension of a liquid or solid phase in a solid. For example, opals are solid emulsions formed when partly hydrated silica fills the interstices between close-packed microspheres of silica aggregates. Gelatin desserts are a type of solid emulsion called a gel, which is soft but holds its shape. Photographic emulsions are gels that also contain solid colloidal particles of light-sensitive materials such as silver bromide. Many liquid crystalline arrays can be considered colloids. Cell membranes form a two-dimensional colloidal structure (Fig. 8.44). 

The nonreactive base structures of cyanine dyes (or carbocyanines) have been used for many years as components in photographic emulsions to increase the range and sensitivity of film and also in CD-R and DVD-R optical disks to record digital information. A major innovation came when Ernst et al. (1989) and Waggoner et al. (1993) recognized that cyanine dyes would make excellent labels for fluorescence detection, and for this reason, they synthesized reactive dye derivatives, which then could be covalently attached to proteins and other molecules. 

The sodium salt of the phenylglycine derivative (33) was investigated as an absorption promoter for the rectal absorption of beta-lactam antibiotics and insulin [80JAP(K)31040 81CPB1998, 81CPB2012], (Naphthothiazol-2-ylidene)malonates (1661 and 1662) were applied in silver halide photographic emulsions as sensitizer dyes [82JAP(K)54936]. 

Photographic emulsions have a very high degree of sensitivity throughout the visible and UV-regions. It is not so sensitive. 

Carroll, B. H., and W. West Optical sensitization of photographic emulsions. Fundamental mechanisms of photographic sensitivity, p. 162. London Butter-worth s Sci. Publ. 1951-... 

B. H. Carroll and C. J. Staud Spectral sensitivity and light absorption of dye-sensitized photographic emulsions. J. chem. Physics S, 878 (1937)-... 

Energy transfer in the photosensitization of silver halide photographic emulsions Optical sensitization, supersensitization and antisensitization. J. chem. Physics 19, 417 (1950-... 

In order to circumvent this sensitivity limitation, the San Jose researchers sought to design resist materials that incorporate chemical amplification of the sort that characterizes the silver halide photographic emulsion system. In these systems a single photo event initiates a cascade of subsequent chemical reactions that ultimately result in the intended function. 

The dyes that perform this function are called spectral sensitisers because they are used to sensitise the photographic emulsion to light across the whole visible spectrum and beyond. Since silver halides are naturally blue sensitive, the green and red spectral sensitiser dyes must also be able to reduce the natural sensitivity of the silver halide emulsion to blue light. The most important class of compounds used in this... 

Beersmans, j. (Gevaert) Methine dyes for sensitizing photographic emulsions. British patent 626470 (July 15, 1949). 

Such dyes found early application as sensitizers in photography and many thousands of related structures have been made. Suitable dyes when added to the photographic emulsion extend the sensitivity of the silver halide from the blue and UV region towards the green, red and near IR. The sensitivity of the dyes can be balanced throughout the visible spectrum to give panchromatic emulsions. 

The photographic emulsion is essentially a dispersion of microcrystals of AgBr in an organic substrate called gelatin . The emulsion therefore consists of microscopic grains which have a specific size distribution. This distribution is important in determining the sensitivity and the resolution of the emulsion. 

A set of color-separation negatives may be prepared by photographing the subject three times on separate color-sensitive emulsions so that each is a record of one of the primary colors. A panchromatic emulsion is generally employed with a set of tricolor filters, the colors of the primaries. It is only necessary, however, to obtain the color records on separate negatives so it is also possible to use for each record any combination of color filter and emulsion sensitivity that will record one of the primary colors. A set of color-separation negatives may be made by exposing (1) each one in tmn in a camera, (2) by ihe use of a colcu camera that will expose them simultaneously, or (3) in a tripack. 

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