Effects of Crystal Habit of Silver Bromide upon Desensitization by Dyes

Abstract

The desensitizing phenomena of phenosafranine (1), 9-methylthiacarbocyanine (2), and 5, 5 -diphenyl-9-ethyl-oxacarbocyanine (3) have been examined in the emulsions composed of cubic and octahedral AgBr grains (-O.7 ). The desensitization by (1) was stronger in the cubic AgBr emulsion than in the octahedral one. On the other hand, the desensitizations by (2) and (3) were stronger in the octahedral AgBr emulsion than in the cubic one. From the measurement of the visible-range refiction spectra of the dyed emulsions, it was found that (1) did not form its aggregate in these emulsions. Therefore, aggregate mechanism for desensitization by dyes is not adequate for dye (1). The aggregate of dye (2) (H-aggregate)was more easily formed in the octahedral AgBr emulsion than in the cubic one, whereas the aggregate of dye (3) (J-aggregate) was easily formed both in the cubic and octahedral AgBr emulsion. Therefore, the dependence of the desensitization by these dyes upon the crystal habit did not correspond to the depe, ndence of their aggregate formation upon the crystal habit. These phenomena were interpreted from the viewpoints of the dependence of the photQgraphic effects of an electron trap ((1)) and positive hole traps ((2) and (3)) upon the nature of AgBr grains.