Electron Trap Depth Distribution in Silver-Halide Emulsions and the Low-Temperature Herschel Effect^*

* Y. Nakajima is a member of the Research Laboratory of the Fuji Photo Film Co., Ltd. of Japan

Abstract

The trap depth distribution in the silver-halide grains of controlled double-jet, boiling and fully ammoniacal type emulsions has been investigated by the temperature dependence of the low temperature Herschel effect (LTH). More superficial shallow recombination traps appear to exist in cubic than in octahedral: in fine than in coarse; in iodobromide than in bromide (octahedral); in primitive than in gold sensitized grains. Chemical sensitization generally modifies shallow traps to deeper ones, suppressing the surface LTH and enhancing the internal LTH. Traces of copper ions markedly strengthen the surface LTH. These results are discussed in terms of a new model of LTH; defect-electrons rather firmly fixed in point defects are released by infra-red exposure and recombine with trapped electrons in shallow traps. Warming to intermediate temperatures, at which ionic motion is still insignificant, releases electrons from shallow traps and transfers them to deeper traps, which are supposed to be less effective recombination centres. Some very deep traps exist which will hold electrons even at room temperature for times long enough to cause latent-image centres to be formed preferentially at these sites. The correlation between trap depth and recombination cross-section is not unique and appears to depend upon the method of emulsion preparation.

Notes

* Y. Nakajima is a member of the Research Laboratory of the Fuji Photo Film Co., Ltd. of Japan