Silver halide emulsion, method of preparing the same, and silver halide color photographic photosensitive material and image-forming method using the emulsion

1. A silver halide emulsion comprising an oxidatively dimerized form of a mesoionic compound having a thiolate structure, and silver chloride of at least 90 mol % by content, the oxidatively dimerized form of a mesoionic compound having a thiolate structure represented by the following formula:

wherein in the formula, f represents a sulfur atom, e represents a carbon atom, and a, b, c, and d are each an unsubstituted or substituted atom constituting an aromatic 5-membered heterocycle having a positive charge and each independently represents a C—R group, an N—R′ group, an oxygen atom, or a sulfur atom, where R and R′ each independently represents a hydrogen atom or a substituent.

2. The silver halide emulsion according to claim 1 , further comprising a gold sensitizer.

3. The silver halide emulsion comprising an oxidatively dimerized form of a mesoionic compound having a thiolate structure according to claim 1 , wherein the oxidatively dimerized form of a mesoionic compound having a thiolate structure is obtained by mixing a mesoionic compound and an Au (III) compound in water, the mesoionic compound being represented by the following formula:

wherein, in the formula, f represents a sulfur atom, e represents a carbon atom, and a, b, c, and d are each an unsubstituted or substituted atom constituting a 5-membered ring of the mesoionic compound and each independently represents a C—R group, an N—R′ group, an oxygen atom, or a sulfur atom, where R and R′ each independently represents a hydrogen atom or a substituent.

4. A silver halide color photographic photosensitive material comprising a support, and, disposed on the support, at least one blue-sensitive silver halide emulsion layer, at least one green-sensitive silver halide emulsion layer, and at least one red-sensitive silver halide emulsion layer, wherein at least one of the blue-sensitive silver halide emulsion layer, the green-sensitive silver halide emulsion layer, and the red-sensitive silver halide emulsion layer comprises the silver halide emulsion according to claim 1 .

5. An image-forming method comprising the steps of:

exposing the silver halide color photographic photosensitive material according to claim 4 on the basis of image information; and

thereafter, developing the silver halide color photographic photosensitive material,

wherein the exposing step comprises the step of scanning the silver halide color photographic photosensitive material with a laser beam modulated on the basis of the image information, with an exposure time per pixel of at most 10 −4 seconds.

6. A method of preparing a composition for use in image formation, the method comprising the steps of:

(a) preparing a silver halide emulsion including silver chloride of at least 90 mol % by content;

(b) adding an oxidatively dimerized form of a mesoionic compound comprising a thiolate structure to the emulsion, the oxidatively dimerized form of a mesoionic compound having a thiolate structure represented by the following formula:

wherein in the formula, f represents a sulfur atom, e represents a carbon atom, and a, b, c, and d are each an unsubstituted or substituted atom constituting an aromatic 5-membered heterocycle having a positive charge and each independently represents a C—R group, an N—R′ group, an oxygen atom, or a sulfur atom, where R and R′ each independently represents a hydrogen atom or a substituent; and

(c) carrying out gold sensitization,

wherein step (b) and step (c) may be carried out simultaneously or in inverse order.

7. The method of preparing a composition for use in image formation according to claim 6 , wherein the step of adding an oxidatively dimerized form is performed by mixing an Au (III) compound with the mesoionic compound comprising a thiolate structure to thereby produce the oxidatively dimerized form.