Silver halide emulsions for use in silver halide photographic light-sensitive materials are, in general, chemically sensitized by using various chemical substances to obtain, for example, desired sensitivity and gradation. As typical methods for the chemical sensitization, various sensitizing methods, such as sulfur sensitization, selenium sensitization, tellurium sensitization; noble metal sensitization using, for example, gold, and combinations of these sensitizing methods, are known. Various improvements in the aforementioned sensitizing methods have been recently made to cope with a strong need, for example, for excellent granularity, high sharpness, and high sensitivity of silver halide photographic light-sensitive materials, and further rapid processing promoted by accelerating development.
It is known that a serenocarboxylate; namely, a sereno ester, may be used as a selenium sensitizer in a selenium sensitization among the aforementioned sensitizing methods. Examples of disclosures showing specific compounds include U.S. Pat. No. 3,297,446, U.S. Pat. No. 3,297,447, and JP-B-57-22090 (“JP-B” means examined Japanese patent publication).
Although there is the case in which the selenium sensitizer has a greater sensitizing effect than a sulfur sensitizer used in the fields of the art, such a sensitizer largely tends to cause much fogging, to result softened gradation, and to cause increased variation of sensitivity during storage. Many patent publications have been disclosed aiming to improve these drawbacks. However, satisfactory results have not yet been brought by these improvements, and there has been a strong need for basic improvement; in particular, for greater suppression of the occurrence of fogging. Also, if sulfur sensitization, selenium sensitization, or tellurium sensitization is used in combination with gold sensitization, respectively, sensitivity is significantly increased in each case. However, fogging is increased at the same time. Although, particularly, gold-selenium sensitization and gold-tellurium sensitization result in greater sensitivity than gold-sulfur sensitization, they also result in much fogging, and they are apt to result increased gradation softness. There remains, therefore, a strong need for development of a selenium sensitizer and a tellurium sensitizer that give increased sensitivity, less fogging, and increased gradation hardness.
In this situation, the following compounds are described as examples of useful selenium sensitizers: diacyl serenide compounds, as described in JP-A-4-271341 (“JP-A” means unexamined published Japanese patent application); compounds in which two carbonyl groups are bonded with a selenium atom, as described in JP-A-5-11385; and selenocarboxylic acid (Se-ester) compounds, as described in JP-A-7-140579. Although these compounds are disclosed to enable suppressing fogging to a low level and achieving high sensitivity, they nonetheless remain unsatisfactory, and compounds that can better suppress fogging and attain higher sensitivity have been desired.
A known chemical sensitizer used is a compound in which gold (I) ion is coordinated with a selenourea, as a known selenium sensitizer. Example references disclosing specific examples of the compound include JP-A-2001-75215, JP-A-2001-75216, and JP-A-2001-75217. Although the aforementioned drawbacks can be improved using such a compound, its effect remains insufficient. It is also disclosed, in JP-A-9-269554, that compounds in which gold (III) ion is coordinated with phosphine selenides as known selenium sensitizers, are used as a chemical sensitizer. However, the effect remains insufficient. Moreover, a gold (I) halide compound coordinated with a chalcogeno ether compound is also disclosed, in JP-A-2002-268170. However, the level reached by this gold halide compound is likewise insufficient.
Further, a gold (I) compound (hereinafter referred to as a meso-ion gold (I) compound) containing a meso-ion ligand is known as a gold compound for use in gold sensitization. It is disclosed, in JP-A-4-267249, that the meso-ion gold (I) compound is useful to produce a highly sensitive and hard gradation (contrast) emulsion. It is, however, known that the meso-ion gold (I) compound has a problem concerning stability in a solution, as disclosed in JP-A-11-218870. It has been desired to improve the stability of the meso-ion gold (I) compound, because stability in solution is an essential condition to produce a light-sensitive emulsion having constant qualities, stably.
As a measure to solve this problem, a method of utilizing a gold (I) complex of a mercapto compound is proposed in JP-A-11-218870. Although this gold sensitizer has improved stability in a solution, it is still a compound that will be decomposed, and it remains only an insufficient solving measure.
It is also known that many selenium compounds and tellurium compounds generally have lower stability than corresponding sulfur compounds. Not a few selenium compounds and tellurium compounds to be used as chemical sensitizers have less comparative stability. When these compounds are stored in a solution state, they resultantly gradually decompose. There is, therefore, a tendency for there to be a large difference in sensitivity, fogging, gradation, and the like, between the case of producing a light-sensitive emulsion just after a solution of a selenium compound or a tellurium compound is prepared, and the case of producing a light-sensitive emulsion a while after the solution is prepared. Therefore, chemical sensitizers that suppress fogging to attain high sensitivity are desired to have higher stability.
In this background, there is strong need for development of a gold-chalcogen sensitizer that can largely increase the sensitivity and causes less occurrence of fogging.