With the recent trends to reduction in size of color negative films and to diversity of photographing conditions, it has been strongly desired to develop films having higher sensitivity and broader latitude of exposure. Under these circumstances, silver halide emulsions to be used have been required to satisfy certain basic performance requirements, i.e., high sensitivity, low fog, and fine graininess. Assurance of these performances makes an important contribution to development of not only color negative films, but also all kinds of silver halide light-sensitive materials. In an attempt to prepare a silver halide emulsion exhibiting high sensitivity and fine graininess, it is desirable to reduce inefficiency involved in the photo-sensitization step and to heighten quantum sensitivity. Possible factors of inefficiency relating to quantum sensitivity include rebinding, latent image dispersion and competitive electron traps due to structural defects. Attempts to use a polyvalent metal compound in silver halide emulsions have hitherto been made. For example, Research Disclosure, Vol. 176, RD No. 17643 (December, 1978) describes use of gold, platinum, palladium, iridium, osmium, rhenium, etc., as a chemical sensitizer. Research Disclosure, Vol. 184, RD No. 18431 (August, 1979) teaches that use of copper, thallium, cadmium, rhodium, tungsten, thorium or iridium during precipitation of silver halide grains brings about sensitization for X-ray photography. Emulsions to be used for light development type light-sensitive materials preferably have high internal sensitivity and low surface sensitivity, and they sometimes contain Cd.sup.2+, Pb.sup.2+, Cu.sup.2+ or a trivalent metal in order to increase internal defects to make electron traps as described in Nippon Shashin Gakkai (ed.), Shashin Kogaku no Kiso, p. 545, Corona (1978). Research Disclosure, Vol. 176, RD No. 17643 (December, 1978) discloses that direct print-out-emulsions are prepared in the presence of lead, copper, cadmium, bismuth, magnesium, rhodium, or iridium. U.S. Pat. No. 3,923,513 suggests that internal latent image type emulsions are prepared by doping with a polyvalent metal ion and that divalent ions, e.g., lead, trivalent ions, e.g., antimony, bismuth, arsenic, gold, iridium, rhodium, etc., and tetravalent ions, e.g., platinum, osmium, iridium, etc., are useful to that effect. As can be seen from these reports, polyvalent metal ion-doped emulsions are generally employed for the purpose of increasing internal sensitivity, and the polyvalent metal ions are considered to increase internal defects or to form electron traps. Therefore, in ordinary high sensitivity emulsions whose photosensitive nuclei are intentionally formed by the use of sulfur sensitizers or gold sensitizers, it is generally regarded as unfavorable from the viewpoint of quantum sensitivity to dope with a polyvalent metal ion since such causes introduction of competitive centers. For example, if emulsion grains whose surface has been chemically sensitized are doped with Rh.sup.3+, a typical polyvalent metal ion, it is well known in T. Tani, J. Chem. Soc. Japan, 1222 (1972) and 1975 (1972), and D. M. Samoylovitch, J. V. Ardasheu, Photogr. Sci. Engineer, Vol. 17, No. 3, pp. 351-353 (1973) that Rh.sup.3+ acts as an electron trap center, thereby tending to cause desensitization and high contrast. Such polyvalent metal ion doping has been practically utilized in light-sensitive materials for printing that require high contrast. Iridium, another typical example of polyvalent metal ions, is specific. When silver halide grains are formed in the presence of iridium in an amount of from 1.times.10.sup.-8 to 1.times.10.sup.-5 mol per mol of silver, improvement of sensitivity or improvement of high intensity reciprocity law failure can be obtained even in emulsions whose surface has been chemically sensitized, as described in Japanese patent publication Nos. 4935/68 and 32738/70 and Japanese patent application (OPI) Nos. 221839/83 AND 152438/84 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"). However, these reports also indicate that the amount of iridium to be added preferably ranges from 1.times.10.sup.-7 to 1.times.10.sup.-6 mol per mol of silver, while amounts of 1.times.10.sup.-5 mol or more are not practical since such cause serious reduction in sensitivity without bringing about overall improvements in photographic characteristics. Accordingly, it has not been practically studies to increase sensitivity of emulsions by addition of polyvalent metal ions in large amounts of 1.times.10.sup.-4 mol or more.
Typical divalent metal ions include Cd.sup.2+, Pb.sup.2+, etc. Examples of applying a large quantity of such a divalent metal compound at the time of grain formation have been reported. For example, it was reported by Wyrsch, International Congress of Photographic Science (1978) that addition of 1.times.10.sup.-1 mol/mol Ag of Cd(NO.sub.3).sub.2 during the preparation of an AgCl emulsion only results in doping of not more than 1.times.10.sup.-6 mol/mol Ag. It was also reported by Hoyen, Journal of Applied Physics, Vol. 47, p. 3784 (1976) that addition of a large amount of Pb(NO.sub.3).sub.2 during the preparation of an AgBr emulsion only results in doping of a very small proportion. As is apparent from these reports, it is known to dope silver halide emulsion grains with a small amount of a divalent metal ion, e.g., Pb.sup.2+ or Cd.sup.2+, e.g., the phrase "a small amount of a divalent metal ion" means an amount that when 0.3 mol/mol Ag of Pb(NO.sub.3).sub.2 was added, 6.1.times.10.sup.-5 mol/mol Ag of Pb.sup.++ was doped, whereas a technique for doping 1.times.10.sup.-4 mol/mol Ag or more of an impurity has been unknown. That is, there has been virtually no apparent consideration in the art with respect to photographic sensitivity of emulsions doped with a large amount of a divalent metal, particularly highly sensitive emulsions that have been subjected to sulfur sensitization or gold sensitization.