Conventional silver halide photographic film loses a large percentage of its photoinduced electrons to fast recombination with holes, thus reducing the film's light-capturing efficiency. Researchers at the Université Paris-Sud (Paris, France) and Agfa-Gevaert (Mortsel, Belgium) have come close to eliminating this problem by doping the silver halide with formate ions. The dopant acts to scavenge holes, preventing the recombination of electron-hole pairs. In addition, the dopant itself produces an electron that acts as a photoinduced electron, raising the theoretical yield by a factor of two. This doubling, which takes place over a span of minutes after the actual exposure, acts strictly in proportion to the light received and thus does not register as noise.
A comparison of the sensitivity of doped and undoped emulsions--after a postexposure delay of 20 minutes--showed that a factor of 10 fewer photons is required to develop half the population of silver halide grains in doped versus undoped film. Exposure efficiency, measured as the ratio of atoms in a silver halide crystal to photons received by the crystal, reached 1.5 in the doped emulsion--close to the theoretical maximum of 2.0. Contact Jacqueline Belloni at [email protected].