In this experiment the microwave absorption and phase-sensitive detection technique was used to detect the time-resolved signal of photoelectrons generated by 35-ps laser pulses in AgCl emulsions uniformly doped with different concentrations of formate ions (HCO<sub>2</sub><sup>-</sup>). According to photoelectron decay signal, the photoelectron decay properties and the trap-capture properties, influencing the efficiency of latent image formation of the cubic AgCl grains, were discussed. The results indicate that when its concentration is 10<sup>-5</sup>mol/molAg, the formate ions act as hole traps obviously, enhancing the escape of electrons from pair recombination, but when its concentration is more than or less than 10<sup>-5</sup>mol/molAg, the formate ions may not act as hole traps effectively. We find that the optimal concentration of uniformly doped formate ions which can increase the photoelectron lifetime effectively is 10<sup>-5</sup>mol/molAg.
Photoelectrons play an important role during the photographic process of silver halide. Electron traps influence the decay of photoelectrons and the photographic process as well. During the preparation of silver halide microcrystal, traps will be formed with different depth, concentration, and capture cross section under different conditions such as temperature, pressure, and nucleation time etc. The electron trap with different depth, concentration and capture cross section has different ability to capture photoelectrons. In this paper, the influences of the three parameters on photoelectron decay are theoretically analyzed from the point of the photoelectron decay kinetics, respectively. It is found that decay amount is determined by capture cross section; decay velocity depends on trap depth; trap concentration influences both decay amount and velocity. Photo-storage or imaging character of silver halide material can be changed and improved by changing the size of capture cross section, depth or concentration under certain condition to control decay amount or velocity.
Dopants can be substitutionally incorporated into AgX crystals and influence the photoelectron action and the latent image formation by introducing appropriate electron traps. The dopant [IrCl<sub>6</sub>]<sup>4-</sup> was introduced in either the core, the subsurface shell or the outer shell of cubic AgCl microcrystals and its concentration was varied from 2.60×10<sup>-7</sup>mol/molAg up to 2.61×10<sup>-</sup><sup>5</sup>mol/molAg. The emulsion sample exposed to a YAG super short pulse laser (355nm, 35ps) were measured by microwave absorption and dielectric-spectrum technique. The experimental results show the photoelectron decay time at room temperature decreases with the doping concentration increasing for any given doping position especially as the doping near the core. Results also show the photoelectron decay time at room temperature increases when the doping position is closer to the surface especially for higher doping concentration at 2.61×10<sup>-5</sup> mol/molAg. This can be explained that [IrCl<sub>6</sub>]<sup>4-</sup> can act as both shallow electron trap and deep electron trap with doping condition varying. When the doping level is lower and doping position is closer to the surface, the sensitivity of AgCl emulsion is higher. The knowledge obtained from this study may be useful for practical microcrystal design making use of dopants.