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.
Photoelectron decay characteristics in latent image formation process directly reflect photographic efficiency of silver halide crystals. Dopants can be substitutionally incorporated into AgX crystals and influence the photoelectron action by introducing appropriate electron traps. Long photoelectron lifetime can improve the photographic efficiency of intrinsic or unsensitized grains. In general, AgCl are intrinsic or unsensitized emulsion. Cubic AgCl microcrystals doped with K<sub>4</sub>Ru(CN)<sub>6</sub> were measured by microwave absorption and dielectric-spectrum technique. Measurement of the photoelectron decay process as a function of doping position and concentration can provide important information about the electronic properties. The experimental results show the photoelectron decay time at room temperature is more or less longer than undoped samples. The photoelectron decay time increases with the doping concentration increasing and with the doping position closer to the core except for position 30%Ag and over high concentration 3.21x10<sup>-5</sup> mol/molAg. When doping position is 30%Ag, the photoelectron decay time reaches its maximum at the doping concentration of 1.5x10<sup>-5</sup> mol/molAg. At doping concentration 3.21x10<sup>-5</sup> mol/molAg, the photoelectron decay time reaches its maximum at the doping position 60%Ag. Through studying the photoelectron decay behavior, we can know the doping can improve the image quality of AgCl emulsion.