Sulphide centres on AgIBr (100) surfaces: characterization and energy levels

Abstract

Sensitometric and spectroscopic techniques are used to characterize sensitizer centres produced by sulphur sensitization of AgIBr cubes. Sulphur sensitization primarily affects the long-wavelength sensitivity in three spectral regions: 550, 700 and 800 nm. The concentration dependence of the long-wavelength sensitivity in these spectral regions shows the first to be associated with single-sulphide centres. The other two spectral regions are attributed to multiple-sulphide species, but thiosulphate concentration-dependent activation energies for long-wavelength sensitivity precluded a more definitive assignment. A prominent 480–490 nm peak is observed in diffuse reflectance spectroscopy of these emulsions that is not observed in the long-wavelength sensitivity measurements. This peak is assigned to a product of the sulphur sensitization that is not photographically active. An energy level scheme was constructed on the basis of the activation energies and photon absorption energies. This scheme showed that all three sulphide centres are poor hole traps, but their electron trap depth increases with increasing absorption wavelength.

Keywords:

• chemical sensitization
• chemical sensitization mechanisms
• sulphur sensitization
• long-wavelength sensitivity
• diffuse reflection spectroscopy