Sulphide centres on (111) AgBr surfaces: energy levels and computer simulated sensitometry

• Published in: The imaging science journal Vol. 51; no. 3; pp. 125 - 139
• Main Authors: Hailstone, R K, French, J, De Keyzer, R
• Format: Journal Article
• Language: English
• Published: Suffolk Taylor & Francis 01.01.2003; Professional Engineering Publishing
• Subjects: chemical sensitization; chemical sensitization mechanisms; computer simulated sensitometry; diffuse reflection spectroscopy; Exact sciences and technology; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; long-wavelength sensitivity; Photography, photographic instruments and techniques; xerography; Physics; sulphur sensitization; Spectroscopy; Developers; Photographic material sensitivity; Computerized simulation; Chemical properties; Experimental study; Sulfur; Silver bromides
• ISSN: 1368-2199; 1743-131X
• DOI: 10.1080/13682199.2003.11784419

Sensitometric and spectroscopic techniques are used to characterize sensitizer centres produced by sulphur sensitization of AgBr octahedra. Activation energies for long-wavelength sensitivity were independent of thiosulphate concentration for the single-sulphide centres (550 nm), but showed a concentration dependence for the multiple-sulphide centres (700 nm). The achievement of maximum photographic speed is associated with the production of the multiple-sulphide centres. Using activation energies for long-wavelength sensitivity, with the lowest one for the multiple-sulphide centres being taken as closest to reality, an energy level scheme was constructed for the two sulphide centres. The single-sulphide centres are estimated to have an electron trap depth between 0 and 0.1 eV, whereas the multiple-sulphide centres have trap depths between 0.25 and 0.45 eV. Deconvolution of thiosulphate-induced absorption spectra suggested that only 65 per cent of the converted thiosulphtate is photographically active and that the single-sulphide centres are the predominant sulphide species. Computer simulated sensitometry based on these ideas was consistent with experimental sensitometry. Computer simulation of the sensitometry for the optimum thiosulphate concentration required a small concentration of the multiple-sulphide centres. Attempts to simulate the sensitometry of the oversensitized emulsion were less successful. Computer simulations based on the single-sulphide centres acting as hole traps were inconsistent with the experimental data.