Sulphide centres on (111) AgBr surfaces: the effect of thiocyanate on electronic properties

• Published in: The imaging science journal Vol. 51; no. 3; pp. 141 - 149
• Main Authors: Hailstone, R K, French, J, Tan, J, De Keyzer, R
• Format: Journal Article
• Language: English
• Published: Suffolk Taylor & Francis 01.01.2003; Professional Engineering Publishing
• Subjects: chemical sensitization; chemical sensitization mechanism; computer simulation; Exact sciences and technology; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Photography, photographic instruments and techniques; xerography; Physics; sulphur sensitization; thiocyanate; Photography; Sulfides; Additives; Electronic properties; Developers; Photographic sensitization; Thiocyanates; Sensitization; Experimental study; Silver bromides
• ISSN: 1368-2199; 1743-131X
• DOI: 10.1080/13682199.2003.11784420

Sensitometric and spectroscopic techniques are used to study the effect of sodium thiocyanate addition to sulphur-sensitized AgBr octahedra. Thiocyanate increased the speed of an oversensitized emulsion, causing it to have a speed comparable to the optimally suphur-sensitized emulsion at high irradiance and greater speed at low irradiance. Thiocyanate decreased the absorption by sulphide centres at shorter wavelengths (500-650 nm), but increased the absorption at longer wavelengths. The long-wavelength sensitivity (> 500 nm) was also increased by thiocyanate, whereas the activation energy for this response was reduced. These results are interpreted with a model that assumes that thiocyanate interacts with multiple-sulphide centres to lower their ground state energy level. This interaction reduces the degree of free-hole/trapped-electron recombination which occurs at these centres and which is responsible for the over-sensitization effect. A computer simulation based on this model gave simulated reciprocity failure data which were qualitatively consistent with the experimental trends. The effects of thiocyanate on absorption are interpreted as a change in extinction coefficient.