Interactions of co-adsorbed spectral sensitizers on the surface of silver halide microcrystals

In many silver halide (AgX) technology based imaging materials, two spectral sensitizers are co-adsorbed on the AgX microcrystal surface in order to adjust the optical spectrum. More importantly, this can give rise to supersensitization, which is crucial for the sensitivity of such systems. Detailed knowledge of these phenomena allows the optimization of the spectral sensitivity and overall image formation efficiency. Our spectroscopic study of the underlying interactions uses a combination of Electron Spin Resonance (ESR) and Diffuse Reflectance Spectroscopy (DRS) to identify the dye radicals formed after electron transfer, providing crucial information about the supersensitization mechanism involved. Identification of dye radicals with ESR is based on determination of their g-values and supported by the DRS observation of new electronic transitions. Additional information is obtained from studying the kinetics of the light-induced radical formation and decay. Unfortunately, an unambiguous identification of the radicals is not always possible. Practical limitations of the experimental procedure, as well as perspectives for improvements are discussed.