The reducing agents dimethylamineborane and SnCl2 were used to produce silver clusters chemically in an AgBr emulsion. These silver clusters were detected with diffuse reflectance spectroscopy at photographically relevant sensitizer concentrations, and their reflectance at 476 nm correlated well with the effects of these reducing agents on photographic sensitivity. Spectroscopy was used to monitor the photochemical reactions of these silver clusters. A portion of the 476-nm peak derived from the Kubelka–Munk transform of the reflectance spectra could be photobleached using band-gap excitation, indicating that some of the silver clusters were destroyed by photogenerated holes. However, some silver clusters did not react with photoholes and these clusters may be electron-trapping. The decrease in peak height upon photobleaching indicated two distinct silver clusters in terms of their ease of bleaching by photoholes. A simple reaction model was found to be consistent with the concentration dependence of the peak height, suggesting that only one size of silver cluster is being produced under most of our reaction conditions.
S. Guo, R. K. Hailstone, "Spectroscopic and Sensitometric Studies of Chemically Produced Silver Clusters" in Journal of Imaging Science and Technology, 1996, pp 210 - 219, https://doi.org/10.2352/J.ImagingSci.Technol.1996.40.3.art00005