Spectral extinction of colloidal silver*

Abstract

Computed and observed extinction spectra of colloidal silver particles with various size and shape distributions are compared. Excellent agreement is achieved through consideration of (i) the effects of surface and internal contamination and particle size on the optical constants of silver, (ii) the appropriate number of terms as a function of size in the Mie equation for spheres, (iii) a formulation of the Gans equation for prolate spheroids, to include the degree of particle orientation that occurs when a swollen gelatin matrix dries, (iv) the method of combining spectral characteristics determined by the Mie (size) and Gans (shape) relations, and (v) stereometric corrections of the particle measurements for the effects of microtome-section thickness and swelling.