Spectrophotometry of Thin Films of Light-Absorbing Particles

Abstract

Thin films of dispersions of light-absorbing solid particles or emulsions containing a light-absorbing solute all have a nonuniform distribution of light-absorbing species throughout the sample volume. This results in nonuniform light absorption over the illuminated area, which causes the optical absorbance, as measured using a conventional specular UV-vis spectrophotometer, to deviate from the Beer-Lambert relationship. We have developed a theoretical model to account for the absorbance properties of such films, which are shown to depend on the size and volume fraction of the light-absorbing particles plus other sample variables. We have compared model predictions with measured spectra for samples consisting of emulsions containing a dissolved light-absorbing solute. Using no adjustable parameters, the model successfully predicts the behavior of nonuniform, light-absorbing emulsion films with varying values of droplet size, volume fraction, and other parameters.

Solid-Phase Fluorescence Filter Effect: Toward Field and Ultrasensitive Detection of Iodine Speciation in Seawater

“…According to eq , the photon fraction is positively correlated with the solid particle density, reflecting the efficiency of the SPFFE during the sensing process under ideal conditions. For the solid iodine particles, the diffuse reflectance absorbance is affected by the particle density and the thickness of the absorbing layer. , The distribution of elemental iodine on different sizes of test paper was characterized by a scanning electron microscope. Figure S4 shows that reducing the headspace area would significantly increase the density of iodine particles and the thickness of the absorption layer.…”