Absorption Anisotropy Measurement

For absorption anisotropy studies, a custom microscope attached with a polarizer and an analyzer was constructed. The light source used involves both halogen and deuterium lamps (Ocean Optics D-2000 BAL) with a wavelength range from 250 to 2500 nm. Figure 7 shows the details of the absorption anisotropy setup. The input light comes through a fibre of about 600 µm core diameter and the light is collimated using a lens. After collimation, the light is passed through a polarizer and a half-wave plate to control the incident light polarization. The light is focused on the sample with a 40x objective. The back-reflected light was passed through a polarization analyser and finally collected into the optical fibre connected to the UV-Vis Spectrophotometer (Ocean Optics Q65000).

Schematic representation of solid state absorption anisotropy setup.

Our measurement range is limited to the polarizer working spectral range from 420 to 680 nm. The samples were mounted on a Teflon substrate and the background signal was measured using blank quartz substrates. Samples were prepared by dropcasting a thin film of nanoparticles dispersed in solvent on quartz plates and were allowed to dry at room temperature before anisotropy measurement.