UV-vis Spectrometry

We use an Ocean Optics HR2000 spectrometer with a D₂/halogen light source and reflection probe to to investigate the optical reflectance and absorbance of semiconductor photocatalysts, YBCO precursor sols and Cu-Ni alloys. The reflection probe measures the diffuse reflectance (light scattered to all angles) as a function of wavelength in a close approximation to the signal obtained from an Integrating Sphere system.

Figure 1: Schematic diagram of UV-vis diffuse reflectance measurement system.

Figure 2: UV-vis diffuse reflectance spectrum for bulk Bi2O3.

The Kubelka-Munk function, F(R), allows the optical absorbance of a sample to be approximated from its reflectance:

For a semiconductor sample this allows the construction of a Tauc Plot - (F(R).hv)ⁿ vs hv. For a direct band gap semiconductor the plot n = ¹/₂ will show a linear Tauc Region just above the optical absorption edge. Extrapolation of this line to the photon energy axis yields the semiconductor band gap- a key indicator of its light harvesting efficiency under solar illumination. Indirect band gap materials show a Tauc Region on the n = 2 plot.

Figure 3: Tauc Plot (n = 1/2) for bulk Bi2O3 after Finlayson et al. Phys. Stat. Sol. (in press).

Selected Publications

[1] Tauc, R. Grigorovici and A. Vancu, Phys. Stat. Sol. 15, 627 (1966).