Spectroscopic and electrical studies of all- trans β-carotene crystals

Abstract

Single crystals of all-trans $\beta$-carotene have been grown and spectroscopic, optical and electrical properties measured. Electronic absorption spectra have been measured at liquid nitrogen and room temperature, and the polarization of the absorption bands in the monoclinic form determined. The polarization behaviour is briefly discussed. The electrical measurements melude a determination of the dark conductivity, giving a value for the electrical activation energy of 1.45 eV. Some crystals were observed to give unusual voltage current characteristics and to give rise to current pulses at a steady applied voltage. Photoconductivity measurements show a weak peak at 25 000 cm$^{-1}$ in the region where maximum light absorption occurs, and a much stronger peak at 13 300 cm$^{-1}$. The various processes which could be responsible for this and for the origin of the latter peak are discussed.