On the Wavelength Threshold for Photoconductivity in Organic Solids

Abstract

In a preivous publication¹ we reported on the photoconductivity of polystyrene for excitation in the vacuum ultraviolet. The threshold for the onset of this photoelectric effect was interpreted as indicating that photon energies which are close to the ionization energy of the free molecules (in this case, benzene) were necessary for the process to occur. In order to investigate whether this requirement holds in general we investigated the effect for a variety of other organic solids; polyuethylene, anthracene, naphthalene, paraffin wax (m.p. 48 °C and m.p. 52 °C), cellulose and glucose. The results are shown in Fig. I Which describes the variation of the photocurrent with excitation wavelength for the various materials. The curves have been normalized to the value 100 for excitation at 584 Å. The intensity of the exciting radiation was normalized by the fluroescence of sodium salicylate. It shall be pointed out that in order to obtain comparative current intensities the applied voltage for cellulose was 10 Volt, for glucose 1 Volt, while the necessary voltage for the other matrerials varied between 200–300 Volts. At 200 Volts, the dark current for glucose and cellulose was already greater than the photocurrent.