Photoconductivity of chlorophyll-a induced by a tunable dye laser

Abstract

Microcrystalline chlorophyll-a is seen to give a photoconductivity signal upon excitation by a pulsed dye laser. The shape of the signal pulse essentially matches that of the laser pulse both at room temperature and at 77°K. An upper limit of the photocurrent response time of about 1 nsec is accordingly estimated. The photocurrent signal can be easily saturated by the light pulse. The light exponent varies from nearly zero at high light intensities to unity at low light intensities. The action spectrum of photoconductivity is found to match the microcrystalline chlorophyll-a absorption spectrum. A lower limit of 0.15 cm2/V sec is estimated for the charge mobility. Electronic conduction in the microcrystal is implicated. The nature of photocharge generation is also briefly discussed in terms of either an intrinsic or an extrinsic process.