Energy Levels and Charge Carrier Generation in Crystalline Chlorophyll-a Studied by Photoconduction and Fluorescence

Photoconduction and fluorescence were studied in solid state chlorophyll-a(Chl-a) films which were composed of microcrystals of Chl-a-water adduct. The transient photocurrent, rising without time delay for an exciting flash, decayed with a second order reaction. Two types of response were distinguished in the action spectrum of photocurrent on continuous illumination: One of them corresponded to the absorption of Chl-a molecular crystal, and the other, appearing longer wavelength (820 nm, 1.51 eV), was ascribed to the direct transition to a conduction band below the first excited singlet state. The thermal band gap of 1.48±0.02 eV was obtained from the activation energy for dark conductivity. The fluorescence of crystalline Chi-a was observed at 794 nm.