FORMATION AND DECAY KINETICS OF LIGHT-INDUCED DYE RADICALS ON SPECTRALLY SENSITIZED AGBR MICROCRYSTALS MEASURED BY ELECTRON-SPIN-RESONANCE SPECTROSCOPY - A QUANTITATIVE MODEL

During optical excitation of spectrally sensitized silver bromide micr ocrystals, dye radicals are generated at the surface of the crystals. For the dyes studied in this work the radicals are oxidized dye molecu les, which have a hole trapped at their doubly degenerate highest occu pied molecular orbital. The dye positive holes can be detected using e lectron spin resonance (ESR) spectroscopy. After optical excitation th e oxidized form of the dye starts to decay. A new method to acquire ki netic data of formation and decay of dye positive holes is introduced, taking into account the variation in linewidth of the ESR signal. By comparing measurements in ambient air, dry air and dry nitrogen gas it is found that moisture and not oxygen influences the kinetic behaviou r of the radicals. A quantitative model is suggested which is able to describe the formation of dye positive holes during optical excitation . This model allows one to predict the decay of the oxidized dye molec ules, using the fitting parameters of the formation curves. (C) 1997 A merican Institute of Physics.