Energy Transfers between Crystals and Adsorbed Dyes I Desensitization*

The electron affinities of several desensitizing dyes have been measured and found to lie in the neighborhood of 3.5 ev, and it seems unlikely that the dye can compete with sensitivity specks for electrons at equilibrium. The dyes produced a desensitization of photoconductivity in cadmium sulfide films, indicating that they can serve as surface electron traps. A mechanism of desensitization is suggested according to which the photoelectrons are loosely bound by one or several dye molecules seriatim, in consequence of which their times of arrival at the sensitivity speck are spread out over a long enough period so that the factors which contribute to the instability of the latent image become effective, and the sensitivity is thereby reduced.