Influence of ambient humidity on the photoconductivity of fine crystals of zinc oxide and work function of the crystals by irradiation were studied.
A typical fine crystal specimen of zinc oxide was prepared by oxidizing pure zinc metal inoxygen. The powdered zinc oxide was mounted in between a gap of two electrodes with adequate pressure, for measuring photoconductivity of the powder form.
Time constant which was obtained from the transient characteristics of the photocurrent was varied through a minimum value during keeping in wet atmosphere. Work function which was changed by irradiation on the powdered zinc oxide was measured with a vibrating reedelectrometer. When the intensity of irradiation was 50 Lux, the measured work function changes were about 130 mV.
The work function changes measured in the sample of the free moisture was linear with the log of the time when the light was extinguished, but in the sample which had adsorbed moisture the change was not linear.

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In order to explain the reason why photoconductive negative effect is easy to occur in the silver halide crystal, of which dark resistance is low, the possibility of interaction of electron or positive hole and lattice defects under the electric field and light illumination were discussed and it was proved that such interaction would result in the decrease of electroconductivity of ionic crystal by using mathematical derivation of conductivity.

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The photoconductivity of colored sulfur-content silver bromide crystal was studied. The crystal irradiated by short wavelength light and by long wavelength light showed photoconductive negative effect and photoconductive positive effect respectively. Repeated illumination of short wavelength light on the crystal resulted in the decrease of photoconductive negative effect and repeated illumination of long wavelength light on the crystal resulted in the decrease of photoconductive positive effect. The intermittent illumination of long wavelength light (or short wavelength light) on the crystal resulted in the increase of photoconductive negative effect (or photoconductive positive effect). Negative effect with short wavelength light and positive effect with long wavelength light both increased with the rise in temperature. The migration of colored band of sulfur-content silver bromide crystal was observed under the electric field at high temperature. The temperature dependence of dark electric conductivity was studied and it was found that the activation energy of electric conductivity of sulfur-content crystal is lower than that of silver bromide. These phenomena were explained by using the S⁼−Ag_n⁺ model. where S⁼ is accompanied. by n interstitial silver ions.

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A report is made in this paper of a condenser of which the dielectrics is a photoconductirtg material.
It is the intent of this paper to present some clues to explaining various phenomena which occur in the electrographic processes, Measurements of capacity were carried out by D. C. ballistic method.
Humidity increases the capacity of ZnO-paper, especially of base-paper.
Pre-illumination and illumination also increase the capacity of ZnO layer.
It should be noted that ZnO-paper decrease their capacity when the applied voltage exceeds a certain value, following the generation of space charge.

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