Recent aspects are reviewed on electronic processes in organic semiconductors, especially on photoconductive processes in anthracene crystals. Optical and photosensitive properties and recently developed experimental techniques are described.
Then a following postulate is proposed on the photoconductive process. Excitons are produced by exciting light and migrate through a crystal. Most of excitons diminish to, emit fluorescence, and the others are trapped in some trapping levels, which may make the trapped excitons ionized. This model may explain activation energies of photoconduction and peaks in a conduction glow curve.

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The results of the previous papers were discussed. Generally the value of particle size obtained from a charge spectrometer was 10-100 time larger than that obtained from ultramicroscopic observation. One of the reason for this difference lays in the problems of which velocity should be used for theoretical calculation. The second is that the particles in the beam ejecting from the jet seemed to act group together as an aggregated particle. Concerning the charge measurement, the problem on flowing method of air and aerosol was described. The mechanism of charging of particles, which passed through a corona discharging tube, in a charge spectrometer was explained as follow: Some of particles may be excited but not ionized in the corona discharging tube, and then ionized in the charge spectrometer by bombardment of electrons or ions or any other particles which are accelerated by the electric field of the charge spectrometer. The mechanism of chrging by ultraviolet ray irradiation Was discussed.

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Measurements of persistent intemal polarization (P. I. P.) were performed with anthracene powders dispersed in a dielectric resin.
Appreciable P. I. P. was observed under Illumination either with near ultraviolet light or even with λ>5200Å far above the absorption edge (4000Å) of anthracene.
It was found that the growth of P. I. P. in commercial materials depended exponentially on polarizing time according to the relation:
[Equation]
where P is polarization, P_const. is polarization after a long polarizing time, τ is a time constant, t is a polarizing time.
On the other hand, P. I. P. of purer anthracene did not obey the above relation under illumination with λ< 5200Å.
It appeared that the distribution of charge carriers in anthracene was affected by the injection of charge carriers from the illuminated electrode.
Sensitization of P. I. P. due to some dyes was also investigated.

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The mechanism of the image formation in the electrophotographic zinc oxide paper has been studied under various conditions. Generally, the quality of electrostatic latent image is determined by the development mothod and the surface voltage. When the charge of the zinc oxide layer does not reach the saturation point, the relation between the surface charge and the developed density is not well determind。The relation between the density and surface voltage changes remarkably by the surface voltage. In the method of development using carrier brush, the developed density are obtained by an attractive effect of the toner and the carrier, which is based on Coulomb force. The relation between the surface charge and the developed density does not follow a linear relation. Therefore the measurement of developed density versus surface voltage shows that there are two distinct surface voltage regions where the relation between above two functions is quite different. At low voltage regions 0-100 volts, the relatlon between the density and the surface voltage is found as a linear function. While at high voltage regions above 200 volt the relation follows an another function. The relations are as follows:
and
The results may be interpreted such that the developed density of the zinc oxide layers depends on the charge distribution.

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