Function of polarized space charge should not be neglected during the formation of a latent image in an electrophotographic process using a photoreceptor overcoated with an insulating film. There, the persistency of the polarized space charge plays an important role. To make the understanding of the role, in the present paper, a process utilizing effectively the polarized space charge produced in a photoconductive layer when such a photoreceptor is used with corona charge has been analysed and the quantitative description has been presented. From this analysis, it has been found that various types of latent image will be produced. Experiments to confirm the prediction have been made. It has been shown that the quantitative description in this paper is probable from the comparison between the prediction and the experiment.

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The processes of build-up and decay of the persistent internal polarization (PIP) of anthracene crystals were experimentally studied. The 1st singlet exciton band absorption (350∼400 mμ) was used for the photogeneration of charge carriers.
The crystals used were very pure ones of the form of a plate about 1 mm thick with ab-crystallographic plane surfaces. The polarization of the crystal sandwiched between transparent and metal electrodes was built up by repetition of pulse illuminations with constant intensity in one case without field and in another with 2000 dc. V/cm field. The produced polarization was determined by observing the depolarization current (light pulse probing method) or the released charge (radiation release method).
The hole-injection-type PIP and the electron-injection-type PIP were built up by making the polarity in the electrode positive and negative on the illuminated side, respectively. The zero-field-built-up PIP was of the hole-injection-type.
The results were examined mainly from the viewpoint of photogeneration of charge carriers.
The growth rate of hole-injection-type PIP is always larger than that of the electron-injection-type. The former can be made very large by the pre-treatment of the surface, that is, the ultraviolet irradiation in the presence of oxygen. The surface oxidation causes the density of surface acceptors to increase where the singlet excitons dissociate so that the conductive holes are generated, the electrons being trapped inthe acceptors. The decay rate of the electron-injection-type PIP due to the radiation release depends on the surface conditions.
The growth rate of the electron-injection-type PIP and the decay rate of the hole injection-type PIP are independent of the surface conditions and are in proportion to the square of light intensity. This is to be explained by assuming that the electron-hole pairs are generated through the exciton-exciton interaction.

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A method for the determination of Zine Oxide in electrophotographic papers by chelatometric titration was established. Zinc ion was extracted wth diluted hydrochloric acid or acetic acid from the photosensitive layer which was composed of zinc oxide microcrystallines, sensitizing dyes and hydrophobic polymeric substances, within rather short time quantitatively. The acid extracts were titrated with M/100 aqueous solution of EDTA-2Na under the presence of an indicator such as Eriochrome Black T (plus triethanolamine; at pH=10) or Xylenol Orange (at pH=5).
Influences of polyvalent metallic ions which were contained in components of electro-photographic paper, particularly in those of the base-paper, such as clay, talc, calcium carbonate, calcium chloride or aluminum, on the determination of zinc oxide were investigated to know that clay (Al₂Si₂O₅ (OH) ₄) in the base-paper caused no error and when metallic aluminum or water-soluble aluminum salts were present, EBT-indicator (plus triethanolamine) had to be used, and that when alkaline earth metals were not to be neglected, XO-indicator had to be used.
The method was applied to commercially available electrophotographic papers in order to determine the weight of coated zinc oxide microcrystallines.

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In order to investigate the mechanism of dye-sensitization, dye-sensitization of zinc oxide was made by evaporating dye and sensitization effect by this method was observed with some dyes. It was shown that one or two molecular layers of the dye on the zinc oxide surface gave highest photoresponse.
The conductivity change by dye-evaporation in the dark and under the illumination with wavelengths in dye-sensitized region was also observed. Counductivity of zinc oxide layer was always increased extremely by dye-evaporation.
The change of the surface potental difference of zinc oxide by dye-evaporation was also observed. The surface potential of zinc oxide positively increased and saturated with the increase of the mass of dye evaporated. This experimental result indicates that dye and zinc oxide make an electronic contact and it is thought from it's polarity that electrons in the dye were injected into zinc oxide layer, when dye was evaporated on zinc oxide.
These experimental results support the presence of electronic contact between dye and zinc oxide, and suggest the “electron transfer mechanism”for dye-sensitization.

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