Abstract
THE effect of colouring of the alkali halides, such as rock salt, with X-rays, radium radiation, or far ultra-violet radiation, is due in the light of modern knowledge to the transference of the valency electron from the chlorine to the sodium. The latter is suspected to be deposited in the lattice in the state of neutral atoms. The new absorption band, causing, for example, the yellow colour of rock salt, can be made to disappear by exposing the coloured salt to the rays it absorbs, that is, the blue-violet ones, or by heating it. A plausible theory is that in this case the backward transference of a valency electron takes place. In both cases the liberated electrons must cause the photo-conductivity effect, and this was indeed observed for the decolorising effect and studied by Pohl and Gudden and their collaborators.
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SAVOSTIANOVA, M. Optical Investigations on the Formation of the Latent Photographic Image. Nature 126, 399 (1930). https://doi.org/10.1038/126399b0
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DOI: https://doi.org/10.1038/126399b0
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