Mechanism of hologram formation in dichromated gelatin with x-ray photoelectron spectroscopy

The mechanism of hologram formation in dichromated gelatin is studied from all aspects with x-ray photoelectron spectroscopy (XPS). It is indicated that the Cr2p(3/2) XPS spectrum of chromium used for hologram formation shows the property of exhibiting a continuousspectrum during the process of dichromated-gelatin hologramformation. By means of curve fitting and drawing a comparisonbetween the obtained spectra and those of some standard substances, itis found that during the process of hologram formation the valence of chromium used for hologram formation changes from Cr(6+) to a quasi-trivalent state to Cr(4+), and finally to Cr(3+). Accordingly, the corresponding compound experiences a change from (NH(4))(2)Cr(2)O(7) to the transient state close to the feature of Cr(OH)(3) to CrO(2), and finally to Cr(3+), cross linking with the gelatin. The essence of the chemical change at different stages of the process of hologram formation was found, and so the present mechanism, which is determined with comparatively abundant proof, should replace previously reported mechanisms, which were too simple, varied, and sometimes even mutually contradictory. According to the experimental results and the fact that a solid-film reaction, which differs from that of the liquid-phase reaction, was studied, possible chemical-reaction equations of the process of hologram formation are established. This becomes the basis for explaining previous findings and expanding further research.