The effect of the content of (NH4)2Cr2O7 in dichromated gelatin (DCG) on the binding energy of the Cr 2P 3/2 level was studied with x-ray photoelectron spectroscopy. It was found that the binding energy of the Cr 2P 3/2 level of chromium in DCG is lower than that of pure ammonium dichromate. When the content of (NH4)2Cr2O7 is not greater than 1%, the chromium in DCG has only one state, near 577.5 eV; when this content is between 1% and 20%, the chromium in DCG has two states, near 577.5 and 579.1 eV. The relative contents of these two states change with the content of (NH4)2Cr2O7. As the (NH4)2Cr2O7 content increases, the relative content of the state near 577.5 eV decreases almost linearly, but its absolute content first increases, then reaches a maximum at ∼10% (NH4)2Cr2O7, and finally decreases. In addition, the absolute content of the state near 577.5 eV changes very slowly between 5% and 15% (NH4)2Cr2O7. According to these experimental results and holography data reported in the literature, it is inferred that the chromium of the state near 577.5 eV is the chromium that forms the latent image center after exposure and then forms the hologram after development. As a result the basis for the optimum content of (NH4)2Cr2O7 is found, and an approach to increasing sensitivity is suggested through this experiment.
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