Reversible Bleaching of a Band in the Absorption Spectrum of Diamond

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Abstract
When diamonds which show the absorption band in the near ultraviolet, characteristic of blue fluorescing samples, are exposed to neutron bombardment, a continuous absorption slowly rising toward shorter wavelength is superimposed upon the band. Heating such a diamond to temperatures between 300° and 600°C decreases the continuous absorption and the structure of the band becomes appreciably sharper. Subsequent exposure to light greatly reduces the height of individual peaks in the band, while the continuous absorption at shorter wavelengths is increased. Renewed heating restores the sharp structure of the band and the cycle can be repeated at will. Heating the crystal to 750°C brings the crystal very nearly back into the state before neutron bombardment in which the reversible bleaching cannot be observed. A similar band accompanies the sharp line at 503 mμ that is produced in the absorption spectrum of diamonds by neutron bombardment and heat. The structure of this band is also altered by heating to various temperatures but is not affected by absorption of light.

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