Some optical properties of thirty-two gamma-counting diamonds have been investigated. These properties include the ultraviolet transmission limit, the infrared absorption spectra, the birefringence, and the luminescence. The approximate percentage of Type I and Type II, estimated by both the ultraviolet and infrared absorption criteria, and the relative counting efficiency of each diamond are shown together on a single chart. One concludes that good gamma-counting diamonds usually have substantial portions that are Type II, but diamonds entirely Type II are not necessarily good counters. In addition to the well-known absorption maximum at a wavelength of 8 microns, Type I diamonds appear to exhibit an absorption maximum at a wavelength of 21 microns. Experimental evidence is given for the existence of normally empty trapping levels 0.5 ev and 0.7 ev below the conduction band and for the existence of point contact rectification in diamond.
R. K. WILLARDSON and G. C. DANIELSON, "Optical Properties of Counting Diamonds," J. Opt. Soc. Am. 42, 42-49 (1952)