MATERIALS AND METHODS
Samples. Three-dimensional fluorescence spectra were collected from 25 faceted diamonds, including 19 natural-color samples and six treated by high-pressure, high-temperature (HPHT) and irradiation (table 1). GIA issues reports on thousands of colored diamonds each year, providing a large selection of samples. The diamonds in this study, all of which carried GIA reports indicating natural- or treated-color origin, were chosen as representative of their respective defect group. While multiple fluorescence-producing color centers occur in most diamonds, each of our samples was dominated by one of the following: