lengths, the two fluorescence peaks were centered at 495 and ~560 nm. The greater resolution of this instrument compared to the CCD spectrometer (figure 9, right) revealed the additional peak at 495 nm. Of the 10 orange diamonds measured by fluorescence spectroscopy, seven showed weak-to-moderate and one showed strong category 3 fluorescence spectra with peaks ranging from 540 to 560 nm.
Several of the diamonds also showed subordinate peaks at ~450 nm. The spectra at different excitation wavelengths illustrated in figure 10 for a Fancy Vivid yellowish orange diamond are representative of the other samples.
Absorption Spectra. FTIR spectra were collected for all eight gray-green (including chameleon) diamonds from the Aurora Butterfly collection with category 3 fluorescence spectra (again, see table 1), and FTIR and UV-Vis-NIR spectra were collected for the five diamonds from the GIA collections showing this fluorescence pattern. The UV-Vis-NIR spectra for these diamonds showed prominent bands centered at ~370 and ~480 nm. The FTIR spectra of three diamonds in the bluegray group indicated that they are type Ia instead of type IIb. Most blue diamonds receive their color from boron and are designated type IIb (see Fritsch and Scarratt, 1992, for an explanation of diamond types). The nitrogen concentrations in the category 3 diamonds generally were much lower for both the A aggregate (up to 114 ppm) and B aggregate (up to 22 ppm) compared to diamonds from categories 1 and 2: up to 415 and 890 ppm, respectively, for the A aggregate and up to 700 and 270 ppm, respectively, for the B aggregate.