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.