diamonds from the GIA collections that had category
2 fluorescence spectra (again, see table 1). All
UV-Vis-NIR spectra showed the H3-related ZPL at
~504 nm. This peak was only observed in diamonds
showing the category 2 fluorescence spectra.
FTIR spectra of these diamonds along with an
additional treated diamond showed they were type
Ia, generally with both A and B aggregates in variable
amounts.
Category 3: Fluorescence Spectra with a Dominant
Peak at ~550 nm. Figure 8 shows a compilation of
the category 3 fluorescence spectra, excited by 350
nm UV radiation, obtained from orange, violet,
gray-green (including chameleon), and the type Ia
diamonds in the blue-gray group.
One violet diamond along with three diamonds in
the blue-gray group had fluorescence spectra with
weak-to-moderate intensity at 525–530 nm. In a related
study, 93% of the 67 gray-to-blue diamonds tested
did not show measurable fluorescence, but showed
phosphorescence spectra that proved to be distinctive
of type IIb diamonds (Eaton-Magaña et al., 2008).
Most of the gray-green (including chameleon) diamonds
indicated weak fluorescence at ~450 nm and
moderate-to-strong fluorescence extending from
~450 to ~650 nm, with the center of the band ranging
from 535 to 558 nm. Data obtained for a graygreen
diamond using a spectrofluorometer at excitation
wavelengths from 220 to 400 nm showed many
interesting features (figure 9, left). The fluorescence
intensity was quite low when excited at short UV
wavelengths. However, as the excitation wavelength
increased, the fluorescence intensity increased, with
contributions from peaks centered at 495 and ~545
nm. The intensity reached a maximum when excited
by UV radiation at 340–345 nm and then
decreased as the wavelength of the excitation intensity
increased further. At the higher excitation wave-