The orange, type Ia blue-gray group, and graygreen
(including chameleon) diamonds that exhibited
category 3 fluorescence spectra and were tested
by FTIR spectroscopy all showed significant concentrations
of hydrogen, as evidenced by the 3107
cm−1 peak.
Natural Diamonds with Other Fluorescence
Behavior. Two yellow-orange natural-color diamonds
(172 and 181) showed fluorescence spectra
(figure 11) with a single dominant peak at ~610 nm.
The one red and two purple diamonds were inert
or did not show measurable fluorescence spectra.
Admittedly, the number of samples we examined
was small, but these colors are among the rarest of
all natural diamonds. In the DeYoung Red, we
observed a barely discernible yellow fluorescence to
long-wave UV (inert to short-wave), which was
noted also by Shigley and Fritsch (1993), who further
documented a green luminescence when excited by
425 nm light. However, we could not discern a fluorescence
spectrum with the CCD instrument. In the
ultra-short-wave UV wavelengths of the DiamondView,
the DeYoung Red showed blue fluorescence
and well-defined growth bands, as well as a few narrow
green zones (figure 12).
Figure 13 provides a summary of the categories of
fluorescence spectra collected for the natural-color
diamonds we examined, organized by key bodycolor.
Gemological Observations. The observed colors and
intensities of long-wave UV fluorescence are summarized
in table 1. Note that the fluorescence spectra
did not always correlate directly to the fluorescence
color observed with a standard UV lamp.