diamond characterization and, ultimately, identification.
The very slightly yellow (G-to-I grade; Fryer
and Koivula, 1986) 127 ct Portuguese Diamond was
also examined to provide an example of how fluorescence
intensity is related to the size of a diamond.
At GIA and the Smithsonian, all samples were
tested for visible fluorescence and phosphorescence
using standard 4-watt long- and short-wave UV
lamps. The color descriptions in table 1 were taken
from grading reports issued by gemological laboratories.
For the purposes of this article, the diamonds are
assigned a “key bodycolor” (see table 1) according to
their dominant bodycolor, although each group may
include various modifying hues. For example, within
the pink color group, most were graded solely as
pink, and a few were purplish pink or reddish purplish
pink. Due to the variety of fluorescence results,
diamonds with a green component are sorted according
to their specific (dominant plus modifying hue)
color description. Several diamonds graded as greenyellow
to yellow-green are grouped together (key
bodycolor given as yellow-green). Similarly, three diamonds
graded as blue-gray or gray-blue are grouped
together (key bodycolor given as blue-gray).
Fluorescence and Phosphorescence Spectroscopy.
The instrumentation used to measure fluorescence
and phosphorescence spectra consisted of a deuterium
lamp UV source (215–400 nm), filters to
control the wavelengths of incident light, a sample
holder, a fiber-optic bundle to deliver incident
light and collect the emitted signal, an Ocean
Optics USB 2000 CCD spectrometer, and a computer
(see figure 2). The UV source used for most
of the fluorescence and phosphorescence spectroscopic
measurements was an Ocean Optics DH-
2000. The UV radiation was filtered to ~250–400
nm, and was transferred through a bundle of six
optical fibers (600 µm diameter each). A seventh
fiber in the core of the bundle channeled the emitted
light from the diamond to the spectrometer
(figure 2, right). The tip of the fiber-optic bundle
was placed directly in contact with the table of
each sample, which enabled us to illuminate and
measure approximately equivalent volumes of
each sample. Thus, we were able to compare relative
intensities of signals from a wide range of
sample sizes. The CCD spectrometer used in these
experiments is described further in box A.
For the fluorescence measurements (again, see
figure 2, right), we used a Corning 7-54 filter to
block visible light (~400–650 nm) from the deuterium
UV source and a variable filter (Ocean Optics
LVF-HL) to deliver only a narrow band (full width at
half maximum [FWHM] = 22 nm) of UV radiation
to the sample. This narrow band was varied
between 250 and 400 nm (e.g., figure 3). The fluorescence
recorded by the spectrometer at each excitation
wavelength was collected for 30 seconds. Since
excitation intensity varied with wavelength (again,
see figure 3), the measured fluorescence spectra
were scaled uniformly over the wavelength range.
Except for one sample to monitor the change, no
radiometric (i.e., wavelength-dependent) calibration