Fluorescence Spectroscopy. The 3D fluorescence spectra of samples 8–11 show an emission maximum at 520 nm with a wide band extending from ~480 to 650 nm, a feature that manifested itself as a green or yellowish green fluorescence (figures 7A and 7B). This emission feature is caused by H3 and has a maximum at 470 nm excitation. Unlike N3, the 503 nm ZPL of H3 is not seen at room temperature. The N3-related fluorescence feature was also observed with various intensities due to different defect concentrations (figure 7B). The spectrum for 365 nm excitation, which most closely approximates the LWUV lamp, showed both H3 and N3 emissions at relatively low intensity. Fluorescence spectra from the HPHT-treated sample (11) were not noticeably different from those of other H3-dominated natural-colored samples.