Absorption and PL Spectroscopy. UV-Vis-NIR spectra showed the typical 480 nm absorption band for all six samples (figure 9D). FTIR analysis identified all of them as type IaA diamonds with traces of isolated nitrogen. Sample 18 contained much higher concentrations of aggregated nitrogen impurities than the other samples. PL spectra at 514 nm excitation showed a wide band from 600 nm to more than 850 nm, typical of diamond with 480 nm bands.
Fluorescence Spectroscopy. 3D fluorescence spectra from 480 nm-band diamonds are complex. All of the samples showed two major features: (1) a wide band centered at ~653 nm (maximum shifts between 630 and 655 nm) that maximized with 485 nm excitation energy, and (2) a ~539 nm-band (maximum shifts between 505 and 541 nm) that increased with 420, 345, and 285 nm excitation energies (figure 9, A–C). The combination of both bands ranged from ~500 to 700 nm and produced yellow to orange fluorescence when excited by visible light (near-LWUV). The band in the red part of the spectrum (630–655 nm) could be excited independently of the ~539 nm band using longer-wavelength light. The fluorescence from this feature is likely the same as the PL broadband seen after excitation with a 514 nm laser. In general, the band’s intensity increased with the size of the 480 nm absorption band. No clear correlations explain the differences in the ~539 nm band. The two HPHT-treated samples showed no obvious systematic differences from the naturally colored samples.