6 mm in diameter, was analysed by GGTL Laboratories during the Diamond Show in Basel in March 2015.
The distinction of natural and synthetic diamonds and imitations with the GGTL DFI Laser+ system is non-automated but very efficient, based on the observation of luminescence colour, distribution and intensity under various excitations, combined with the simultaneous analysis of the photoluminescence (PL) and Raman spectra of the diamonds.
Luminescence was observed under 254 nm short-wave (SW) and 365 nm long-wave (LW) UV radiation from a 6 W lamp (model UVP UVSL-26P), and also under broadband UV from the GGTL DFI system using the three different excitations that made the sample luminesce distinctly: 250-350 nm (SW/ LW band), 300-410 nm (LW band 1) and 355375 nm (LW band 2).
PL spectra were recorded with the GGTL PL-7 system using 405, 473, 532, 635 and 785 nm laser excitations, and a high-resolution echelle spectrograph by Catalina Scientific equipped with an Andor Neo sCMOS camera (resolution of 5 megapixels) that was thermoelectrically cooled to -30[degrees]C.
The PL spectra recorded with all five laser excitations at 77 K confirmed what was clearly indicated by the GGTL DFI system: that the sample was an as-grown (untreated) CVD synthetic diamond, high in silicon-vacancy defects (Figure 4).
Dr Thomas Hainschwang FGA is director and research scientist at GGTL Laboratories, Gnetsch 42, LI-9496 Balzers, Liechtenstein.