Reevaluation of Type I Diamonds for Infrared and Raman Spectroscopy in High-Pressure Diamond Anvil Cells

Types Ia, IIa, and IIb diamonds have been compared for their use as anvils in infrared and Raman high-pressure spectroscopy. In the mid-infrared region above 2700 cm⁻¹, type Ia diamonds have better transmission than type IIa diamonds. In the far-infrared region between 600 and 300 cm⁻¹ type IIa diamonds have in general better transmission than type Ia but at lower frequencies the transmissions are comparable. Type IIa diamond anvils, which have been tested for their use in Raman spectroscopy throughout the whole vibrational region and showed large fluorescence in this region when 514.5 nm laser excitation was used, yielded in general extremely low fluorescence with 363.8 nm excitation thus making them ideal for Raman spectroscopy with ultraviolet lasers.