Luminescence properties of diamond prepared in the presence of rare-earth elements

The feasibility of high-pressure diamond synthesis in rare earth–carbon binary systems has been studied for the first time with a view to producing new luminescence centers in diamond. The results demonstrate that, at a pressure of 8 GPa in the Eu–C system, graphite transforms into diamond near the melting point of the EuC2 carbide (1900–2200°C), whereas in the Er–C and Tm–C systems diamond is formed at temperatures below the melting points of the respective carbides: ErC2 and TmC2 (1600–1800°C). The presence of Eu-, Er-, or Tm-related optically active defects in diamond was not revealed by cathodoluminescence spectroscopy. The observed catalytic activity of the rare-earth elements for the transformation of graphite into diamond suggests a new interpretation of the increased rare-earth concentration in carbonado, a polycrystalline variety of natural diamond.