Abstract
Diamond attracts considerable attention as a versatile and technologically useful material. For many demanding applications, such as recently emerged quantum optics and sensing, it is important to develop new routes for fabrication of diamond containing defects with specific optical, electronic and magnetic properties. Here we report on successful synthesis of diamond from a germanium-carbon system at conditions of 7 GPa and 1,500–1,800 °C. Both spontaneously nucleated diamond crystals and diamond growth layers on seeds were produced in experiments with reaction time up to 60 h. We found that diamonds synthesized in the Ge-C system contain a new optical centre with a ZPL system at 2.059 eV, which is assigned to germanium impurities. Photoluminescence from this centre is dominated by zero-phonon optical transitions even at room temperature. Our results have widened the family of non-metallic elemental catalysts for diamond synthesis and demonstrated the creation of germanium-related optical centres in diamond.
Highlights
This stimulates further search for new substances capable of converting graphite to diamond
We have experimentally demonstrated the catalytic ability of germanium for the conversion of graphite to diamond at HPHT conditions
Unlike the previous work[30] reported minute seeded growth of diamond from germanium, diamond crystallization via spontaneous nucleation and growth is achieved in the present study with the overall degree of the graphite-to-diamond conversion being as high as 90–95%
Summary
This stimulates further search for new substances capable of converting graphite to diamond. The use of silicon as a catalyst for the conversion of graphite to diamond is obstructed by its ability to form carbide phases. Germanium unlike silicon does not form known carbide phases and having relatively low melting temperature (650 °C at 7 GPa) deserves a detailed investigation. Diamond formation via spontaneous nucleation and growth on the seed crystals is established proving the role of germanium as the catalyst for diamond formation. Spectroscopic studies of the synthesized diamonds reveal a new previously unreported optical centre with a zero-phonon line (ZPL) system at 2.059 eV, emitting spectrally narrow luminescence at room temperature. We assign this new optical centre to defects involving germanium impurities in diamond
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