Man-made synthesis of ultrafine photoluminescent nanodiamonds containing less than three silicon-vacancy colour centres

Silicon-vacancy (SiV) centred diamond exhibits near infrared emission at 738 nm with narrower zero- phonon line and shorter lifetime comparative with nitrogen-vacancy (NV) centre, considered as a promising room-temperature single-photon source. However, unlike NV centred nanodiamonds easily obtained by detonation, man-made synthesis of ultrafine SiV nanodiamonds is a key challenge. Here, we provide a controllably method for synthesizing nanodiamonds with one or few SiV emitters by reducing their size to the near minimum via oxygen plasma treatments. The size of nanodiamond is uniformly reduced from 11 to 1.7 nm under different treatment durations. It is found that nanodiamonds of a size between 2.1 and 4 nm contain fewer than three emitters. Size dependence of microstructure and pho- toluminescence suggests that SiV centres exist in the outer shell of nanodiamonds with diameter larger than ~2 nm. This material has significant applications in nanophotonics platform, quantum communi- cations and quantum photonics