Unveiling the high quantum efficiency of single silicon-vacancy centers through dielectric tuning of their local environment

We use a simple and effective experimental method for determining the radiative quantum yield of single silicon-vacancy centers (SiV) in nanometric-sized diamonds (NDs). It is based on variations in the luminescence lifetimes of SiVs induced by a controlled change in the NDs' dielectric environment. The deposition of a high refractive index immersion oil on a thin polymer sample containing NDs with an average size of 20 nm induces a noticeable shortening of SiV lifetimes, a clear signature of a strong radiative contribution to the decays. While SiV centers were generally considered to be weak quantum emitters, we demonstrate that single SiV centers in nanodiamonds have a quantum efficiency up to 60%, under ambient conditions. This quantum efficiency is very similar to that of the negatively charged nitrogen-vacancy centers, which we measured using the same approach. This feature makes single SiV attractive as bright, high-purity single-photon sources for quantum technologies.