SiV⁰ centres in diamond: effect of isotopic substitution in carbon and silicon

The neutrally charged silicon-vacancy defect (SiV0) is a colour centre in diamond with spin S = 1, a zero-phonon line (ZPL) at 946 nm and long spin coherence, which makes it a promising candidate for quantum network applications. For the proper performance of such colour centres, all of them must have identical optical characteristics. However, in practice, there are factors that influence each individual centre. One of these factors is non-uniform isotope composition for both carbon atoms in diamond lattice and silicon atoms of dopant. In this work, we studied the isotopic shifts of SiV0 centres for CVD-grown epitaxial layers of isotopically enriched C-12 and C-13 diamonds, as well as for diamond with natural isotope composition but doped only with one isotope of Si (Si-28, Si-29 and Si-30). The detected shift was 1.60 meV for C-12/C-13 couple and 0.33 meV for Si-28/Si-29 and Si-29/Si-30 couples, which are close to the previously obtained values of the isotopic shift for the negatively charged silicon vacancy (SiV-), which indicates a similar model of interaction with the environment for these two charge states of the SiV colour centres.