Effect of Negative Thermal Expansion on the Zero-Phonon Line of Implanted Silicon Vacancy Color Centers in Diamond

The charged silicon vacancy (SiV^-) color center in diamond can be created by focused ion beam (FIB) implantation, allowing deterministic creation of single photon emitters. Here, we create FIB-implanted SiV^- color centers in a diamond substrate spanning 8 orders of magnitude of the ion beam fluence. We show that the SiV^- zero-phonon line (ZPL) brightness at 4 K is constant with increasing ion beam fluence, while exhibiting slight inhomogeneous broadening. The temperature-dependent ZPL line shift revealed a blue-shift below 70 K that we attribute to the negative thermal expansion of diamond, showing the SiV^- ability as a sensitive probe of its host crystal environment. We demonstrate a versatile line shift model constructed on the basis of the Grüneisen parameter description of the thermal expansion coefficient and the electron-phonon interaction.