Stimulated emission depletion spectroscopy of color centers in hexagonal boron nitride

We demonstrate the use of Stimulated Emission Depletion (STED) spectroscopy to map the electron-optical-phonon sideband of the ground state of the radiative transition of color centers in hexagonal boron nitride emitting at 2.0–2.2 eV, with in-plane linear polarization. The measurements are compared to photoluminescence of excitation (PLE) spectra that maps the electron-optical-phonon sideband of the excited state. The main qualitative difference is a red-shift in the longitudinal optical phonon peak associated with E1u symmetry at the zone center. We compare our results to theoretical work on different defect species in hBN and find they are consistent with a carbon-based defect.