Abstract
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.
Highlights
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
One area of particular promise are light-emitting defects in hexagonal boron nitride, which show bright emission of single photons with narrow PL line widths compared to other single photon emitters in solids[3,4] and Fourier transformlimited photoluminescence of excitation (PLE) line widths, even at room temperature,[5] and with a low degree of emission into phonon-mediated modes.[6,7] hBN’s graphene-like two-dimensional structure allows straightforward incorporation into photonic devices,[8−10] and means that defects are always close to the device surface, which is desirable for the development of quantum sensors.[11,12]
The issue is complicated by numerous candidate defects with similar zero-phonon line (ZPL) energies, motivating a search for additional spectroscopic signatures in optically detected magnetic resonance (ODMR),[13,14] or in the phonon sidebands.[15−18] For emitters at 2.0−2.2 eV, the strongest case to date has been made for a carbon-related defect.[19]
Summary
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. In STED an emitter is excited with two lasers with photon energies above and below the zero phonon line. STED and PLE probe the vibronic manifold of the radiative ground and excited states, respectively.
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