Fig. 1. Spectral superresolution reveals chemical states of hBN surface defects.

(A) Spectral SMLM setup with an hBN crystal in contact with the solvent. Colored dots represent photoluminescence signal emanating from single defects at the surface of the flake. The inset shows the chemical structure of pristine hBN flake (boron in blue and nitrogen in green). The photoluminescence signal emitted from the flake’s surface is split into spatial (i) and spectral (ii) channels. In the spatial channel (i), emission from individual defects leads to diffraction-limited spots (highlighted by red boxes), localized with subpixel nanometric accuracy. In the spectral channel (ii) vertical dispersion by a prism allows the simultaneous measurement of the spectra of these individual emitters (highlighted by colored vertical lines). (B and C) Ensemble emission spectrum of hBN defects in contact with (B) water and (C) dodecane, showing two main emission lines with λ_A ≈ 585 nm (2.08 eV) and λ_B ≈ 630 nm (1.97 eV), respectively. Representative spectra from individual emitters are shown in the inset. In (B), emission λ_A is due to the protonation-induced transition between non-emissive deprotonated defect $V_{\mathrm{B}}^{-}$ and emissive protonated defect V_BH, with excited state V_BH^*. In the excited state, V_BH^* can either relax radiatively to its ground state (green arrow) or undergo excited state proton transfer and relax back to $V_{\mathrm{B}}^{-}$ (black arrow). a.u., arbitrary units. In (C), emission λ_B is due to interaction of the apolar hydrophobic alkyl group (─CH₃) with defect D₂ (see the Supplementary Materials). Defect zero-phonon line is around 630 nm, and the second peak visible around 670 nm corresponds to the phonon sideband.