Nonlocal optical recombination of molecular-like defects in hexagonal boron nitride

BySarah Ross

Gabriele Grosso
City University of New York, Advanced Science Research Center – New York, New York, USA
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Hexagonal boron nitride (hBN) has emerged as a promising material for quantum photonics due to its ability to host single-photon emitters (SPEs) that operate at room temperature with high brightness and stability [1,2]. Emitters in hBN exhibit significant variability in their photophysical properties, including a broad spectral distribution, varying radiative lifetimes, polarization, and spin structures [3]. Despite extensive studies, the microscopic origins of most emitters remain unclear, limiting the full characterization of their emission mechanisms and hindering their integration into quantum technologies.

In this work, we present recent advances achieved through the combination of resonant inelastic X-ray scattering (RIXS) and photoluminescence (PL) spectroscopy, providing newinsights into the fundamental electronic excitations governing SPEs in hBN. Our RIXS measurements reveal an elementary excitation at 285 meV in defective hBN, which gives rise to a sequence of harmonics that correlate with the emission energies of quantum emitters [4]. These excitations are linked to nitrogen ?* anti-bonding orbitals and exhibit a well-defined harmonic series resembling the vibronic structure of N2 molecules.

Complementary PL spectroscopy at cryogenic temperatures on the same samples further confirms the presence of multiple SPE peaks. By analyzing the PL spectra with a model that includes nonlocal recombination processes [5], similar to donor–acceptor pairs (DAP), we uncover a direct correlation between PL emission energies and the harmonics observed with RIXS. This result demonstrates the presence of a common mechanism underlying SPEs with different spectral properties in hBN, arising from the combination of harmonics at the N-?* orbitals with their nonlocal recombination across different lattice sites.

Furthermore, the analysis of spectral instabilities confirms that the emission properties of these SPEs are governed by recombination processes that occur through the formation and breaking of defect pairs with large dipole moments. We associate the discrete spectral jumps in emission energy, which are frequently observed in hBN emitters, with the dynamic formation of defect pairs arising from interactions among harmonic states of nitrogen ? orbitals in delocalized defective sites [6]. These findings establish a fundamental link between single-photon emission and elementary excitations in hBN, offering a predictive model for spectral instabilities and emission tuning.

  1. Tran, T. T., et.al., Nat. Nanotechnol. 11, 37–41 (2016)
  2. Grosso, G. et al. Nat. Commun. 8, 705 (2017)
  3. Tran, T. T., et.al., ACS Nano 10, 7331 (2016)
  4. Pelliciari, J., et al. Nat. Mater. 23, 1230 (2024)
  5. Mejia, E., et al. Opt. Mater. Express 14, 2122 (2024)
  6. Mejia, E., et al. J. Phys. Chem. C (2025), 10.1021/acs.jpcc.4c07147

Email: ggrosso@gc.cuny.edu

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