Fig. 4: Coupling to two-level systems and the effects of annealing on emitter stability.

a A 0-0 zero-phonon line (ZPL) of a terrylene molecule in the main site followed for 20 min on an hBN flake that was annealed at 750 °C for 12 h, excited by a vibronic transition with 532 nm light. The excitation intensity is raised after each frame of 200 s. The associated power densities, relative to the initial intensity \({I}_{0}\), are shown in (b), together with the number of spectral jumps that are observed in the 200 s time window and the integrated intensity of the 0-0 ZPL for a period of 1 s. Without annealing, the spectral time trace typically exhibits complex spectral diffusion as shown for example in (c). Initially, the molecule wanders around a relatively small spectral region, but extends over a much wider region from about 70 s. After annealing, the amplitude of spectral diffusion is typically strongly reduced, as in (d), even though the laser power is doubled at each 100 s interval. Some molecules do not show any spectral diffusion on the scale resolved by the spectrometer, as is the case for the leftmost molecule in (e). The spectra in (c) are measured on a different sample than the spectra in (d, e). More examples of spectral traces can be found in Supplementary Fig. 18.