Fig. 2: Fluorescence spectra of single terrylene molecules and the effects of temperature.

a Emission spectra of a single terrylene molecule around 582 nm, taken at two temperatures, 2 K (blue) and 77 K (black). All spectra have been normalized to unity relative to the intensity of the 0-0 zero-phonon line (ZPL). b Linewidth of the 0-0 ZPL of a single terrylene molecule (not the one shown in (a)) on annealed hBN (750 °C for 12 h). The linewidth was fitted to the equation in inset, where \({\Gamma }_{{TLS}}\) scales linearly with temperature and \({\Gamma }_{{LFM}}\) is given by the Arrhenius law, described in the main text. The linewidth at the lowest temperature was limited by the spectrometer resolution (1.7 ± 0.1 cm⁻¹). Some spectra of this molecule can be found in Supplementary Notes 3. c Zoomed-in version of the spectrum at 2 K in (a) with vibrational peaks annotated by their energy in cm⁻¹. The part of the spectrum after 400 cm⁻¹ has been magnified by a factor 4. d Details of a spectrum of a molecule with 0-0 ZPL located at 602 nm. Note that the vibronic lines are quite weak compared to those in the spectrum of (c) requiring for visibility a magnification factor of 10 for the part after 400 cm⁻¹. The Debye-Waller factors, which are known as the intensity of the 0-0 ZPL with respect to the combined intensity of the 0-0 zero-phonon line (ZPL, red area) and the phonon sideband (PSB, purple area), thereby excluding intramolecular vibrational peaks, are around 0.7 ± 0.1 for the molecule at 582 nm and 0.8 ± 0.1 for the molecule at 602 nm. The peak around 19 cm⁻¹ in (d) was included in the phonon sideband.