Fig. 2: Electron-phonon coupling in fluorescence.

a Fluorescence spectra (π-polarization) at various temperatures. The shadow region is the phonon-triggered emission window. A similar σ-polarization emission is plotted in Fig. S2. b Emission cross sections in 1140–1240 nm window. The fluorescence lifetimes of various emission are fitted in Supplementary Fig. S3-S4. c Configuration coordinate model. The forced electronic transition by phonon is represented by the orange arrow, the horizontal dashed lines represent the phonon states, and the vibrational wave functions were plotted as shadow area in the case of quasi-harmonic oscillators. d The emission cross-section at 1176 nm and the calculated Huang-Rhys S factors at various temperatures.