where γ 0 is the anharmonic coefficient of the phonon mode which is related to λ , the optical phonon -acoustic phonon coupling matrix, in Eq. 1. Γ 0 is a temperature independent dephasing rate and as discussed by Němec , it represents the scattering of phonons by defects in the lattice , apart from the pure intrinsic dephasing. Such an analysis is not possible, unfortunately, for mode M1 due to its temperature independent behaviour and diminished anharmonic nature.