Significant attention has been recently focused on the realization of high precision nano-thermometry using the spin-resonance temperature shift of the negatively charged nitrogen-vacancy (NV-) center in diamond. However, the precise physical origins
of the temperature shift is yet to be understood. Here, the shifts of the centers optical and spin resonances are observed and a model is developed that identifies the origin of each shift to be a combination of thermal expansion and electron-phonon interactions. Our results provide new insight into the centers vibronic properties and reveal implications for NV- thermometry.
