A theoretical investigation was made of multiphonon effects upon the optical emission spectra of the negatively charged nitrogen-vacancy (NV−) center in diamond and find that the fluorescence emission spectra described by the single frequency model agree quite well with the experimental data. From a comparison between the present theory and the experimental results, a reduction of the anti-Stokes shift of the emission spectra at high temperature was also found. This was contradictory to the linear hole-phonon interaction model. This contradiction was resolved by adding the quadratic hole-phonon interaction to the model. The theoretical analyses show that this may reduce the lattice relaxation energy. As a consequence, fewer phonons were emitted in the optical transition, therefore explaining the reduction of the anti-Stokes shift at high temperature.

Multiphonon Effects on the Optical Emission Spectra of the Nitrogen-Vacancy Center in Diamond at Different Temperatures. W.L.Ma, S.S.Li: Journal of Applied Physics, 2012, 111[6], 063519