In general, regarding the spectroscopy, let us consider the words by Orazio Svelto, 1970, about the homogeneous broadening of the photon emission. In the case that we have a dipole damped oscillator model, we can observe the spectral line of the spontaneous emission with a "natural" or "intrinsic" broadening. This homogeneous broadening produces a line profile described by a Lorentzian function. Orazio Svelto is also mentioning the photon-phonon interaction as generating homogeneous broadening and therefore a Lorentzian line shape too. An inhomogeneous broadening (such as those caused by the Doppler effect and thermal effect) is giving a Gaussian line shape. However, the most observed case is that of an intermediate profile, given by the convolution of the resonance relative probability and the broadening function, because natural band can be modified by different mechanisms .