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Optical phonons in SiO2 samples prepared by the sol‐gel method and colored by doping with Fe and Cu were studied using X‐ray diffraction, electron spin resonance and infrared spectroscopy. The vibration modes in pure and Cu‐ or Fe‐doped glasses are investigated as a function of doping concentration and annealing temperature. It is found that the heat treatments in air atmosphere have a remarkable influence on the width of the stretching absorption bands related to the asymmetric vibrations in the SiO2 matrix. A simple description of the different types of vibration modes in the quasilinear Si–O–Si chain is given and correlated with the characteristics of the phonon bands observed. A relation between the bandwidth of these modes and the change in the phonon scattering rate caused by the Cu or Fe doping is established. Based on this model, the percentage of Cu incorporated on the Si sites into SiO2 matrix was calculated. The behavior of the vibration spectra in Fe‐doped glasses is different and it indicates less incorporation of this element into the SiO2 matrix.

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