Theory of Resonant Secondary Radiation due to Impurity Centres in Crystals

The resonant secondary radiation spectrum of impurity centres in crystals is studied on the basis of a second‐order approximation for the interaction between the electromagnetic field and the material. It is shown that for the case of excitation in the phonon wing of the absorption band, the main part of the secondary radiation represents the ordinary luminescence. The spectrum also contains Rayleigh and Raman scattering which is considerably weaker (by about four orders of magnitude). Formulas are obtained for the intensities of Rayleigh‐ and Raman scattering; particular consideration is made for the case of large Stokes' losses. It is also shown that excitation in the region of the pure‐electronic line yields a spectrum consisting of the Rayleigh and the pure‐electronic line, and the phonon wing of the luminescence.