1. C. Poole, The Technique of EPR Spectroscopy (Mir, Moscow, 1970), 557 pp. [Russian translation]
2. J. Taner, B. Rampton, Hypersound in Solid State Physics (Mir, Moscow, 1975), 453 pp. [Russian translation]
3. A.F. Dite, V.I. Revenko, V.B. Timofeev, Fiz. Tverd. Tela 16(7), 1953–1957 (1974)
4. I.I. Geru, Low Frequency Resonance of Excitons and Impurity Centers (Stiinta, Chisinau, 1976), 194 pp.
5. H. Haken, H. Sauermann, Z. Phys. 176(1), 47–62 (1963)