Diamond is a purely covalent crystal possessing, consequently, no dipole moment. Due to this the ideal diamond lattice does not absorb light in the one-phonon spectral region. The intrinsic absorption of perfect diamonds is observed only in two- and three-phonon regions: that is, in the spectral region spreading from single to triple Raman frequencies (1332 to about 4000 cm−1) (Bokii et al. 1986; Davies 1994a; Koidl and Klages 1992; Willingham et al. 1991; Klein et al. 1992; Hardy and Smith 1961; Charette 1966; Kluev 1971; Kluev et al. 1972a). This absorption is about two orders of magnitude weaker than that in the one-phonon bands of the ionically bonded crystals. A weak one-phonon absorption caused by lattice defects is also usually seen in most diamonds. Vibronic spectroscopy of diamond is performed using mostly IRA and IRE methods.
KeywordsNeutron Irradiation Diamond Film Spectral Position Natural Diamond Synthetic Diamond
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