Vibronic Absorption

Abstract

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.