ELECTRONIC RAMAN AND INFRARED-SPECTRA OF ACCEPTORS IN ISOTOPICALLY CONTROLLED DIAMONDS

The Lyman spectrum of substitutional boron accepters in diamonds with natural composition and that in a C-13 diamond exhibit remarkably simi lar features, but shifted to higher energies in the latter by 0.4-1.5 meV. Additional lines appear when the spectra are recorded as a functi on of temperature, indicating the thermal population of a level Delta' similar to 2 meV above the ground state; this can be interpreted as th e spin-orbit splitting of the Is acceptor ground state into 1s(p(3/2)) and Is(p(1/2)), the latter located Delta' above the former. The Raman -allowed 1s(p(3/2))--> 1s(p(1/2)) electronic transition is directly ob served at 2.07(1) and 2.01(1) meV in the Raman spectrum of natural and C-13 diamond, respectively. Polarization features of the Delta' Raman line reveal that it is predominantly Gamma(5) in character, as predic ted by a theoretical calculation formulated in terms of the known valu es of Luttinger parameters. The theoretical expression for the Raman c ross section for Delta' enables the acceptor concentration to be deduc ed from an intercomparison of the intensity of the Delta' line and tha t of the zone-center optical phonon. The presence of boron accepters p roduces a quasicontinuous absorption spectrum in the range of the opti cal phonon branch, flanked by a sharp feature at the zone-center optic al phonon frequency; their appearance can be attributed to the partial breakdown of the translational symmetry and the activation of otherwi se inactive vibrations.