Zeeman spectroscopy of crystal-field transitions of Co-doped InP

The 474.0 meV and 785.8 meV crystal-field transitions of Co I 2 n + in InP observed in photoluminescence (PL) and optical absorption respectively are studied in magnetic fields of up to 10 T. The 474.0 meV PL line is shown to arise from a Gamma 8 - Gamma 8 transition in T d symmetry between the lowest spin-orbit state ( Gamma 8 ) of the 4 T 2 (F) level of Co I 2 n + and the spin-only Gamma 8 ( 4 A 2 (F)) ground state. The anisotropic g-values of the excited state, g 1 and g 2 , are 5.48+or-0.2 and -2.98+or-0.15 respectively. An isotropic g-value of 2.14+or-0.05 is obtained for the ground state, in agreement with the results of electron spin resonance on Co I 2 n + . The Zeeman pattern of the 785.8 meV absorption line shows a marked trigonal (C 3v ) symmetry due to Jahn-Teller (JT) coupling to T 2 distortion modes in the excited state. The Zeeman data are shown to be consistent with the behaviour expected from the 4 A 2 (F) to 4 T 1 (F) transition of Co I 2 n + , the 4 T 1 (F) state undergoing an almost static JT distortion. Anticrossings in the anisotropy plot of the Zeeman pattern are observed at the main symmetry directions. This cannot be explained on a model of static C 3v trigonal complexes, and is attributed to tunnelling between the magnetically equivalent distortion directions. Analysis of the Zeeman data gives g mod mod =0.96+or-0.05 and g perpendicular to =3.76+or-0.05 for the 4 T 1 (F) excited state and g=2.10+or-0.10 for the 4 A 2 (F) ground state.