Interplay between Jahn-Teller coupling and axial crystal fields: GaP :(Cr,S)

We investigate the intracenter transitions T-5(2)(D) --> E-5(D) of negative ly charged chromium Cr2+(3d(4)) in GaP. The effect of uniaxial stress on th e zero-phonon-absorption lines helps to identify the transitions and emphas izes the importance of the Jahn-Teller coupling of the D-5 states. In GaP c odoped with chromium and sulfur a new spectrum is observed. The stress resp onse of the corresponding optical center evidences trigonal symmetry C-3v W e identify the center with the (Cr2+ - S) pair on substitutional next-neigh bor sites. The trigonal crystal field strongly quenches the Jahn-Teller cou pling inherent in isolated GaP:Cr2+. (C) 1999 Elsevier Science B.V. All rig hts reserved.