Abstract
Piezoabsorption and Zeeman measurements of the 9934 cm-1 line in GaP:Ni have identified this line as a zero-phonon line of the 3T1(F) to 3T1(P) transition within a Ni(3d8) substitutional at a gallium site. Obtained splittings, polarisation and intensities of optical transitions are consistent with a model of isolated Ni(3d8) centre suffering tetragonal Jahn-Teller distortion in the 3Ti(P) state. It is shown that the epsilon -mode Jahn-Teller effect in the 3T1(P) state is the dynamical regime, close to the static one.