OPTICAL-TRANSITIONS IN (ZNCO)SE AND (ZNFE)SE - ROLE OF AN EFFECTIVE P-D EXCHANGE

In this paper we discuss photoluminescence (PL) and Raman excitations in the diluted magnetic semiconductors Zn1-xCoxSe and Zn1-xFexSe. The PL spectra associated with isolated crystal field d levels are found t o rapidly weaken and/or broaden as the transition metal ion concentrat ion approaches and increases beyond a critical value. In addition a Ra man continuum, that overlaps with the optical phonon, is observed to d evelop when the PL features are modified. In the corresponding Zn1-xCo xSe samples the optical phonons acquire a characteristic Fano line sha pe suggestive of its coupling to the Raman continuum. It is proposed t hat these changes to the optical transitions arise from the enhancemen t of an effective p-d hybridization between low-lying d levels and ban d electrons with increasing x-an effect largely due to the proximity o f the Co2+ and Fe2+ crystal field ground levels to the valence band ma ximum.