OPTICAL-TRANSITIONS IN ZN1-XCOXSE AND ZN1-XFEXSE - STRONG CONCENTRATION-DEPENDENT EFFECTIVE P-D EXCHANGE

Results of photoluminescence (PL) and resonant Raman scattering from s ingle crystalline epitaxial films of Zn1-xCoxSe and Zn1-xFexSe are pre sented. Samples with Co concentrations up to x = 0.1 and Fe concentrat ions in the range 0 < x < 0.75 were studied. For x < 0.03 (Co) and x < 0.30 (Fe) the optical emission associated with the 3d deep levels are observed as discrete transitions that broaden very rapidly and weaken as the doping further increases. It is proposed that the increase in concentration x leads to an increase in the exchange between low-lying crystal-field split d levels and band electrons, and thus to the chan ges in the photoluminescence. Concomitant with the onset of broadening of the PL, a continuum of Raman excitations extending from zero to ab out 4000 cm-1 is observed which is resonantly enhanced as the energy o f the exciting radiation approaches the alloy band gap from below. The Raman-scattering features are discussed in terms of electronic scatte ring within the 3d-ion band manifold located in the gap of the insulat ing host. The role of strong disorder and correlations on the electron ic Raman excitations in these insulating structures are briefly addres sed.