Photoluminescence and absorption mechanisms in Eu monochalcogenides

Photoluminescence mechanism in Eu monochalcogenides is investigated in deta il to be consistent with various experimental results including absorption mechanism due to 4f-5d magnetic exciton with a large amplitude of 5d electr on at the central site. A new screening effect due to p-d and p-f mixing wa s particularly studied in detail, even though an actual numerical calculati on is difficult. In the luminescence, a rich variety of relaxation mechanis ms is shown by introducing a new Kondo-type screening, and the magnetic pol aron state trapped by a 4f hole at the central site with an amplitude of mo re than 30% is shown to explain various experimental results consistently e ven though the energy difference with the delocalized 5d electron is expect ed to be small. (C) 1999 Elsevier Science B.V. All rights reserved.