Near infrared absorption and emission spectra due to the transitions ZT,of the Cu2+ ion in cubic ZnS have been measured a t 4K. The distinct vibronic sidebands of the absorption spectrum exactly correspond to various critical point energies of TA, TO, and LO lattice modes, whereas the structure of the luminescence spectrum cannot be interpreted in terms of lattice phonon satellites. A dynamic Jahn-Teller interaction in the ,T2 ground state being in the same order of magnitude as static lattice spin-orbit splitting and phonon energy is shown to produce this deviation from the mirror symmetry. Weak and strong coupling approximations in the cluster limit have been extended t o include vibronic states with up to six E-modes.Absorptions-und Emissions-Spektren im nahen Infrarot hervorgerufen , durch die Ubergange 2T, -,E des Cu2+ in kubischem ZnS, wurden bei 4 K aufgenommen. Die ausgepragten vibronischen Seitenbanden des Absorptionsspektrums entsprechen exakt den Energien verschiedener kritischer Punkte der TA-, TO-und LO-Gittermoden, wahrend das Emissionsspektrum nicht durch Phononenenergien des ungestorten Gitters zu erklaren ist. Es wird gezeigt, da13 eine dynamische Jahn-Teller-Wechselwirkung im 2T,-Grundzustand von der GroBenordnung der statischen Spin-Bahn-Aufspaltung und Phononenenergie diese Abweichung von der Spiegelsymmetrie hervorruft. Die Naherungen schwacher und starker Kopplung im Cluster-Mode11 werden auf vibronische Zustande mit bis zu sechs E-Moden ausgedehnt.
The copper defect is that transition-metal impurity in II-VI compounds for which the most complete set of information has been compiled so far experimentally and theoretically. This makes it a favored system to study the mechanisms determining the optical spectra. The interpretation of the observed Cu 2ϩ transitions in ZnS and CdS crystals is made using a coupling of the electronic states to a local vibrational mode of E symmetry and a moderate Jahn-Teller effect with a Huang-Rhys factor of Sϭ0.8 for ZnS and Sϭ1.1 for CdS. We report on parameter-free calculations of the magnetic-field splitting of Cu 2ϩ centers in II-VI compounds, which show a general agreement with the observed spectra. For ZnS:Cu 2ϩ the calculated g factors agree with the observed values, though a stronger nonlinear behavior with respect to the magnetic field had been found for some of the calculated energy levels. For CdS:Cu 2ϩ the nonlinear behavior of the magnetic-field splitting is also reproduced by the calculation and the g factors agree for the 2 E excited-state doublets, whereas there are some differences for the g factors of the 2 T 2 ground-state doublets, which are due to the neglect of the T 2 mode coupling in the Jahn-Teller calculation.
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