Periodic solutions and locking-in on the periodic surface

Periodic solutions (on the torus) are studied for the differential equation on the torus θ' = 1 + ge6(t/T), θ, T, ?). This equation, for example, governs solutions on the periodic surface for a periodically perturbed autonomous system. The set of all points in a horizontal strip of the T — ? plane containing ? = 0 for which the equation has periodic solutions are characterized, and the characterization is shown to be best possible. Locking-in is also discussed.     

New high-energy luminescence bands from Co2+ in ZnSe

Three sharp absorption features in the energy range 2.36–2.55 eV have been detected in the transmission spectrum of Co-diffused ZnSe, and a number of luminescence transitions originating from the lowest of these states at 2.361 eV have been observed. Photoluminescence excitation spectra prove that these are high energy excited states of the Co²⁺_Zn impurity, a conclusion confirmed by comparison of measured and predicted luminescence energies. This represents the first identification of luminescence branching from a higher excited state of a transition metal ion in any semiconductor. The sharp, weakly phonon-coupled transitions involve either intra-impurity excitation or transitions from the impurity to localised states split off from a minimum in the conduction band. The implications of these observations for the mechanism of host-impurity energy transfer and for the nature of the excited state wavefunctions are discussed.