Abstract
Transients of Mn internal 3d5 luminescence in ZnS/Mn nanowires are strongly non-exponential. This non-exponential decay arises from an excitation transfer from the Mn ions to so-called killer centers, i.e., non-radiative defects in the nanostructures and is strongly related to the interplay of the characteristic length scales of the sample such as the spatial extensions, the distance between killer centers, and the distance between Mn ions. The transients of the Mn-related luminescence can be quantitatively described on the basis of a modified Förster model accounting for reduced dimensionality. Here, we confirm this modified Förster model by varying the number of killer centers systematically. Additional defects were introduced into the ZnS/Mn nanowire samples by irradiation with neon ions and by varying the Mn implantation or the annealing temperature. The temporal behavior of the internal Mn2+ (3d5) luminescence is recorded on a time scale covering almost four orders of magnitude. A correlation between defect concentration and decay behavior of the internal Mn2+ (3d5) luminescence is established and the energy transfer processes in the system of localized Mn ions and the killer centers within ZnS/Mn nanostructures is confirmed. If the excitation transfer between Mn ions and killer centers as well as migration effects between Mn ions are accounted for, and the correct effective dimensionality of the system is used in the model, one is able to describe the decay curves of ZnS/Mn nanostructures in the entire time window.
Highlights
In semiconductor systems, many processes, such as energy transfer processes, will be modified in nanostructures with respect to bulk semiconductors because of geometric restrictions
The Mn concentration of this sample is 2.8·10-3 at.%, which corresponds to a large mean distance between Mn ions of about 11.4 nm, with a low resonant energy transfer effect between the Mn atoms
In the case of bulk ZnS/Mn samples with low Mn content, the transients of the internal Mn PL can be well described by the so-called Förster model [5] and its extension [10] based on dipole-dipole interaction between Mn ions and defect-related killer centers
Summary
Many processes, such as energy transfer processes, will be modified in nanostructures with respect to bulk semiconductors because of geometric restrictions. By considering excitation transfer between Mn ions and killer centers as well as migration effects between Mn ions and using the correct dimensionality, we were able to describe the size and concentration dependence of the decay curves of ZnS/Mn nanostructures, such as wires and ribbons, from a few microseconds to several milliseconds [6].
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