Differences in Mn content in the central
rod can act as nucleation sites for the secondary structures. After
this nucleation process, the nanoplates start to growth, almost Mn
free. In fact, CL spectra and images performed on the nanoplates
(not shown here) show a decrease in Mn related luminescence band
which agrees with this assumption. The CL images do not show the
presence of the spinel phase detected in the CL spectra. A possible
reason is that this phase is dispersed in regions with sizes below
the resolution of the CL technique.