The emission centered at 2.5 eV is the well known green band
of ZnO which has been related to the existence of different native
defects in the material such as zinc interstitials [20] or oxygen
vacancies [21]. In our Mn doped samples this band only appears as
a shoulder in the spectra indicating a small concentration of such
defects in the structures. This low intensity is consistent with the
fact that by adding MnCO3 we introduce an excess of oxygen which
could partially fill the vacancies causing a decrease in the intensity
of the green component. Introduction of Mn into ZnO has been
reported to induce the opposite effect and an intense green band
has been found in Mn doped nanowires and nanorods [1,3]. This shows that the intensity of the band depends on the experimental
doping conditions.