The most intense components 1.8 eV and 2.37 eV are both
related to the presence of Mn in the structures. In particular, emission
close to the observed 1.8 eV band has been previously observed
in Mn doped ZnO. A broad low energy photoluminescence band in
the approximate range 1.8–2 eV has been reported in Mn doped
ZnO ceramics [22]. Guo et al. [6] also observed a red photoluminescence
band at about 1.98 eV in colloidal Mn doped ZnO nanorods
and attributed it to intraionic transitions in Mn2+ ions. The 2.37 eV
band has been reported before in ZnO:Mn sintered ceramics [23].