3. Results and discussion
3.1. Characterization of the MPA-capped Mn-doped ZnS QDs
The size of MPA-capped Mn-doped ZnS QDs was tested to be
about 3.5 nm (Fig. 2a) by TEM. The maximum excitation peak
occurred at 295 nm and the narrow emission band was centered
at 595 nm: hv1 is the fluorescence occurred from the surface defect
of ZnS QDs while hv2 is the phosphorescence attributed to the transition
of Mn2+ from the triplet state (4
T1) to the ground state (6
A1)
(Fig. 2b). As reported, Mn-doped ZnS QDs exhibited an orange
phosphorescence emission (about 595 nm) [33], which is attributed
to the energy transferred from the band gap of ZnS to Mn2+
dopant and subsequent 4
T1 to 6
A1 transition of the Mn2+ incorporated
into the ZnS host lattice [34].