Luminescence decay kinetics ofMn2+-doped ZnS nanoclusters grown in reverse micelles

We report the synthesis and luminescence decay kinetics of 1.2-nm ${\mathrm{Mn}}^{2+}$-doped ZnS nanoclusters grown in reverse micelles. The preparation method produces small particles with narrow-size distribution and fluorescence bands near 400–450 nm and 585 nm. Time-dependent fluorescence decay measurements using picosecond, nanosecond, and millisecond techniques reveal relaxation processes on all three time scales. In the doped sample, the red emission detected at 600 nm exhibits a 1–2 ms decay in addition to faster decays with time constants on the order of hundreds of ps, a few ns and tens of μs. While the slow decay is the same as that of bulk ${\mathrm{Mn}}^{2+}$-doped ZnS, the fast decays are present for both doped and undoped samples and are unique to nanocluster ZnS, which are attributed to deep trap-state emission. The blue luminescence near 400–450 nm is attributed to shallow trap-state emission of ZnS. These results help to resolve the controversy in the literature regarding the lifetime of the ${\mathrm{Mn}}^{2+}$ emission in Mn-doped ZnS nanoparticles.