Efficient Photoluminescence of Mn²⁺ Ions in MnS/ZnS Core/Shell Quantum Dots

Abstract

We have studied the mechanism of photoluminescence (PL) from MnS/ZnS core/shell quantum dots (QDs) synthesized via hot solution phase chemistry using a nucleation-doping strategy. Efficient PL of the Mn 2+ ions with a quantum yield (QY) of over 35% is demonstrated in the resulting QDs coated with a thick ZnS shell on the MnS core. The MnS/ZnS core/shell QDs with a thick shell exhibit PL enhancement with increasing temperature in the range between 140 and 300 K, resulting from the thermal activation of charge carriers localized at the interface between the MnS core and the ZnS shell. The PL decays of the Mn 2+ ions in the core/shell QDs consist of three exponential components with time constants on the scales of 1-2 ms, hundreds of µs, and tens of µs. Surprisingly, the PL lifetimes of Mn 2+ ions show a very weak dependence on the shell thickness, which is clearly different from that of the PL QY of the QDs. The experimental results indicate that the mechanism for improving the PL QY in MnS/ZnS QDs can be understood in terms of a significantly enhanced energy transfer from the ZnS shell to Mn 2+ ions and a slightly decreased nonradiative relaxation rate from Mn 2+ ions to surface states/traps of the ZnS shell by the surface passivation of the QDs with a thick ZnS shell.

Au:CdHgTe quantum dots for in vivo tumor-targeted multispectral fluorescence imaging

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