Manganese-doped zinc sulfide quantum dots (QDs) were synthesized by chemical precipitation in an aqueous solution in the presence of glutathione as the capping agent. Obtained samples show dual emission band with maximums at 2.11 eV (Mn2+) and about 3.1 eV (intrinsic defects of ZnS QDs ). A large number of radiation centers in QDs promotes strong dependence of electron transfer process in QD on its surface state. That makes QDs very attractive for implementation in luminescent sensors based on electron transfer from QD to the analyte molecule. If the QD is close to the molecule, which lowest unoccupied molecular orbital has lower energy than conduction band edge of the QD, a photoinduced electron transfer from the QD to the electron acceptor occurs. As a result, the luminescence of the QD is consequently quenched.
In order to examine the efficiency of luminescent sensor response of proposed ZnS:Mn2+ QDs, methane as the analyte had been chosen. Under exposure to relatively low methane concentration, the ZnS:Mn2+ Photoluminescence (PL) spectrum is changed significantly. Bubbling of 100 ppm of methane through the QD solution leads to the 30 % rising of VS and IZn related emission bands and a negligible (up to 5 %) intensity increasing of DSurf and Mn2+ emission bands. Moreover, the IZn related PL band is shifted from 3.11 eV to 3.15 eV. Taking into account that the organic shell is bonded with QD surface through zinc ions, it can be suggested that observed PL spectrum changings are related to methane sorption by organic shell determining the QD electron transfer. To the best of our knowledge, this is the first time wherein ZnS QDs (as well as another sulfide QDs) is used for luminescent methane detection.
This study was supported by Russian Science Foundation (project No. 14-50-00034)
S. Joicy, R. Saravanan, D. Prabhu, et al., Mn2+ ion influenced optical and photocatalytic behaviour of Mn–ZnS quantum dots prepared by a microwave assisted technique // RSC Advances.-2014. 4. -№. 84. -P. 44592-44599.