Origin and chemical composition of the amorphous material from the intergrain pores of self-assembled cubic ZnS:Mn nanocrystals

Publication date: 31 December 2017
Source:Applied Surface Science, Volume 426
Author(s): Mariana Stefan, Ioana Dorina Vlaicu, Leona Cristina Nistor, Daniela Ghica, Sergiu Vasile Nistor
We have shown in previous investigations that the low temperature collective magnetism observed in mesoporous cubic ZnS:Mn nanocrystalline powders prepared by colloidal synthesis, with nominal doping concentrations above 0.2 at.%, is due to the formation of Mn²⁺ clusters with distributed antiferromagnetic coupling localized in an amorphous phase found between the cubic ZnS:Mn nanocrystals. Here we investigate the composition, origin and thermal annealing behavior of this amorphous phase in such a mesoporous ZnS:Mn sample doped with 5 at.% Mn nominal concentration. Correlated analytical transmission electron microscopy, multifrequency electron paramagnetic resonance and Fourier transform infrared spectroscopy data show that the amorphous nanomaterial consists of unreacted precursor hydrated zinc and manganese acetates trapped inside the pores and on the surface of the cubic ZnS nanocrystals. The decomposition of the acetates under isochronal annealing up to 270°C, where the mesoporous structure is still preserved, lead to changes in the nature and strength of the magnetic interactions between the aggregated Mn²⁺ ions. These results strongly suggest the possibility to modulate the magnetic properties of such transition metal ions doped II–VI mesoporous structures by varying the synthesis conditions and/or by post-synthesis thermochemical treatments.

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