Manganese-mediated Growth of ZnS Shell on KMnF3:Yb,Er Cores towards Enhanced Up/downconversion Luminescence

Epitaxially growing a semiconductor shell on the surface of up-conversion nanocrystals to form core/shell structure is believed to be a promising strategy to improve the luminescent efficiency of lanthanide ions doped in particle cores, and meanwhile enrich the optical properties of the resulting nanocrystals. However, liquid-phase synthesis of such core/shell structured nanocrystals comprised of lanthanide ion-doped core and semiconductor shell remains challenging due to the chemical incompatibilities between lanthanides and most intermediate-gap semiconductors. In this context, the successful growth of ZnS shell on KMnF3 core co-doped with Yb3+/Er3+ ions is reported to enhance the upconversion luminescence of Er3+ ions. The underlying core/shell formation mechanism is elucidated in detail combining hard-soft-acid-base theory with structural analysis of the resulting nanocrystals. Quite unexpectedly, Mn2+ diffusion across the core/shell interface occurs during ZnS shell growth, giving rise to Mn2+ emissi...