Bifunctional upconverting luminescent-magnetic FeS2@NaYF4:Yb3+,Er3+ core@shell nanocomposites with tunable luminescence for temperature sensing†

Advanced optically active materials have experienced significant development in recent years. Light-emitting materials combined with materials that exhibited magnetic properties result in bifunctional materials with an expanded range of capabilities and applications. New functionalities as a result of the core@shell structure enable interactions with the light and the external magnetic field as well. Continuous progress in materials science leads to innovations that enhance data storage and transmission, bioimaging, sensing, optical thermometry, and other applications crucial to advanced technology. In this research, we have focused on the optimization of the synthesis of a nano-sized FeS2 material as an optically active, magnetic component of the core, and NaYF4:Yb3+,Er3+ nanoparticles (NPs) as a temperature sensitive, up-conversion (UC) luminescence part of the shell. The synthesized core@shell type nanocomposite (NC) material FeS2@NaYF4:Yb3+,Er3+ exhibits simultaneously the unique features of the core and shell components. The recorded UC emission spectra under 975 nm laser excitation show the possibility of tuning the UC luminescence color with the application of a highly absorbing FeS2 component in the composite material. Moreover, the magnetic properties of the FeS2 core nanoparticles and the synthesized NC were compared to confirm the potential application of the NC as a novel bifunctional luminescent-magnetic sensing platform. For both materials the luminescence color changed with the increasing laser power density, allowing color-tunable light generation. Additionally, optical temperature sensing properties of the NPs and NC were compared, resulting in a very high relative temperature sensitivity of ∼2.0% K−1 for both materials.