Facile synthesis of well-dispersed SrF2:Yb3+/Er3+ upconversion nanocrystals in oleate complex systems

Well oil-dispersible SrF2:Yb3+/Er3+ upconversion (UC) nanocrystals (NCs) were easily synthesized in the water-ethanol-oleic acid-sodium oleate complex systems. The as-prepared NCs all show size-uniformity, and their sizes, morphologies can be controlled by varying the solvent and reaction time, and rectangular SrF2:Yb3+/Er3+ nanosheets with the sizes of 5-25 nm can be obtained. The possible mechanism on the nucleation and growth of nanocrystals occurred at the oleic acid/sodium oleate interface was also discussed. The size and morphology dependent UC luminescence behaviors have been observed in SrF2:Yb3+/Er3+ NCs, and their UC luminescence transitions were proposed. The as-prepared UC nanocrystals are expected to fulfill the demand for biological applications.

Research highlights▶ In this paper, to our knowledge, it is first time that well oil-dispersible SrF2:Yb3+/Er3+ nanocrystals have been successfully prepared in the water-ethanol-oleic acid-sodium oleate complex systems. ▶ The size and shape of the NCs were controlled by adjusting the amount of OA/NaOA, temperature and reaction time. ▶ A systematic study on the photoluminescence of Yb3+/Er3+-doped SrF2 samples with different size and shapes has shown that the optical properties of products are strongly dependent on their size.