Facile fabrication of versatile PMMA/CNF–NaYF4:Yb/Er composite microspheres by Pickering emulsion system

• Versatile PMMA/CNF–NaYF4:Yb/Er composite microspheres (CRs) were easily fabricated.
• The CRs simultaneously exhibited upconversion and downconversion luminescence.
• The NaYF4:Yb/Er nanoparticles can facilitate the formation of CRs.
• The CRs also presented excellent drug delivery performance.

Composite microspheres (CRs) assembled from various functional materials have been considered as excellent candidates for many applications. Herein, we report a straightforward method to fabricate multifunctional model drug methyl red-loaded polymethyl methacrylate (PMMA)/cellulose nanofiber (CNF)–NaYF4:Yb/Er CRs by Pickering emulsion system. The obtained CRs were characterized by optical microscope, scanning electric microscope, and emission spectrum. The results revealed that the CRs with relatively uniform size distribution exhibited both strong upconversion and downconversion luminescence and fine drug release performance. Considering the facile operation process and versatile properties of the CRs, this work offers an easy and universal method to prepare various multifunctional CRs for meeting the requirements of diverse applications.