NaBiF 4 :Yb 3+ ,Tm 3+ submicron particles as luminescent probes for in vitro imaging of cells.

Upconversion materials have attracted considerable research interest for their application in bioimaging due to their unique optical properties. NaREF ₄ (RE = Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) based host lattice, which is widely used for upconversion, requires expensive rare-earth elements and tedious reaction conditions. Hence there is a need to develop environmentally friendly and cost effective materials for upconversion. In this study, we propose NaBiF ₄ as a host material for upconversion which is based on environmentally friendly and cost-effective bismuth. NaBiF ₄ has not been explored as an imaging probe before. We report efficient Yb ³⁺ /Tm ³⁺ doped NaBiF ₄ based upconversion submicron particles which exhibit a photostable, wide upconversion emission range (NIR-to-NIR and Vis) under NIR (980 nm) excitation, and in-vitro non-cytotoxic uptake by mammalian cancer cell lines as well as bacterial cells with a high signal to background ratio. The synthesis of the chosen host material co-doped with Yb ³⁺ /Tm ³⁺ has not been reported earlier through such a non-aqueous quaternary reverse micelle route. Here, we functionally validate these submicron particles as viable alternatives to currently available upconversion nanomaterials and highlight their potential as luminescent probes for bioimaging.