Simultaneous evolutions in composition, structure, morphology, and upconversion luminescence of BiOxFy:Yb/Er microcrystals and their application for ratiometric temperature sensing

Lanthanide upconversion luminescent materials featuring multi-peak and tunable emissions allow for ratiometric luminescence thermometry in a remote detection manner. However, wide explorations are still required to develop relevant materials for efficient thermometric performances. Herein, Yb 3+ /Er 3+ co-doped non-stoichiometric analogues of bismuth oxyfluoride were obtained by simply tuning the F − /(Bi 3+ + Ln 3+ ) molar ratio of the reactants in a solid-state reaction method, for the first time. We achieved simultaneous regulations in composition , structure, morphology, and upconversion luminescence properties of BiO x F y :Yb/Er (2/1 mol%) microcrystals . Compositional analysis revealed not only the predictable increase of fluorine content, but also the constant O/(Bi + Ln) atomic ratios in all nominal BiO x F y :Yb/Er. Experimental results showed the structure and morphology evolutions from hexagonal-phase micro-flowers, to tetragonal-phase microplates , and further to orthorhombic-phase irregular microcrystals . Benefiting from adjustable composition, structure and morphology, up-conversion luminescence with adjustable intensity and color was obtained. Temperature dependent upconversion properties and ratiometric thermometric performances based on the thermally coupled levels, 2 H 11/2 and 4 S 3/2 of Er 3+ , were explored. BiOF:Yb/Er, BiO 0.67 F 1.66 :Yb/Er, and BiF 3 :Yb/Er microcrystals were found as suitable temperature sensing candidates with operating temperature range as wide as 298−673/723 K, high relative sensitivity up to 1.24% K -1 , and minimum temperature uncertainty of 0.15 K. These results benefit not only further explorations for high-performance lanthanide-based luminescence thermometers, but also the chemistry of fluorides made from the solid-state reaction method.