Upconversion of Yb3+/Ho3+ co-doped bismuth oxyfluoride and fluoride microcrystals for high-performance ratiometric luminescence thermometry

Ratiometric luminescence thermometry is awfully applicable for non-contact temperature detection. Lanthanide luminescent materials available for high-performance ratiometric thermometry are still highly desirable until now. Herein, two novel upconversion phosphors, Yb 3+ /Ho 3+ co-doped BiOF and BiF 3 microcrystals , were synthesized and investigated systematically in terms of their crystalline structure, room temperature and temperature-dependent upconversion properties. Under 980 nm laser excitation, both microcrystals bring forth the characteristic emissions of Ho 3+ , with an identical overall luminescent color of green, while the intensity is much higher in BiF 3 :Yb/Ho microcrystals. When increasing temperature, the upconversion intensity at various wavelengths for both microcrystals is reduced, meanwhile fluorescence intensity ratios of both 545/656 nm and 752/656 nm decrease highly regularly, establishing a ratiometric thermometry therefore. BiF 3 :Yb/Ho microcrystals were demonstrated to have significantly superior thermometric performance than BiOF:Yb/Ho, and a high relative sensitivity up to 5.41% K −1 as well as a wide temperature sensing range of 298–673 K were obtained.