Highly temperature-sensitive and blue upconversion luminescence properties of Bi2Ti2O7:Tm3+/Yb3+ nanofibers by electrospinning

Pure pyrochlore phase Bi2Ti2O7 matrix nanofibers with various molar ratios (Tm3+/Yb3+ =1: 2-20) were synthesized by electrospinning technology. The nanofibers were about 200-300 nm in diameter and tens of micrometer in length with a rough surface. The emission bands in the range of 400-800 nm were realized and derived from the transitions of (1)G(4) -> H-3(6), (1)G(4) -> F-3(4), F-3(2,3) -> H-3(6), and H-3(4) -> H-3(6), respectively. The strong blue emission can be seen with the naked eye, revealing an excellent blue upconversion feature. In addition, the temperature sensing properties of Bi2Ti2O7:Tm3+/Yb3+ fibers (Tm3+/Yb3+ = 1:8) were investigated in the temperature range of 300-505 K, showing a relative high sensitivity value of 0.024 K-1 at 300 K. For comparison, both contactless methods, thermal infrared imager and fluorescence intensity ratio (FIR) techniques were used to detect the temperature of a designed object coated with Bi2Ti2O7:Tm3+/Yb3+ nanofibers. Our results indicated that the FIR technique possessed enhanced temperature-sensing properties beyond the thermal infrared imager for surface temperature detection. This work will arouse extensive interest in upconversion studies in bismuth-based oxides and pave the way for further development of contactless FIR temperature-sensing applications of upconversion materials.