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 1G4 ? 3H6, 1G4 ? 3F4, 3F2,3 ? 3H6, and 3H4 ? 3H6, 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.