Coprecipitation synthesis, structural, optical properties, and thermometry application of Tm3+/Yb3+ co-doped YPO4 phosphor

Abstract

Coprecipitation synthesis and characterization of upconverting YPO4: Tm3+, Yb3+ phosphor is reported in the present work. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Scanning electron microscopy (SEM) were used to examine the structure and morphology of the synthesized phosphor. Tm3+ and Yb3+ co-doped YPO4 material have the tetragonal xenotime crystal structure of space group I41/amd. Upconversion luminescence properties of prepared phosphor are studied under the near-infrared (NIR) 980 nm laser excitation. The intense emission peaks are observed at ∼473 nm and ∼796 nm due to electronic transitions (1G4→3H6) and (3H4→3H6), respectively, and relatively weak emission peaks are observed at 654 nm and 700 nm which are attributed to (1G4→3F4) and (3F2,3→3H6) transitions of Tm3+, respectively. Tm3+ (0.3 mol%)/Yb3+(10 mol%) is the optimized concentration that gives intense and sharp emission in NIR (∼796 nm) region. Power dependence studies have been done to understand the upconversion emission mechanism. The fluorescence intensity ratio of (3F2,3→3H6)/(3H4→3H6) transitions of Tm3+ in the temperature range 323 K–598 K is analyzed. Relative and absolute temperature sensitivity are also calculated. Maximum relative sensitivity is 1.86% K−1 at 323 K and absolute sensitivity increases with rising temperature. Excellent sensitivity, avoidable spectral overlap, and intense upconversion emission, in the first biological window under NIR excitation, show that the prepared material is multifunctional and may have potential applications in temperature sensing and optical heaters for bio-molecules.