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

Coprecipitation synthesis and characterization of upconverting YPO 4 : Tm 3+ , Yb 3+ phosphor is reported in the present work. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Field emission scanning electron microscopy (FESEM) were used to examine the structure and morphology of the synthesized phosphor. Tm 3+ and Yb 3+ co-doped YPO 4 material have the tetragonal xenotime crystal structure of space group I 41/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 ( 1 G 4 → 3 H 6 ) and ( 3 H 4 → 3 H 6 ), respectively, and relatively weak emission peaks are observed at 654 nm and 700 nm which are attributed to ( 1 G 4 → 3 F 4 ) and ( 3 F 2, 3 → 3 H 6 ) transitions of Tm 3+ , respectively. Tm 3+ (0.3 mol%)/Yb 3+ (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 ( 3 F 2, 3 → 3 H 6 )/( 3 H 4 → 3 H 6 ) transitions of Tm 3+ 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. • We report a temperature sensing-luminescent nanomaterial YPO 4 : Tm 3+ , Yb 3+ which can emit in blue and NIR region under NIR (980 nm) excitation. • The luminescent material may serve as a multifunctional material (non-contact optical thermometry/imaging and in display devices). • YPO4 doped with Tm 3+ , Yb 3+ phosphor crystalizes into tetragonal crystal structure with space group I 41/amd. Nonlinear photon upconversion properties of co-doped materials were studied under NIR (980 nm) laser excitation. • From the laser input power dependence studies, three photon involvements for blue and 2 photon for NIR emission were observed. • A possible mechanism for energy transfer and for possible transitions is also suggested and discussed in details using energy level diagram. • The phosphor material's temperature-dependent upconversion data were recorded in order to determine the material's sensitivity, which justifies its utility as a non-contact temperature sensing probe.