Spectroscopic in-depths of upconverting NaZr2(PO4)3 phosphors for LIR-based thermometry

This study employed solid-state synthesis to develop the green emitting Er³⁺-Yb³⁺:NaZr₂(PO₄)₃, NASICON material. Using Rietveld refinement, the crystallographic variables of the synthesized phosphors were precisely calculated. The upconverting phenomenon was seen with naked eye when exposed to 980 nm laser radiation. The intermediate excited state dependency on the unusual photon number dependence on the green and red emission has been understood using the steady-state rate law equations. Further, the temperature sensing performances with good repeatability were compared with different laser densities, and it was found that the prepared phosphors could be an ideal material for upconverting and temperature sensing applications.

Strategies for designing low thermal quenching upconverting temperature sensors

The Er³⁺/Yb³⁺:NaGd(WO₄)₂ phosphors and the phosphor-in-glass (PIG) have been synthesized employing a typical approach to investigate their structural, morphological and optical properties. Several PIG samples containing different amounts of NaGd(WO₄)₂ phosphor have been manufactured by sintering the phosphor and glass [TeO₂-WO₃-ZnO-TiO₂] frit together at 550 °C, and its impact on the luminescence characteristics has been extensively studied. It has been noticed that the upconversion (UC) emission spectra of PIG under 980 nm excitation display similar characteristic emission peaks to the phosphors. The maximum absolute sensitivity of the phosphor and PIG is 17.3 × 10^-3 K^-1 @ 473 K and the maximum value of relative sensitivity is 10.0 × 10^-3 K^-1 @ 296 K and 10.7 × 10^-3 K^-1 @ 298 K, respectively. However, thermal resolution at room temperature has been improved in the case of PIG as compared to the NaGd(WO₄)₂ phosphor. As compared to the Er³⁺/Yb³⁺ codoped phosphor and glass, the less thermal quenching of luminescence has been observed in PIG.