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Optical temperature sensing is widely realized by using upconversion (UC) emission in lanthanide-doped phosphors. There are so many various parameters that are responsible for UC intensity of the phosphor like particle shape and size, type of symmetry that exist at the site position, distribution of lanthanide ions in the phosphor, and so on. However, a comparative study of the bulk and nanostructure on the temperature sensing ability of such phosphor is rare. In the present work, we have taken Ca0.79Er0.01Yb0.2MoO4 phosphors as a model system and synthesized its bulk (via solid-state reaction method, named SCEY) and nanostructures (via solution combustion route, named CCEY). We further studied their phase, crystal structure, phonon frequency, optical excitation, and emission (upconversion & downshifting) properties. Finally, the optical temperature sensing behavior of SCEY and CCEY, in the range 305 K - 573 K, have been compared. The maximum relative sensitivity of the phosphor SCEY and CCEY are 0.0061 K-1 at 305 K and 0.0094 K-1 at 299 K, respectively, while, the maximum absolute sensitivities are 0.0150 K-1 at 348 K, and 0.0170 K-1 at 398 K, respectively. We thus conclude that the temperature sensing ability of nanoparticle-based Ca0.79Er0.01Yb0.2MoO4 phosphor is better compared to its bulk phosphor.

The ability of rare-earth-doped ferroelectric oxides to achieve outstanding upconversion (UC) performances under NIR irradiation despite possessing intrinsic electric properties drives researchers all over the globe to work in this field. The structural and spectroscopic characteristics of the Bi4Ti3O12 phosphor integrated with Er3+, Yb3+, and Al3+ have been thoroughly investigated in this study. The considerable increase in UC emission ~three times caused by the addition of Al3+ ions has been observed and discussed. The processes connected with the UC emission related to the pump power variation have been realized using the rate law equation. Aside from having high sensitivity of 0.011 K-1 at room temperature, the prepared phosphor possesses excellent thermal stability, i.e., it retains ~ 73% of its initial intensity with the addition of Al3+ ions.

Er3+-Yb3+ co-doped NaGd(MoO4)2 phosphors with different concentrations of Er3+ and Yb3+ ions have been successfully synthesized via a high-temperature solid-state reaction method. Phase confirmation and morphological studies have been done...

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