Temperature sensing using bulk and nanoparticles of Ca_0.79Er_0.01Yb_0.2MoO₄phosphor

Optical temperature sensing is widely realized by using upconversion (UC) emission in lanthanide-doped phosphors. There are 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 Ca_0.79Er_0.01Yb_0.2MoO₄phosphors 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^-1at 305 K and 0.0094 K^-1at 299 K, respectively, while, the maximum absolute sensitivities are 0.0150 K^-1at 348 K, and 0.0170 K^-1at 398 K, respectively. We thus conclude that the temperature sensing ability of nanoparticle-based Ca_0.79Er_0.01Yb_0.2MoO₄phosphor is better compared to its bulk phosphor.