Monoclinic Er3+-doped Y2O3 phosphor: advancing ratiometric optical temperature sensing beyond the cubic phase

Abstract

Luminescence thermometry has been established as a reliable technique for remote temperature sensing in cases where traditional contact methods are unsuitable. Er³⁺-doped oxide materials are frequently utilized for optical thermal sensing due to the fact that the erbium ion possesses a complex energy level structure, which includes both thermally and nonthermally coupled levels suitable for providing a ratiometric strategy. The diversity of oxide structures offers opportunities for crystal phase engineering to optimize properties. Monoclinic Y₂O₃:Er³⁺ nanoparticles were demonstrated, for the first time, as ratiometric thermal sensors across a wide temperature range of 98–873 K. The thermometric performance of the monoclinic nanoparticles is comprehensively compared with that of the conventional cubic Y₂O₃:Er³⁺ sample. The best relative thermal sensitivity of ∼1.2% K⁻¹@298 K was found to be comparable for both crystal phases, while the monoclinic polymorph exhibited a superior temperature resolution, reaching a maximum of 0.24 K. These results highlight the potential of monoclinic Y₂O₃:Er³⁺ as a superior alternative to cubic phase counterparts for high precision luminescence thermometry applications.