Optical thermometry based on thermal population of low-lying levels of Eu3+ in Ca2.94Eu0.04Sc2Si3O12

Abstract

Non-contact optical thermometry using rare-earth materials has attracted a lot of attention due to its realization of non-invasive and real-time temperature determination. In the current work, a new mechanism, differing from the conventional approach utilizing the ratio of intensities emitted from two thermally coupled excited levels, was developed and demonstrated for temperature sensing using Eu³⁺-doped Ca₃Sc₂Si₃O₁₂ (CSSO). Under the excitation of 610.6 nm-wavelength light, Eu³⁺ ions at the ⁷F₂ multiplet became excited to the ⁵D₀ state, and then the luminescence intensity originating from the ⁵D₀ state increased significantly as the temperature was increased from 123 K to 273 K. The thermoequilibrium of the ⁷F₂ multiplet with the ⁷F₀ ground state at a weak excitation ensured a steady increase of the luminescence intensity I with temperature T, which well fit the equation I = A exp (−B/T) for the transitions to both ⁷F₁ and ⁷F₄ multiplets. A relative sensitivity S_R of 1008/T² was obtained for the ⁷F₁ case, with a value of 1.35% at 273 K. This scheme, as a result of detecting the blue-shifted emission, has the advantages of being less disturbed by stray light from the host and the object of the thermometry. In addition, the high quantum efficiency of a one-photon excited photoluminescence scheme has the advantage of improving the resolution of the thermometry. Furthermore, a near-infrared broadband emission observed in the sample can be adopted as a reference, so as to transform the scheme into one using a luminescence intensity ratio. These results indicated that CSSO:Eu³⁺ may be used in practical temperature sensing applications.