Optical thermometry based on the stark sub-levels of Er³⁺ in Y₂Mo₃O₁₂: Yb³⁺, Er³⁺ particles synthesized by sol–gel method

To settle the challenges of both excellent luminescent property and high sensitivity for optical thermometry, a series of Y₂Mo₃O₁₂: Yb³⁺, Er³⁺ submicron particles with different Yb³⁺ contents were prepared via a citric-assisted sol–gel technique. Under 980 nm excitation, the samples exhibit characteristic emissions ascribed to the transitions of ²H_11/2 and ⁴S_3/2 levels to the ground state of Er³⁺ ion. The Stark splitting of ⁴S_3/2 and ²H_11/2 is observed. According to the emission spectra, the optimal doping concentration of Yb³⁺ and Er³⁺ is concluded to be 15 mol% and 1 mol%, respectively. Then, the temperature-dependent luminescent behavior of Y₂Mo₃O₁₂: 15%Yb³⁺, 1%Er³⁺ sample was further investigated, which exhibits good temperature stability with a slight decrease as temperature rises. Based on the fluorescence intensity ratio technique, the maximal absolute sensitivity S_A of 0.0243 K⁻¹ and relative sensitivity S_R of 1.161%K⁻¹ were achieved using the Stark sub-levels (I_H/I_S2), which are 1.75 and 1.07 folds than that of the traditional thermal-coupled levels (I_H/I_S1+S2) of Er³⁺ ion. The results show that the Stark sub-levels can be utilized as an effect strategy to improve thermometry sensitivity and Y₂Mo₃O₁₂: Yb³⁺, Er³⁺ phosphor could be considered as a promising temperature sensing material.