Designing Optical Thermometers Using Down/Upconversion Ca₁₄Al₁₀Zn₆O₃₅: Ti⁴⁺, Eu³⁺/Yb³⁺, Er³⁺ Thermosensitive Phosphors

Abstract

Down/upconversion Ca14Al10Zn6O35 inorganic phosphors codoped with Ti4+/Eu3+ or Yb3+/Er3+ were prepared. The crystal structure and downconversion luminescence properties of Ca14Al10Zn6O35:Ti4+, Eu3+ phosphors were studied in detail. Ti4+ and Eu3+ occupied Al3+ and Ca2+ sites in the host lattice, respectively. Under the excitation of 273 nm, the emission peak in the 300–570 nm band originated from the 2T2 → O2– transition of Ti4+. The f–f transition of Eu3+ ions generated multiple peaks in the 570–800 nm range. The emission intensity of Ti4+ and Eu3+ ions can be used as a fluorescence intensity ratio (FIR) signal. Based on the FIR technology, the maximum relative sensitivity (S r) and the minimum temperature uncertainty (δT) reached 1.41% K–1 and 0.07 K, respectively. Meanwhile, the temperature-sensing behaviors were explored by the temperature-dependent upconversion spectra of Er3+- and Yb3+-codoped Ca14Al10Zn6O35 phosphors. Based on the fluorescence intensity ratio of thermal coupling levels (Er3+:2H11/2/4S3/2), the maximum S r and minimum δT of upconversion phosphors reached 1.28% K–1 and 0.08 K in the temperature range of 293–473 K, respectively. Ca14Al10Zn6O35:Ti4+/Eu3+ (Yb3+/Er3+) phosphors realize temperature sensors with higher relative sensitivity, and it is a good candidate material for optical temperature measurement.

Thermochromic Upconversion Emission in Tm3+/Yb3+-Codoped La2Mo3O12 Microparticles via Negative Thermal Expansion Engineering for Ultrahigh Sensitivity Optical Thermometry

“…Compared with the conventional contacted thermometers, a lot of attention has been attracted by luminescence thermometers, which utilize temperature-associated fluorescence characteristics, such as fluorescence intensity ratio (FIR), band position, decay time, full width at half-maximum of emission band, etc., − of luminescent materials because of their advantages of rapid response, high accuracy/resolution, and contactless characteristic. , Particularly, by adopting the FIR technique, optical thermometry is extensively adopted, in which the temperature-related emission intensities of thermally coupled levels (TCLs) of rare-earth ions are investigated. , Fu et al revealed that the thermometric properties of rare-earth ions, which were based on their TCLs, can be adjusted by controlling the excitation wavelength and utilizing tridoping engineering. , However, the optical thermometers based on the TCLs of rare-earth ions possess low relative sensitivity ( S r ) triggered by the small energy band gap of TCLs (200 ≤ Δ E ≤ 2000 cm –1 ). , For the purpose of addressing this issue, researchers proposed a new route, namely, using the FIR technique to deal with the temperature-dependent emission intensities of non-TCLs of luminescent compounds. To date, some compounds, such as BaTiO 3 :Er 3+ /Ho 3+ /Yb 3+ , La 3 Li 3 W 2 O 12 :Eu 3+ /Mn 4+ , Na 5 Y 9 F 32 :Ce 3+ /Tb 3+ , YVO 4 :Eu 3+ /Nd 3+ , LaGaO 3 :Cr 3+ /Nd 3+ , and Ca 14 Al 10 Zn 6 O 35 :Ti 4+ /Eu 3+ , − with good thermometric properties, in which the non-TCLs are used, have been developed to realize contactless temperature sensing. Thereby, the utilization of the temperature-dependent FIR value of non-TCLs is a facile strategy to manipulate the thermometric behaviors of luminescent materials.…”