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

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 → O^2- 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⁺:²H_11/2/⁴S_3/2), 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.