Designing Optical Thermometers Using Down/Upconversion CaAlZnO: Ti, Eu/Yb, Er Thermosensitive Phosphors.

Down/upconversion CaAlZnO inorganic phosphors codoped with Ti/Eu or Yb/Er were prepared. The crystal structure and downconversion luminescence properties of CaAlZnO:Ti, Eu phosphors were studied in detail. Ti and Eu occupied Al and Ca sites in the host lattice, respectively. Under the excitation of 273 nm, the emission peak in the 300-570 nm band originated from the T → O transition of Ti. The f-f transition of Eu ions generated multiple peaks in the 570-800 nm range. The emission intensity of Ti and Eu ions can be used as a fluorescence intensity ratio (FIR) signal. Based on the FIR technology, the maximum relative sensitivity () and the minimum temperature uncertainty (δ) reached 1.41% K and 0.07 K, respectively. Meanwhile, the temperature-sensing behaviors were explored by the temperature-dependent upconversion spectra of Er- and Yb-codoped CaAlZnO phosphors. Based on the fluorescence intensity ratio of thermal coupling levels (Er:H/S), the maximum and minimum δ of upconversion phosphors reached 1.28% K and 0.08 K in the temperature range of 293-473 K, respectively. CaAlZnO:Ti/Eu (Yb/Er) phosphors realize temperature sensors with higher relative sensitivity, and it is a good candidate material for optical temperature measurement.