Multisignal optical temperature-sensing properties of Eu³⁺ -doped NaYF₄ nanoparticles

In this paper, the multisignal (different emissions/colours) temperature sensing of NaYF₄ :Eu³⁺ nanoparticles is investigated, which is based on fluorescence intensity ratios (FIRs) between ⁵ D₀ →⁷ F_J (J=1-4) and ⁵ D₁ →⁷ F_J' emissions. The ⁵ D₁ →⁷ F_J' (J'=0-2) emissions can be clearly observed due to the low photon energy of NaYF₄ . Based on the FIRs between different ⁵ D₀ →⁷ F_J and ⁵ D₁ →⁷ F_J' emissions, higher absolute/relative temperature sensitivities are obtained. Compared with the FIR between whole ⁵ D₀ →⁷ F_J and ⁵ D₁ →⁷ F_J' emissions, the maximum value of S_a was improved from 0.27 K^-1 to 5.02 K^-1 and that of S_r was improved from 0.89%·K^-1 to 1.27%·K^-1 . Furthermore, the FIRs between different colours of emissions were investigated for the application of wide-range multicolour temperature sensing.