Selective enhancement of green upconversion luminescence from NaYF4:Yb, Er microparticles through Ga3+ doping for sensitive temperature sensing

Temperature sensors based on upconversion luminescence (UCL) intensity ratio have attracted great attention due to the high sensitivity. The enhancement of UCL is helpful to improve the sensitivity of temperature sensor. Doping is an effective way to achieve the UCL enhancement. Ga 3+ ions doped NaYF 4 :18%Yb,2%Er have been prepared through a facile one-pot solvothermal method . Upconversion (UC) emission intensity was significantly enhanced by introducing Ga 3+ ions into the lattice of NaYF 4 :Yb,Er, especially the green UC emission. With Ga 3+ concentration increasing, the size of the resulting NaYF 4 :Yb,Er,x%Ga particles decreases gradually. By doping 25% Ga 3+ , the green UC emission is increased by 30 times, while the red emission is enhanced by only 8 times. The morphology of particles and local symmetry around Er 3+ ions have been changed, resulting in the selective enhancement of green UC emission. In addition, the temperature-dependent UCL properties of NaYF 4 :Yb,Er,25%Ga and NaYF 4 :Yb,Er were investigated. The maximum thermal sensitivity of NaYF 4 :Yb,Er,25%Ga could reach 0.0046 K −1  at 498 K. Therefore, NaYF 4 :Yb,Er,25%Ga with strong green UCL could be served as a potential candidate for sensitive temperature sensing.