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

Abstract

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. Ga3+ ions doped NaYF4:18%Yb,2%Er have been prepared through a facile one-pot solvothermal method. Upconversion (UC) emission intensity was significantly enhanced by introducing Ga3+ ions into the lattice of NaYF4:Yb,Er, especially the green UC emission. With Ga3+concentration increasing, the size of the resulting NaYF4:Yb,Er,x%Ga particles decreases gradually. By doping 25% Ga3+, 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 Er3+ ions have been changed, resulting in the selective enhancement of green UC emission. In addition, the temperature-dependent UCL properties of NaYF4:Yb,Er,25%Ga and NaYF4:Yb,Er were investigated. The maximum thermal sensitivity of NaYF4:Yb,Er,25%Ga could reach 0.0046 K−1 at 498 K. Therefore, NaYF4:Yb,Er,25%Ga with strong green UCL could be served as a potential candidate for sensitive temperature sensing.