title: Enhanced upconversion emission in Yb3+ and Er3+ codoped NaGdF4 nanocrystals by introducing Li+ ions.
abstract: β-NaGdF(4) : Yb(3+)/Er(3+) nanoparticles (NPs) codoped with Li(+) ions were prepared for the first time via a thermal decomposition reaction of trifluoroacetates in oleylamine. The influence of site occupancy of Li(+) on the upconversion emission of β-NaGdF(4) : Yb(3+)/Er(3+) NPs was investigated in detail. The upconversion emission intensity was significantly enhanced by introducing different concentrations of Li(+) ions. In contrast to lithium-free β-NaGdF(4) : Yb(3+)/Er(3+), the green and red UC emission intensities of the NPs codoped with 7 mol% Li(+) ions were enhanced by about 47 and 23 times, respectively. The luminescence enhancement should be attributed to the distortion of the local asymmetry around Er(3+) ions. The mechanisms for the enhancement of upconversion emission were discussed. In addition, it was found in our research work that β-NaGdF(4) : Yb(3+)/Er(3+) NPs exhibited paramagnetic features at room temperature and the magnetization was slightly increased by introducing Li(+) ions.
authors.affiliation: National Key laboratory of Materials Behaviours & Evaluation Technology in Space Environments, Harbin Institute of Technology, Harbin, 150001, PR China.
authors.forename: Qian
authors.initials: Q
authors.lastname: Cheng
authors.forename: Jiehe
authors.initials: J
authors.lastname: Sui
authors.forename: Wei
authors.initials: W
authors.lastname: Cai