title: Enhanced near-infrared upconversion luminescence of GdF3:Yb3+, Tm3+ by Li+.
abstract: GdF3:0.23Yb3+, 0.005Tm3+, x%Li+ (x = 0-7) NIR to NIR upconversion nanocrystals (UCNPs) were synthesized by a hydrothermal method. Their XRD patterns show that they are all orthorhombic phase despite of different Li+ ion concentrations. The detailed analysis indicates that lithium ions substitute Gd3+ sites at x < 3. As the Li+ content increases, more Li+ ions enter host lattice interstitially. The doped Li+ ions affect the crystal field symmetry around Tm3+ ions, which results in the change of the irradiation transition probabilities between their corresponding transition levels. Compared with GdF3:0.23Yb3+, 0.005Tm3+, the NIR to NIR upconversion emission intensity of GdF3:0.23Yb3+, 0.005Tm3+, 0.03Li+ nanocrystals (excitation at 980 nm, emission at 808 nm) increases 2.2 times.
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Chuai
authors.forename: Zhenyu
authors.initials: Z
authors.lastname: Liu
authors.forename: Ye
authors.initials: Y
authors.lastname: Liu
authors.forename: Chunfeng
authors.initials: C
authors.lastname: He
authors.forename: Weiping
authors.initials: W
authors.lastname: Qin