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Download fileNa(1‑x)Lix(Gd0.39Y0.39Yb0.2Er0.02)F4 (0 ≤ x ≤ 1) Solid Solution Microcrystals: Li/Na Ratio-Induced Transition of Crystalline Phase and Morphology and Their Enhanced Upconversion Emission
journal contribution
posted on 2018-10-08, 00:00 authored by Ran Luo, Tao Li, Yang Chen, Zhanglei Ning, Yan Zhao, Mengjiao Liu, Xin Lai, Cheng Zhong, Chao Wang, Jian Bi, Daojiang GaoNa(1‑x)Lix(Gd0.39Y0.39Yb0.2Er0.02)F4 (0
≤ x ≤ 1) (denoted
as Na(1‑x)LixReF4) solid solution microcrystals with different
microstructures have been synthesized by a facile hydrothermal method.
The influences of Li+ ion concentration on the morphology,
crystal structure, grain size, and upconversion emission of the microcrystals
are deeply investigated. It is found that the substitution concentration
of Li+ not only causes the phase transition but also induces
variation in morphology and size. When the substitution concentration
of Li+ ions is lower (x ≤ 0.3),
the obtained Na(1‑x)LixReF4 microcrystals possess hexagonal structure
and exhibit hexagonal prism in morphology. Whereas at the higher substitution
concentration of Li+ ions (x ≥
0.6), the crystalline phase of the final Na(1‑x)LixReF4 microcrystals
transformed into tetragonal structure and their morphology changed
into octahedron except for the sample Na(1‑x)LixReF4 with x = 0.9. Predictably, the obtained Na(1‑x)LixReF4 microcrystals
at the moderate substitution concentration of Li+ ions
(x = 0.4 and 0.5) own the coexistent phases of hexagonal
and tetragonal and display the obvious symbiotic morphologies of hexagonal
prism and octahedron. All the samples showed characteristic emission
peaks in green and red region with center wavelengths at 522 nm, 542
nm, and 652 nm respectively, and their upconversion intensities initially
lift and then drop with the increasing x, giving
the maximum at x = 0.5. Specifically, for the codoped
Na0.5Li0.5ReF4 microcrystal, its
UC intensity of the strongest green emission at 542 nm is about 18
times and 73 times greater than that of the codoped NaReF4 and LiReF4 microcrystals, respectively. Moreover, the
variation amplitude of intensity for the green emission bands is much
greater than that of the red emission with the increasing x. It could obtain a superior host matrix for upconversion
luminescence by means of the formation of Na(1‑x)LixReF4 solid
solution at the feasible substitution concentration of Li+ (0.2 < x ≤ 0.6).