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Phase and morphology evolution of luminescent NaLnF4 (Ln= La to Yb) micro-crystals: Understanding the Ionic radii and surface energy dependent solution growth mechanism

Abstract

Lanthanide (Ln)-based NaLnF4 micro-crystals (MCs) exhibit great advantages and strong feasibility to be integrated into micron size photonic devices. However, there is still lack of thermodynamically understanding on solution growth mechanisms of NaLnF4 MCs. Here we prepared hexagonal NaLnF4 MCs with various morphologies (rod, disk and flaky like) and crystal size (100 nm to 10 μm) through a hydrothermal route. Morphologies and sizes of NaLnF4 MCs were revealed to be highly dependent on the ionic radius of different Ln3+. We subsequently proposed a ligand adsorption driven oriented growth model and a surface energy dominant nucleation model to well interpret the above phenomena. Firstly, citrate (Cit3-) adsorption on the {10-10} lattice plane primarily leads to different morphology of NaLnF4 MCs. Secondly, different surface energies required for nucleation are responsible for crystal size evolution from NaYbF4 to LaF3.Thirdly, alternative phase type from NaLnF4 to LnF3 is related with Ln-F bond energy and Goldschmidt's law of crystal chemistry. In addition, surface ligand removal is beneficial to luminescence enhancement of NaLnF4 MCs. The results eventually provide a thermodynamic understanding for researchers to develop NaLnF4 MCs with aimed morphology and size.

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Supplementary files

Publication details

The article was received on 15 Aug 2019, accepted on 30 Sep 2019 and first published on 30 Sep 2019


Article type: Paper
DOI: 10.1039/C9CE01287G
CrystEngComm, 2019, Accepted Manuscript

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    Phase and morphology evolution of luminescent NaLnF4 (Ln= La to Yb) micro-crystals: Understanding the Ionic radii and surface energy dependent solution growth mechanism

    X. Sun, X. Wang, B. Chen, F. zhao, X. Xu, K. Ren, Y.H. Lu, X. Qiao, G. Qian and X. Fan, CrystEngComm, 2019, Accepted Manuscript , DOI: 10.1039/C9CE01287G

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