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A Mechanistic Understanding of Non-Classical Crystal Growth in Hydrothermally Synthesized Sodium Yttrium Fluoride Nanowires

preprint
revised on 21.01.2020 and posted on 22.01.2020 by Alex Bard, Xuezhe Zhou, Xiaojing Xia, Guomin Zhu, Matthew Lim, Seung Min Kim, Matthew Johnson, Justin Kollman, Matthew Marcus, Steven Spurgeon, Daniel Perea, Arun Devaraj, Jaehun Chun, James De Yoreo, Peter Pauzauskie
Sodium yttrium fluoride (NaYF4) is an upconverting material with many potential uses in chemistry, materials science, and biology that can be synthesized hydrothermally in both cubic (α) and hexagonal (β) crystallographic polymorphs. Understanding the mechanisms underlying the phase conversion between the cubic and hexagonal polymorphs is of great interest to help inform future efforts to synthesize atomically-precise quantum materials with well-defined sizes and morphologies. In this work, we use a combination of analytical transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), powder X-ray diffraction (XRD), in situ liquid cell TEM, atom probe tomography (APT), and extended x-ray absorption fine structure (EXAFS) measurements to show evidence suggesting that the hexagonal NaYF4 nanowires form through a non-classical crystal growth mechanism involving the formation and subsequent oriented attachment of mesocrystals consisting of cubic (α) plase units. EXAFS spectroscopy also suggests that substitutional Yb3+ point defects within NaYF4 are distributed evenly throughout the crystal lattice without clustering, and also that they may exhibit selective substitution into one of the two possible trivalent yttrium sites in the unit cell for hydrothermally synthesized NaYF4.

Funding

DoE BES KC020105-FWP12152

NW IMPACT

NSF ECC-1542101

History

Email Address of Submitting Author

abard124@uw.edu

Institution

University of Washington

Country

USA

ORCID For Submitting Author

0000-0002-9000-3277

Declaration of Conflict of Interest

no conflict of interest

Version Notes

This version resubmitted to Chemistry of Materials on 1/20/2019

Exports