A Mechanistic Understanding of Nonclassical Crystal Growth in Hydrothermally Synthesized Sodium Yttrium Fluoride Nanowires

Bard, Alexander B.; Zhou, Xuezhe; Xia, Xiaojing; Zhu, Guomin; Lim, Matthew B.; Kim, Seung Min; Johnson, Matthew C.; Kollman, Justin M.; Marcus, Matthew A.; Spurgeon, Steven R.; Perea, Daniel E.; Devaraj, Arun; Chun, Jaehun; Yoreo, James J. De; Pauzauskie, Peter J.

doi:10.1021/acs.chemmater.9b04076

Cited by 30 publications

(55 citation statements)

References 101 publications

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“…The primary particle formation pathway is not likely Ostwald ripening, where smaller particles dissolve into atomic precursors and redeposit on larger particles. Instead, during coarsening, multiple smaller nanoparticles likely coalesce to form larger particles, a reasonable conclusion given the polycrystalline nature of the nanoparticles ( vide infra ) and the recently reported nonclassical nucleation pathway of NaYF 4 …”

Section: Resultssupporting

confidence: 52%

“…Instead, during coarsening, multiple smaller nanoparticles likely coalesce to form larger particles, a reasonable conclusion given the polycrystalline nature of the nanoparticles (vide inf ra) and the recently reported nonclassical nucleation pathway of NaYF 4 . 50 After the final thermal treatment where the samples are held at 350 °C for 2 h, the nanoparticles crystallize, and the PEG fully degrades. The SAED spectrum of a sample shows a pattern consistent with α-NaYF 4 (Figure 3C), in line with the conclusion based on the PXRD measurement of the precursor ink (Figure 2B, bulk thin film).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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Site-Isolated Upconversion Nanoparticle Arrays Synthesized in Polyol Nanoreactors

Wahl

et al. 2021

J. Phys. Chem. C

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A versatile approach for synthesizing Yb 3+ -and Er 3+ -doped NaYF 4 upconversion nanoparticle (UCNP) arrays is presented. The nanoparticles are positioned at precisely defined locations through the tip-directed deposition of polyol nanoreactors and subsequent thermal conversion. This method is based on conducting a solution-phase polyol synthesis in nanometerscale reactors, which provide isolated and confined reaction vessels for the thermal decomposition of a fluoride precursor and the coarsening of fluoride nanoparticles. When the nanoreactors are annealed at 350 °C, the polyol degrades, and the nanoparticles, which exhibit upconversion properties, crystallize. Single nanoparticles are attained in each nanoreactor by tuning the precursor concentration, nanoreactor size, and temperature ramping rate. This strategy enhances the scope of nanostructures that can be synthesized by tip-directed routes and, when combined with massively parallel pen approaches such as polymer pen lithography, provides a generalizable platform for the high-throughput synthesis, screening, and discovery of nanomaterials for photonics and other applications.

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Section: Resultssupporting

confidence: 52%

Section: ■ Results and Discussionmentioning

confidence: 99%

Site-Isolated Upconversion Nanoparticle Arrays Synthesized in Polyol Nanoreactors

Wahl

et al. 2021

J. Phys. Chem. C

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“…Many studies involved the α → β phase conversion for NaYF 4 nanocrystals and proposed related crystal growth mechanisms based on the oriented growth of nanoparticles. 12,15,16 However, these theories cannot give a good reason for the appearance of the α phase in the low-temperature range (<200 °C), which occurs as high-temperature solid solutions with less NaF than REF 3 in the phase diagrams. 17,18 In addition, a β → α transition happens in NaREF 4 when the temperature increases, 19,20 and the thermodynamics of the phase conversion in aqueous solutions needs further research.…”

Section: ■ Introductionmentioning

confidence: 99%

Thermochemical Investigation of the Stability and Conversion of Nanocrystalline and High-Temperature Phases in Sodium Neodymium Fluorides

et al. 2021

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As important upconversion materials, sodium rare-earth fluorides (nominally NaREF4 in composition but actually often harboring sodium deficiency, especially in nanophase materials) have been subjected to intensive studies, particularly in the synthesis and applications of nanocrystals. However, the mechanisms of the conversion between the two phases (α and β) of NaREF4 nanocrystals during the synthesis are still controversial and lack thermodynamic investigations, which limit the rational design, synthesis, and processing of these materials. In this work, aiming at NaREF4 with light rare-earth elements, the thermochemistry of the NaF–NdF3 system, including the α and β phases in nanocrystalline/nanophase and bulk stoichiometric samples, is systematically studied by thermogravimetry and differential scanning calorimetry and high-temperature oxide melt solution calorimetry. With the help of compositional analysis and structural characterization, a strong Na deficiency is found in nanocrystals with small crystal sizes, which leads to the formation of cubic (α) crystallographic polymorphs at the nucleation stage, possibly because of the relative thermodynamic stability of the α phase compared to the β phase in such compositions. After converting to the hexagonal (β) structure, the crystal growth is accompanied by an increase of Na content in nanocrystals with increasing energetic stability until the formation of the stoichiometric compound (β-NaNdF4). On the contrary, the stoichiometric α phase (α-NaNdF4) is metastable at room temperature but is the intermediate phase as the temperature increases. We show that the α → β phase conversion in aqueous solution synthesis is distinct from the β → α transition driven by temperature because of composition differences.

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“…Due to the importance of the variable stoichiometry of this system to our paper, we instead use the shorthand NaYF when referring to this material. The majority of aqueous syntheses of NaYF use either microemulsion solvent systems 22 or organic capping ligands 23 for the purpose of controlling both the size and shape of discrete nanocrystals 24 . In this work we synthesized ligand-free NaYF materials to provide a clear understanding of the role of solvated aqueous ion dynamics by eliminating ion chelation and surface passivation by organic species.…”

Section: Introductionmentioning

confidence: 99%

Multi-Step Crystallization and Chemical Evolution of Sodium Yttrium Fluoride

Pauzauskie

Bard

Felsted

et al. 2021

Preprint

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Two-step crystallization mechanisms based on spinodal decomposition followed by nucleation are commonly observed both in the laboratory and in nature. While this pathway may require chemical reactions, subsequent nucleation and growth are often considered as separate, discrete events from the reaction itself. Recent work has also shown a distinct intermediate step involving the formation of an amorphous aggregate. Here we report a novel four-step mechanism in the aqueous synthesis of sodium yttrium fluoride involving 1) the segregation of aqueous ions into a dense liquid phase, 2) the formation of an amorphous aggregate, 3) nucleation of a cubic YF3 phase, and 4) subsequent solid-state diffusion of sodium and fluoride ions to form a final NaYF4 phase. The final step involves a continuous, gradual change of the solid phase’s chemical stoichiometry from YF3 toward NaYF4. Unlike previously studied nucleation and growth mechanisms, the stoichiometry of the final solid phase evolves throughout the crystallization process rather than being determined at nucleation. This novel four-step mechanism provides a new perspective into the nucleation and growth of many other crystalline materials given the ubiquity of nonstoichiometric compounds in nature.

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A Mechanistic Understanding of Nonclassical Crystal Growth in Hydrothermally Synthesized Sodium Yttrium Fluoride Nanowires

Cited by 30 publications

References 101 publications

Site-Isolated Upconversion Nanoparticle Arrays Synthesized in Polyol Nanoreactors

Site-Isolated Upconversion Nanoparticle Arrays Synthesized in Polyol Nanoreactors

Thermochemical Investigation of the Stability and Conversion of Nanocrystalline and High-Temperature Phases in Sodium Neodymium Fluorides

Multi-Step Crystallization and Chemical Evolution of Sodium Yttrium Fluoride

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