Ostwald Ripening, Particle Size Focusing, and Decomposition of Sub-10 nm NaREF4 (RE = La, Ce, Pr, Nd) Nanocrystals

Autor(en): Raj, A. Naduviledathu
Rinkel, T.
Haase, M. 
Stichwörter: Chemistry; Chemistry, Physical; EARTH FLUORIDE NANOCRYSTALS; ER3+; GROWTH; Materials Science; Materials Science, Multidisciplinary; NAGDF4 NANOPARTICLES; NAYF4 NANOCRYSTALS; NAYF4-YB,ER; PHASE-CONTROLLED SYNTHESIS; STRATEGY; TRANSITION; UP-CONVERSION
Erscheinungsdatum: 2014
Herausgeber: AMER CHEMICAL SOC
Journal: CHEMISTRY OF MATERIALS
Volumen: 26
Ausgabe: 19
Startseite: 5689
Seitenende: 5694
Zusammenfassung: 
NaREF4 nanocrystals of the lighter rare earth elements RE = La, Ce, Pr, Nd are more difficult to prepare than those of the heavier lanthanides because the materials are sensitive to decomposition. Here, we present a procedure for the synthesis of sub-10 nm particles of beta-NaLaF4, beta-NaCeF4, beta-NaPrF, and beta-NaNdF4, as well as of alpha-NaCeF4, alpha-NaPrF4, and alpha-NaNdF4. These particles were used to study the decomposition reaction taking place in the standard oleic acid/octadecene solvent. Ostwald ripening of the beta-phase particles in this solvent leads to the expected particle growth and broadening of the particle size distribution only in the case of RE = Ce, Pr, Nd, whereas particles of NaLaF4 decompose to LaF3. Ostwald ripening of the alpha-phase particles in oleic acid/octadecene yields two products: larger particles of the hexagonal beta-phase with a very narrow size distribution and smaller particles of the rare earth trifluoride REF3. The yield of the nearly monodisperse beta-NaREF4 particles decreases from Nd to Ce and becomes negligible for the latter. X-ray fluorescence analysis reveals that the decomposition into the REF3 phase is caused by a strong sodium deficiency of the cubic alpha-NaREF4 nanocrystals, which is observed even if these particles are prepared in the presence of a 6-fold excess of sodium ions. We show that larger particles of phase-pure, beta-NaCeF4, beta-NaPrF4, and beta-NaNdF4 can nevertheless be prepared by Ostwald ripening of the corresponding cubic alpha-NaREF4 particles, if the sodium deficiency of the latter is compensated for during their conversion to the beta-phase.
ISSN: 08974756
DOI: 10.1021/cm502532r

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