Skip to Content
Merck
  • Ostwald-ripening and particle size focussing of sub-10 nm NaYF₄ upconversion nanocrystals.

Ostwald-ripening and particle size focussing of sub-10 nm NaYF₄ upconversion nanocrystals.

Nanoscale (2014-10-28)
Thorben Rinkel, Jörg Nordmann, Athira Naduviledathu Raj, Markus Haase
ABSTRACT

We have studied the growth behaviour of sub-10 nm NaYF₄ upconversion nanocrystals of the hexagonal β-phase and the cubic α-phase. Ostwald-ripening of such particles in oleic acid/octadecene solvent results in broadening of the particle size distribution if the colloid contains particles of one crystal phase only. Narrow size distributions are formed only if β-phase particles grow in the presence of an excess of α-phase particles. Such binary mixtures of α-phase and β-phase particles form intrinsically when colloids of α-phase particles are heated for a sufficiently long time, because seeds of the β-phase nucleate in the solution after some time at high temperatures. Since the number of seeds determines the final size of the β-phase product, control of the nucleation is crucial for controlling the final particle size. We show that the number of β-phase seeds strongly depends on the composition of the α-phase known to form solid solutions Na₁-xYF₄-x in the range from x = 0 to x = 4/9. Sodium-deficient α-phase particles form a negligible number of β-phase seeds whereas α-phase particles with high sodium content yield a very large number of seeds. By taking advantage of this dependence and modifying the synthesis of the α-phase particles accordingly, small phase-pure β-NaYF₄:Yb,Er particles with a size smaller than 6 nm can be prepared in oleic acid/octadecene just as well as much larger particles.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Oleic acid, SAJ first grade, ≥70.0%
Sigma-Aldrich
Sodium oleate, ≥95% (capillary GC)
Sigma-Aldrich
Sodium oleate, ≥99%
Sigma-Aldrich
1-Octadecene, technical grade, 90%
Supelco
1-Octadecene, analytical standard, ≥99.0% (GC)
Sigma-Aldrich
1-Octadecene, ≥95.0% (GC)
Sigma-Aldrich
Oleic acid, meets analytical specification of Ph, Eur., 65.0-88.0% (GC)
Sigma-Aldrich
Oleic acid, BioReagent, suitable for cell culture
Sigma-Aldrich
Oleic acid, ≥99% (GC)
Supelco
Oleic acid, Selectophore, ≥99%
Supelco
Oleic acid, analytical standard
Sigma-Aldrich
Oleic acid, natural, FCC
Sigma-Aldrich
Oleic acid, technical grade, 90%
Oleic acid, European Pharmacopoeia (EP) Reference Standard
Erbium, rod, 100mm, diameter 10.0mm, cast, 99%
Erbium, foil, 25x25mm, thickness 1.0mm, as rolled, 99%
Erbium, rod, 50mm, diameter 6.35mm, cast, 99%
Erbium, foil, 50x50mm, thickness 0.125mm, as rolled, 99%
Erbium, rod, 50mm, diameter 2.0mm, cast, 99%
Erbium, foil, 50x50mm, thickness 1.0mm, as rolled, 99%
Erbium, rod, 100mm, diameter 6.35mm, cast, 99%
Erbium, wire reel, 50mm, diameter 1.0mm, hard, 99.9%
Erbium, wire reel, 100mm, diameter 1.0mm, hard, 99.9%
Erbium, rod, 50mm, diameter 10.0mm, cast, 99%
Erbium, foil, 25x25mm, thickness 0.125mm, as rolled, 99%
Erbium, foil, not light tested, 25x25mm, thickness 0.005mm, as rolled, 99%
Erbium, foil, not light tested, 50x50mm, thickness 0.025mm, as rolled, 99%
Sigma-Aldrich
Ytterbium, powder, ≥99.9% trace rare earth metals basis
Sigma-Aldrich
Ammonium fluoride, SAJ special grade, ≥97.0%
Sigma-Aldrich
Yttrium, chips, 99.9% trace rare earth metals basis