Chemistry Reference
In-Depth Information
Other unusual structures have also been reported. For example,
during a shape-evolution experiment of ceria nanoparticles with a
relatively large amount of oleylamine, Hyeon
. [120] reported
tadpole-shaped nanowires. Tadpole-shaped nanowires consist of a
spherical head with a diameter of 3.5 nm and a wire-shaped tail with
a diameter of 1.2 nm and length of 27 nm. The low-magnification
TEM image and HRTEM images of the tadpole nanostructures are
shown in Fig. 2.29a. In a separate study, Li
et al
et al
. [52] came across rice-
nanoparticles (Fig. 2.29b) composed of short nanorods and
aggregation of nanocrystals. The authors attributed the formation of
rice-like nanoparticles to selective adsorption of surfactant molecules
in certain planes, which induce further tendency to grow along that
direction. For example, surfactant linoleate induces growth along
<111> direction for YF
like YF
3
nanoparticles, which further agglomerate to
form rice-like structure.
3
Figure 2.29
(a) TEM images of tadpole-shaped ceria nanocrystals; insets:
HRTEM images of a tadpole-shaped nanocrystal [120]. (b) YF
3
rich-like nanocrystals [52].
2.3.7
Phase Control of Rare Earth Nanostructures
Control of the nanocrystalline phase is one of the fundamental
ways to tune morphology. Crystal phases of the nanostructures not
only influence shape and morphology of the nanocrystals but also
modulate the characteristics of the materials [40].
has been investigated as one of the most efficient
upconversion hosts, and it exists in two polymorphs: cubic α-NaREF
NaREF
4
4
and hexagonal β-NaREF
. Between this two, β-phase NaREF
induces
4
4
high efficiency upconversion emission. Mai
et al
. [92] reported an
