调控六角NaYF4：Yb3+/Er3+纳米/微结构的水热合成与形态决定的上转换发光
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本研究论文聚焦于六角形NaYF4：Yb3+/Er3+纳米/微结构的制备及其形态调控下的上转换发光性质。通过对实验条件如pH值和氟化物源的精确控制，研究人员成功地在水热合成过程中生成了具有明确形态和尺寸的六方NaYF4晶体。X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)以及高分辨率透射电子显微镜(HRTEM)等表征技术被用于详尽分析这些产物，揭示了内在晶格结构与合成条件之间的密切关系。
文章详细探讨了在不同反应时间下，样品形态的演变机制，基于XRD分析和SEM观察，提出了一系列可能的β-NaYF4形貌形成途径。特别关注的是，研究者对Yb3+和Er3+共掺杂的样品进行了系统性的上转换(UC)发光特性的研究，这种发光现象是在近红外光激发下，材料吸收能量后发出可见光的过程。通过调控晶体的形态，研究人员观察到上转换发光强度和光谱分布随形貌变化而变化，这表明了形态对于上转换效率有着显著的影响。
这项研究不仅提供了关于六角形NaYF4合成方法的宝贵信息，还为理解复杂稀土氟化物化合物的形态控制合成策略开辟了新路径。这对于开发新型光电器件，如激光器、显示器和生物成像标记器等领域具有重要的应用潜力。此外，通过深入理解形貌对上转换发光的影响，未来的研究可能能够优化这类材料的性能，以满足特定应用中的需求，比如提高亮度、色纯度或响应速度等。这一工作在纳米材料科学和光子学领域具有深远的意义。
M.
Ding
et
al.
/
Applied
Surface
Science
333
(2015)
23–33
25
Fig.
2.
The
XRD
patterns
of
the
as-synthesized
samples
using
NaBF
4
as
fluoride
source
at
different
pH
values
and
the
standard
data
of
hexagonal
NaYF
4
(JCPDS
No.
28-1192)
as
a
reference:
(a)
pH
7,
(b)
pH
9,
(c)
pH
11.
intensities
of
(1
0
0),
(1
0
1),
(1
1
0)
and
(2
0
1)
peaks
vary
with
dif-
ferent
pH
values,
indicating
the
morphology
evolution
of
the
final
products.
When
NaBF
4
is
used
as
fluoride
source,
the
XRD
patterns
of
the
as-obtained
samples
at
different
pH
values
(pH
7,
9,
11)
are
also
investigated
and
shown
in
Fig.
2.
The
result
reveals
that
all
samples
exhibit
diffraction
patterns
corresponding
to
highly
crys-
talline
hexagonal-system
NaYF
4
.
Obviously,
the
relative
intensities
of
all
the
peaks
are
distinctively
different
from
those
synthesized
using
NaF
as
fluoride
source.
If
NH
4
F
is
adopted
as
fluoride
source,
the
XRD
patterns
(Fig.
3)
indicate
that
all
the
diffraction
peaks
of
the
three
samples
obtained
under
different
pH
values
(pH
7,
9,
11)
can
be
well
indexed
with
the
standard
data
of
hexagonal
NaYF
4
phase.
On
the
basis
of
the
above
analysis,
it
can
be
concluded
that
pure
-phase
of
NaYF
4
can
successfully
synthesized
by
using
three
fluoride
sources
under
different
pH
values.
However,
the
difference
from
each
other
in
the
relative
intensities
of
diffraction
peaks
for
these
as-obtained
products
reveals
the
possibility
of
different
pref-
erential
orientation
growth,
leading
to
morphology
evolution
of
the
as-synthesized
-NaYF
4
crystals.
3.2.
Morphologies
The
morphologies,
dimensions
and
aspect
ratios
of
the
samples
obtained
under
different
experimental
conditions
are
summarized
Fig.
3.
The
XRD
patterns
of
the
as-synthesized
samples
using
NH
4
F
as
fluoride
source
at
different
pH
values
and
the
standard
data
of
hexagonal
NaYF
4
(JCPDS
No.
28-1192)
as
a
reference:
(a)
pH
7,
(b)
pH
9,
(c)
pH
11.
in
Table
1.
It
can
be
seen
from
Table
1
that
the
fluoride
sources
and
pH
values
of
reaction
solution
have
a
great
impact
on
shapes
and
sizes
of
the
final
samples.
In
this
study,
the
detailed
effects
of
the
fluoride
source
and
pH
value
on
the
morphologies
and
dimensions
of
the
products
are
investigated
in
detail
in
the
following
sections.
3.2.1.
NaF
as
fluoride
sources
The
typical
FE-SEM
images
for
-NaYF
4
samples
synthesized
using
NaF
as
fluoride
source
at
different
pH
values
are
shown
in
Fig.
4.
At
pH
3,
the
sample
(S1)
is
composed
of
relatively
uniform
microtubes,
of
which
the
length
is
about
6–8
m
and
diameter
is
about
600–800
nm.
The
magnified
SEM
image
(Fig.
4b)
displays
a
close-up
review
of
one
isolated
microtube,
which
clearly
reveals
the
hollow
characteristic.
In
the
case
of
pH
5,
the
SEM
image
in
Fig.
4c
indicates
that
the
as-obtained
products
(S2)
consists
of
fairly
uni-
form
submicrorods
with
0.6–1
m
in
length
and
200–500
nm
in
diameter.
From
the
magnified
SEM
image
in
Fig.
4d,
we
can
clearly
see
the
hexagonal
prism
structure
of
those
submicrorods.
When
the
pH
value
is
adjusted
to
7,
the
general
images
of
the
as-synthesized
samples
are
shown
in
Fig.
4e
and
f,
respectively.
It
clearly
reveals
that
nanorods
of
-NaYF
4
(S3)
can
be
obtained.
Moreover,
the
mean
size
is
calculated
to
be
about
0.65
m
in
length
and
70
nm
in
diameter
(aspect
ratio
of
10).
Interestingly,
these
nanorods
present
well-faceted
planes
at
both
ends
and
side
surfaces,
and
arrange
into
large-scale
ordered
2D
nanoarrays.
3.2.2.
NaBF
4
as
fluoride
sources
When
NaF
is
replaced
by
NaBF
4
as
fluoride
source
and
the
other
experimental
conditions
remain
unchanged,
the
morphologies
of
the
final
samples
have
comparatively
dramatic
differences
relative
to
the
former.
At
pH
7,
the
SEM
image
in
Fig.
5a
indicates
that
-NaYF
4
consists
of
hollow
microtubes
with
14.46
m
in
length
and
1.79
m
in
diameter
(S4).
The
close-up
view
of
one
isolate
microtube
(Fig.
5b)
displays
the
inside
hollow
and
outside
prismatic
structure
of
the
sample,
which
has
open
ends
with
wall
thickness
from
400
to
600
nm.
With
the
rise
of
pH
value
to
9,
the
sample
S5
is
composed
of
a
mixture
of
microrods
and
nanorods,
as
shown
in
Fig.
5c.
The
mean
length
and
diameter
of
microrods
are
esti-
mated
as
10.65
and
0.33
m,
respectively.
From
the
enlarged
SEM
image
(Fig.
5d),
a
great
deal
of
nanorods
with
average
length
of
0.87
m
and
average
diameter
of
100
nm
is
clearly
observed.
When
the
experiment
is
performed
at
pH
11,
the
as-obtained
-NaYF
4
crystals
are
composed
of
large-scale
microrods
with
size
of
7.9
m
in
length
and
1.04
m
in
diameter,
as
presented
in
Fig.
5e
(S6).
More
careful
examination
of
the
enlarged
SEM
image
(Fig.
5f)
shows
clearly
that
the
length
and
aspect
ratio
of
microrods
are
reduced
with
the
increase
of
pH
value
from
9
to
11.
3.2.3.
NH
4
F
as
fluoride
sources
Upon
replacing
NaF
and
NaBF
4
with
NH
4
F
while
keeping
the
other
experimental
parameters
unchanged,
the
shape
and
size
of
the
products
are
quite
different
from
those
observed
using
NaF
and
NaBF
4
as
fluoride
sources,
as
presented
in
Fig.
6.
At
pH
7,
-NaYF
4
submicrorods
with
length
about
5.53
m
and
diameter
about
0.89
m
are
successfully
synthesized
(Fig.
6a
and
b).
With
the
increment
of
pH
value
from
7
to
9,
the
product
consists
of
a
large
scale
of
submicrorods
(Fig.
6c).
The
mean
length
and
diam-
eter
of
these
submicrorods
are
4.07
m
and
0.75
m,
respectively
(
Fig.
6d).
Upon
a
further
increase
of
pH
value
to
11,
the
product
is
of
a
great
deal
of
submicrorods
with
smooth
surface
and
remarkable
uniformity
(Fig.
6e).
Further
investigation
under
higher
magnifica-
tion
shows
the
hexagonal
prism
structure
of
these
submicrorods
(
Fig.
6f).
Analysis
of
a
number
of
the
submicrorods
reveals
that
these
microcrystals
have
an
average
size
of
0.48
m
in
length
and
0.23
m
in
diameter.
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