Well-defined barium molybdate hierarchical architectures with different morphologies: Controllable synthesis, formation process, and luminescence properties

Article abstract of DOI:10.1016/j.jallcom.2013.11.075

Uniform and well-dispersed barium molybdate (BaMoO₄) hierarchical microspheres and microflowers have been successfully synthesized via a hydrothermal route by using sodium dodecyl benzenesulfonate (SDBS) as surfactant. The reaction conditions, including SDBS additive, pH value of the initial solution, as well as reaction temperature, have great effect on the size and morphology of the BaMoO₄ products. The possible formation process of the BaMoO₄ microspheres has been investigated by time-dependent experiments. The as-synthesized BaMoO₄:Ln³⁺ (Ln = Eu, Tb, Dy, and Sm) phosphors show intense characteristic red, green, green-yellow, and orange-red emissions under ultraviolet light excitation, which might find potential applications in the fields of light emitting phosphors, advanced flat panel displays, and light-emitting diodes (LEDs).

Full text of DOI:10.1016/j.jallcom.2013.11.075

Journal of Alloys and Compounds 589 (2014) 185–191
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jalcom
Well-defined barium molybdate hierarchical architectures with
different morphologies: Controllable synthesis, formation process, and
luminescence properties
⇑
⇑
Cuimiao Zhang , Lei Zhang, Changying Song, Guang Jia, Shuying Huo, Shigang Shen
Key Laboratory of Medicinal Chemistry and Molecular Diagnosis of the Ministry of Education, Key Laboratory of Chemical Biology of Hebei Province, College of Chemistry
and Environmental Science, Hebei University, Baoding 071002, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 17 July 2013
Received in revised form 13 November 2013
Accepted 13 November 2013
Available online 22 November 2013
Uniform and well-dispersed barium molybdate (BaMoO ) hierarchical microspheres and microflowers
have been successfully synthesized via a hydrothermal route by using sodium dodecyl benzenesulfonate
4
(
SDBS) as surfactant. The reaction conditions, including SDBS additive, pH value of the initial solution, as
well as reaction temperature, have great effect on the size and morphology of the BaMoO products. The
possible formation process of the BaMoO microspheres has been investigated by time-dependent exper-
4
4
3
+
4
iments. The as-synthesized BaMoO :Ln (Ln = Eu, Tb, Dy, and Sm) phosphors show intense characteristic
Keywords:
red, green, green–yellow, and orange–red emissions under ultraviolet light excitation, which might find
potential applications in the fields of light emitting phosphors, advanced flat panel displays, and light-
emitting diodes (LEDs).
Barium molybdate
Hydrothermal synthesis
Morphology
Lanthanide ions
Ó 2013 Elsevier B.V. All rights reserved.
Luminescence properties
1
. Introduction
The chemical and physical properties of functional materials
growth, morphology, and orientation of the nanoparticles [6]. So
they always play an important role in controlling the dynamics
of crystal growth and determining the final morphology of the
hierarchical nano/microstructures [7–9].
As an important class of inorganic compounds, rare earth ions
doped molybdates with a scheelite structure have gained much
attention due to their attractive luminescence and structural prop-
erties, supporting various promising applications such as phosphor
materials in fields of light-emitting diodes (LEDs), and optical
fibers, biolabels, lasers etc. [10–12]. Among the molybdates mate-
consisting of either inorganic compounds or inorganic/organic hy-
brids are fundamentally related to their size, shape, and dimen-
sionality [1–3]. Constructing materials with fascinating
hierarchical architectures are of great importance and highly de-
manded not only due to the fundamental scientific interest but
also for potential technological applications [4]. Large-scale self-
assembled hierarchical micro- and nanoparticles in phosphors
have attracted great attention due to their ease of processing into
devices with high resolution, high screen coverage, intense emis-
sion, and long service life [5]. Thus, many efforts have been dedi-
cated to develop novel synthesis routes for the fabrication of
high-quality hierarchical nano/micostructures. Among various
synthesis routes, the hydrothermal method, due to its mild reac-
tion conditions, ease of operation, and large-scale production capa-
bility, has been proved to be an effective and convenient synthesis
technique in achieving a variety of hierarchical architectures. Dur-
ing the hydrothermal process, the chelating agents, and/or surfac-
tants often provide an effective way to regulate the nucleation,
4
rials, barium molybdate (BaMoO ) has been widely applied as an
eminent candidate for the matrix of lanthanide activator ions. Up
to now, many studies have been recently reported [13–16] on
4
the luminescent properties of BaMoO doped with different lantha-
3
+
3+
3+
4
nide activator ions, such as Eu , Pr , and Sm . BaMoO hierarchi-
cal micro- and nanoparticles with different morphologies have
been prepared, such as hollow spheres [14], nanocrystallites [17],
nanobelts [18], shuttle-like [19], nest-like [20], octahedron-like
[21], and bundle-like [22] nano/microstructures. However, the
synthesis of uniform and well-dispersed barium molybdate hierar-
chical microspheres was seldom reported. On the other hand, it is
well-known that the spherical morphology with narrow size
distribution and proper particle size is beneficial for high bright-
ness because such phosphors exhibit high packing densities and
low scattering of light [23,24]. Therefore, it is of significance and
desirable to develop easily controllable methods for the fabrication
⇑
Corresponding authors. Address: College of Chemistry and Environmental
Science, Hebei University, Baoding 071002, PR China. Tel./fax: +86 312 5079359.
E-mail addresses: cmzhanghbu@163.com (C. Zhang), shensg@hbu.edu.cn
(
S. Shen).
0
925-8388/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jallcom.2013.11.075

1
86
C. Zhang et al. / Journal of Alloys and Compounds 589 (2014) 185–191
of spherical lanthanide ions doped BaMoO
with promising novel properties.
4
luminescent materials
:Ln3+
In this paper, uniform and well-dispersed BaMoO
Ln = Eu, Tb, Dy, and Sm) hierarchical microspheres and microflow-
4
(
ers have been successfully synthesized through a simple and
friendly hydrothermal process with SDBS as surfactant. The struc-
ture, morphology, possible formation process, and luminescence
properties of the as-synthesized BaMoO
tigated in detail.
4
samples have been inves-
2
. Experimental section
2.1. Synthesis
Fig. 1. XRD patterns of BaMoO
additive at (a) pH 5, (b) pH 4 and (c) without SDBS as surfactant. The standard data
of tetragonal BaMoO (JCPDS No. 29-0193) is presented as a reference.
4
samples prepared at 160 °C for 12 h with SDBS
Ln(NO
by dissolving Ln
3
)
3
(Ln = Eu, Dy, and Sm) and Tb(NO
3
)
3
aqueous solutions were obtained
solution with heat-
2
O
3
(99.99%) and Tb (99.99%) in dilute HNO
4
O
7
3
ing with agitation. All other chemicals were of analytical grade and used directly
without further purification.
4
In a typical synthesis, 2 mmol of Ba(Ac)
deionized water. Subsequently, 2 mmol (0.697 g) of sodium dodecyl benzenesulfo-
nate (SDBS, C18 29NaO S) were added into the above solution under stirring. Then,
mmol of Na MoO aqueous solution (15 mL) was introduced to the former solu-
2
(0.511 g) was dissolved in 20 mL of
H
3
4
2
4
tion. The pH value of the mixture was adjusted to 5 or 4 with acetic acid solution.
After additional agitation for 10 min, the as-obtained mixing solution was trans-
ferred into a 50 mL Teflon bottle held in a stainless steel autoclave, sealed, and
maintained at 160 °C for 12 h. The precipitate was separated by centrifugation after
the autoclave cooled to room temperature naturally. Finally, precipitate was
washed with deionized water and ethanol in sequence, and then dried in air to a
constant weight for further investigation.
A similar process were employed to prepare Eu3+, Tb3+, Dy3+, or Sm3+ doped
BaMoO
Tb(NO
stage. For comparison, the experiment was performed to prepare BaMoO
4
samples except for adding a stoichiometric amount (5 mol%) of Eu(NO
, Dy(NO , and Sm(NO aqueous solution instead of Ba(Ac) at the initial
sample
3 3
) ,
)
3 3
3
)
3
)
3 3
2
4
by a similar process without using SDBS as additive. Moreover, different hydrother-
mal reaction temperature (200 °C, 12 h) and time (160 °C, 4 h, 8 h) were selected to
investigate the formation process of the BaMoO
4
microspheres.
2.2. Characterization
The samples were characterized by powder X-ray diffraction (XRD) performed
on a D8 Advance diffractometer (Bruker). Fourier transform infrared spectroscopy
FT-IR) spectra were measured with a Perkin–Elmer 580B infrared spectrophotom-
(
eter with the KBr pellet technique. The morphology and composition of the samples
were inspected using JSM-7500F cold field scanning electron microscope JEOL
equipped with an energy-dispersive X-ray (EDX) spectrum. Transmission electron
microscopy (TEM) images were obtained by an FEI Tecnai G2 S-Twin transmission
electron microscope. Photoluminescence (PL) excitation and emission spectra were
recorded with a Hitachi F-4500 spectrophotometer equipped with a 150 W xenon
lamp as the excitation source. The luminescence decay curves were obtained from
a Lecroy Wave Runner 6100 Digital Oscilloscope (1 GHz) using a tunable laser
(
pulse width =4 ns, gate =50 ns) as the excitation (Continuum Sunlite OPO). All
measurements were performed at room temperature.
3
. Results and discussion
Fig. 1a and b shows the XRD patterns of the samples prepared
with SDBS as surfactant at pH 5 and 4 (160 °C, 12 h). The diffraction
peaks of two samples can be well indexed to the tetragonal schee-
lite-type structure of BaMoO
I41/a, No. 88). No additional peaks of other phases can be detected,
revealing the formation of pure tetragonal phase of BaMoO . The
XRD pattern of the sample prepared without adding SDBS as addi-
tive also coincides with scheelite-type BaMoO (Fig. 1c). Moreover,
the crystallite size of the BaMoO samples can be estimated by
4
(JCPDS No. 29-0193, space group:
4
Fig. 2. (a) EDX and (b) FT-IR spectra of the BaMoO sample prepared at pH 5.
4
4
of barium (Ba), molybdenum (Mo), and oxygen (O) elements (Si
from the silicon substrate). No other impurity peaks can be
4
Scherrer’s equation: D = 0.89k/bcosh, where D is the average grain
size, the factor 0.89 is characteristic of spherical objects, k is the
X-ray wavelength (0.15405 nm), b and h are the full-width at
half-maximum and diffraction angle of an observed peak, respec-
tively. The estimated average crystallite sizes of the spherical and
detected, which confirms the pure phase of BaMoO
tively support the XRD result of the sample. Fig. 2b shows the FT-IR
spectrum of the BaMoO sample prepared with SDBS as surfactant
4
and can effec-
4
(pH 5). The absorption bands centered at 2338 and 3296
À1
(1608) cm are attributed to the atmospheric adsorbed CO
2
and
flower-like BaMoO
The energy dispersive X-ray (EDX) spectrum was further used
to investigate the as-obtained BaMoO sample (pH 5). The EDX
spectrum (Fig. 2a) of the BaMoO sample confirms the presence
4
samples are 43.9 and 38.8 nm, respectively.
the absorbed water on the surface of BaMoO
4
sample. The peak
À1
at 1450 cm is assigned to the deformation vibration of C–H bond
(dCH), which can be attributed to the characteristic frequencies of
residual SDBS [25]. The intense absorption band centered at
4
4

C. Zhang et al. / Journal of Alloys and Compounds 589 (2014) 185–191
187
À1
8
18 cm is due to F
2
(m
3
) antisymmetric stretching vibration orig-
morphology of the products. Fig. 3 shows the SEM and TEM images
of the BaMoO sample prepared with SDBS as surfactant at pH 5
(160 °C). It can be clearly seen from the low-magnification SEM
image (Fig. 3a) that the as-obtained BaMoO sample consist of high
yield and well-dispersed microspheres with uniform diameters of
about 4 m. From the high-magnification SEM images (Fig. 3b
2
À
inating from the Mo–O stretching vibration in MoO tetrahedron
4
4
2À
[
26,27], confirming the presence of MoO4 groups in the product.
The FT-IR result provides additional evidence for the formation of
the BaMoO product after the hydrothermal process, which is in
good accordance with the XRD and EDX results (Figs. 1 and 2a).
The SEM and TEM images were used to characterize the mor-
4
4
l
and c), the hierarchical microspheres show rough peripheral sur-
phology of the as-prepared BaMoO
4
samples. It should be men-
faces and contain many irregular microcrystals. The TEM image
of the BaMoO sample exhibits the perfect spherical morphology
4
with good uniformity and dispersion (Fig. 3d). Moreover, the rough
edges of the microspheres can also be confirmed by TEM images.
In order to disclose the growth process of these hierarchical
architectures, the time-dependent experiments were carried out
3
+
3+
tioned that doping a small amount of lanthanide ions (Eu , Tb
,
3
+
3+
Dy , or Sm ) in the BaMoO
tallization, and morphology of the BaMoO
work, which agrees well with the previous reports [15,28]. So here
we only select pure BaMoO as an example to illustrate the
4
host does not change the phase, crys-
4
products in our present
4
Fig. 3. (aÀc) SEM and (d) TEM images of the BaMoO
4
microspheres (pH 5).
Fig. 4. SEM images of the as-synthesized hydrothermal product at 160 °C for (a) 4 h, (b) 8 h and (c, d) 200 °C for 12 h (pH 5).

1
88
C. Zhang et al. / Journal of Alloys and Compounds 589 (2014) 185–191
4
Fig. 5. SEM images of the BaMoO samples prepared with SDBS (a,b) at pH 4 and (c,d) without SDBS as surfactant (160 °C, 12 h).
Fig. 6. XRD patterns of (a) BaMoO
4 4 4
:Eu3+, (b) BaMoO :Tb3+, (c) BaMoO :Dy3+ and (d)
BaMoO
4
:Sm3 microspheres.
+
(
160 °C, pH 5). The SEM images of the products obtained after dif-
ferent hydrothermal times are shown in Fig. 4a and b. After 4 h of
hydrothermal treatment, the scheelite structured BaMoO formed
with low crystallinity (Fig. S1a, supplementary information), and
the product consists of many multilayered disks with 3–4 m in
diameter and about 2 m in thickness (Fig. 4a). When the reaction
time was extended to 8 h, the BaMoO sample with high crystallin-
4
l
l
4
ity was obtained (Fig. S1b, supplementary information), and the
hydrothermal product converts to quasi-microspheres with
diameters of about 3–4
nanoparticles (Fig. 4b). A great deal of uniform and well-dispersed
BaMoO microspheres can be obtained (Fig. 3) when the reaction
lm, which are composed of many tiny
4
time was increased up to 12 h. Considering the SEM results, the
possible conversion process may be as follows. In the early stages
2
+
of the reaction, Ba ions in the reaction medium formed complex
2À
coordinate bonds with SDBS, which reacted with the MoO4 ions,
forming BaMoO monomers. After the nucleation, the BaMoO
monomers grew into BaMoO nanocrystallites stabilized by SDBS.
Fig. 7. Photoluminescence (a) excitation and (b) emission spectra of hierarchical
spherical, flower-like, and shuttle-like BaMoO :Eu samples.
4
4
4
3+
4
As the reaction continued, the nanocrystallites grew along specific
directions at the expense of the smaller ones according to the Ost-
wald ripening, leading to the formation of hierarchical multilayer
disks. After further hydrothermal treatment, the multilayered disks
underwent a further crystal growth and crystallization process
driven by minimization of the total surface energy of the system,
giving rise to the formation of complex spherical microstructures.

C. Zhang et al. / Journal of Alloys and Compounds 589 (2014) 185–191
189
On the other hand, the influence of reaction temperature on the
morphology of products was also investigated. Fig. 4c, d shows the
crucial role in determining the ultimate shape of the product in
our current synthesis. To substantiate the important influence of
SDBS, a controlled experiment was carried out in the absence of
SEM images of BaMoO
It can be clearly seen that the as-obtained highly crystalline
BaMoO sample (Fig. S1c, supplementary information) is composed
of spherical particles with diameters of about 2 m. Obviously, the
4
sample prepared at 200 °C for 12 h (pH 5).
SDBS during the synthesis process. The as-synthesized BaMoO
4
4
sample consists of a great deal of relatively uniform shuttle-like
microcrystals with sharp tips and protrusions in the middle
l
particle size is smaller than that of prepared at 160 °C (Fig. 3). The
reduction of particle size is attributed to the influence of the rate of
nucleation and crystal growth at different temperatures. Increasing
of the reaction temperature normally results in an increase of the
reaction rate; therefore at a relatively high temperature more
(Fig. 5c and d). The shuttle-like BaMoO
4
crystals are about 10 lm
in length and 2–3 m in width for the middle section, which basi-
l
cally agrees with the previous literatures [19,32].
Fig. 6 shows the XRD patterns of the lanthanide activator ions
Ln3+ (Ln = Eu, Tb, Dy, and Sm) doped BaMoO
samples with SDBS
as surfactant (pH 5). One can see that the diffraction peaks of
4
4
BaMoO nuclei would form simultaneously before the growth pro-
3
+
cess. Thus, the growth for each seed is suppressed due to the rapid
decrease of supersaturation, resulting in the formation of
small-sized product. The similar situation holds for the synthesis
BaMoO
BaMoO
4
:Ln samples agree well with tetragonal scheelite-type
3
+
4
, but all diffraction peaks of Ln -doped samples shift
3+
slightly to the higher angle side, indicating that the Ln (Ln = Eu,
Tb, Dy, and Sm) ions have been effectively doped into the BaMoO
4
of LiFePO
4
[29], NiSe [30], and BaTiO
3
[31] materials reported in
the previous literatures.
host lattice. The result can be explained by the Bragg equation 2d
sinh = k (d is the distance between two crystal planes, h is the dif-
fraction angle of an observed peak, and k is the X-ray wave-
The pH value of the initial solution has great effect on the size
and morphology of the hydrothermal product. When the pH value
of the initial solution is adjusted to 4 (with SDBS as surfactant, other
reaction parameters remaining the same), the morphology of the
2
+
length). When the Ba
4
ions in BaMoO host lattice were
substituted by lanthanide activator ions with smaller radii, the
crystal lattice constants and d-spacing decreased, and thus the
diffraction angles shifted to the higher angle side. In order to
investigate the lanthanide activator dopants, the EDX spectra of
4 4
BaMoO sample changes evidently. The BaMoO product is com-
posed of large scale hierarchical microflowers, which are con-
structed by numerous microflakes, acting as the petals (Fig. 5a
and b). The microflakes extend outward from the center of the flow-
ers, and organize closely. The diameter of the assembled flower is
3
+
4
BaMoO :Ln (Ln = Eu, Tb, Dy, and Sm) samples were performed.
From the EDX spectra (Fig. S2, supplementary information), we
can clearly observe the characteristic peaks of Eu, Tb, Dy, and
about 7–8
about 100 nm. When the pH value was fixed at 7 or higher, the
as-synthesized BaMoO samples were composed of a mixture of
lm, while the thickness of the petal-like flakes is
Sm elements besides BaMoO
thanide activator ions have been effectively doped into the
BaMoO host lattice, which is in good accordance with the XRD
result (Fig. 6).
4
. The result indicates that the lan-
4
aggregated nanoparticles and irregular microcrystals (not shown).
On the other hand, it is found that the SDBS additive also plays a
4
Fig. 8. Photoluminescence excitation and emission spectra of (A) BaMoO
4 4 4
:Tb3+, (B) BaMoO :Dy3+, (C) BaMoO :Sm3+ microspheres and (D) CIE chromaticity diagram of
3+
3+
3+
3+
3+
4
BaMoO :Ln samples: (a) Eu , (b) Tb , (c) Dy and (d) Sm .

1
90
C. Zhang et al. / Journal of Alloys and Compounds 589 (2014) 185–191
The photoluminescence (PL) properties of the as-synthesized
second strongest emission intensity, and shuttle-like sample has
3+
pure BaMoO
were characterized by the PL excitation and emission spectra. Un-
der ultraviolet light excitation, the BaMoO sample without doping
4
4
and BaMoO :Ln (Ln = Eu, Tb, Dy, and Sm) samples
the weakest luminescence. It is well-established that a spherical
morphology with narrow size distribution for phosphors is good
for high brightness because high packing densities and low scatter-
ing of light can be obtained by using such phosphors [23,24].
4
lanthanide ions nearly does not show any luminescence. The slight
emission from 350 to 400 nm is from the xenon lamp background
in measurement process (Fig. S3, supplementary information).
3
+
Therefore, the spherical BaMoO
4
:Eu sample exhibits the stron-
gest luminescence.
When the lanthanide activator ions were doped into the BaMoO
4
On the basis of the above result, it can be concluded that the
spherical BaMoO sample exhibits the strongest emission intensity.
Here we take the spherical sample as an example to investigate the
host, the as-obtained samples exhibited intense characteristic
emissions of activators. From Fig. 7, it can be found that the shape
and profile for the excitation and emission spectra of the spherical,
4
3
+
3+
3+
luminescence properties of Tb , Dy , and Sm -doped BaMoO
4
3+
3+
flower-like, and shuttle-like BaMoO
4
:Eu samples are similar. The
samples. The PL excitation spectra of BaMoO
4
:Ln (Ln = Tb, Dy,
2
À
excitation spectra (Fig. 7a), which was obtained by monitoring the
and Sm) microspheres also consist of a broad band of MoO groups
4
3
+
5
7
3+
3+
3+
emission of the Eu
D
0
– F
2
transition at 617 nm, consists of a
and the characteristic f–f transitions of Tb , Dy , and Sm ions
(Fig. 8A–C), which is similar to that of BaMoO
:Eu3+ sample. Upon
excitation into the MoO groups, the emission spectra of the as-
broad band with a maximum at about 290 nm and some sharp
peaks between 350 and 500 nm. The broad band can be assigned
to the charge transfer from the oxygen ligands to the central
4
2
4
À
3
+
4
obtained BaMoO :Ln (Ln = Tb, Dy, and Sm) samples are composed
2À
5
7
3+
4
6
molybdates atom inside the MoO4 groups. The dominant sharp
of D
4
– F
J
(J = 6,5,4,3) transition lines of Tb ions, F9/2– H
J
(J = 15/
(J = 5/2,7/
2,9/2,11/2) transition lines of Sm ions, respectively (Fig. 8A–C).
7
5
3+
3+
4
6
peaks at 395 and 464 nm can be attributed to the
F
0
– L
6
and
2,13/2,11/2) transition lines of Dy ions, and G5/2– H
J
7
0 2
F – D
transitions within the 4f6 configuration of Eu ions,
5
3+
2
À
3+
3+
3+
respectively [13,33]. Upon excitation into the MoO groups at
The result agrees well with other Tb , Dy , and Sm activated
luminescent materials in previous literatures [13,34,35]. The spher-
4
3+
2
90 nm, the emission spectra of BaMoO
4
:Eu samples are com-
3
+
posed of a group of lines at about 536, 593, 617, 656, and
4
ical BaMoO :Ln (Ln = Eu, Tb, Dy, and Sm) samples exhibit intense
5
7
5
7
7
02 nm, which can be attributed to
D
1
– F
1
and
D
0
– F
J
red, green, green–yellow, and orange–red emissions under ultravi-
olet excitation, which can be confirmed by the CIE (Commission
(
(
(
J = 1,2,3,4) transition lines of the Eu3+ ions, respectively
5
7
Fig. 7b). The emission spectra are dominated by the
D
0
– F
2
Internationale de I’Eclairage 1931 chromaticity) coordinates for
617 nm) transition of Eu3 , which is an electric-dipole allowed
+
the emission spectra of the BaMoO
3+
4
:Ln samples (Fig. 8D). The
3
+
transition and hypersensitive to the environment. From the com-
chromaticity coordinates of BaMoO :Ln (Ln = Eu, Tb, Dy, and
4
3+
parative PL spectra of BaMoO
4
:Eu samples, it can be seen that
Sm) samples are calculated to be x = 0.597, y = 0.318 (point a);
x = 0.268, y = 0.611 (point b); x = 0.404, y = 0.453 (point c); and
x = 0.561, y = 0.377 (point d), located in the red, green, green–
yellow, and orange–red region, respectively.
the three samples show similar spectral patterns, but the emission
3+
4
intensity changes obviously. The spherical BaMoO :Eu sample
shows the strongest emission, the flower-like sample gives the
4 4 4 4
Fig. 9. Decay curves for the as-prepared spherical samples: (a) BaMoO .
:Eu3+, (b) BaMoO :Tb3+, (c) BaMoO :Dy3+ and (d) BaMoO :Sm3+

C. Zhang et al. / Journal of Alloys and Compounds 589 (2014) 185–191
191
3
+
The PL decay curves of the luminescence of the Eu (617 nm,
References
5D
– F
7
), Tb (544 nm,
3+
5
D
– F
Sm (646 nm, G5/2– H9/2) ions in the BaMoO
investigated (Fig. 9). It can be seen that all the decay curves can be
well fitted into a single exponential function as I (t) = I
exp (Àt/
is the initial emission intensity at t = 0 and is the 1/e lifetime of
the emission center), and the lifetimes of BaMoO
Dy, and Sm) samples are determined to be 0.55, 0.82, 0.21, and
7
), Dy (574 nm, 4
3+
F
9/2–6H13/2), and
0
2
4
5
3
+
4
6
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