Hydrothermal synthesis of Y(V, P)O4:Ln3+ (Ln = Eu, Yb, and Er) with shape- and size-controlled morphologies

Article abstract of DOI:10.1016/j.jallcom.2014.05.012

In this paper, controllable morphologies for Y(V, P)O₄ and Y(V, P)O₄:Ln³⁺ (Ln = Eu, Yb, and Er) were obtained via a facile hydrothermal route under different reaction conditions, and their luminescence properties were investigated. The time-dependent experiments reveal that the pH value is the main influential factor in the different morphological formations of Y(V, P)O₄, and well-separated nanocrystals and monodisperse microspherical particles can be obtained by employing the Y(OH)CO ₃:Yb³⁺, Er³⁺ colloidal spheres as a sacrificial template in the hydrothermal process under pH values of 7.5 and 10, respectively. For upconversion application, the emission spectrum of Y _0.78(V_0.5, P_0.5)O₄:0.2Yb ³⁺, 0.02Er³⁺ nanocrystals with the average diameter of about 9.2 nm exhibits yellowish green color upon 980 nm excitation, and the upconversion luminescence mechanisms was studied by the pump power dependence of the emission intensities. For application in plasma display panels, the Y _0.89(V_0.5, P_0.5)O₄:0.11Eu ³⁺ microspherical particles with the average diameter of about 1.2 μm after heat-treatment exhibits an enhanced red emission with chromaticity coordinates of (0.65, 0.35) upon 147 nm excitation. And its morphological and luminescent characteristics demonstrate the good application prospect in 3D plasma display panels.

Full text of DOI:10.1016/j.jallcom.2014.05.012

Accepted Manuscript
3
+
Hydrothermal Synthesis of Y(V, P)O :Ln (Ln = Eu, Yb, and Er) with Shape-
4
and Size-Controlled Morphologies
Jia Zhang, Zhangyin Zhai, Guibin Chen
PII:
S0925-8388(14)01078-0
DOI:
http://dx.doi.org/10.1016/j.jallcom.2014.05.012
JALCOM 31201
Reference:
To appear in:
Received Date:
Revised Date:
Accepted Date:
26 November 2013
30 April 2014
3 May 2014
3
+
Please cite this article as: J. Zhang, Z. Zhai, G. Chen, Hydrothermal Synthesis of Y(V, P)O :Ln (Ln = Eu, Yb, and
4
Er) with Shape- and Size-Controlled Morphologies, (2014), doi: http://dx.doi.org/10.1016/j.jallcom.2014.05.012
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3
+
Hydrothermal Synthesis of Y(V, P)O :Ln (Ln = Eu, Yb, and Er) with
4
Shape- and Size-Controlled Morphologies
Jia Zhang*, Zhangyin Zhai, Guibin Chen
School of Physics and Electronic Electrical Engineering, Huaiyin Normal University,
1
11 West Chang Jiang Road, Huai'an 223001, China
*Corresponding author.
E-mail address: zhangjia@hytc.edu.cn

Abstract
In this paper, controllable morphologies for Y(V, P)O
3
+
4
4
and Y(V, P)O :Ln (Ln =
Eu, Yb, and Er) were obtained via a facile hydrothermal route under different reaction
conditions, and their luminescence properties were investigated. The time-dependent
experiments reveal that the pH value is the main influential factor in the different
morphological formations of Y(V, P)O
4
, and well-separated nanocrystals and
monodisperse microspherical particles can be obtained by employing the
3
+
3+
Y(OH)CO
3
:Yb , Er colloidal spheres as a sacrificial template in the hydrothermal
process under pH values of 7.5 and 10, respectively. For upconversion application, the
3+
3+
emission spectrum of Y0.78(V0.5, P0.5)O :0.2Yb , 0.02Er nanocrystals with the
4
average diameter of about 9.2 nm exhibits yellowish green color upon 980 nm
excitation, and the upconversion luminescence mechanisms was studied by the pump
power dependence of the emission intensities. For application in plasma display
3
+
panels, the Y0.89(V0.5, P0.5)O :0.11Eu microspherical particles with the average
4
diameter of about 1.2 µm after heat-treatment exhibits an enhanced red emission with
chromaticity coordinates of (0.65, 0.35) upon 147 nm excitation. And its
morphological and luminescent characteristics demonstrate the good application
prospect in 3D plasma display panels.
Keywords: Phosphors; Luminescence; Optical spectroscopy

1. Introduction
Recently, tremendous efforts in materials science have been progressively devoted
to the design and construction of inorganic materials with both nanoscale dimensional
and three-dimensional (3D) hierarchical structure, not only for the fundamental
scientific interest but also for the technological applications in fields such as
biological labeling and imaging, catalysis, lighting and display [1, 2]. During these
applications, the concept of using upconversion (UC) luminescence as fluorescent
labels has attracted great attention due to its advantages over downconversion
fluorescence, such as low optical background, good biocompatibility, and high
excitation-penetration depths in tissues [3, 4]. On one hand, the considered organic
fluorescent dyes and inorganic semiconctor quantum dots (QDs) have some intrinsic
disadvantages, including rapid photobleaching for organic dyes and less chemically
stable, potentially toxic for QDs, which have limited their applications in biomedical
field [5, 6]. On the other hand, the biological applications require the nanomaterials to
be small (< 30 nm) and uniform whilst maintaining well-dispersion and
biocompatilility, which will facilitate the practical applications. In addition to
biological field, another important application for luminescence materials with regular
morphology is in display and lighting areas. Especially, the interest in 3D displays has
steadily grown currently due to increasing needs for advanced image devices. The
plasma display panels (PDPs) excited by vacuum ultraviolet (VUV) can generate 3D
image by the field-sequential technique, which divides one TV frame into two
separate parts for the left and right images [7]. To fulfill these application

requirements, new challenges such as morphology and decay time of phosphors have
been key scientific problems. The ideal morphology of VUV phosphor includes a
perfectly spherical shape,
a
narrow size distribution (0.5-2 µm), and
non-agglomeration, which are advantageous for high brightness and resolution due to
the high packing densities and low scattering of light [8, 9].
4
ABO (A = Y or Gd, B = V or P) compounds, as a kind of important optical host
materials, have many wonderful characteristics including good thermal, mechanical,
and optical properties, which make it play an important role in almost any device
3
+
involving the artificial production of light and display fields. For instant, GdVO
4
:Yb ,
3
+
3+
3+
Er , Tm , Ho was reported to have potential applications in biomedical imaging
3
+
[
5]. The YVO
luminescence could be useful as biological labels due to its water-solubility and
biocompatibility [10]. The optical and magnetic properties for YP :Eu@GdPO
with core-shell structure promised outstanding fluorescent-magnetic bifunctional
4
:Er nanocrystals prepared by hydrothermal route with UC
x 1-x
V O
4
4
3
+
nanomaterials [11]. Especially, Eu -doped YVO
4
is known to be an important
commercial red-emitting phosphor used in PDPs [12]. So far, many improvements on
3
+
5+
its morphology and luminous efficiency, such as doping Gd and P , have been
made to promote the performance of PDPs [13-17]. Nevertheless, the properties of
3
+
current Y(V, P)O :Eu still couldn’t meet the standers for 3D PDP, and much
4
modification is needed. As is known, regular and uniform nano- to micro-materials
can be prepared by several methods, during which the hydrothermal process always
provides a hydrophilic, clean and active surface for further modification and practical

applications [11]. Therefore, the hydrothermal method is a good choice to achieve
regular morphologies of samples.
Considering the above points, in this paper, we developed a facile hydrothermal
synthesis route with a template-assisted idea to produce nano- and micro-materials of
3
+
Y(V, P)O :Ln (Ln = Eu, Yb, and Er) by adjusting the pH value of the reaction
4
solution. The morphological formation mechanisms and the luminescence properties
were investigated.
2. Experimental
The starting materials were Y
2
O
3
(4N), Eu
HPO (98.5%), and [CO(NH
were used directly without further purification.
.1 Preparation of Y(OH)CO and Y(OH)CO
Nanospheres
Typically, the Y(OH)CO
homogeneous precipitation method [18]. 0.2330 g of Y
HNO solution (1:1 v/v) by heating to 80 °C with agitation to form clear Y(NO
aqueous solution. Superfluous HNO was evaporated by continuous heating until the
pH value of the Y(NO solution reaches about 4. The 3.0 g of urea was dissolved in
deionized water (30 mL), then added into the above Y(NO solution (30 mL) drop
2
O
3
(4N), Yb
2
O
3
(4N), Er
2
3
O (4N),
Ho
2
O
3
(4N), NH
4
VO
3
(99%), (NH
4
)
2
4
)
2 2
]. All of them
3
+
2
3
3
:Ln (Ln = Eu, Yb, and Er)
3
precursor was synthesized by a modified urea-based
was dissolved in dilute
2
O
3
3
3 3
)
3
3 3
)
)
3 3
by drop. The mixture was stirred continuously at room temperature for half an hour,
and then heated to 90 °C for 2 h in the water bath. The resulting suspension was
separated by centrifugation and collected after washing with deionized water for three

3
+
times. The Ln (Ln = Eu, Yb, and Er) doped Y(OH)CO
3
were prepared by the same
was added to Y(NO
procedures except that a stoichiometric amount of Ln(NO
3
)
3
3 3
) .
3
+
3+
2
.2 Preparation of Y(V0.5, P0.5)O
For a typical Y(V0.5, P0.5)O synthesis, the as-obtained Y(OH)CO
dispersed into 10 mL of deionized water by ultrasonic. Then the mixture of NH
0.1219 g) and (NH HPO (0.1383 g) was dissolved in deionized water (10 mL)
4 4
and Y(V0.5, P0.5)O :Yb , Er Nanocrystals
4
3
precursor was
VO
4
3
(
4
)
2
4
with stirring and heating, and dripped into the above suspension followed by stirring.
After the mixture was agitated at 70 °C for half an hour, the final pH value was
measured to be about 7.5. Then it was transferred into a Teflon bottle held in a
stainless-steel autoclave and heated at 200 °C for 12 h. After cooling down naturally
to room temperature, the product was separated from the reaction media by
centrifugation, washed several times with deionized water and ethanol, and finally
3
+
3+
dried overnight at 50 °C. The Y(V0.5, P0.5)O
same procedure except for using Y(OH)CO
.3 Preparation of Monodisperse Spherical Y(V, P)O
The general procedure is similar to that in Section 2.2, except that the final pH
4
:Yb , Er samples were prepared by the
3
+
3+
3
:Yb , Er as precursors.
3
+
2
4
:Eu
value was adjusted to 10.0 with diluted ammonia before the mixture was transferred
into the Teflon bottle. The obtained power was then annealed at 900 °C for 2 h in a
-1
muffle furnace with a heating rate of 60 °C h .
2.4 Characterization
Power X-ray diffraction (XRD) measurements were performed on a Rigaku
D/MAX-2400 diffractometer with Cu Kα radiation (λ = 1.54178 Å) operating at 40

kV and 60 mA. The morphologies of the as-prepared samples were inspected by field
emission scanning electron microscope (FESEM, Hitachi, S-4800), transmission
electron microscopy (TEM) and high-resolution transmission electron microscopy
(
FEI Tecnai F30, operated at 300 kV). The chemistry component was analyzed by
Fourier transform infrared spectroscopy (FT-IR, Nicolet NEXUS 670). The
photoluminescence (PL) and photoluminescence excitation spectra were measured by
a FLS920T spectrophotometer equipped with VM504 vacuum monochromator, and
the excitation spectra were corrected by the sodium salicylate at the same
measurement conditions. The upconversion (UC) PL spectra were measured by using
the 980 nm laser diode (DL) as excitation source, with the HORIBA Jobin Yvon
Fluorlog-3 Spectrofluorometer system. All the spectra measurements were performed
at room temperature.
3
. Results and Discussion
.1 Structure and morphology for Y(V, P)O
3
+
3
4
4
and Y(V, P)O :Ln (Ln = Eu, Yb,
and Er)
Fig. 1a shows the XRD pattern of the Y(OH)CO
3
precursor. Two main broad
bands around 29° and 47° can be observed, indicating the obtained sample is almost
amorphous, and the pattern agrees with that in Ref. [18]. To further examine the
chemical composition of Y(OH)CO
3
, FT-IR spectroscopy was carried out, as shown
-1
in Fig. 1b. The absorption bands of O–H (3400 cm ), νasO–C–O (1520 and 1400
-1
-1
2-
-1
2-
-1
cm ), C–O (1080 cm ), π–CO
3
(841 cm ), and δ–CO
3
(750 and 690 cm ) are
observed, revealing the presence of the hydroxyl and carbonate groups [10, 19]. All

the feature peaks in the FT-IR spectroscopy have been detected and almost no other
obviously impure absorption peaks exist, implying the successful generation of
Y(OH)CO
nanoparticles of about 30 nm are gained, which demonstrates good dispersion.
The XRD patterns of the Y(V0.5, P0.5)O samples synthesized by hydrothermal
3 3
. Fig. 1c presents the SEM image of Y(OH)CO . The subglobose
4
route with pH values of 7.5 and 10 are displayed in Fig. 2a. It can be confirmed that
the desired samples are successfully synthesized, since their three strongest diffraction
peaks are located between the peak positions in the JCPD Standard Cards (No.
72-0861 for YVO
4
and No. 83-0658 for YPO ), which is due to the different ionic
4
5
+
5+
radii of P and V . Nevertheless, the two samples exhibit completely different
morphologies. Fig. 2b shows the SEM image of Y(V0.5, P0.5)O
4
prepared under pH =
.5. Lots of small nanorods are found, with the average diameter of about 9.2 nm (Fig.
c, which is taken from statistics analysis by measuring approximate 100 particles).
7
2
Fig. 2d presents the selected area electron diffraction (SAED) pattern. The concentric
spotty diffraction rings are corresponding to the specific (200), (112), and (321)
planes of the YVO
4
or YPO
4
lattice, revealing the polycrystallite nature. Fig. 2e
prepared under pH = 10. Obviously,
shows the SEM image of Y(V0.5, P0.5)O
4
monodisperse microspherical particles are obtained. Under higher magnification in
the inset of Fig. 2e, it can be seen that every microsphere is assembled with numerous
nanoparticles, which may result from the agglomeration of the Y(OH)CO
3
nanoparticles in the initial reaction process. The average diameter of the
microspherical particles is estimated to be about 1.2 µm from statistics analysis by

measuring approximate 100 particles, as shown in the inset of Fig. 2f. The
3
+
4
energy-dispersive X-ray (EDX) analysis spectrum of Y0.89(V0.5, P0.5)O :0.11Eu
given in Fig. 2f implies that all the composing elements of the sample have been
detected, and no other impure elements are found.
To study the effect of pH value on the morphologies of Y(V0.5, P0.5)O ,
4
time-dependent shape evolution experiments were performed by intercepting
intermediate products at different reaction stages under the pH values of both 7.5 and
1
0. Firstly, for pH value of 7.5, the TEM images of the Y(OH)CO
products by hydrothermal treatment for 0, 3, and 12 h are shown in Fig.
a-3d, respectively. Nanocrystals with diameter of about 30 nm were gained for
Y(OH)CO (Fig. 3a), subsequently uniform and well-dispersed submicron spheres
with the diameter of about 800 nm were assembled with these nanoparticles in the
stirring and heating process after the NH VO and (NH )HPO mixed solutions were
dripped into the Y(OH)CO suspension (Fig. 3b). When the reactant was treated
3
precursor and the
Y(V0.5, P0.5)O
4
3
3
4
4
4
4
3
hydrothermally for 3 h, the forming submicron spheres were being disintegrated
gradually into small nanorods (inset of Fig. 3c) and the remaining spheres
demonstrate irregular profiles with decreased scale of about 350 nm (Fig. 3c). After
the hydrothermal time was prolonged to 12 h, the submicron spheres have been
disassembled entirely, and uniform nanocrystals were obtained (Fig. 3d). A schematic
diagram is depicted in Fig. 3A to illustrate the growth process of the nanocrystals. The
corresponding XRD patterns are shown in Fig. S1, from which it can be seen that the
diffraction peaks became stronger with increasing reaction time, implying the

single-phase samples were crystallized gradually. Secondly, for pH value of 10, TEM
and SEM investigations (Fig. 3e, 3f, and inset of Fig. 3f) indicate that the
morphologies of both the Y(OH)CO
3 3
precursor and the mixture of Y(OH)CO +
NH VO + (NH HPO for t = 0 h are similar to those in Fig. 3a and 3b, respectively.
4
3
4
)
2
4
However, after hydrothermal treatment for 3 h, the spherical morphology (Fig. 3g)
was maintained and improved greatly. The microspherical particles have grown up on
the whole, and the size would not increase further with prolonged reaction time by
contrast with the final product after reaction for 12 h (Fig. 3h), but the crystallinity
was increased largely during this prolonged time, as reflected from the XRD patterns
(
Fig. S2). The corresponding schematic illustration is given in Fig. 3B to interpret the
growth process. The above discussion indicates ammonia used for adjusting the pH
value is an inducement to form the microspherical product, since ammonia has been
reported to have a strong tendency to coordinate with inorganic cations, which may be
a determinative factor in the formation of the novel hierarchical structure [20].
3
+
As we know, YVO
doping an appropriate amount of P could enhance its emission intensity effectively
12, 13]. For the practical application in 3D PDP, spherical particles with narrow size
4
:Eu is commercially used as a red phosphor in PDPs, and
5
+
[
5
+
distribution (0.5-2 µm) are the most suitable, so we studied the effect of P content
on the spherical morphology by a series of Y(V1-x, P )O (0 ≤ x ≤ 1) samples which
x
4
were prepared under pH value of 10. The corresponding XRD patterns are shown in
Fig. 4. With increasing x value, the diffraction peak positions shift toward high angle
5
+
5+
direction regularly due to the smaller ionic radius of P than V , and the as-prepared

samples are single-phase except that for x = 1. The YPO
contain impure phase of YPO ·8H O (JCPD Standard Card No. 42-0082), and this
impure phase can be removed by heat-treatment at 900 °C for 2 h. Fig. 5a shows the
4
sample was determined to
4
2
5
+
SEM image of the YVO sample without P . Unexpectedly, the microspherical
4
morphology disappear completely, and ellipsoid-like particles of about 200 nm are
produced. From the enlarged image, it can be found that every ellipsoid is composed
5
+
of many small nanocrystals. However, if the P exists, the morphologies of the
samples have changed entirely. The typical SEM images of Y(V1-x, P )O (0.25 ≤ x ≤
) are given in Fig. 5b-5d. It is obvious that microspherical particles can be generated
x
4
1
5
+
5+
for any P doping content, implying the adding of P is also a requirement to form
the spherical product.
5
+
To sum up, the presence of P in Y(V, P)O
microspherical structure under the initial stirring and heating process, and the alkaline
environment maintains the spherical morphology of Y(V, P)O in the next
hydrothermal process. In these preparations of nanorods and microspheres, the
4
urges the embryonic form of the
4
3
+
Y(OH)CO
Based on the above result, the monodisperse microspherical particles of Eu
could be considered to apply to 3D PDP. For practical
applications, heat-treatment is necessary to enhance the brightness of hydrothermally
derived phosphors. Fig. 6 presents the SEM image of Y(V0.5, P0.5)O after annealing at
00 °C for 2 h. Well-dispersed and uniform microspherical particles are maintained at
this calcination temperature. The magnified SEM image (inset in Fig. 6) exhibits the
3
colloidal spheres participate as either the Y source or the template.
3
+
activated Y(V0.5, P0.5)O
4
4
9

specifics of the microspheres, which show no difference with those before
heat-treatment.
3
+
3.2 Luminescence Properties of Y(V0.5, P0.5)O
4
:Ln (Ln = Eu, Yb, and Er)
3
:Yb , Er Nanocrystals
+
3+
3
.2.1 UC Luminescence Properties of Y(V0.5, P0.5)O
4
3
+
3+
Yb -Er codoped phosphors are well known to be used for the UC luminescence.
3
+
Thus, Fig. 7a presents the UC emission spectrum of Y0.78(V0.5, P0.5)O
4
:0.2Yb ,
3
+
0
.02Er under DL excitation of 980 nm at the pump power of 370 mW. The three
2
4
emission peaks around 526, 554, and 676 nm could be attributed to H11/2- I15/2
,
4
4
4
4
3+
S
3/2- I15/2 and F9/2- I15/2 transitions of Er , respectively [21]. The red emission is
predominated, which could be owing to the strong phonon-assisted non-radiative
relaxation in the UC process. To better understand the UC mechanism, the pump
power dependence of the UC emissions was measured. For unsaturated UC processes,
the number of photons which are required to populate the upper emitting state can be
obtained by the following relation [22]:
n
I f ∝ P
(1)
where I
f
is the fluorescent intensity, P is the pump power, and n is the number of
photons required to populate the emitting state. For the two intense emission peaks at
3
+
5
26 and 676 nm of Er , a plot of lnI versus P yields a straight line with slope n, as
f
shown in the inset of Fig. 7a, and the n values obtained equal to 1.95 and 1.45,
respectively. Hence, both the emissions are two-photon processes. In this case, an
energy level diagram to propose the UC mechanisms can be depicted in Fig. 7b.
3
+
Initially, Yb absorbs a 980 nm photon from laser source and subsequent transferred

3
+
3+
4
the energy to a nearby Er populating Er at I11/2 level, a second 980 nm photon or
3
+
4
3+
3+
ET from Yb can further populate the F7/2 level of Er , afterwards Er relaxes
2
4
4
2
nonradiatively to the H11/2 or S3/2 or F9/2 levels, resulting in the green ( H11/2
,
4
4
4
4
3+
4
S
3/2)- I15/2 and red F9/2- I15/2 emissions of Er . On the other hand, the F9/2 level may
4
3+
be also populated from the I13/2 level of Er by absorbing a 980 nm photon or energy
3
+
4
transfer from Yb , with the I13/2 state being initially populated via nonradiative
4
4
I
11/2- I13/2 relaxation. In these processes, the large probabilities of the phonon-assisted
4
4
4
4
non-radiative relaxations from the S3/2 to F9/2 and from I11/2 to I13/2 levels result in
the strong red emission around 676 nm, since the phonon energy in oxide hosts is
usually large, which facilitates the relaxation processes. The chromaticity coordinates
calculated from the emission spectrum by using the 1931 CIE (Commission
International de l’Eclairage France) system are obtained to be (0.309, 0.659),
indicating a yellowish green color.
3
+
3
.2.2 Luminescence Properties of Y(V0.5, P0.5)O
Excitation
As a well-known red phosphor for PDP, the photoluminescence properties of Y(V,
4
:Eu Microspheres upon VUV
3
+
P)O
excitation spectrum of the typical Y0.89(V0.5, P0.5)O
heat-treatment by monitoring 619 nm, which contains a very strong and broad
4
:Eu under VUV excitation are investigated in this work. Fig. 8 shows the
3
+
4
:0.11Eu
sample after
3
-
excitation band. The weak excitation band below 200 nm is attributed to PO
4
and
3
-
VO
4
absorption of the host, and the strong excitation band from 200 to 350 nm could
2
-
3+
5+
2-
be ascribed to the overlap of the O -Eu and V -O CTBs [12]. The emission

3
+
spectra of Y0.89(V0.5, P0.5)O
4
:0.11Eu before and after heat-treatment upon 147 nm
excitation are also given in Fig. 8. Both the predominated emission peaks are located
5
7
3+
at 619 nm, ascribed to the hypersensitive D
0 2
- F transition of Eu [23]. It is obvious
that the emission intensity has almost doubled when the sample is annealed at 900 °C
5
7
for 2 h. What is worth mentioning, the red emission intensity of D
0
- F
2
transition is
5
7
much stronger than that of D
0 1
- F transition, so it exhibits an excellent red color
3
+
purity. The chromaticity coordinates of Y0.89(V0.5, P0.5)O
4
:0.11Eu upon 147 nm
excitation were calculated to be (0.65, 0.35), which are very close to the (0.67, 0.33)
standard of the National Television System Committee for red phosphors. To observe
3
+
the emission color visually, a photo of Y0.89(V0.5, P0.5)O
4
:0.11Eu under 254 nm
ultraviolet lamp irradiation is given in inset (a), from which it can be seen the sample
3
+
exhibits bright red emission. To find the optimal concentration of Eu in this host, a
3
+
4
series of Y1-y(V0.5, P0.5)O :yEu (0.02 ≤ y ≤ 0.15) samples were prepared. Inset (b) of
3
+
3+
Fig. 8 presents the dependence of the Eu emission intensities on Eu concentration
3
+
under 147 nm excitation, which indicates the optimal Eu -doping concentration is for
11 mol%.
3. Conclusions
In summary, well-dispersed Y(V, P)O
4
nanorods and microspheres were
synthesized hydrothermally under different reaction conditions, and their growth
processes were studied by time-dependent experiments. For pH = 7.5, small nanorods
were obtained with the average diameter of about 9.2 nm, and the UC luminescence
3
+
3+
properties of Yb -Er codoped sample were evaluated, which reveal the sample

emits yellowish green light upon 980 nm excitation. In an alkaline hydrothermal
environment for pH = 10, monodisperse Y(V, P)O microspherical particles used for
D PDP were formed. And the regular morphology was maintained after annealing at
4
3
9
P
00 °C. Under 147 nm excitation, red emission is gained in Y0.89(V0.5
,
3
+
0.5)O :0.11Eu with the chromaticity coordinates of (0.65, 0.35). The regular and
4
uniform morphology as well as the good color purity presents its application potential
in 3D PDPs.
Acknowledgements
This work was supported by the National Natural Science Foundation of China
(
Grant No. 11174101) and Natural Science Foundation of the Jiangsu Higher
Education Institutions of China (Grant No. 11KJB140001).

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Figure captions
Fig. 1 (a) XRD patterns, (b) FT-IR spectrum, and SEM image of Y(OH)CO
3
precursor.
Fig. 2 (a) XRD patterns of Y(V0.5, P0.5)O
hydrothermal process for pH = 7.5; (c) Particle size distribution for Y(V0.5, P0.5)O
nanocrystals; (d) SEAD pattern of Y(V0.5, P0.5)O
by hydrothermal process for pH = 10; and (f) EDX spectrum of Y(V0.5, P0.5)O
shows particle size distribution for Y(V0.5, P0.5)O microspheres.
Fig. 3 TEM and SEM images for the product evolution. For pH = 7.5: (a) Y(OH)CO
at different hydrothermal times ((b) 0 h; (c) 3 h and inset shows
the enlarged image of the nanocrystals; and (d) 12 h); for pH = 10: (e) Y(OH)CO and
at different hydrothermal times ((f) 0 h and inset shows its TEM
image; (g) 3 h; and (h) 12 h); (A) and (B) show the schematic illustrations for the
formation processes of Y (V0.5, P0.5)O nanocrystals and microspheres, respectively.
Fig. 4 XRD patterns of Y(V1-x, P )O
Fig. 5 SEM images of Y(V1-x, P )O
.25, (c) x = 0.75, (d) x = 1.00.
Fig. 6 SEM image of Y(V0.5, P0.5)O
hydrothermal process at pH value of 10 after heat-treatment.
Fig. 7 (a) UC emission spectrum of Y0.78(V0.5, P0.5)O :0.2Yb , 0.02Er under DL
excitation of 980 nm, inset shows dependence of UC emission intensity on excitation
4
; (b) SEM image of Y(V0.5, P0.5)O by
4
4
4
; (e) SEM image of Y(V0.5, P0.5)O
4
4
, inset
4
3
and Y (V0.5, P0.5)O
4
3
Y (V0.5, P0.5)O
4
4
x
4
(0 ≤ x ≤ 1).
x
4
obtained at pH value of 10, (a) x = 0.00, (b) x =
0
4
microspherical particles obtained by
3
+
3+
4
3
+
3+
powder; and (b) Schematic representation of the energy level diagram for Yb -Er ,

and the proposed UC mechanisms to produce the green and red up-converted
emissions.
3
+
4
Fig. 8 Excitation and emission spectra of Y0.89(V0.5, P0.5)O :0.11Eu , inset (a) shows
3
+
the photo of Y0.89(V0.5, P0.5)O
4
:0.11Eu under 254 nm ultraviolet lamp irradiation,
3
+
3+
inset (b) shows Eu emission intensity with varying Eu concentration under 147 nm
excitation.

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Research Highlights:
＞
＞
Different morphologies can be achieved by controlling the reaction conditions.
Nanocrystallines with diameter below 10 nm are obtained for upconversion
application.
＞
＞
Monodisperse microspheres with the suitable diameter are prepared for 3D PDP.
3
+
4
The Y0.89(V0.5, P0.5)O :0.11Eu shows good color purity and intense emission.