Comparative characterization of microstructure and luminescence of europium doped hydroxyapatite nanoparticles via coprecipitation and hydrothermal method

Accepted Manuscript
Title: Comparative characterization of microstructure and
luminescence of europium doped hydroxyapatite
nanoparticles via coprecipitation and hydrothermal method
Author: Thang-Cao Xuan Nguyen Ngoc Trung Vuong-Hung
Pham
PII:
DOI:
Reference:

S0030-4026(15)01205-X
/>IJLEO 56341

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Accepted date:

10-11-2014
11-9-2015

Please cite this article as: T.-C. Xuan TrungV.-H. Pham Comparative characterization
of microstructure and luminescence of europium doped hydroxyapatite nanoparticles
via coprecipitation and hydrothermal method, Optik - International Journal for Light
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Comparative characterization of microstructure and luminescence of europium doped
hydroxyapatite nanoparticles via coprecipitation and hydrothermal method

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Thang-Cao Xuana, Nguyen Ngoc Trung b, Vuong-Hung Phama, *
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Advanced Institute for Science and Technology (AIST), Hanoi University of Science and Technology (HUST), No
01, Dai Co Viet road, Hanoi, Vietnam
b

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School of Engineering Physics, Hanoi University of Science and Technology (HUST), No 01, Dai Co Viet road,
Hanoi, Vietnam

*Corresponding author: Vuong-Hung Pham

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[Tel: +84-4-36230435, Fax: 84 43 6230 293, E-mail: ]

Keywords: nanoparticles; luminescence; hydroxyapatite, europium, hydrothermal, Nanobiophosphors

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Abstract
This paper reports the first attempt to compare the microstructure and luminescence of europium doped
hydroxyapatite (HA) nanostructure to achieve strong and stable luminescence of hydroxyapatite nanophosphor,

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particularly, by co-precipitation and hydrothermal synthesis method. The Raman spectra analysis indicates that all
modes are related to the HA phase. The morphology of Eu doped HA nano particles was depended on the

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synthesized method that was observed to have a nanowire structure to nanorod morphology. The creation of highly

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nanophosphor, which was potential application in nanomedicine.

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nanocrystalline Eu-doped HA with nanorod morphology resulted in a significantly enhancing luminescence of the

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1. Introduction
Hydroxyapatite (HA) has received considerable attention in nanomedicine in designing the functional
materials because of its highly biocompatibility and easily to acceptation a wide variety of dopants based on

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flexibility of the apatitic structure [1,2]. In order to obtain a nanoparticle for potential application in bioimaging and
nanomedicine, a combination of various properties is needed: excellent biocompatiblity, photostability, sphere shape

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nanoparticles [3,4 ]. Therefore, considerable effort has been made to functionalize hydroxyapatite nanoparticle by
incorporation of its materials with organics dye [5,6], semiconductor quantum dots [7,8], and rare earth elements

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[9,10]. Organics dyes conjugated into nanoparticles are considered as the effective materials for bioimaging but
there is still a risk of photobleaching and in vivo instability because organic dye placed in aqueous biological

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environments reduces luminescent intensity over the time [11]. Another promising approach to enhance the
performance of bioimaging materials is to conjugate their materials with a semiconductor such as CdS [12], ZnSe

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[13], and (CdSe) [14], which would not face with late photobleaching but there is still a concern of its late toxicity
[15,16].

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As one of the rare earth elements, europium has received considerable attention as an activator for doping

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into calcium based materials due to their exhibiting importance advantages compared with available phosphor such
as lower toxicities, photostabilities, high thermal and chemical stabilities, and high luminescence quantum yield

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[17,18]. Nevertheless, there are only a few reports on the synthesis of luminescence hydroxyapatite for potential

applications as bioimaging and nanomedicine [19, 20, 21,22]. In particular, in our knowledge, there are no reports
on the comparative characterization of the microstructure and luminescence of europium doped HA nanoparticle via
coprecipitation and hydrothermal method.

Therefore, this study reports a way of controlling the microstructure, crystallinities and light emission of
the Eu doped HA, as well as the mechanism in a variation of luminescence of two different methods. The
microstructure and chemical composition of the Eu doped HA were characterized by transmission electron
microscope (TEM). The crystal structure of the specimen was characterized by Raman spectroscopy. The
luminescence was also determined by photoluminescence

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2. Experimental procedure
Europium doped hydroxyapatite was synthesized through a coprecipitation and hydrothermal method, as
follows: an aqueous solution with stoichiometric amount of (NH4)2 HPO4 (0.2M, 99% purity, Aldrich) were added

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over an aqueous solution containing Ca (NO3)2 .4H2O (0.2M, 99% purity, Aldrich), and 0.3 mol % Eu(NO3)3.
Eu(NO3)3 were obtained by dissolving stoichiometric Eu2O3 (99% purity, Aldrich) in HNO3 with vigorous stirring.

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The reaction mixture was stirred for 0.5 h followed by precipitation method at 80 oC and the pH was adjusted to 11
by using aqueous ammonia. For hydrothermal synthesis, the mixture was transferred into 200 ml Teflon-lined

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autoclave, and then the autoclave was sealed and maintained at 150 oC for 12 h. The resulting precipitates were
washed three times, and then dried at 100 oC for 6h. The crystalline structures of the Eu doped HA were

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characterized by a micro Raman spectroscopy (Renishaw, United Kingdom). The microstructure of the Eu doped
HA was determined by field emission scanning electron microscopy (JEOL, JSM-6700F, JEOL Techniques, Tokyo,

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Japan). Photoluminescence (PL) tests were performed to evaluate the optical properties of the Eu doped HA.
NANO LOG spectrofluorometer (Horiba, USA) equipped with 450 W Xe arc lamp and double excitation

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3. Results and discussion

The PL spectra were recorded automatically during the measurements.

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monochromators was used.

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Figures 1 (A) and (B) show the typical Raman patterns of the Eu doped HA processed with the variation of
synthesis method. The coprecipitation specimen of Eu doped Si-HA showed a Raman shift = ~ 962 cm-1
corresponding to the symmetric stretching ν 1 mode of PO4 3- of the crystalline hydroxyapatite, as well as peaks at

Raman shift = ~ 433 cm-1 was attributed to bending ν 2 of the PO4 3- ion (Fig. 1 (A)). On the other hand, when a
hydrothermal synthesis was applied, strong Raman peak situated at about ~ 962 cm-1 and ~ 433 cm-1 was assigned
to the to the symmetric stretching ν 1 mode of PO4 3- and bending ν 2 of the PO4 3-, respectively with additional peak
at 1054 cm -1 corresponding to the antisymmetric stretching ν 3 of the PO4 3- ion (Fig. 1 (B). These results indicate
that all Raman modes are related to the HA phase.

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Fig. 1. Raman spectra of Eu doped HA (A) co-

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precipitation, (B) hydrothermal method.

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The representative microstructure of the Eu doped HA nanophosphor was characterized by TEM, as shown
in Figs. 2 (A) – (D). The co-precipitation specimen showed a long nanowire microstructure (Fig. 2(A)) with length

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up to 500 nm and diameter less than 50 nm. On the other hand, the hydrothermal specimen showed nanorod-like
morphology with aspect ratio of 5 (Fig. 2(C)), which is expected to enhance luminescence due to the high packing

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density and reduction of light scattering. Electron diffraction (ED) revealed that all the Eu doped HA displayed

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nanocrystal materials. However, it should be noted that the crystalline of the sample increases with the hydrothermal

method.

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synthesis method (Fig. 2(D), which is due to the application of higher synthesis temperature via hydrothermal

Fig. 2. TEM and Electron
diffraction (ED) analysis of the
Eu doped HA ((A), (B)):
coprecipitation, ((C), (D)):
hydrothermal.

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The photoluminescence of the Eu doped HA were evaluated by photoluminescence spectroscopy (PL), a
nondestructive method which is very useful for analyzing the efficiency of trapping, migration and transfer of
charge carriers and understanding the crystallization behavior of the luminescent materials [23,24]. The typical
photoluminescence spectra of the Eu doped HA are shown in Figs. 3. All the Eu doped HA showed strong visible

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Do

F3 , 5Do

7

5

Do

F1, 5Do

7

7

F2,

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emission peaks appeared at about 590, 616, 650 and 700 nm and they can attributed to the
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F4 transitions within Eu3+ ion, respectively. However, it should be noted that PL intensity of Eu

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doped HA increased with the sample prepared by hydrothermal method. It is well known that the coprecipitation

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method that generally creates amorphous or less crystalline materials, the hydrothermal technique allows for the
creation of well-crystalline structure via higher temperature [25,26,27]. The enhancing PL intensities of Eu doped

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HA should be mainly due to their well-crystalline of the sample prepared by hydrothermal method.
Fig. 3. Photoluminescence spectra of Eu

hydrothermal method.

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doped HA with coprecipitation and

4. Conclusions

We herein demonstrated that the photoluminescence of hydroxyapatite could be obtained effectively by
doping with rare earth europium. The Raman spectra analysis indicates the formation of HA single phase.

Photoluminescence intensity of the Eu doped HA increases on the sample prepared by hydrothermal method with
the characteristic emission of Eu 3+. This enhancement of the PL was mainly attributed to the particle morphology

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and well-crystalline material via hydrothermal method. These phosphors show potential application in
nanomedicine where require a combination of biocompatibility and light emission.
Acknowledgment

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This research is funded by Vietnam National Foundation for Science and Technology Development

(NAFOSTED) under grant number “103.99-2013.05”. Author acknowledges technical support for TEM imaging

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from Bui Van Dong, Geology, Geotechnique, Geo-environment Climate Change lab, Vietnam National University.

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Figures
Fig. 1. Raman spectra of Eu doped HA (A) co-precipitation, (B) hydrothermal method.
Fig. 2. TEM and Electron diffraction (ED) analysis of the Eu doped HA ((A), (B)): coprecipitation, ((C), (D)):

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hydrothermal.

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Fig. 3. Photoluminescence spectra of Eu doped HA with coprecipitation and hydrothermal method.

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