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

Accepted ManuscriptTitle: Comparative characterization of microstructure and luminescence of europium doped hydroxyapatite nanoparticles via coprecipitation and hydrothermal method Autho

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

DOI: http://dx.doi.org/doi:10.1016/j.ijleo.2015.09.136

To appear in:

Received date: 10-11-2014

Accepted date: 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

and Electron Optics (2015), http://dx.doi.org/10.1016/j.ijleo.2015.09.136

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Accepted Manuscript

Comparative characterization of microstructure and luminescence of europium doped

hydroxyapatite nanoparticles via coprecipitation and hydrothermal method

Thang-Cao Xuana, Nguyen Ngoc Trung b, Vuong-Hung Phama, *

a Advanced Institute for Science and Technology (AIST), Hanoi University of Science and Technology (HUST), No

01, Dai Co Viet road, Hanoi, Vietnam

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

Hanoi, Vietnam

*Corresponding author: Vuong-Hung Pham

[Tel: +84-4-36230435, Fax: 84 43 6230 293, E-mail: vuong.phamhung@hust.edu.vn]

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

Accepted Manuscript

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,

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

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

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

nanophosphor, which was potential application in nanomedicine

Accepted Manuscript

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

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

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

[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

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

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

[15,16]

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

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

[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

Accepted Manuscript

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

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

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

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

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,

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

monochromators was used The PL spectra were recorded automatically during the measurements

3 Results and discussion

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 ν1 mode of PO4 3-of the crystalline hydroxyapatite, as well as peaks at

Raman shift = ~ 433 cm-1 was attributed to bending ν2 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-1was assigned

to the to the symmetric stretching ν1 mode of PO4 3-and bending ν2 of the PO4 3-, respectively with additional peak

at 1054 cm -1 corresponding to the antisymmetric stretching ν3 of the PO4 3-ion (Fig 1 (B) These results indicate

that all Raman modes are related to the HA phase

Accepted Manuscript

Fig 1 Raman spectra of Eu doped HA (A)

co-precipitation, (B) hydrothermal method

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

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

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

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

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

method

Fig 2 TEM and Electron

diffraction (ED) analysis of the

Eu doped HA ((A), (B)):

coprecipitation, ((C), (D)):

hydrothermal

Accepted Manuscript

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

emission peaks appeared at about 590, 616, 650 and 700 nm and they can attributed to the 5Do 7F1, 5Do 7F2,

5Do 7F3 , 5Do 7F4 transitions within Eu3+ ion, respectively However, it should be noted that PL intensity of Eu

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

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

HA should be mainly due to their well-crystalline of the sample prepared by hydrothermal method

Fig 3 Photoluminescence spectra of Eu

doped HA with coprecipitation and hydrothermal method

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

Accepted Manuscript

and well-crystalline material via hydrothermal method These phosphors show potential application in

nanomedicine where require a combination of biocompatibility and light emission

Acknowledgment

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

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

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