Hybrid nanomaterials YVO
4
:Eu/Fe
3
O
4
for optical
imaging and hyperthermia in cancer cells†
Laishram Priyobarta Singh,
a
Neena V. Jadhav,
b
Sachil Sharma,
c
Badri N. Pandey,
b
Sri Krishna Srivastava
a
and Raghumani Singh Ningthoujam
*
d
YVO
4
:xEu nanoparticles having a spherical shape at different concentrations of Eu (x ¼ 0.02, 0.05, 0.07 and
0.10 at%) are prepared by a polyol method at 120
C and their luminescence properties at different
annealing temperatures (as-prepared, 500 and 900
C) are studied. In the luminescence study, the
typical emission peaks of Eu
3+
ion at 590 and 612 nm are observed for all samples. The intensity of the
emission peak increases with the increase of annealing temperature due to the decrease of the
contribution from the non-radiative process arising from the surface dangling bond/OH. The crystallite
size calculated from the X-ray diffraction is found to increase with annealing from 500 to 900
C but the
as-prepared sample has a larger crystallite size than the 500
C annealed sample. This can be explained
by the incorporation of C in the interstitial sites of the lattice after heating the as-prepared sample at
500
C. The C residue remains after decomposition of ethylene glycol at 500
C. Luminescence decays
for the
5
D
0
level of Eu
3+
are studied under 395 nm (direct excitation) and 270, 320 nm (indirect
excitation). The energy transfer process from V–O to Eu
3+
is studied from decay curves. The quantum
yields for as-prepared, 500 and 900
C annealed samples of 5 at% Eu
3+
doped YVO
4
nanoparticles are 1,
14 and 46%, respectively. We have also synthesized YVO
4
:10Eu/Fe
3
O
4
hybrid nanocomposites and
determined their intracellular localization as well as hyperthermia efficacy in tumor cells. These materials
will have potential application in the diagnosis as well as therapy of cancer cells.
1. Introduction
Rare-earth (RE) doped AVO
4
(A ¼ Y, La, Gd; RE
3+
¼ Eu
3+
, Dy
3+
,
Er
3+
, Sm
3+
, Tm
3+
) nanoparticles (NPs) are widely studied for their
interesting luminescence properties.
1–5
Eu
3+
doped AVO
4
mate-
rials are used as a red phosphor in cathode ray tubes and scin-
tillators.
6,7
Rare-earth-doped luminescence materials have wide
applications, including phosphors, display devices, bio-imaging,
scintillators, and ampliers for ber-optic communications.
8–10
Sm
3+
and Tm
3+
doped AVO
4
NPs are used as orange and blue
emitters, respectively.
11–13
The particle size of the host lattice
(AVO
4
) also affects the luminescence intensity when it reduces to
the nanosize. The agglomeration of particles reduces the lumi-
nescence intensity due to cross-relaxation as well as non-radiative
processes. To overcome these disadvantages, surfactants and
capping agents need to be used. Even if such nanoparticles cap-
ped by ligands are heated at higher temperatures, agglomeration
of particles is less than that in the case of particles prepared
without capping agents. Ethylene glycol (EG) is a suitable capping
ligand as well as solvent and this can be removed easily aer heat
treatment above 500
C.
14
Since the boiling point of EG is 190
C,
many reactions for the formation of different particle sizes of
nanoparticles can be performed below this temperature. In Eu
3+
doped YVO
4
, there are two processes such as V–O charge transfer
(from VO
3
) and Eu–O charge transfer through which efficient
luminescence can be achieved.
15,16
Ionic radii of Eu
3+
and Y
3+
are
1.07 and 1.01
˚
A, respectively, and both have similar chemical
behavior. Based on the space group I4
1
/amd, YVO
4
has four
chemical formulae per unit cell (z ¼ 4).
17,18
V
5+
has four neigh-
boring oxygen ligands to form a tetrahedron (VO
4
) having a bond
distance of 1.706
˚
A. Y
3+
has eight neighboring oxygen ligands to
form a bisdisphenoid with two different bond lengths of Y–O
(2.299 and 2.244
˚
A) leading to the formation of a highly asym-
metric environment around Y
3+
ion.
18
In Eu
3+
doped YVO
4
, Eu
3+
ions occupy Y
3+
sites, having a highly asymmetric environment,
which is highly sensitive to the electric dipole transition of Eu
3+
ions (
5
D
0
/
7
F
2
).
a
Department of Chemistry, Manipur University, Imphal-795003, India
b
Radiation Biology and Health Sciences Division, Bhabha Atomic Research Center,
Mumbai-400085, India
c
Department of Chemistry, Indian Institute of Technology, Kanpur-208016, India
d
Chemistry Division, Bhabha Atomic Research Center, Mumbai-400085, India. E-mail:
rsn@barc.gov.in; nraghu_mani@yahoo.co.in; Fax: +91-22-25505151; Tel: +91-22-
25592321
† Electronic supplementary information (ESI) available: XRD data of as-prepared,
500 and 900
C annealed samples (Fig. SI 1–3), TGA–DTA data (Fig. SI 4), FTIR
spectra (Fig. SI 5) and excitation spectra (Fig. SI 6), emission and decay data of
YVO
4
(Fig. SI 7), emission intensity of 900
C annealed sample using 5 nm slit
widths (Fig. SI 8), integrated area, FWHM, and asymmetric ratio of
5
D
0
–
7
F
1
(Fig. SI 9) and magnetization vs. applied eld plot (Fig. SI 10). See DOI:
10.1039/c4tc02636e
Cite this: DOI: 10.1039/c4tc02636e
Received 18th November 2014
Accepted 31st December 2014
DOI: 10.1039/c4tc02636e
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