Available online at http://www.urpjournals.com
International Journal of Nanomaterials and Biostructures
Universal Research Publications. All rights reserved
ISSN 2277-3851
Original Article
Photoluminescence of Eu3+, Dy3+ and Sm3+ codoped Y2O3 nano phosphors
K.Suresh1,*, Niyaz Parvin Shaik2, N.V.Poornachandra Rao3 and K.V.R.Murthy4
1
Department of Physics, CSR Sarma College, Ongole -523 001, A.P., India
Department of Physics, Govt. Junior College, Sathupally, Khammam District, Telengana state -507303, India
3
Department of Physics, Rajiv Gandhi University of Knowledge Technologies,
IIIT, Basara-504101, Telengana state, India
4
Department of Applied Physics, Faculty of Engineering and Technology,
M.S. University of Baroda, Vadodara-390 001, India
*Corresponding author e-mail: sureshkukkamalla@gmail.com
2
Received 15 June 2014; accepted 02 July 2014
Abstract
Y2O3:x Eu3+(x=0.5,1.0,1.5 mol%), 0.5mol% Sm3+, 1.0mol% Dy3 phosphor fired at 1200oC were synthesized via solid state
reaction method. The dependence of photoluminescence spectra of Y2O3 phosphor on doping ‘Eu’ concentration under
near-ultraviolet (nUV) and visible excitations has been investigated. The excitation spectrum of RE3+ ions doped Y2O3
phosphors monitored under 613nm wavelength was characterized by a broad band ranging from 200-550nm with sharp
emission peaks at 395nm, 467 and 535nm in the nUV and visible region along with CT band peak at 260nm. The emission
spectra of RE3+ ions doped Y2O3 phosphors under excitations at 467nm (blue)and 535nm exhibited peaks at 583nm,
589nm, 595nm, 601nm, 632nm and a very high intense red peak at 613nm, assigned to the 5D0→7F2 electric dipole
transition of Eu3+ ion. The phosphor shows weak photoluminescence emission under 395nm excitation wavelength. The
CIE co-ordinates of Y2O3: RE3+ phosphor are x = 0.674 and y = 0.325 indicates red colour. This is promising phosphor to
produce white light under blue (467nm) excitation.
© 2014 Universal Research Publications. All rights reserved
host material for rare-earth (RE) ion doping in optical
1. Introduction
In recent years, light-emitting diodes have emerged as a applications [5-7] on account of its excellent chemical
prominent class of lighting devices and the study of red, stability, broad transparency range (0.2 to 8 μm) with a
green, blue (RGB) tri colour phosphors suitable for near- band gap of 5eV, high refractive index, and low phonon
ultraviolet (nUV) or red, green (RG) two colour phosphors energy. Furthermore, the similarities in the chemical
suitable for blue excitation has been attracting more properties and ionic radius of RE ions and Y2O3 make it an
attention for fabricating white LEDs. For generation of attractive choice as a host material [8]. The color tunability
white light emission, three different approaches are of yttria-based phosphors can be achieved by codoping the
developed. These are blue LED with yellow phosphors; an host material with some specific rare-earth elements.
ultraviolet (UV) LED with red, green and blue phosphors; Therefore, research into Y2O3 codoped with other different
and a device that combines red, green and blue LEDs. The RE activators is important because the color-tunable
advantage of the blue LED with yellow phosphors is its properties can be used in a wide range of applications.
higher efficacy compared to the other two approaches. Although many studies have examined the optical
Therefore, today’s white LEDs are commonly made by a properties of RE ion-doped Y2O3 phosphors, only a few
combination of III-nitride based blue LEDs and a coating have investigated the codoping of two or more different
of yellow phosphors such as cerium-doped yttrium ions in the same yttria host material [9].
aluminium garnets [1-2], which are becoming less available Y2O3:Eu3+ phosphor, one of the most promising oxidessince they contain rare-earth metals.The cubic phase Y2O3 based red phosphors, was studying for a long time because
is a good host material for rare earth ions. Eu3+-doped Y2O3 of its efficient luminescence under ultraviolet (UV) and
is a promising redemitting phosphor [3,4], and its cathode-ray excitation. Y2O3:Eu3+ with micrometer size
photoluminescence (PL) characteristics have been reported grains were used as the red component in three chromatic
for various optical applications.
lamps and projection color television.Numerous studies
Yttrium oxide (Y2O3) has been investigated widely as a
were focused on synthesis and optical properties of
41
International Journal of Nanomaterials and Biostructures 2014; 4(3): 41-45
Y2O3:Eu3+ phosphors [10-16]. Like many oxide-based
materials, rare-earth-doped Y2O3 has a high resilience to
ionizing radiation. Synthesis of rare-earth-doped Y2O3
based phosphors has been accomplished through a variety
of techniques including homogeneous precipitation, solid
state reaction method, chemical vapour synthesis,
combustion synthesis, and the sol–gel method [17-23]. The
wide variety of dopants that can be incorporated allows the
material to be tuned to emit in the blue (Tm3+), green
(Tb3+), or red (Eu3+) regions of the electromagnetic
spectrum [24]. Eu3+ exhibits an atomic-like transition in red
region at 612 nm.
In the present study, rare earth ions co-doped Y2O3
phosphors have been studied for many applications due to
the high stability, emission range and intensity. Y2O3:x
Eu3+ (x=0.5,1,1.5 mol%), 0.5mol% Sm3+, 1.0mol% Dy3+
phosphors were prepared by the conventional solid state
reaction method in air atmosphere for 3 hours at 12000C.
The optical properties of the synthesized particles were
explored by photoluminescence spectroscopy. Y2O3
particles with different concentrations of codoped Eu3+,
Sm3+ and Dy3+ was investigated, and the luminescence
intensity of these particles was found to be strongly
dependent
on
the
activator
concentration.
Photoluminescence studies and CIE co-ordinates of RE3+
ions doped Y2O3 under 465nm and 535nm excitations will
be discussed.
2. Experimental methods
Y2O3: x Eu3+(x=0.5,1.0,1.5 mol%), 0.5mol% Sm3+,
1.0mol% Dy3+ phosphors were synthesized by the
conventional solid state reaction method.The starting
materials were yttrium oxide (Y2O3) assay(99.9%) as raw
material was taken for the host and samarium oxide
(Sm2O3), dysprosium oxide (Dy2O3), europium oxide
(Eu2O3), with purity 99.9% were taken as activators.They
were weighed in appropriate compositions. Keeping the codopants Sm and Dy concentrations at constant and varied
the Eu concentration in each sample as 0.1, 0.5,
1.5mol%.The composite powders were grounded in an
agate mortar and pestle about an hour and then placed in an
alumina crucible with the lid closed. After the powders had
o
been sintered at 1200 C for 3 hr in a muffle furnace with a
heating rate of 5oC/min and then cooled to room
temperature. All the samples were again ground into fine
powder using an agate mortar and pestle about an hour.
The emission and the excitation spectra of the synthesized
powders were characterized with a spectroflurophotometer
(Shimadzu RF 5301 PC) with xenon lamp as excitation
source. Emission and excitation spectra were recorded
using a spectral slit width of 1.5nm. All the spectra were
recorded at room temperature. The Commission
International de l’Eclairage (CIE) co-ordinates were
calculated by the spectrophotometric method using the
spectral energy distribution. The chromatic coordinates (x,
y) of prepared materials were calculated with colour
calculator version 2, software from Radiant Imaging [25].
3 Results and Discussions
3.1 Photoluminescence Study
A series of Y2O3:xEu3+(x=0.5,1.0,1.5 mol%), 0.5mol%
Sm3+, 1.0mol% Dy3+ phosphors heated at 12000C were
42
Figure 1 Excitation spectrum of Y2O3: RE3+ phosphor
monitored under 613nm wavelength
prepared and the effect of Eu3+ concentration on the
emission intensity was investigated. Fig.1 exhibits the PL
excitation spectra of Y2O3: x Eu3+, 0.5mol% Sm3+,
1.0mol% Dy3 phosphors. The excitation spectrum
monitored under 613nm wavelength, show the broadband
ranging from 200-550nm divided in to two regions, (1) the
intense broad band centered at 260nm is attributed to the
charge transfer (CT) transition between ligand (O2-) to
metal (Eu3+) ion, (2) the intense broad band range from 380
to 550nm, the sample shows the characteristic intra
configuration 4f–4f transitions of the Eu3+ ion is split into
three levels, which are located in UV and visible regions,
attributed to 7F0→ 5L6 transition at 395nm and 7F0→5D2
transition at 467nm and 7F0→5D1 transition at 535nm. The
excitation intensity is of the order of 535nm > 467nm >
395nm. It is also observed that the intensity is increases as
the Eu concentration increases in the Y2O3: RE3+
phosphor.The 467nm is well matched with the blue LED
chip in the visible region which is useful for LED
applications for white light generation.
The luminescence emission of phosphor materials depends
strongly on the synthetic route, size of the phosphor
materials, and concentration of dopant ions. The emission
intensity is strongly depends on phosphor crystallinity
therefore the phosphors were calcinated at 1200oC. A series
of Y2O3: x Eu3+(x=0.5,1.0,1.5 mol%), 0.5mol% Sm3+,
1.0mol% Dy3 phosphors heated at 12000C were prepared
and the effect of Eu3+ concentration on the emission
intensity was investigated.
Fig.2(a) & (b) shows the emission spectra under 467 and
535nm excitation wavelengths respectively. The shape of
the emission spectra and emission peak wavelength is
independent of the excitation wavelengths. No emission
line was observed under 260nm excitation wavelength of
CT band.
Upon excitation at 467nm, the emission spectrum of Y2O3:
x Eu3+, 0.5mol% Sm3+, 1.0mol% Dy3 phosphors emits a
broad band range from 575-625nm with four peaks at 583,
589, 595, 601, 632nm and a very strong intense peak at
613nm (red) with the full width at half maximum (5nm) as
shown in fig.2(a). The Stokes shift is 353nm (2.738eV),
determined from the difference between the first excitation
maximum (260nm) and the emission maximum (613nm).
The 5D0–7F2 electric dipole transition of Eu3+, which
is responsible for red emission, strongly depends on the
International Journal of Nanomaterials and Biostructures 2014; 4(3): 41-45
Table 1 Transitions at different emission peaks
Peak No.
1
2
3
4
5
6
7
8
9
Peak Wavelength (nm)
535
539
556
583
589
595
601
613
632
Figure 2(a) Emission spectrum of Y2O3: RE3+ phosphor
under 467nm excitation wavelength
Figure 2(b) Emission spectrum of Y2O3:RE3+ phosphor
under 535nm excitation wavelength
Figure 2(c) Energy level diagram of Y2O3:Eu3+ with
possible electric dipole transitions within energy levels of
Eu3+ ions.
43
RE ion
Eu
Eu
Sm
Eu
Eu
Eu
Sm
Eu
Eu
Transition
5
D1 → 7F1
5
D1 → 7F1
4
G5/2 → 6H5/2
5
D0 → 7F1
5
D0 → 7F1
5
D0 → 7F1
4
G5/2 → 6H7/2
5
D0 → 7F2
5
D0 → 7F3
crystal field symmetry around Eu3+ ion [7, 8]. Transitions at
different emission peaks repoted in table 1.
In the PL spectra (Fig. 2a, b) a number of sharp peaks
associated with forced electric dipole transition from
excited 5D0→7FJ(J = 1, 2, 3) levels of Eu3+ activator ions.
The deep red peak corresponding to 613nm is attributed to
5
D0→7F2 electric dipole transition with FWHM of 5nm,
whereas the 589 nm orange emission originates due to
magnetic dipole transition 5D0→7F1. Lower symmetry of
crystal field near the activator Eu3+ ion results in higher
ratio of red and orange peak intensity (R/O value) [9-14].
The R/O value strongly depends on local symmetry of
activator Eu3+ ion.The ratio of the emission intensity of the
C3i site to the emission intensity of the C2 site decreases
with increasing europium content due to strong energy.
Fig.2(b) shows the same samples under 535nm excitation.
In this case, the emission spectrum exhibited luminescence
spectra is same, except for a increase of the luminescence
intensity. The intensity of peak at 613nm under 535nm
excitation is more when compared with the emission under
467nm excitation. The emission spectrum of Y2O3 particles
co-doped with different Eu3+, Sm3+ and Dy3+ concentrations
was similar due to the same f-f transitions within the
specific RE ion. Therefore, the concentration of co-doped
RE ions plays an important role and should be strongly
considered during the phosphor fabrication process.
It was observed that the PL emission intensity of Y2O3:
xEu3+ (x=0.5, 1.0, 1.5 mol%), 0.5mol% Sm3+, 1.0mol%
Dy3 under 467 and 535nm excitations, enhances with the
increase of Eu3+ concentration. From the emission spectrum
except the transitions of Eu3+ and Sm3+, the transitions of
Dy3+ ions around 480/575/655nm was not found. The
presence of Sm3+ RE ion transition in the phosphor around
556nm and 601nm was evident but the intensity is very low
this may be due to the domination of Eu ion transition.
However, the luminescence intensity of Ln3+ ions in such
semiconductors is relatively low due to poor energy
transfer from semiconductor host to Ln3+ ions. One possible
reason is that Sm3+ ions occupy on the surface rather than
lattice sites of semiconductor host due to large ionic size
differences between Ln3+ and metal ions. Due to the codapants in the Y2O3 phosphor the FWHM value is increased
of the well known 613nm red peak. fig.2(c) shows the
energy level diagram of Eu3+ ion in the Y2O3 phosphor
3.2 CIE study
The CIE co-ordinates of (chart -1931) were calculated by
the Spectrophotometric method using the spectral energy
distribution. Based on the emission spectra, it was possible
to see the color of the emission of each sample in the CIE
International Journal of Nanomaterials and Biostructures 2014; 4(3): 41-45
Figure 3 CIE co-ordinates of Y2O3: RE3+ phosphor
diagrams 1931. Fig.3 shows the CIE coordinates depicted
on the 1931 chart of Y2O3: RE3+ phosphor. In the fig.3, the
color co-ordinates for Y2O3: RE3+ phosphor are x = 0.674
and y = 0.325 indicates red colour.
4. Conclusions
Y2O3 phosphor co-doped with Eu3+, Sm3+ , Dy3+ phosphor
powders were successfully synthesized by the high
temperature solid state reaction method. The prepared
phosphor powders emit their characteristic lines. The
luminescence color emission could be controlled by the
excitation wavelength. Therefore, the emission wavelength
and color output of the same Y2O3: RE3+ phosphor can be
adjusted by switching the radiation from 467 to 535nm.
The Stoke shift and the FWHM of the emission of Y2O3:
RE3+ were characteristic of a ligand-to-metal charge
transfer (CT) emission. The Stoke shift of Y2O3: RE3+
phosphor under 467nm excitation is more than Stoke shift
under 535nm excitation and observed that the emission
intensity is less.
The 5D0–7FJ (J =0, 1, 2, etc.) transitions of Eu3+ were
recorded in the all of samples. The ratio of the emission
intensity of the C3i site to the emission intensity of the C2
site decreases with increasing europium content as well as
decreasing crystal size due to strong energy transfer from
the C3i to the C2 site. The Commission International de
1’Eclairage [CIE] co-ordinates of Y2O3:RE3+ phosphor
exhibit red colour. Y2O3: x Eu3+(x=0.5, 1.0, 1.5 mol%),
0.5mol% Sm3+, 1.0mol% Dy3 phosphors may be a red
component for white light generation in LEDs under blue
LED chip (467nm) excitation.
Acknowledgements
The author (K. Suresh) is gratefully thanking the University
Grant Commission (UGC), New Delhi, India for financial
assistance under Faculty Development Programme (FDP).
44
References
1. S.Nakamura, T.Mukai, M.Senoh, Appl. Phys. Lett., 64,
1687-1689(1994)
2. Shi Ye, Xiao-Ming Wang, and Xi-Ping Jing, Journal of
the Electrochemical Society 155, J143-J147(2008)
3. Liu Xingren, Zhang Xiao, Zhang Yinglan, Lu Shuhua.
Chinese Journal of Luminescence, 03(1989)
4. W.J.Park, M.K.Jung, S.M.Kang, T.Masaki and
D.H.Yoon, Journal of Physics and chemistry of Solids
69, 1505-1508(2008)
5. T.Nakanishi, S.Tanabe, Physica Status Solidi (a)
206:919–922(2009)
6. S.W.Choi, S.H.Hong, Y.J.Kim,Journal of the
American Ceramic Society,92: 2025–2028(2009)
7. T.K.Anh, T.Ngoc, P.T.Nga, V.T.Bich, P.Long, and W.
Strek, Journal of Luminescence,39,4, 215–221(1988)
8. S.Shionoya, W. M. Yen, Phosphor Handbook, CRC
Press, Boca Raton, Fla, USA(1999)
9. G. Blasse and B. C. Grabmaier, Luminescent
Materials, Springer, Berlin, Germany(1994)
10. S. L. Jones, D. Kumar, K. G. Cho, R. Singh, P. H.
Holloway, Displays,19,151–167(1999)
11. R. Schmechel, M. Kennedy, H.V. Seggern, H.
Winkler, M. Kolbe, R.A. Fischer, L. Xaomao, A.
Benker, M. Winterer, H. Hahn, J. Appl. Phys.
89,1679–1686(2001)
12. H. Eilers and B. M. Tissue, Chemical Physics
Letters,251,1-2,74–78(1996)
13. M. Kottaisamy, D. Jeyakumar, R. Jagannathan,
M.M.Rao, Materials Research Bulletin, 31,8, 1013–
1020(1996)
14. B. Bihari, H. Eilers, and B. M. Tissue, Journal of
Luminescence,75,1,1–10(1997)
International Journal of Nanomaterials and Biostructures 2014; 4(3): 41-45
15. T.Ye,Z.Guiwen,Z.Weiping,X. Shangda, Materials
Research Bulletin,32,5,501–506, (1997)
16. K.E.Bower,Y.A.Barbanel,Y.G.Shreter,G.W.Bohnert,P
olymers, Phosphors,and Voltaics for Radioisotope
Microbatteries, vol.1, CRC Press, Boca Raton,
FL(2002)
17. J. Silver, M.I. Martinez-Rubio, T.G. Ireland, G.R.
Fern, R. Withnall, J. Phys. Chem.B 105,9107–
9112(2001)
18. J.Silver, M.I.Martinez-Rubio, T.G.Ireland, G.R.Fern,
R.Withnall,J.Phys.Chem.B, 105, 948–953(2001)
19. J.Silver,T.G.Ireland, R.Withnall, J. Electron. Chem.
Soc. 151,H66–H68(2004)
20. D.Matsuura, Appl. Phys. Lett. 81,4526–4528(2002)
21. S.Narukawa, G.Fasol, the Blue Laser Diode: GaN
Based Light Emitters and Lasers, Springer, Berlin,
216(1997)
22. P.Schlotter, J.Baur, Ch.Hielscher, M.Kunzer, H.Obloh,
R.Schmidt, J.Schneider, Mat. Sci. & Eng. B. 59, 390394(1999)
23. W. Tews, G. Roth, S. Tews, Proc., Phosphor Global
Summit 2007, Korea (2007)
24. Y. Fukuda, Proc. Phosphor Global Summit 2007,
Korea (2007)
25. G. Blasse, B. C. Grabmaier, Luminescent Materials,
Springer, New York, 143(1994)
26. Wang H, Yang J, Zhang CM, Lin J: J Solid State
Chem,182:2716–2724(2009)
27. Liu Z, Yu L, Wang Q, Tao Y, Yang H. J
Lumin,131:12–16(2011)
Source of support: Nil; Conflict of interest: None declared
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International Journal of Nanomaterials and Biostructures 2014; 4(3): 41-45