materials
Article
Tunable Luminescence in Sr2MgSi2O7:Tb3+,
Eu3+Phosphors Based on Energy Transfer
Minhong Li, Lili Wang, Weiguang Ran, Zhihan Deng, Jinsheng Shi * and Chunyan Ren *
Department of Chemistry and Pharmaceutical Science, Qindao Agricultural University, Qingdao 266109, China;
[email protected] (M.L.); [email protected] (L.W.); [email protected] (W.R.);
[email protected] (Z.D.)
* Correspondence: [email protected] (J.S.); [email protected] (C.R.);
Tel.: +86-532-8803-0161 (J.S.); Fax: +86-532-8608-0213 (J.S.)
Academic Editors: Jonathan Kitchen and Robert Elmes
Received: 22 December 2016; Accepted: 17 February 2017; Published: 24 February 2017
Abstract: A series of Tb3+ , Eu3+ -doped Sr2 MgSi2 O7 (SMSO) phosphors were synthesized by
high temperature solid-state reaction. X-ray diffraction (XRD) patterns, Rietveld refinement,
photoluminescence spectra (PL), and luminescence decay curves were utilized to characterize each
sample’s properties. Intense green emission due to Tb3+ 5 D4 →7 F5 transition was observed in the
Tb3+ single-doped SMSO sample, and the corresponding concentration quenching mechanism was
demonstrated to be a diople-diople interaction. A wide overlap between Tb3+ emission and Eu3+
excitationspectraresults in energy transfer from Tb3+ to Eu3+ . This has been demonstrated by
the emission spectra and decay curves of Tb3+ in SMSO:Tb3+ , Eu3+ phosphors. Energy transfer
mechanism was determined to be a quadrupole-quadrupole interaction. And critical distance of
energy transfer from Tb3+ to Eu3+ ions is calculated to be 6.7 Å on the basis of concentration quenching
method. Moreover, white light emission was generated via adjusting concentration ratio of Tb3+ and
Eu3+ in SMSO:Tb3+ , Eu3+ phosphors. All the results indicate that SMSO:Tb3+ , Eu3+ is a promising
single-component white light emitting phosphor.
Keywords: energy transfer; single-component; white light
1. Introduction
With the increasing seriousness of environmental problems and energy issues, white light emitting
diodes (w-LEDs) have attract great attention in the lighting and display field due to their environmental
friendliness, lower energy consumption, long lifetime, and extraordinary luminous efficiency compared
with traditional incandescent or fluorescent lamps [1–4]. In general, three effective strategies can be
used to generate white light. First is the combination of multiple LED chips (red, green, and blue)
in a single device, called RGB-LEDs [5]. However, it is uneconomic to combine three or more LED
chips to fabricate w-LEDs due to low efficiencies and expensive cost. The second approach to generate
white light is the assembly of a single LED chip with red, green, and blue phosphors or a single-phase
phosphor, which is called phosphor converted white LEDs (pc-WLEDs) [6]. Nowadays, leading
commercial w-LEDs are fabricated by a “blue (InGaN) LED chip + yellow (YAG:Ce3+ ) phosphor” [7,8].
However, inherent weaknesses such as high correlated color temperature (CCT > 7000 K) and poor
color rendering index (CRI < 80) were caused by the absence of red component, which greatly limiting
its application [9,10]. In order to overcome these drawbacks, UV LED chip excited tricolor phosphors
were prepared, which can provide high color-rendering index and quality of light [11]. However, poor
luminescence efficiency was caused by mixing of multiemission bands, which contributed to strong
reabsorption. As an alternative, it is obligatory to develop single-phase phosphor.
Materials 2017, 10, 227; doi:10.3390/ma10030227
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Materials 2017, 10, 227
Materials 2017, 10, 227
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Rare earth
earth ions
ions doped
doped silicate
silicate phosphors
phosphors have
have been
been investigated
investigated extensively
extensively due
due to
to their
their cheap
cheap
Rare
raw
materials
and
good
chemical
and
physical
stability,
which
originates
from
the
strong
and
rigid
raw materials and good chemical and physical stability, which originates from the strong and rigid
frameworks with
with covalent
covalent Si–O
Si–O bonds
bonds [12].
[12]. Recently,
Recently, Zhou
Zhou et
et al.
al. reported
reported aa single-component
single-component
frameworks
3+3+
MgY
2Si3O10:Bi3+3+
,
Eu
phosphor
that
can
give
white
light
emission
under
excitation
light and
and
MgY2 Si3 O10 :Bi , Eu phosphor that can give white light emission under excitation of
of UV
UV light
2+
provide potential
potential application
application for
forwhite-LEDs
white-LEDs[13].
[13]. Effective
Effective energy
energytransfer
transferwas
wasobserved
observedfrom
fromEu
Eu2+
provide
2+
2+
2+
to Mn
Mn2+ in
in Mg
Mg2Al
Al4Si
5O18:Eu 2+
, Mn 2+
phosphor,
2014,
to
phosphor,which
whichwas
wasresearched
researchedby
byChen
Chenet
et al.
al. [14].
[14]. In
In 2014,
2
4 Si5 O18 :Eu , Mn
3+, Tb
3+, Eu3+
3+ phosphor, which gives
Wang
et
al.
reported
the
luminescence
properties
of
Y
2SiO5:Ce
3+
3+
Wang et al. reported the luminescence properties of Y2 SiO5 :Ce , Tb , Eu phosphor, which gives
3+ [15]. In addition to similar host
white light
light emission
emission via
viaenergy
energytransfer
transferfrom
fromCe
Ce3+3+ to
toTb
Tb3+3+ to
to Eu
Eu3+
white
[15]. In addition to similar host
materials, on
onthethe
other
hand,
energy
transfer
was observed
in rare
earthphosphors.
co-doped
materials,
other
hand,
energy
transfer
processprocess
was observed
in rare earth
co-doped
phosphors.
It
is
well
known
that
energy
transfer
from
sensitizers
to
activators
plays
an
important
It is well known that energy transfer from sensitizers to activators plays an important role in realizing
3+ ions have been widely
role in realizing
emission
[16].
Forfamily,
the rare
earth family,
trivalent
tunable
emissiontunable
[16]. For
the rare
earth
trivalent
Tb3+ ions
haveTb
been
widely studied due
5D4→7FJ transitions in green region (J = 6, 5, 4
studied
to 5D3→7FJ transitions
in blue
region
7 F transitions
7 F transitions
5 D →due
5 D →and
to
in
blue
region
and
in
green
region
(J = 6, 5, 4 and 3)
3
J
4
J
and 3)onbased
on different
doping concentration
[17,18].
It can transfer
effectively
transfertoits
energy to
to
based
different
doping concentration
[17,18]. It can
effectively
its energy
activators
3+ is an effective red
activators
to
improve
the
luminescence
intensity
of
co-activators
[19].
Eu
3+
improve the luminescence intensity of co-activators [19]. Eu is an effective red component due to
component
to its 5D0→7F2 electric dipole transition, which subsititute sites without symmetry
5 D →7 F due
its
0
2 electric dipole transition, which subsititute sites without symmetry center. In order to
3+
3+
center.tunable
In order
to realize
emission
color, Tb
SMSO (Sr2MgSi2O7)
realize
emission
color,tunable
Tb3+ and
Eu3+ co-doped
SMSOand
(Sr2Eu
MgSico-doped
2 O7 ) phosphors were prepared
phosphors
were
prepared
in
this
experiment.
in this experiment.
3+, Eu3+
In this
single-phased
SMSO:Tb
were synthesized
via high temperature
3+phosphors
In
thiswork,
work,new
new
single-phased
SMSO:Tb
, Eu3+ phosphors
were synthesized
via high
solid
state
reaction.
Crystal
structure,
photoluminescence
properties,
Commission
International
De
temperature solid state reaction. Crystal structure, photoluminescence properties, Commission
L’Eclairage
(CIE)
chromaticity
coordinates,
and
luminescence
lifetimes
have
been
investigated
in
International De L’Eclairage (CIE) chromaticity coordinates, and luminescence lifetimes have been
3+
3+
3+
3+
detail. Energy
from Tb
to Eu
in Tb
SMSO:Tb
was investigated,
and
the corresponding
3+ to Eu3+, Eu
3+ , Eu3+ was
investigated
in transfer
detail. Energy
transfer
from
in SMSO:Tb
investigated,
and the
energy
transfer
mechanism
was
determined
to
be
a
quadrupole-quadrupole
interaction.
Moreover,
corresponding energy transfer mechanism was determined to be a quadrupole-quadrupole interaction.
tunable emission
blue from
to white,
to red-orange,
was observed
under excitation
of UV light.
Moreover,
tunablefrom
emission
blueup
to white,
up to red-orange,
was observed
under excitation
of
3+
3+
All
results
show
that
SMSO:Tb
,
Eu
is
a
potential
single-component
phosphor.
3+
3+
UV light. All results show that SMSO:Tb , Eu is a potential single-component phosphor.
2. Results
Results
2.
2.1.Phase
2.1.Phase and
and Structure
Structure Analysis
Analysis
3+ ions
Figure
ions single-doped or co-doped SMSO phosphors
Figure 11gives
givesthe
theXRD
XRDpatterns
patternsofofTb
Tb3+3+ and
and Eu
Eu3+
phosphors
◦ C for 3 h. It can be found that all diffraction
prepared
by
high
temperature
solid
state
reaction
at
1300
prepared by high temperature solid state reaction at 1300 °C for 3 h. It can be found that all
peaks
of phosphors
wellmatched
with SMSO
demonstratingdemonstrating
that prepared
diffraction
peaks ofmatched
phosphors
wellphase
with (JCPDS#15-0016),
SMSO phase (JCPDS#15-0016),
3+ and
3+ ions
samples
are single-component
and a small quantity
Tb3+ and
Eu3+ of
ions
notEu
induce
any
other
that prepared
samples are single-component
and aofsmall
quantity
Tbwill
will
not
significant
for SMSOchanges
lattice. for SMSO lattice.
induce anychanges
other significant
3+ and SMSO:0.08Tb
3+,
3+
Figure 1.
1. XRD
XRD patterns
patternsof
ofSMSO
SMSO(Sr
(Sr2 MgSi
2MgSi2O
O7) host, SMSO:0.08Tb3+3+, SMSO:0.10Eu3+
Figure
2 7 ) host, SMSO:0.08Tb , SMSO:0.10Eu and SMSO:0.08Tb ,
3+
0.04Eu3+ phosphors.
0.04Eu
phosphors.
Figure 2a depicts the crystal structure of SMSO crystallizes in a tetragon, with cell parameters of
a = b = 8.01 Å, c = 5.16 Å, V = 331.34 Å3, Z = 2. Rare earth ions preferred to occupy Sr2+ rather than Mg2+
Materials 2017, 10, 227
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Figure 2a depicts the crystal structure of SMSO crystallizes in a tetragon, with cell parameters
Materials 2017, 10, 227
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of a = b = 8.01 Å, c = 5.16 Å, V = 331.34 Å3 , Z = 2. Rare earth ions preferred to occupy Sr2+ rather
2+
than sites
Mg2+because
sites because
similar
ionic
radius
of SrÅ2+for(rCN
= 1.26
for
CN
= 8),Å Mg
2+ (r = 1.26
2+ (r
of similarofionic
radius
of Sr
= 8),Å
Mg
= 0.57
for CN(r= =4),0.57
Tb3+Å for
3+
3+
CN =(r4),
Tb Å(rfor=CN
1.04= 8)
Å and
for CN
andÅEu
(r == 8)
1.06
Å In
fororder
CN =
[20]. identify
In orderthe
to influence
further identify
= 1.04
Eu3+=(r8)
= 1.06
for CN
[20].
to8)
further
of
the influence
of
doping
ions
on
crystal
structure,
structure
refinement
of
powder
XRD
patterns
doping ions on crystal structure, structure refinement of powder XRD patterns of SMSO:0.08Tb3+, of
3+ , SMSO:0.10Eu
3+ and 3+
3+ , 0.04Eu
3+ performed
3+ and SMSO:0.08Tb
SMSO:0.10Eu
, 0.04Eu3+ samples
were
by the
general by
structure
SMSO:0.08Tb
SMSO:0.08Tb
samples were
performed
the general
analysis
system
(GSAS)
method.
The final
results
were were
summarized
in Table
1. The
structure
analysis
system
(GSAS)
method.
The final
results
summarized
in Table
1. original
The original
structure
model
with
crystallographicdata
data of
of SMSO
SMSO (ICSD
was
used
to refine
the above
structure
model
with
crystallographic
(ICSD#155330)
#155330)
was
used
to refine
the above
samples. Corresponding patterns for Rietveld refinements of SMSO:0.08Tb3+, 3+
SMSO:0.10Eu3+ and
3+ and
samples. Corresponding
patterns
for
Rietveld
refinements
of
SMSO:0.08Tb
,
SMSO:0.10Eu
3+, 0.04Eu3+ samples at room temperature are displayed in Figure 2b,c, respectively. The
SMSO:0.08Tb
3+
3+
SMSO:0.08Tb , 0.04Eu samples at room temperature are displayed in Figure 2b,c, respectively.
results indicate that rare earth ions doped SMSO phosphors with space group of P-421m have a
The results
indicate
that rare earth ions doped SMSO phosphors with space group of P-421m have a
tetragonal
structure.
tetragonal structure.
Table 1. Refinement, Crystallographic, and Structure. Parameters of the SMSO:0.08Tb3+, SMSO:0.10Eu3+,
3+, 0.04Eu3+ samples.
Tableand
1. Refinement,
and Structure. Parameters of the SMSO:0.08Tb3+ , SMSO:0.10Eu3+ ,
SMSO:0.08TbCrystallographic,
and SMSO:0.08Tb3+ , 0.04Eu3+ samples.
Formula
SMSO
SMSO:0.08Tb SMSO:0.10Eu SMSO:0.08Tb, 0.04Eu
Crystal System
Tetragonal
Tetragonal
Tetragonal
Tetragonal
Formula
SMSO
SMSO:0.08Tb
SMSO:0.10Eu
SMSO:0.08Tb, 0.04Eu
Space Group
P-421m (113) P-421m (113)
P-421m (113)
P-421m (113)
Crystal System
Tetragonal
Tetragonal
Tetragonal
Tetragonal
a/Å
8.01
8.0111
8.0112
8.0108
Space Group
P-421m (113)
P-421m (113)
P-421m (113)
P-421m (113)
b/Å
8.01
8.0111
8.0112
8.0108
8.01
8.0111
8.0112
8.0108
a/Å
c/Å
5.16
5.1667
5.1657
5.1650
8.01
8.0111
8.0112
8.0108
b/Å
v/Å3
331.34
331.58
331.53
331.45
5.16
5.1667
5.1657
5.1650
c/Å
331.34
331.58
331.53
331.45
v/Å
Z3
2
2
2
2
Z Type
22
2
2
Radiation
Cu−Kα
Cu−Kα
Cu−Kα
Radiation Type
Cu−Kα
Cu−Kα
Cu−Kα
Wavelength/Å
1.5405
1.5405
1.5405
1.5405
1.5405
1.5405
Wavelength/Å
◦
◦
◦
◦
◦
Profile
Range/°
10°−90°
10°−90°
10°−90°
Profile Range/
10 −90
10 −90
10◦ −90◦
Rp/%
-8.75
8.46
7.97
Rp/%
8.75
8.46
7.97
Rwp/%
-11.95
11.51
10.9
Rwp/%
11.95
11.51
10.9
3.552
3.721
4.157
χ2 2
χ
3.552
3.721
4.157
Figure 2. (a) Crystal structure of SMSO. Experimental (black crosses) and calculated (red solid line)
Figure
2. (a) Crystal structure of SMSO. Experimental (black crosses) and calculated (red solid line)
XRD patterns and their difference (blue solid line) for (b) SMSO:0.08Tb3+; (c)3+SMSO:0.10Eu3+ and (d)
XRD patterns and
their difference (blue solid line) for (b) SMSO:0.08Tb ; (c) SMSO:0.10Eu3+ and
3+, 0.04 Eu3+ samples by the GSAS program. The short magenta vertical lines show the
SMSO:0,08Tb3+
(d) SMSO:0,08Tb , 0.04 Eu3+ samples by the GSAS program. The short magenta vertical lines show
position of Bragg reflections of the calculated patterns.
the position of Bragg reflections of the calculated patterns.
Materials 2017, 10, 227
Materials 2017, 10, 227
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2.1.2.2.
Photoluminescence
Photoluminescenceand
andEnergy
EnergyTransfer
Transfer
3+ phosphor. The excitation
Figure
3a3a
gives
Figure
givesthe
theexcitation
excitationand
andemission
emission spectra
spectra of
of SMSO:0.08Tb
SMSO:0.08Tb3+ phosphor.
The excitation
spectrum
monitored
atat
545
nm
spectrum
monitored
545
nmshows
showsa abroad
broadband
bandranging
rangingfrom
from200
200to
to250
250 nm
nm with
with the
the maximum
maximum at
3+
229atnm,
originated
from
4f-5d
spin-allowed
transition
of of
TbTb.3+Other
229 which
nm, which
originated
from
4f-5d
spin-allowed
transition
. Otherweak
weakabsorption
absorption bands
bands in
theinregion
of 250
to 350
nmnm
areare
ascribed
toto
4f-4f
Whenexcited
excited
nm,
the region
of 250
to 350
ascribed
4f-4fspin-forbidden
spin-forbidden transitions.
transitions. When
at at
229229
nm,
55D →77 F (J = 3, 4 and 5) and5 5 D →
7 F (J = 3, 4, 5 and 6)
7
thethe
emission
spectrum
composes
of
both
emission spectrum composes of both D33 FJ J (J = 3, 4 and 5) and D4→
4 FJ (JJ = 3, 4, 5 and 6)
3+ 3+emission except for the
transitions.
It can
bebe
observed
that
there
is is
nono
other
important
change
forfor
TbTb
transitions.
It can
observed
that
there
other
important
change
emission except for
the luminescence
intensity
under
different
excitation
conditions.
luminescence
intensity
under
different
excitation
conditions.
3+ sample; (b) The emission spectra
Figure
3. 3.
(a)(a)
The
excitation
Figure
The
excitationand
andemission
emissionspectra
spectra of
of SMSO:0.08Tb
SMSO:0.08Tb3+ sample;
(b) The emission spectra
3+
3+
of of
SMSO:xTb
0.08, 0.10
0.10and
and0.15)
0.15)samples.
samples.
0.02, 0.04,
0.04, 0.06, 0.08,
SMSO:xTb (x(x==0.02,
3+samples with different Tb3+ 3+
Figure
displaysthe
theemission
emissionspectra
spectraof
ofSMSO:xTb
SMSO:xTb3+
Figure
3b3b
displays
samples with different Tb concentration
concentration
3+ according
under
excitation
of
229
nm.
The
inset
shows
the
change
of
luminescence
under excitation of 229 nm. The inset shows the change of luminescenceintensity
intensityofofTb
Tb3+
according
3+doping concentration. It can be seen that luminescence intensity of SMSO:xTb3+
to different Tb
3+
to different Tb doping concentration. It can be seen that luminescence intensity of SMSO:xTb3+
samples increases gradually with increasing 3+
Tb3+ content from 0 to 8 mol %, and then decreases
samples increases gradually with
increasing Tb content from 0 to 8 mol %, and then decreases when
3+
when the concentration of Tb is enhanced over 8 mol %. It is due to the concentration quenching
the concentration of Tb3+ is enhanced over 8 mol %. It is due to the concentration quenching
effect,
effect, which is assigned to non-irradiative energy transfer between3+ adjacent Tb3+ ions. For
which is assigned to non-irradiative energy transfer between adjacent Tb ions. For investigating the
investigating the concentration quenching mechanism, it is necessary to calculate the critical distance 3+
concentration
mechanism,
it is necessaryquenching
to calculatetheory,
the critical
distance
(Rc ) between
Tb
(Rc) betweenquenching
Tb3+ ions. According
to concentration
Rc was
determined
by [21,22]:
ions. According to concentration quenching theory, Rc was determined by [21,22]:
ଷ௏ 1/3
]
Rc = 2[
(1)
ସ஠௑೎ ே
1/3
3V
Rc =
2[ N is the] number of host cations in the unit cell, and(1)
where V corresponds to the volume of unit
cell,
4πXc N
Xc is the critical concentration of dopant ions. In this paper, V = 331.34 Å3, N = 2 and Xc is 0.08 for Tb3+
doped
SMSO phosphor,
a consequence,
RcNwas
calculated
7.9cations
Å. Generally,
non-radiative
where
V corresponds
to theas
volume
of unit cell,
is the
number to
of be
host
in the unit
cell, and Xc is
3
3+ doped
energy
transfer
was
occurred
due
to
exchange
interaction,
radiation
re-absorption,
and
the critical concentration of dopant ions. In this paper, V = 331.34 Å , N = 2 and Xc is 0.08 for Tbelectric
3+
multipolar
interactions
[23]. For SMSO:xTb
samples,
Rc 7.9
wasÅ.calculated
be 7.9 Å. As
a
SMSO
phosphor,
as a consequence,
Rc was calculated
to be
Generally, to
non-radiative
energy
consequence,
we candue
speculate
that exchange
interaction
is weak
in this sample
since exchange
transfer
was occurred
to exchange
interaction,
radiation
re-absorption,
and electric
multipolar
3+ samples,
interaction[23].
occurred
when Rc less
than 5 Å R
[24].
Also, radiation re-absorption plays no role in Tb3+
interactions
For SMSO:xTb
c was calculated to be 7.9 Å. As a consequence, we can
concentration
quenching
process because
of this
poorsample
overlap
between
Tb3+ interaction
excitation and
emission
speculate
that exchange
interaction
is weak in
since
exchange
occurred
when
spectra. In consequence, electric multipolar interaction is major in Tb3+3+concentration quenching.
Rc less than 5 Å [24]. Also, radiation re-absorption plays no role in Tb concentration quenching
According to Dexter’s energy transfer theory, the concentration quenching mechanism for SMSO:xTb3+
process because of poor overlap between Tb3+ excitation and emission spectra. In consequence, electric
phosphors was calculated by the follow equation [25]:
multipolar interaction is major in Tb3+ concentration quenching. According to Dexter’s energy transfer
3+ phosphors was calculated by
I/C = k1for
/β ×SMSO:xTb
Cs/3
(2) the
theory, the concentration quenching mechanism
follow
equation
where
I is the [25]:
emission intensity of activator, C is the related concentration of Tb3+, k1 and β are
I/C same
= k1 /β
× Cs/3 wavelength in SMSO matrix, and s(2)
constants for each interaction under the
excitation
represents the different electric multipolar interactions which is that when s are equal to 6, 8 and 10,
Materials 2017, 10, 227
5 of 11
where I is the emission intensity of activator, C is the related concentration of Tb3+ , k1 and β are
Materials 2017, 10, 227
5 of 11
constants for each interaction under the same excitation wavelength in SMSO matrix, and s represents
thecorresponding
different electric
multipolar interactions which is that when s are equal to 6, 8 and 10, corresponding
to dipole–diople (d–d), diople−quadrupole (d–q), and quadrupole–quadrupole (q–q)
to interacitions,
dipole–dioplerespectively
(d–d), diople
−quadrupole
(d–q),
quadrupole–quadrupole
[26].
Figure 4 gives
the and
linear
relationship of log(I/C) (q–q)
versusinteracitions,
log(C) in
3+
respectively
[26].
Figure
4
gives
the
linear
relationship
of
log(I/C)
versus
log(C)
SMSO:Tb
SMSO:Tb3+ phosphor. The value of s was calculated to be 5.66 (blue emission) andin5.31
(green
phosphor.
Theindicating
value of s was
to be 5.66
and 5.31
(green emission),
indicating
emission),
that calculated
d-d interaction
is (blue
majoremission)
concentration
quenching
mechanism
for
3+ phosphor.
3+
that
d-d
interaction
is
major
concentration
quenching
mechanism
for
SMSO:Tb
SMSO:Tb phosphor.
Materials 2017, 10, 227
5 of 11
corresponding to dipole–diople (d–d), diople−quadrupole (d–q), and quadrupole–quadrupole (q–q)
interacitions, respectively [26]. Figure 4 gives the linear relationship of log(I/C) versus log(C) in
SMSO:Tb3+ phosphor. The value of s was calculated to be 5.66 (blue emission) and 5.31 (green
emission), indicating that d-d interaction is major concentration quenching mechanism for
SMSO:Tb3+ phosphor.
3+ phosphors. ((a) represents concentration of
Figure
Dependenceofoflg(I/C)
lg(I/C)on
onlg(C)
lg(C)for
forSMSO:xTb
SMSO:xTb3+
Figure
4. 4.
Dependence
phosphors. ((a) represents concentration of
3+). 3+
blue
emission;
(b)
represents
concentration
of
green
emission;
the
concentration
of Tb
blue emission; (b) represents concentration of green emission;CCrepresents
represents
the
concentration
of Tb
).
3+ sample and simple
Figure 5 exhibits the excitation and emission spectra
of SMSO:0.10Eu
3+ phosphors. ((a) represents
3+ sample
Figure 4. Dependence
of lg(I/C)
on emission
lg(C) for SMSO:xTb
concentration
Figure
5
exhibits
the
excitation
and
spectra
of
SMSO:0.10Eu
andofsimple energy
3+
energy levelblue
transitions
ofrepresents
Eu , respectively.
Broad
excitation
band from
200 to 450ofnm
emission;
(b)
concentration of
green emission;
C represents
the concentration
Tb3+).was observed
3+
level
transitions
of nm.
Eu The
, respectively.
Broad
excitation
band
from 200
to 3+450
was transfer
observed
monitored
at 616
strongest peak
at about
270 nm
is ascribed
to Eu
−O2−nm
charge
3+ −O2− charge transfer
3+Eu
monitored
at
616
nm.
The
strongest
peak
at
about
270
nm
is
ascribed
to
Figure
5
exhibits
the
excitation
and
emission
spectra
of
SMSO:0.10Eu
sample
and
simple
3+
transition (CTB) from negative oxygen 2p orbit to the empty 4f orbit of Eu , which is easy to
energy level
transitions
Eu3+, respectively.
Broad
excitation
band
from
200
to3+450
nm was
observed
transition
(CTB)
from
negativeofoxygen
2p orbit
to the
empty 4f
orbit
of
Eu
, which
is
easy
to influence
influence
by host
environment
[27]. Other
narrow
absorption
peaks
in
the
regionof
300
to 450
nm at
monitored at 616 nm. The strongest peak at about 270 nm is ascribed to Eu3+−O2− charge transfer
7F0→5D
7to
5Dnm
by363,
host382,
environment
[27].nm
Other
narrow
absorption
peaks
in5G
the
300
450
at
363,
382,
394,
and
467
are
attributed
to
4, 7F0→
4, 7regionof
F
0→5L6, and
F
0
→
2
transitions,
transition (CTB) from negative oxygen 2p orbit to the empty 4f orbit of Eu3+, which is easy to
7 F →5 D , 7 F →5 G , 7 F 3+→5 L , and 7 F →5 D transitions, respectively.
394,
and
467
nm
are
attributed
to
respectively.
Under
excited
at 270
nm,
represents
0[27].
4 SMAO:0.10Eu
0
4
0 phosphor
6
0regionof
2 300atoseries
influence
by host
environment
Other
narrow
absorption
peaks
in the
450 nmofat narrow
3+ phosphor
5D4, represents
7F0→
5G4, 7592,
7of
5D2 transitions,
Under
excited
at ranging
270
nm,467
SMAO:0.10Eu
series
lines
emission
lines
from
to 750
nm
579,
654,
and
705emission
nm, which
363,
382,
394, and
nm500
are attributed
to 7Fat
0→about
F0→a5L616,
6, and
F0→narrow
3+ phosphor represents a series of narrow 5
7FJexcited
respectively.
Under
SMAO:0.10Eu
corresponding
D
0→
(J about
= 0,at1,270
2, nm,
3,592,
and
4) transitions.
can corresponding
find that the position
of7 FJ
ranging
from
500 to
to 5750
nm
at
579,
616,
654, and
705And
nm,we
which
to D0 →
emission lines ranging from 500 to 750 nm at about 579, 592, 616, 654, and 705 nm, which
occur obvious
migration
different
excitation
wavelength.
(J =emission
0, 1, 2, 3,peak
and don't
4) transitions.
And we
can findunder
that the
position
of emission
peak don’t occur obvious
corresponding to 5D0→7FJ (J = 0, 1, 2, 3, and 4) transitions. And we can find that the position of
migration emission
under different
wavelength.
peak don'texcitation
occur obvious
migration under different excitation wavelength.
Figure 5. The excitation and emission spectra of SMSO:0.10Eu3+ sample and simple energy level
Figure 5. The excitation
and emission spectra of SMSO:0.10Eu3+ sample and simple energy level
transitions of Eu3+. (Note: The all energy levels were not positioned in an energy level diagram due
3+
3+ sample
transitions
Eu excitation
. (Note:
The
energy spectra
levels were
not positioned
in an energy
level diagram
due to
Figure 5.
The
andall
emission
of SMSO:0.10Eu
and simple
energy level
toofelectrons
transitions.)
3+
electrons
transitions.)
transitions of Eu . (Note: The all energy levels were not positioned in an energy level diagram due
to electrons transitions.)
Materials 2017, 10, 227
Materials 2017, 10, 227
6 of 11
6 of 11
The important spectra overlap of Tb3+ emission and Eu3+ excitation bands was observed from
Materials 2017, 10, 227
6 of 11
Figures
3b and 5, indicating that there may
exist energy transfer
from Tb3+ to Eu3+. In consequence,
3+ emission
3+ excitation
The
important
spectra
overlap
of
Tb
and
Eu
bands
was
observed
from
3+ phosphor to improve the red emission of Eu3+. Figure 6 gives
Tb3+ was introduced
intospectra
SMSO:Eu
3+ emission and Eu3+ excitation bands
3+ to Eu
3+observed
of Tbexist
was
from
Figures 3bThe
andimportant
5, indicating
thatoverlap
there may
energy3+transfer from
Tb
.
In
consequence,
3+ phosphor. Excited at 229 nm,
the excitation
emission
spectra
of may
SMSO:0.08Tb
0.04Eufrom
3+
3+ there
Figures
3band
and 5,
indicating
that
exist
energy,transfer
Tb3+ of
to Eu
consequence,
Tb3+ was
introduced
into
SMSO:Eu
phosphor
to
improve
the
red
emission
Eu3+. .InFigure
6 gives the
3+ characteristic emissions in blue and green
3+
3+
as-prepared
sample
not
only
displays
Tb
bands,
but also
Tb was introduced into SMSO:Eu phosphor
to improve
the red emission of Eu3+. Figure
6 gives
3+
3+
excitation and emission spectra of SMSO:0.08Tb , 0.04Eu phosphor.
Excited
at
229
nm,
as-prepared
3+
3+
3+
gives athe
strong
red emission
band with
theof
center
at 616 nm, from
Eu phosphor.
. Monitoring
at 545
excitation
and emission
spectra
SMSO:0.08Tb
0.04Eu
Excited
atnm
229emission
nm,
sample not
only displays Tb3+ characteristic3+emissions in blue and green
bands, but also gives a strong
3+blue
samplespectrum
not only displays
characteristic
emissions
in
and
green
bands,
but
also
from as-prepared
Tb3+, excitation
shows Tb
similar
profiles
with
Tb
single-doped
SMSO
sample.
3+ . Monitoring at 545 nm emission from Tb3+ ,
red emission
band red
with
the center atwith
616 nm
fromatEu
3+. Monitoring at
gives at
a strong
emission band
616 nm
from Euconsists
nm emission
Monitored
616 nm emission
from Eu3+the
, thecenter
excitation
spectrum
of Tb3+ 545
absorption
peak at
3+
excitation
spectrum
shows
similar
profiles
with
Tb
single-doped
SMSO
sample. Monitored
at 616 nm
3+
3+ single-doped
from
Tb
,
excitation
spectrum
shows
similar
profiles
with
Tb
SMSO
3+
2−
3+
229 nm, Eu −O 3+
charge transfer band at 270 nm as well 3+
as other sharp emission lines sample.
from
3+ −Eu
2−,
3+
emission
from Eu
, the
spectrum
consists
of3+Tb
absorption
peak
at
229
nm,
Eu
O
Monitored
at 616
nmexcitation
emission from
Eu3+, the
excitation
spectrum
consists
of
Tb
absorption
peak
at
which gives direct evidence of energy transfer from Tb →Eu3+.
3+−O2−at
3+,
charge229
transfer
270 nm
as well
as at
other
sharp
emission
lines
from
Eu3+ , which
gives
nm, Euband
charge
transfer
band
270 nm
as well
as other
sharp
emission
lines from
Eudirect
3+
3+
which
gives direct
evidence
energy
transfer
evidence
of energy
transfer
fromofTb
→Eu
. from Tb3+→Eu3+.
3+
3+ phosphor
(a) excitation
The excitation
spectrum
of
SMSO:Tb
Eu3+
phosphor
at at
616616
nm;nm;
(b) (b)
TheThe
3+, ,Eu
6. (a) 6.
The
excitation
spectrum
of SMSO:Tb
SMSO:Tb
monitored
FigureFigure
6.
The
spectrum
of
phosphormonitored
monitored
at
616
3+, Eu3+ phosphor monitored at 545 nm and emission
excitation spectrum (red line) of SMSO:Tb
3+
3+
3+
3+
excitation spectrum (red line)
phosphor monitored
monitored at
at 545
545 nm and emission
line) of
of SMSO:Tb
SMSO:Tb , Eu phosphor
3+, Eu3+ phosphor excited at 229 nm.
spectrum (blue line) of SMSO:Tb
3+,, Eu
spectrum (blue line) of SMSO:Tb3+
Eu3+3+phosphor
phosphorexcited
excitedatat229
229nm.
nm.
3+
3+
The emission spectra of SMSO:0.08Tb3+, yEu3+ phosphors with fixed Tb3+ concentration and
3+ yEu3+
3+ concentration and
3+
3+
The
emission
spectra of
of SMSO:0.08Tb
SMSO:0.08Tb
phosphors
with
fixed
Tbemission
The
emission
spectra
yEu 3+ 7a.
phosphors
with fixed
Tb
concentration
changed
Eu3+ concentration
were reveled in,, Figure
We can observe
that the
intensitiesand
3+
3+
changed
Eu
concentration
were
reveled
in
Figure
7a.
We
can
observe
that
the
emission
intensities
3+
3+
changed
Eu decrease
concentration
were
reveled
in Figure 7a.intensities
We can observe
the monotonously
emission intensities
of Tb
gradually
while
the luminescence
of Eu that
increase
with of
3+ decrease gradually
3+ increase monotonously with
3+
3+
3+
of
Tb
while
the
luminescence
intensities
of
Eu
increasinggradually
Eu dopingwhile
content,
can be observed
intuitively
fromincrease
Figure 7b.monotonously
The result showswith
Tb decrease
thewhich
luminescence
intensities
of Eu
3+ ions in SMSO:Tb
3+, Eu3+
that energy
transfer
processwhich
occurs
from
to Euintuitively
increasing
Eu
content,
can
be Tb
observed
fromfrom
Figure
7b.phosphors.
The
shows
increasing
Eu3+3+doping
doping
content,
which
can
be3+observed
intuitively
Figure
7b.result
TheThe
result
3+
3+
3+
3+ ions
3+, Eu
3+ phosphors.
luminescence
intensity
of
Eu
was
improved
2
times
compared
with
Eu
single-doped
sample.
3+
3+
3+
3+
that
energy
transfer
process
occurs
from
Tb
to
Eu
in
SMSO:Tb
The
shows that energy transfer process occurs from Tb to Eu ions in SMSO:Tb , Eu phosphors.
3+
3+
3+
3+
luminescence
intensity
of Eu
was improved
2 times
compared
withwith
Eu Eu
single-doped
sample.
The
luminescence
intensity
of Eu
was improved
2 times
compared
single-doped
sample.
Figure 7. (a) The emission spectra of SMSO:0.08Tb3+, yEu3+ (y176815 = 0.01, 0.02, 0.03, 0.04 and 0.05)
phosphors excited at 229 nm; (b) The changing of luminescence intensities of Tb3+ and Eu3+ based on
different Eu3+ concentration.
3+ (y176815 = 0.01, 0.02, 0.03, 0.04 and 0.05)
3+ , yEu3+
Figure 7.
7. (a)
(a) The
The emission
emission spectra
spectra of
ofSMSO:0.08Tb
SMSO:0.08Tb3+
(y176815 = 0.01, 0.02, 0.03, 0.04 and
3+3+ and Eu3+
phosphors excited
excited at
at 229
229 nm;
nm; (b)
(b)The
Thechanging
changingof
ofluminescence
luminescenceintensities
intensitiesofofTb
Tb
and Eu3+ based on
3+
3+
different Eu concentration.
concentration.
Materials 2017, 10, 227
7 of 11
Materials 2017, 10, 227
7 of 11
Tb3+
Eu3+ ,
To further confirm energy transfer behavior from
to
luminescence lifetimes of Tb3+
3+ to Eu3+, luminescence lifetimes of
To
further confirm energy transfer behavior from Tb3+
7
3+
4 → F5 transition at 545 nm were measured in SMSO:0.08Tb , yEu samples under the excitation
Tb3+ 5D4→7F5 transition at 545 nm were measured in SMSO:0.08Tb3+, yEu3+ samples under the
of 229 nm UV light. As demonstrated in Figure 8, the fluorescent decay curves are described
excitation of 229 nm UV light. As demonstrated in Figure 8, the fluorescent decay curves are described
distinctly with increasing Eu3+ doping concentration. Therefore, the luminescence lifetimes of Tb3+
distinctly with increasing Eu3+ doping concentration. Therefore, the luminescence lifetimes of Tb3+
revealed double-exponential types in all samples. The luminescence curves can be matched well with
revealed double-exponential types in all samples. The luminescence curves can be matched well
double-exponential expression:
with double-exponential expression:
5D
I(t)I(t)
= I0=+I0A+1A
exp(
−t/τ11)) ++ A
exp(−t/τ
1exp(−t/τ
A22exp(−t/τ
2) 2 )
(3)
(3)
whereI Iand
and
0 represents
luminescence
intensity
att time
0, A1 and A2 are constants, t
where
I0 Irepresents
the the
luminescence
intensity
at time
and 0,t Aand
1 and A2 are constants, t represents
represents
the
time,
and
τ
1
and
τ
2
represents
the
luminescence
lifetimes
forcomposition.
the exponential
the time, and τ1 and τ2 represents the luminescence lifetimes for the exponential
As a
composition.
As
a
function
of
these
parameters,
the
average
luminescence
lifetimes
(τ) was
function of these parameters, the average luminescence lifetimes (τ) was determined as follow equation:
determined as follow equation:
τ = (A1 τ1 2 +2 A2 τ2 22)/(A1 τ1 + A2 τ2 )
(4)
τ = (A1τ1 + A2τ2 )/(A1τ1 + A2τ2)
(4)
3+, yEu3+
3+3+ in
Figure8.8.PL
PLdecay
decaycurves
curvesofofTb
Tb
in SMSO:0.08Tb
SMSO:0.08Tb3+
Figure
, yEu3+samples
samplesunder
under229
229nm
nmradiations.
radiations.
For SMSO:0.08Tb3+, yEu3+ phosphors, average lifetimes of Tb3+ emission under excitation of
For SMSO:0.08Tb3+ , yEu3+ phosphors, average lifetimes of Tb3+ emission3+under excitation of
229 nm were calculated to be 32.58, 24.48, 18.19, 12.09,9.21 and 7.59 µs when Eu concentration were
229 nm were calculated to be 32.58, 24.48, 18.19, 12.09,9.21 and 7.59 µs when Eu3+ concentration were
0, 0.01, 0.02, 0.03, 0.04 and 0.05, respectively, indicating that energy transfer occurred from Tb3+3+ to
0, 0.01,
0.02, 0.03, 0.04 and 0.05, respectively, indicating that energy transfer occurred from Tb to
3+, as prospective.
Eu3+
Eu , as prospective.
Moreover, the energy transfer efficiency (η) from Tb3+ to Eu3+ in SMSO:0.08Tb3+, yEu3+ matrixwas
Moreover, the energy transfer efficiency (η) from Tb3+ to Eu3+ in SMSO:0.08Tb3+ , yEu3+ matrixwas
calculated by the expression as follow [28]:
calculated by the expression as follow [28]:
ηET = 1 − IS/IS0
(5)
η ET = 1 − IS /IS0
(5)
where ηET represents the energy transfer efficiency, IS and IS0 represent the corresponding
3+, respectively. Figure 9 reveals
luminescence
intensities
of Tb3+transfer
in the presence
and
of the Euthe
where
η ET represents
the energy
efficiency,
IS absence
and IS0 represent
corresponding luminescence
3+, yEu3+ samples excited at 229 nm
the energyof
transfer
fromand
Tb3+
to Eu3+ofinthe
SMSO:0.08Tb
intensities
Tb3+ inefficiency
the presence
absence
Eu3+ , respectively.
Figure 9 reveals the energy
3+ concentration.
based
on
different
Eu
It
can
be
seen
that
η
ET increases monotonously within
3+
3+
3+
3+
transfer efficiency from Tb to Eu in SMSO:0.08Tb , yEu samples excited at 229 nm based on
3+ into SMSO:Eu3+ sample, which can reach the maximum value of 65%. Therefore, the
corporation
Tbconcentration.
different
Eu3+
It can be seen that η ET increases monotonously within corporation Tb3+
3+
3+ ions is efficient to improve Eu3+ luminescence.
energy
transfer
from
Tb
to
Eu
into SMSO:Eu3+ sample, which can
reach the maximum value of 65%. Therefore, the energy transfer
from Tb3+ to Eu3+ ions is efficient to improve Eu3+ luminescence.
Materials 2017, 10, 227
8 of 11
Materials 2017, 10, 227
8 of 11
Materials 2017, 10, 227
8 of 11
3+ in SMSO:0.08Tb3+, yEu3+ phosphors as a
Figure
Energy
transfer
efficiencies(η(η)T)from
fromTb
Tb
to Eu
Eu3+
3+3+ to
Figure
9. 9.
Energy
transfer
efficiencies
in SMSO:0.08Tb3+ , yEu3+ phosphors as a
T
3+ concentration.
function of different Eu
function of different Eu3+ concentration.
According to the Commission International De L’Eclairage 1931 chromaticity coordinates, the
CIE chromaticity diagram of Tb3+ and Eu3+ single-doped or co-doped SMSO samples were portrayed
in Figure 10 and corresponding values were summarized in Table 2. Under excitation of 229 nm,
SMSO:0.08Tb3+ displays intense blue-green emission, while SMSO:0.10Eu3+ sample gives bright red
emission excited at 270 nm. Furthermore, we can observe that the emission color was varied from blue
to white, eventually to red-orange light with enhancing Eu3+ doping concentration from 0.01 to 0.05
in Tb3+ and Eu3+ co-doped phosphors. It is due to3+energy
transfer from Tb3+ to Eu3+ ions. And CIE
Figure 9. Energy transfer efficiencies (ηT) from Tb to Eu3+ in SMSO:0.08Tb3+, yEu3+ phosphors as a
3+
3+
chromaticity
coordinate
ofEu
SMSO:0.08Tb
sample is close to standard white light.
3+ concentration. , 0.04Eu
function
of different
Figure 10. CIE chromaticity coordinates for SMSO:0.08Tb3+ (a1), SMSO:0.10Eu3+ (a2) and SMSO:0.08Tb3+,
yEu3+ (b1–b5) phosphors.
According to the Commission International De L’Eclairage 1931 chromaticity coordinates, the
CIE chromaticity diagram of Tb3+ and Eu3+ single-doped or co-doped SMSO samples were portrayed
in Figure 10 and corresponding values were summarized in Table 2. Under excitation of 229 nm,
SMSO:0.08Tb3+ displays intense blue-green emission, while SMSO:0.10Eu3+ sample gives bright red
emission excited at 270 nm. Furthermore, we can observe that the emission color was varied from
blue to white, eventually to red-orange light with enhancing Eu3+ doping concentration from 0.01 to
0.05 in Tb3+ and Eu3+ co-doped phosphors. It is due to energy transfer from Tb3+ to Eu3+ ions. And CIE
3+
3+ (a2) and SMSO:0.08Tb3+,
Figure 10. CIE chromaticity coordinates 3+
for SMSO:0.08Tb
3+ (a1),
3+ (a2) white
3+ ,
chromaticity
coordinate
of SMSO:0.08Tb
0.04Eu3+ sample
isSMSO:0.10Eu
close to standard
light.
Figure 10.
CIE
chromaticity
coordinates for ,SMSO:0.08Tb
(a1),
SMSO:0.10Eu
and SMSO:0.08Tb
3+ (b1–b5) phosphors.
yEu
3+
As revealed
above, critical distance Rc was calculated to be 6.7 Å as a function of Equation (1)
yEu
(b1–b5) phosphors.
3+, yEu3+ samples, in which the different Xc was contributed to critical content
for SMSO:0.08Tb
According to the Commission International De L’Eclairage 1931 chromaticity coordinates, the
3+ , yEu
3+
(XTable
c was total
Tb3+3+ and
andEu
Eu3+3+single-doped
ions, temperature
Xc = 0.13).
The
shows
that
electric
multipole
2. CIEconcentration
chromaticity
coordinates
and
color
for result
SMSO:0.08Tb
CIE chromaticity
diagram of
of Tb
or co-doped
SMSO
samples
werephosphors
portrayed
3+ to Eu3+. On account of
interaction
plays
an
important
role
in
energy
transfer
process
from
Tb
excited
at 229
nm. corresponding values were summarized in Table 2. Under excitation of 229 nm,
in Figure
10 and
3+ sample
Dexter’s
energy3+ transfer
for multipolar
and Reisfeld’s
approximation,
SMSO:0.08Tb
displays mechanism
intense blue-green
emission, interaction
while SMSO:0.10Eu
gives bright redthe
3+
3+
following
No.given:
y) emission
CCT
(K)was varied from
SMSO:xTbwe, yEu
emissionexpression
excitedSample
at can
270 be
nm.
Furthermore,
can observe CIE
that(x,
the
color
blue to white, eventually
lightywith
enhancing Eu3+ doping concentration
from 0.01 to
a1 to red-orange
x = 0.08,
7191
I=S00/ISCθ/3 (0.2796, 0.4359)
(6)
3+
3+
0.05 in Tb and Eu co-doped
phosphors.
due to energy
transfer
from Tb3+
to Eu3+ ions. And CIE
a2
x = 0, yIt= is
0.10
(0.5646,
0.3272)
4937
3+, y0.04Eu
3+ sample
x =intensity
0.08,
= 0.01
(0.2424,
0.2137)
164,473
where
IS0 and IScoordinate
are theb1
luminescence
of sensitizer
with
activator.
chromaticity
of SMSO:0.08Tb
iswithout
close
toand
standard
white
light.C represents
b2
x
=
0.08,
y
=
0.02
(0.2682,
31,313
3+
3+
the doping
concentration
of Tb distance
and Eu
ion.calculated
The value
θ =Å 6,
10 corresponding
As revealed
above, critical
Rc was
to for
be0.2263)
6.7
as 8a and
function
of Equation (1) to
b3 3+
x = 0.08, y = 0.03
(0.2943, 0.2337)
13,267
3+, yEu
for SMSO:0.08Tb
samples,
inquadrupole-quadrupole
which the different Xc was
contributed
critical
content
dipole-dipole,
dipole-quadrupole,
and
interactions.
Thetolinear
relation
of
b4
x
=
0.08,
y
=
0.04
(0.3271,
0.2644)
5827
3+ and Eu3+ ions, Xc = 0.13). The result shows that electric multipole
(Xc was total concentration
of
Tb
b5
x = 0.08, y = 0.05
(0.3821, 0.2857)
2768
interaction plays an important role in energy transfer process from Tb3+ to Eu3+. On account of
Dexter’s energy transfer mechanism for multipolar interaction and Reisfeld’s approximation, the
following expression can be given:
IS0/ISCθ/3
(6)
where IS0 and IS are the luminescence intensity of sensitizer without and with activator. C represents
the doping concentration of Tb3+ and Eu3+ ion. The value for θ = 6, 8 and 10 corresponding to
Materials 2017, 10, 227
Materials 2017, 10, 227
9 of 11
9 of 11
Table 2. CIE chromaticity coordinates and color temperature for SMSO:0.08Tb3+, yEu3+ phosphors
excited
at 229above,
nm. critical distance R was calculated to be 6.7 Å as a function of Equation (1) for
As
revealed
c
3+ samples, in which the 3+
SMSO:0.08Tb3+ , yEu
to critical
Sample
No. SMSO:xTbdifferent
, yEu3+ Xc was
CIEcontributed
(x, y)
CCT
(K) content (Xc was
3+
3+
total concentration of Tb a1and Eu ions,
Xc = 0.13).
shows
that electric
x = 0.08,
y = 0 The result
(0.2796,
0.4359)
7191multipole interaction
3+ to Eu3+ . On account of Dexter’s energy
plays an important role in
energy
transfer
process
from
Tb
a2
x = 0, y = 0.10
(0.5646, 0.3272)
4937
transfer mechanism for multipolar
interaction
Reisfeld’s
approximation,
the following expression
b1
x = 0.08, y and
= 0.01
(0.2424,
0.2137) 164,473
can be given:
b2
x = 0.08, y = 0.02
(0.2682, 0.2263)
31,313
θ/3
(6)
S ∝C
b3
x = 0.08, IyS0=/I
0.03
(0.2943, 0.2337)
13,267
b4
x =intensity
0.08, y = of
0.04
(0.3271,
0.2644)
5827
where IS0 and IS are the luminescence
sensitizer
without
and with
activator. C represents
b5
x
=
0.08,
y
=
0.05
(0.3821,
0.2857)
2768
3+
3+
the doping concentration of Tb and Eu ion. The value for θ = 6, 8 and 10 corresponding to
dipole-dipole, dipole-quadrupole, and quadrupole-quadrupole interactions. The linear relation
θ/3 are revealed in Figure 11. R2 value was calculated to be 0.96646 when θ = 10 for
S0/IS and C
θ/3
of IS0I/I
are revealed in Figure 11. R2 value was calculated to be 0.96646 when θ = 10
S and C
3+
3+
3+ was
SMSO:0.08Tb
,
yEu
demonstrating
that
transfer from
from Tb
Tb
→Eu
3+
3+ samples,
3+3+→
for SMSO:0.08Tb , yEusamples,
demonstrating
thatthe
the energy
energy transfer
Eu3+ was
evaluatedto
tobe
beaaquadrupole-quadrupole
quadrupole-quadrupoleinteraction.
interaction.
evaluated
6/3
8/3 ; and
3+ on
6/3; ;(b)
10/3 10/3 .
Figure
11. Dependence
/ISTb
of3+Tbon
CEu3+
(b)CCEu3+
Eu3+8/3; and
(c)(c)CC
Eu3+
Figure
11. Dependence
of IS0of
/ISIS0of
(a) (a)
CEu3+
Eu3+.
3. Materials
Materials and
and Methods
Methods
3.
3.1.
3.1. Sample
Sample Preparation
Preparation
3+,, Eu
A
Eu3+3+ phosphors
phosphors were
were prepared
prepared by high temperature
A series
seriesofofSrSr
2MgSi
O77:Tb3+
temperature solid
solid state
state
2 MgSi
22O
reaction
(A.R.),
Tb
O
(99.99%),
and
reaction in
inair
airatmosphere
atmosphereatat1300
1300◦ C.
°C.SrCO
SrCO3 3(A.R.),
(A.R.),MgO
MgO(A.R.),
(A.R.),SiO
SiO
2
(A.R.),
Tb
4
O
7
(99.99%),
and
2
4 7
Eu
Eu22O
O33 (99.99%) were used as
as raw
raw materials.
materials. They
They were
were weighed
weighed according
according to
todesired
desiredcomposition
composition
and
and mixed
mixed thoroughly
thoroughly in
in ball
ball mill
mill with
withappropriate
appropriate ethanol
ethanol for
for 44h,
h,then
thenthe
thepowder
powdersamples
sampleswere
were
moved
C. After
movedto
toculture
culturedish
dishto
todry
dryfor
for1.0
1.0hhat
at60
60◦°C.
After that,
that, they
they were
were transferred
transferredinto
intoceramic
ceramiccrucible
crucible
and
C for
andcalcined
calcinedin
inhigh
hightemperature
temperaturetubular
tubularfurnace
furnaceatat1300
1300◦°C
for33h.
h. The
The final
final samples
sampleswere
wereobtained
obtained
by
byregrinding
regrindingfor
for33min.
min.
3.2.
3.2. Measurements
Measurementsand
andCharacterization
Characterization
Bruker
diffractmeter
(voltage
40 kV40and
40 mA) at
scanning
of 10 deg/min
BrukerD8
D8Focus
Focus
diffractmeter
(voltage
kVcurrent
and current
40a mA)
at arate
scanning
rate of
◦ to 50◦ with graphite monochromatized CuKα radiation (λ = 0.15405 nm)
over
the
2θ
range
from
10
10 deg/min over the 2θ range from 10° to 50° with graphite monochromatized CuKα radiation
3+ , Eu3+ samples. F-4600
was
to record
patterns
of SMSO:Tb
(FL-Spectorphotomet)
(λ =used
0.15405
nm) XRD
was used
to record
XRD patterns
of SMSO:Tb3+, device
Eu3+ samples.
F-4600 device
with
a 150 W xenon lamp
was
used
to measure
theused
excitation
and emission
spectra.
(FL-Spectorphotomet)
withlight
a 150source
W xenon
lamp
light
source was
to measure
the excitation
and
3+ , SMSO:Eu3+ and SMSO:Tb
3+ , Eu3+ sampleswere
3+
3+
Structure
refinement
of
SMSO,
SMSO:Tb
performed
emission spectra. Structure refinement of SMSO, SMSO:Tb , SMSO:Eu and SMSO:Tb3+,
◦ (2θ)/0.1 s scanning
3+sampleswere
by
(Generalperformed
Structure Analysis
program
with
radiation
at a 0.01
EuGSAS
by GSASSystem)
(General
Structure
Analysis
System)
program
with radiation
step.
UV-vis
diffuse
reflectance
spectra
were
measured
using
a
UV–Vis
spectrophotometer
at a 0.01°(2θ)/0.1 s scanning step. UV-vis diffuse reflectance spectra were measured using(TU–1901).
a UV–Vis
spectrophotometer (TU–1901).
Materials 2017, 10, 227
10 of 11
4. Conclusions
In summary, a series of Tb3+ and Eu3+ doped SMSO phosphors were prepares by high temperature
solid-state reaction at 1300◦ C for 3 h. The characteristic emissions of Tb3+ (blue, 5 D3 →7 F3 and
green, 5 D4 →7 F5 ) and Eu3+ (red, 5 D0 →7 F2 ) were observed in SMSO:Tb3+ and SMSO:Eu3+ samples,
respectively. For the SMSO:Tb3+ , Eu3+ sample, efficient energy transfer was observed from Tb3+
to Eu3+ , which is deduced by the spectra overlap of Tb3+ emission and Eu3+ excitation. This was
further proved by the emission spectra and decay curves of Tb3+ in the SMSO:Tb3+ , Eu3+ sample.
The corresponding energy transfer mechanism was demonstrated to be a quadrupole-quadrupole
interaction. The emission color was tuned from green to white, up to the red region, by adjusting
the concentration ratio of Tb3+ and Eu3+ in SMSO:Tb3+ , Eu3+ phosphors. All results indicate that
SMSO:Tb3+ , Eu3+ is a promising single-component white light emission phosphor.
Acknowledgments: This work was supported by the National Natural Science Foundation of Young
(Grant No. 130696) and the Science and Technology Development Plan of Shandong Province, China
(2014GNC110013).
Author Contributions: Minhong Li conceived and designed the experiments and wrote the manuscript;
Zhihan Deng performed the experiments; Lili Wang and Weiguang Ran analyzed the data; Chunyan Ren
contributed reagents/materials/analysis tools; Jinsheng Shi revised the paper.
Conflicts of Interest: The authors declare no conflict of interest.
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