Synthesis, optical properties and application of Y7O6F9:Er3+ for sensing the chip temperature of a light emitting diode

Article abstract of DOI:10.1039/c8tc05307c

Submicron-sized Er³⁺ doped Y₇O₆F₉ phosphors were synthesized via the precipitation method and a subsequent annealing process. The influence of the Er³⁺ doping concentrations and the heating temperature on the luminescence of Y₇O₆F₉:Er³⁺ was investigated under the excitation of the Er^{3+ 4}G_11/2 level at 378 nm. Upon raising the Er³⁺ doping concentration, both the intensity and lifetime of the Er³⁺ green emission at 547 nm originating from ⁴S_3/2 → ⁴I_15/2 decrease, which is proved to be caused by energy transfer via cross relaxation between two neighboring Er³⁺ ions. The thermal sensing properties of Y₇O₆F₉:Er³⁺ were evaluated using the temperature dependent intensity ratio between the ²H_11/2-⁴I_15/2 and ⁴S_3/2-⁴I_15/2 transitions of Er³⁺ under 378 nm excitation. The experimental results show that the thermal sensitivity decreased with an increase in the Er³⁺ doping content, which is caused by the increased energy transfer probability among Er³⁺. The increased energy transfer of Er³⁺ reduces the thermalized population of Er³⁺ in the ²H_11/2 levels, which in turn decreases the thermal sensitivity. The applicability of Er³⁺ doped Y₇O₆F₉ as a thermal sensor was demonstrated by measuring the chip temperature of a 1 W InGaN type near-ultraviolet light emitting diode (n-UV LED).

Full text of DOI:10.1039/c8tc05307c

Journal of
Materials Chemistry C
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PAPER
Synthesis, optical properties and application of
3
+
Y O F :Er for sensing the chip temperature of a
7
6 9
Cite this: J. Mater. Chem. C, 2018,
, 13352
light emitting diode
6
Deyin Wang, * Pengpeng Zhang, Qiang Ma, Jiachi Zhang * and
Yuhua Wang
*
3+
Submicron-sized Er doped Y
7
O
6
F
9
phosphors were synthesized via the precipitation method and a
3+
subsequent annealing process. The influence of the Er
doping concentrations and the heating
3
+
3+ 4
temperature on the luminescence of Y
7
O
6
F
9
:Er was investigated under the excitation of the Er
G
11/2
3+
3+
level at 378 nm. Upon raising the Er doping concentration, both the intensity and lifetime of the Er
4
4
green emission at 547 nm originating from
3/2
S - I15/2 decrease, which is proved to be caused by
3+
energy transfer via cross relaxation between two neighboring Er ions. The thermal sensing properties
3+
2
4
of Y
7 6 9
O F :Er were evaluated using the temperature dependent intensity ratio between the H11/2– I15/2
4
4
3+
and
S
3/2– I15/2 transitions of Er under 378 nm excitation. The experimental results show that the
3
+
Received 21st October 2018,
Accepted 26th November 2018
thermal sensitivity decreased with an increase in the Er doping content, which is caused by the
3+
3+
increased energy transfer probability among Er . The increased energy transfer of Er
reduces
11/2 levels, which in turn decreases the thermal sensitivity.
as a thermal sensor was demonstrated by measuring the chip
temperature of a 1 W InGaN type near-ultraviolet light emitting diode (n-UV LED).
3+
2
the thermalized population of Er in the
H
DOI: 10.1039/c8tc05307c
3+
7 6 9
The applicability of Er doped Y O F
rsc.li/materials-c
the temperature. However, a careful look at the existing literature
1
. Introduction
3+
reveals that the previously reported Er -based thermal sensor
Accurate temperature measurement is important in many mainly utilized the up-conversion (anti-stokes luminescence)
3
+ 12–16
applications, and temperature measurement at the micro/nano luminescence of Er ,
and a few works examined the thermal
3
+
scale is a particularly challenging task, because measuring the sensibility by using the Stokes luminescence from Er . It is well
temperature in the field, such as in intracellular or micro/nano known that the up-conversion luminescence is a non-linear
electronics is impractical when using a conventional thermo- process and generally has a low efficiency (the efficiency is
1–5
10
meter. To solve this problem, different temperature measurement strongly dependent on the power of the incident light). Apart
techniques have been developed, including nanolithographic from the low efficiency of the up-conversion, the thermal effect
thermometry, the scanning thermal microscope method, the caused by high powered near infrared light excitation (e.g.
resistance thermometry technique, optical techniques, and so 980 nm) may make the measured temperature deviate from the
6
–8
11,12
forth. Among these different techniques, optical temperature actual temperature.
On the contrary, the efficiency of the
sensors based on the fluorescence intensity ratio (FIR) technique Stokes luminescence is independent of the excitation power and
2,9–21
have attracted great attention,
as this kind of sensor has the the thermal effect caused by the excitation light in Stokes
advantages of a rapid response time and immunity to a harsh luminescence can be ignored. Meanwhile, whether or not the
environment when compared to traditional contact thermo- sensor utilizes the up-conversion or Stokes luminescence, host
2
,10,11
3+
meters.
Er is commonly used in the above mentioned materials with a low phonon energy are preferred, as such host
1
2–16
temperature sensors,
because the two thermally coupled materials can depress the multiphonon relaxation process, result-
2
4
3+
H
11/2 and S3/2 levels of Er give an intense green emission and ing in a higher luminescence efficiency from the luminescent
their relative emission shows an obvious change depending on center, which is beneficial for the accuracy of the measurement.
3
+
In this work, we synthesized different concentrations of Er
doped Y O F via a co-precipitation method, and investigated
7
6 9
National & Local Joint Engineering Laboratory of Light-conversion Materials and
Technology, School of Physical Science and Technology, Lanzhou University,
Lanzhou 730000, China. E-mail: wangdy@lzu.edu.cn, zhangjch@lzu.edu.cn,
wyh@lzu.edu.cn
3
+
the effects of the Er doping concentrations on the luminescence
3
+
3+
7 6 9
and thermal sensitivity of Y O F :Er under excitation of the Er
G
4
3+
7 6 9
11/2 level at 378 nm. Finally, the potential use of Y O F :Er as
1
3352 | J. Mater. Chem. C, 2018, 6, 13352--13358
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an efficient optical temperature sensing material has been
demonstrated by determining the chip temperature of a 1 W
near-ultraviolet light emitting diode (n-UV LED).
2. Experimental
2
.1 Materials and synthesis
The raw materials for Y (99.9%), Er
99.99%) were purchased from Aladdin Chemical reagent company
and used without further purification.
2
O
3
2 3 4
O (99.9%) and NH F
(
3
+
7 6 9
Powder samples Y O F :xEr (x = 0, 1%, 3% and 5%) were
3
+
prepared using a co-precipitation method. The Er doping
concentration refers to the nominal concentration in mol%.
ꢀ
1
In detail, stock solutions of 0.5 mmol ml
Y(NO3)3 and
were prepared in advance by dis-
in hot nitric acid, and the residual nitric
acid was evaporated by heating. The weighed trivalent lanthanide
nitrate solution was added dropwise into the NH F solution by
ꢀ1
0.005 mmol ml Er(NO
3 3
)
solving Y and Er
2
O
3
2 3
O
4
using a separatory funnel under continuous stirring. The resulting
white precipitate was separated by centrifugation and dried at
80 1C in an oven for 12 h. Finally, the precipitate was annealed
at 600 1C for 2 h followed by 800 1C for 2 h in air with
intermediate grounding.
2.2 Characterization
The X-ray diffraction (XRD) data were measured using a Bruker
D2 Phaser powder X-ray diffractometer. The photoluminescence (PL)
and photoluminescence excitation (PLE) spectra were measured
using a Fluorlog-3 spectrophotometer. The decay curves and
quantum efficiency were measured using the FLS 980 spectro-
meter. Scanning electron microscopy (SEM) was recorded by
using the Hitachi S-4800 electron microscope. Transmission
electron microscope (TEM), high-resolution transmission electron
microscope (HRTEM) and selected area electron diffraction (SAED)
images were taken on a JEM-2010 electron microscope. Elemental
mapping was obtained on a TECNAI G2 TF20 electron microscope.
Fig. 1 (a) XRD patterns of the precursor prepared using the precipitation
method and the samples annealed at different temperatures. (b) XRD
3+
7 6 9
patterns of Y O F :xEr .
The as-fabricated precursor dried at 80 1C is identified as
YF (JCPDS No. 281449). When the precursor is subject
ꢁ1.5NH
to post-annealing at 600 1C, it transforms into the orthorhombic
phase YF (JCPDS No. 701935). With further increasing of the
post annealing temperature to 800 1C, the final product becomes
an orthorhombic phase Y (JCPDS No. 801126), and when
3
3
3+
The Er doping concentration in all samples was determined by
using inductively coupled plasma-atomic emission spectrometry
3
(ICP-AES) (PlasmaQuant 9000). The electroluminescent (EL)
spectrum was measured using an EVERFINE spectrophotometer
with an integral sphere under ambient conditions at room
temperature.
7 6 9
O F
the post annealing temperature is increased up to 1000 1C,
Y O F is converted into a mixture of YOF (JCPDS No. 712100)
7
6 9
3+
and Y O (JCPDS No. 895592). Based on the XRD results, the Er
2
3
doped precursor samples were firstly annealed at 600 1C then at
00 1C with intermediate grinding to obtain the pure phase of
. Fig. 1b shows the XRD patterns of Y doped with
7 6 9
O F consists of a single YO layer sand- different concentrations of Er . The diffraction patterns for all of
3
. Results and discussion
8
Y
3.1 Morphology and phase identification
7 6
O
F
9
7 6 9
O F
+
3+
The structure of Y
ꢀ
3+
wiched between F layers. There are two coordination environ- the Er doped samples were found to be identical to the
3+
2ꢀ
7 6 9
ments for Y in Y O F , viz. one site is coordinated by four O and reference data (JCPDS No. 801126) and no other impurities were
ꢀ
2ꢀ
3+
three F anions, the other site is coordinated by four O and four observed, indicating the introduction of Er did not change the
ꢀ
22
3+
F anions. In view of same valence and similar ionic radius of Er
r = 89 pm) and Y (90 pm), the Er ions are expected to occupy Er (r = 89 pm) is very close to that of Y (r = 90 pm) and owing
the Y sites in Y O F . Fig. 1a shows the XRD patterns of the to the successful substitution of Y by Er , the diffraction
7 6 9
crystal structure Y O F . In addition, because the ionic radius of
7 6 9
3+
23
3+
3+
3+
23
(
3
+
3+
precursor prepared using the precipitation method and the pattern demonstrated almost has no changes upon doping with
3
+
3+
samples after being annealed at different temperatures for 2 h. Er . To give the quantitative data for the doping amount of Er
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3+
Table 1 Nominal and measured Er doping concentrations in different
samples
Nominal concentration Measured concentration
3+
3+
Sample
of Er (wt%)
of Er (wt%)
3+
Y
7
Y
7
Y
7
Y
7
O
O
O
O
6
6
6
6
F
9
F
9
F
9
F
9
:0.5 mol%Er 0.66
0.63
1.27
3.75
6.51
3
+
+
+
:1 mol%Er3
1.30
3.88
6.38
:3 mol%Er
:5 mol%Er
3
3+
Fig. 3 Elemental mapping of Y
7
O
6
F
9
:1%Er
.
Fig. 2 SEM (a), TEM and HRTEM images (b and c), and SAED pattern (d) for
3+
7 6 9
Y O F :1%Er .
in each sample, spectral analysis using ICP-AES technique was
conducted. The obtained results are listed in Table 1, from which
3+
it can be seen that the measured Er concentration in each
sample was close to the corresponding nominal concentration.
Fig. 2a–d shows the SEM, TEM and HRTEM images together
3
+
with the SAED pattern of Y O F :1%Er , respectively. It can be
7
6 9
seen from Fig. 2a and b that the obtained sample has an
irregular shape with the presence of agglomerates, which are
probably caused by the subsequent high temperature calcinations.
From some of separated particles presented in Fig. 2a and b, it can
be seen that the agglomerates are composed of particles with a size
of around 500–700 nm. The HRTEM image (Fig. 2c) clearly exhibits
lattice fringes with an interval of 0.315 nm, corresponding to
the (171) lattice plane of the orthorhombic phase Y O F . The
7
6 9
well-resolved lattice fringes indicate the high crystallinity of the
obtained sample. The bright diffraction spots in the SAED pattern
3+
(
7 6 9
Fig. 2d) further reveal the high crystallinity of Y O F :Er , and
this is probably because the area of the sample selected by the
aperture in the TEM contains only a few crystals, the SAED pattern
3+
7 6 9
is made up of spots. The elemental mapping of Y O F :1%Er is
shown Fig. 3, which clearly indicates the uniform distribution of
the four elements (F, O, Y, and Er) over the whole particle.
3
+
Fig. 4 (a) PLE and (b) PL spectra for Y
7
O
F
6 9
:xEr .
3
+
3
.2 Concentration dependent luminescence of Y
7
O
6
F
9
:Er
3+
4
to the transitions of Er from its ground state I
to its excited
5/2
1
4
2
4
4
4
2
18,24,25
Fig. 4 shows the PLE and PL spectra of Y O F doped with states G9/2/ K15/2, G11/2, F5/2, F7/2 and H11/2, respectively.
different amounts of Er . All of the PLE spectra are same Upon the strongest absorption at 378 nm, corresponding to the Er
except for the intensity. The sharp absorption peaks at 365, 378,
7
6 9
3
+
3+
4
4
I15/2 - G11/2 transition, all of the emission spectra for the samples
450, 490 and 520 nm observed in the PLE spectra are ascribed are composed of an intense green emission at 547 nm and a weaker
1
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2
4
4
3+
red emission at 670 nm, originating from the H11/2/ S3/2 - I15/2 two sites decrease (the average lifetime of the Er emission at
4
4
3+
21,22
and F9/2 - I15/2 transitions of Er , respectively.
emission intensity increases with an increased Er doping which is caused by the increased energy transfer among the
concentration because of the increased number of luminescent Er –Er and Er -defects.
centers. When the Er doping concentration exceeds 1%, its
emission intensity starts to decrease owing to the concentration
The overall 547 nm decreases from 173 ms at x = 0.5% to 29 ms at x = 5%),
3
+
3
+
3+
3+
3+
3+
To further clarify the energy transfer process in the Er doped
Y O F , the Vis-NIR-IR emission spectra for Y O F :xEr excited
7 6 9 7 6 9
3
+
quenching effect caused by the energy transfer. The internal at 378 nm were measured (Fig. 6a). The near-infrared emission at
3+
quantum efficiency of the 1%Er doped sample was determined around 1000 nm and the infrared emission at around 1550 nm
4
4
to be 40.1%.
were assigned to transitions from the excited states I11/2 and I13/
4
3+
24,25
To provide further evidence for the occurrence energy transfer
2
to the ground state I15/2 of Er ions, respectively.
When the
3
+
3+
in Y O F :xEr , the luminescence decay curves monitoring the Er doping contents are increased, the visible green emission at
7
6 9
green emission at 547 nm under 378 nm excitation were 547 nm deceases while the infrared emissions at 1000 nm and
measured and the results are shown in Fig. 5. The decay curves 1550 nm increase. This phenomena can be rationalized by a cross
3
+
were normalized on the maximum intensity and plotted as a relaxation energy transfer between the two neighboring Er ions
3
+ 4
4
3+ 4
4
semi-logarithmic plot. The decay curves were fitted using a via (Er
double exponential function:
S
3/2 - I13/2:Er
I
15/2 - I11/2) as indicated by the pink
2
6
dotted line shown in Fig. 6b. Owing to the energy migration
process, the population of the Er in S3/2 state decreases, while
that in I13/2 and I11/2 increases, as a consequence, the green
3
+
4
I(t) = A exp(ꢀt/t ) + A exp(ꢀt/t )
(1)
1
1
2
2
4
4
4
In which I is the luminescence intensity and A
1
and A
and t
2
are emission from the S3/2 state decreases while the two infrared
. The emissions increase accordingly.
2
4,25
the fractional contributions of the decay lifetimes t
average lifetime t is determined by:
1
2
These results suggest that
3+
the cross relaxation process between the two nearby Er is the
main depopulation process of the Er at S3/2 state.
3+
4
2
2
A1 ꢂ t1 þ A2 ꢂ t2
A1 ꢂ t1 þ A2 ꢂ t2
t ¼
(2)
The fitting parameters of each decay curve are summarized
3
+
in Table 2. The two decay components correspond to Er in two
3
+
different sites in Y
7 6 9
O F . When the Er doping concentrations
3
+
are increased, the lifetimes of both of the Er emissions from the
3+
Fig. 5 Decay curves (dotted lines) for the Er emission at 547 nm in
3+
7 6 9
Y O F :xEr under excitation at 378 nm. The solid lines are the fitted
results.
3+
Table 2 Fitting parameters for the decay curve for Y
7
O
6
F
9
:xEr under
excitation at 378 nm
2
x (%)
A
1
t
1
(ms)
A
2
t
2
(ms)
T (ms)
R
0
1
3
5
.5
0.393
0.511
0.842
0.925
0.058
0.045
0.025
0.017
0.607
0.488
0.158
0.075
0.196
0.177
0.090
0.067
0.173
0.149
0.051
0.029
0.9997
0.9996
3
+
7 6 9
Fig. 6 (a) Vis-NIR-IR PL spectra for Y O F :xEr under excitation at
3+
0.9996 378 nm. (b) Energy level diagram for Er and the proposed luminescence
3+ 4
0.9995 process under excitation in the Er
G11/2 level.
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3
+
3.3 Thermal sensing performance of Y
7 6 9
O F :Er
3
+
To examine the application potential of Er doped Y
7
3
O
6
F
9
for
determining temperature, the dependence of the Er green
+
2
4
4
emission originating from the H11/2/ S3/2 - I15/2 transitions
on temperature in a temperature region from 300 to 550 K was
3
+
measured. Temperature sensing using Er is based on the
measurement of the intensity ratio between the luminescence from
2
4
two closely separated energy levels, H
and S , whose relative
3/2
11/2
16–19
population is determined by the Boltzmann distribution:
FIR = I522nm/I547nm = C exp(ꢀDE/kT)
(3)
In which I522nm and I547nm are the integrated intensities of
2
11/2 - 4
4
4
3+
the
H
I15/2 and
S
3/2
-
I15/2 transitions of Er ,
3
+
respectively, C is a constant, DE is the energy difference between Fig. 8 Thermal sensitivity of Y O F :xEr in the temperature range from
7
6 9
2
4
16–19
H11/2 and S3/2, and k is the Boltzmann constant.
Fig. 7a 300 to 550 K. The points show the experimental values and the solid lines
show the theoretical values.
illustrates the green emission spectra obtained upon raising the
3
+
temperature for the lowest Er concentration, the 0.5% doped
sample, which was normalized to the strongest intensity of the
increasing temperature, which can be explained using eqn (3).
Fig. 7b shows the dependence of the FIR between the H11/2
15/2 and S3/2 - I15/2 emission bands of Er on the absolute
temperature for the different concentrations of Er doped Y
4
4
S
3/2 - I15/2 emission peak to better show the intensity variation
2
-
2
4
from the H11/2 and S3/2 levels. It can be seen from Fig. 7a that the
intensity ratio between the two levels gradually increases with the
4
4
4
3+
I
3+
7 6 9
O F . It
can be seen from Fig. 7b that the FIR increases slowly in the doped
3+
sample with a higher concentration of Er , which is considered to
3+
be caused by the re-absorption of Er . There is an obvious spectral
2
4
overlap between the emission
H
11/2
-
I
15/2 and absorption
4
2
3+
I
15/2 - H11/2 of Er in the 500–530 nm region (see Fig. 4a and b).
When the Er doping concentrations and heating temperature
increase, the distance between the Er ions is reduced, and as
a consequence of thermal assisted energy transfer, re-absorption
among the neighboring Er is increased. Therefore, at a higher
given temperature, the FIR is decreased with the increasing Er
doping concentration. In addition, the dependence of the FIR on
temperature for the different Er doped samples can be well
fitted by using eqn (3), and the corresponding fitted function is
listed in Fig. 7b. In all samples, the DE determined from the
3+
3
+
3
+
3+
3
+
ꢀ
1
ꢀ1
fitting results is close (DE0.5% = 730 cm , DE1% = 726 cm
DE3% = 690 cm and DE5% = 670 cm ) to that determined from
the emission spectra (DE = 766 cm ).
,
ꢀ1
ꢀ1
ꢀ1
For optical temperature sensing applications, sensitivity (S)
is an important index that reflects the performance of the
obtained sensor, and the sensitivity is defined as the rate of
1
6–19
change of the FIR with temperature:
dFIR
DE
¼ FIR ꢁ kT2
S ¼
(4)
dT
Fig. 8 shows the dependence of the sensitivity (S) of
3
+
Y O F :xEr on the temperature from 300 to 550 K. The solid
7
6 9
line is the theoretical line based on eqn (4). It is observed that a
ꢀ
1
maximum sensitivity of 0.0050 K was achieved at 498 K in the
3
+
lowest Er doped sample, and that the value was almost
3
+
1
.7 times higher compared to the highest Er doped sample.
Fig. 7 (a) Temperature dependent green emission spectra of Y
7
O
6
F
9
:0.5%
:xEr . The intensity of the
H11/2 - I15/2 transition was integrated from 510 nm to 540 nm, while that
3
.4 Demonstration of the temperature measurement
3+
3+
7 6 9
Er . (b) Dependence of FIR on temperature in Y O F
3
+
3+ 2
4
7 6 9
To demonstrate the potential application of Y O F :Er as a
temperature sensing material, Y O F :Er was used to determine
7 6 9
Er
of the S3/2 - I15/2 transition was integrated from 540 nm to 580 nm.
4
4
3+
1
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Journal of Materials Chemistry C
3
+
3+
cross relaxation process between two neighboring Er via (Er
4
4
3+ 4
4
S
3/2 - I13/2:Er
I
15/2 - I11/2) and the increased re-absorption of
3+
Er owing to the large spectral overlap between the emission and
absorption green bands from Er , respectively. As a proof of
concept, Y O F :1%Er was used to determine the temperature
3
+
3
+
7
6 9
of a LED chip. The chip temperature of a 1 W InGaN type n-UV
LED chip operating at U = 3.5 V and I = 300 mA was determined
to be about 95 1C.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
3
+
Fig. 9 EL spectrum of the LED coated with Y
3
7 6 9
O F :1%Er and operated at U =
The authors grateful acknowledge support for this research
.5 V and I = 300 mA. The left upper inset is the emission spectrum of the LED,
and the right upper inset photographs are the naked LED, the LED coated with from the National Natural Science Foundation of China (grant
3+
Y
7
O
6
F
9
:1%Er without and with a driven current (300 mA), respectively.
no. 51602137) and Lanzhou Chengguan Science and Technology
Bureau (grant no. 2018KJGG0097).
the chip temperature of a 1 W InGaN type n-UV LED (epileds
products; wavelength peak: 375–380 nm; chip size: 40 ꢂ 40 mil;
forward voltage: 3.4–3.8 V). In a practical experiment, a few
Notes and references
3
+
7 6 9
milligrams of Y O F :1%Er was glued just on the top of the
P. Haro-Gonz ´a lez, L. Mart ´ı nez-Maestro, I. R. Mart ´ı n,
J. Garc ´ı a-Sol ´e and D. Jaque, Small, 2012, 8, 2652–2658.
R. G. Geitenbeek, P. Tim Prins, W. Albrecht, A. van Blaa-
deren, B. M. Weckhuysen and A. Meijerink, J. Phys. Chem. C,
1
LED chip (see inset in Fig. 9). The n-UV LED chip was selected
because it is can be used as either the heater or light source to
2
3
+
excite the Y
Fig. 4a). This selection greatly simplified the experimental
procedure, because if the selected LED was unable to excite
7 6 9
O F :1%Er with the strongest absorption at 378 nm
(
2017, 121, 3503–3510.
3
F. Vetrone, R. Naccache, A. Zamarr o´ n, A. Juarranz de la
Fuente, F. Sanz-Rodr ´ı guez, L. M. Maestro, E. Mart ´ı n Rodri-
guez, D. Jaque, J. G. Sol ´e and J. A. Capobianco, ACS Nano,
3+
Y O F :Er , then light from a spectrometer would need to be
7
6 9
used, however, the small size of the chip makes measurement
difficult. In the meantime, an appropriate electrical current must
be applied to allow the LED to work. Both of these factors will
make the measurement of the temperature complicated. The EL
spectrum of the chip is shown in the right upper inset in Fig. 9.
As the EVERFINE spectrophotometer used for the EL spectra
measurement does not show a response below 380 nm, the
emission spectrum of the LED was measured using a Fluorlog-3
spectrophotometer and is presented separately. Fig. 9 shows the
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6
7
8
9
3
+
EL spectrum of the 1 W LED coated with Y
7 6 9
O F :1%Er and
operated at U = 3.5 V and I = 300 mA, and emission color of
3
+
7 6 9
Y O F :1%Er is shown in the inset. From the reference data
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11 J. Cai, L. Zhao, F. Hu, X. Wei, Y. Chen, M. Yin and C. Duan,
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4
. Conclusions
3
+
In summary, different concentrations of Er doped Y
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3
3
3
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By increasing the Er doping concentration, the lifetime of the
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7
O
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6 9
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