Pump-wavelength dependence on emission properties of
Er-Yb-Bi triply doped borosilicate glasses
Dong Hoon Son, Seung Ho Lee, and Won-Taek Han*
Department of Photonics and Applied Physics / School of Information and Communications*
Gwangju Institute of Science and Technology (GIST), Gwangju, 500-712, South Korea
Bok Hyeon Kim
Advanced Photonics Research Institute (APRI), GIST, Gwangju, 500-712, South Korea
The pump-wavelength dependence on the emission properties of Er-Yb-Bi triply doped
borosilicate glasses with different concentrations of bismuth was investigated. The peak intensity
of the 1538 nm emission of Er3+ ions in the glass with 2 mol% of Bi2O3 upon the 980 nm
excitation was found to increase 14.5 times compared to that after the 805 nm excitation. The
lifetime of the 1538 nm emission slightly decreased with the addition of 0.5 mol% of Bi2O3 but
increased with the increase of the bismuth concentration up to 2 mol% upon the 980 nm
excitation (774 → 913 μs). The efficiency of the energy transfer from Yb3+ to Er3+ ions increased
by increasing the bismuth concentration and the highest efficiency was 10.4 % when 2 mol% of
Bi2O3 was added.
PACS number: 42.70.Ce, 42.70.Hj
Keywords: erbium-doped glass, bismuth, photoluminescence, lifetime.
Email: wthan@gist.ac.kr
Fax: +82-62-715-2299
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I. INTRODUCTION
Recently, bismuth-doped glasses were widely investigated because of their excellent ultra-broadband
emission property covering 1100 ~ 1600 nm in various glass systems such as silicate, germanate,
borate, phosphate, and chalcogenide glasses upon pumping at various excitation wavelengths [1-5]. It is
known that bismuth ions have absorption bands near 470, 700, 800, and 1000 nm and much attention
has been paid to investigate emission properties of the bismuth-doped glasses upon pumping at 800 nm
or 980 nm [1-3]. Pump wavelength dependence of the bismuth-doped glasses was also studied and the
peak wavelength and the full width at half maximum (FWHM) were found to be influenced by the
pumping wavelength [3, 4].
For the last decades, rare-earth (RE) doped glasses were intensively studied due to their important
emission properties for use in lasers and amplifiers for optical communications. Especially Er3+ and
Yb3+-codoped glasses have attracted great interest because of the emission in Er3+ ions near 1.5 μm and
the enhancement of the emission due to the codoping with Yb3+ ions [6-8]. More recently, emission
properties of bismuth/RE codoped glasses, such as Yb-Bi or Er-Bi codoped glass, were investigated for
application of broadband amplifiers and their intensity enhancement was attributed to the energy
transition between RE3+ and bismuth ions [9-11].
In this study, we investigated pump wavelength dependence on the emission properties of Er-Yb-Bi
triply doped borosilicate glasses with the different concentrations of bismuth. The UV/VIS/NIR
absorption and emission properties of the glasses upon 805 and 980 nm excitations were measured,
respectively. The effect of the bismuth concentration on the emission lifetime and the energy transfer
efficiency of the glasses was also investigated.
II. EXPERIMENTS AND RESULTS
2
The composition of SiO2-B2O3-Al2O3-Na2O-ZnO-Ga2O3-In2O3 (SBA) glasses was fixed to be SiO2:
54 mol%, B2O3: 10 mol%, Al2O3: 15 mol%, Na2O3: 10 mol%, ZnO: 8 mol%, Ga2O3: 1 mol%, and
In2O3: 2 mol%. Reagent grades (99.5 ~ 99.99 %) of SiO2, B2O3, Al2O3, Na2CO3, ZnO, Ga2O3, In2O3,
Er2O3, Yb2O3, and Bi2O3 were used as raw materials. The glasses were codoped with different
concentrations of bismuth in the range of 0 ~ 2 mol%. Rare-earth chemicals such as Er2O3, Yb2O3, and
Bi2O3 were additionally incorporated to the batches as doping materials. The detailed glass
compositions with dopant concentrations are listed in Table 1. Each 50 g batch was mixed and placed
in an alumina crucible and then it was melted at 1550 °C for 60 min in air. The melt was casted onto a
preheated brass mold at 500 °C and annealed for 2 hours. The glass samples were cut in the size of
10x10 mm and the thickness of ~450 μm, and then both sides of the samples were polished for optical
measurements.
Optical absorption spectrum of the SBA-A glass without bismuth was measured using a
UV/VIS/NIR spectrophotometer (V-570, Jasco), which equipped with a halogen lamp light source in
the output spectral range of 300 ~ 1700 nm as shown in Fig. 1. The spectrum was measured with the
resolution of 1 nm. Eight absorption bands of Er3+ peaks were found to appear at 379, 407, 452, 487,
522, 652, 795, and 1530 nm corresponding to the absorptions from the ground state of 4I15/2 to the
excited states of 4G11/2, 2G9/2, 4F5/2, 4F7/2, 2H11/2, 4F9/2, 4I9/2, and 4I13/2, respectively [12]. Note that a
strong absorption peak appeared at 976 nm is due to the overlapped transitions, 2F7/2 → 2F5/2 of Yb3+
ions and 4I15/2 → 4I11/2 of Er3+ ions. Effect of bismuth ions on the absorption spectra is shown in inset
of Fig. 1. The absorption spectra sorely by bismuth ions were obtained by subtracting the absorption
spectrum of the SBA-A glass (doped with Er3+ and Yb3+ and without bismuth ions) from those of the
SBA-B, C, and D. A clear absorption band centered at 470 nm by bismuth was obtained in the glasses
of SBA-B, C, and D and the intensity increased by increasing bismuth concentration. Two weak
absorption bands near 700 nm and 800 nm were also observed [1-3].
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Emission spectra were obtained with the spectrophotometer (SpectraPro 2150i, Acton) by optical
pumpings at 805 and 980 nm at the input power of 100 mW by use of a cw-Ti:sapphire laser (Mira900, Coherent) and a laser diode (LD) (CS5000L, Coset), respectively. An InGaAs detector (ID441,
Acton) was used to collect the emission spectra of the glasses in the near-infrared (NIR) wavelength
range from 850 to 1700 nm.
The measured emission spectra of the glasses by the 805 and 980 nm excitations are shown in Fig.
2(a). Three emission bands originated from Er3+, Yb3+, and bismuth ions were observed by the both
excitations. The intensity of the emission near 1538 nm of Er3+ ions upon the 980 nm excitation was
14.5 times higher than that after the 805 nm excitation. In the case of the 980 nm excitation, because of
the large absorption cross-section of Yb3+ ions near 980 nm, the pump energy was absorbed by Yb3+
ions and transferred efficiently from the 2F5/2 level of Yb3+ to the 4I13/2 level of Er3+ ions, resulting in
the observed strong emission [6-8]. On the other hand, however, when the glasses were pumped at 805
nm, the absorbed energy by Er3+ ions at the 4I13/2 energy level was excited to higher energy levels of
Er3+ ions by excited state absorption (ESA) then returned to the ground state with visible band
emissions. This ESA process in Er3+ ions upon the 805 nm excitation may weaken the intensity of 1538
nm emission.
As shown in the inset of the Fig. 2(a), an emission band due to the energy transition from the 2F5/2
level to the 2F7/2 level of Yb3+ ions also appeared at 1020 nm by the 980 nm excitation and the intensity
of the emission was much larger than that obtained by the 805 nm excitation because of the large
absorption of Yb3+ ions as explained above. The weak emission by the 805 nm excitation was thought
to be due to energy transfer from Er3+ and bismuth ions to Yb3+ ions, because there was no absorption
band for Yb3+ ions at 805 nm [11]. As for the emission by bismuth ions, while the peak appeared at
1231 nm upon 805 nm excitation, it appeared at the slightly shorter wavelength of 1183 nm upon 980
nm excitation. Note that such pump wavelength dependent emission peak position of the glass is still
controversial [13, 14].
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Fig. 2(b) compares the effect of Bi2O3 concentration on the emission intensity of Er3+ ions under the
both excitations. As shown in the figure, the change of the peak intensity upon pumping at 805 nm was
negligibly small even with the bismuth incorporation. When the glasses were pumped at 980 nm,
however, the peak intensity slightly decreased with the addition of 0.5 mol% of Bi2O3 but increased
with the increase of Bi2O3 up to 2 mol% and the increase rate was about 1.3.
The effect of the Bi2O3 concentration on the lifetimes of the emission bands was investigated as
shown in Fig. 3(a). Decay curves of the emissions by Er3+ and bismuth ions were measured by use of
the InGaAs photo-detector and recoded by a storage digital real-time oscilloscope (TDS 220,
Tektronix) under the 980 nm excitation. The lifetime of the 1538 nm emission by Er3+ ions slightly
decreased from 807 to 774 μs when 0.5 mol% of Bi2O3 was introduced but began to increase with the
increase of the Bi2O3 concentration up to 2 mol% (774 → 913 μs). In the case of the emission at 1183
nm by bismuth ions, on the other hand, the lifetime gradually decreased from 407 to 357 μs by
increasing the Bi2O3 concentration from 0.5 to 2.0 mol%. Note that the lifetime was not obtained for
the SBA-A glass because no emission was found at 1183 nm in the glass without Bi2O3.
Fig. 3(b) shows the measured lifetime of the emission at 1020 nm of Yb3+ ions with respect to the
Bi2O3 concentration. The energy transfer (ET) efficiency, η, for the transition from Yb3+ (2F5/2) to Er3+
(4I13/2) ions was calculated by using the well-known equation [8, 11],
(1)
where
and
represent the lifetimes of the 1020 nm emission band (Yb3+: 2F5/2) in the SBA
glasses doped with and without bismuth ions, respectively. The lifetime of the band was changing as
181, 192, 176, and 162 μs with the increase in the Bi2O3 concentrations of 0, 0.5, 1 and 2 mol%,
respectively. The ET efficiency for the transition from Yb3+(2F5/2) to Er3+(4I13/2) ions increased with the
increase of the bismuth concentration larger than ~ 1.0 mol % and the highest value of 10.5 % was
obtained from the SBA-D glass (2 mol% of Bi2O3).
5
The decrease in the lifetime of the emissions by Yb3+ and bismuth ions and the increase in the
lifetime of Er3+ emission with increasing the bismuth concentration indicated that the absorbed energy
by Yb3+ and bismuth ions was transferred to Er3+ ions. The ET efficiency from Yb3+ to Er3+ ions
increased with the increase of the bismuth concentration. These results confirm that bismuth is an
efficient co-dopant to improve the pumping efficiency for the 1538 nm emission of Er3+ ions in the
Er3+/Yb3+ codoped SBA glass system.
III. SUMMARY
The emission properties of the Er-Yb-Bi triply doped borosilicate glass in the NIR wavelength
region were investigated by pumping at 805 and 980 nm. The glasses with fixed 1 mol% of Er2O3 and 1
mol% of Yb2O3 and different concentrations of Bi2O3 in the range of 0 ~ 2 mol% were prepared by the
conventional glass melting process.
The emission spectra were obtained upon the excitations by use of the 805 nm cw-Ti:Sapphire laser
and the 980 nm laser diode, respectively. The peak intensity of the 1538 nm emission of Er3+ ions upon
the 980 nm excitation was 14.5 times higher than that upon the 805 nm excitation due to the large
absorption of Yb3+ ions at 980 nm and the efficient energy transfer process from Yb3+ to Er3+ ions.
The lifetime of the 1538 nm emission of Er3+ ions slightly decreased when 0.5 mol% of Bi2O3 was
introduced. However, the emission lifetime of Er3+ began to increase (774 → 913 μs) and that of
bismuth gradually decreased (407 → 357 μs) with the increase of the bismuth concentration up to 2
mol%. The energy transfer efficiency from Yb3+ to Er3+ was improved by increasing the bismuth
concentration and the highest ET efficiency was 10.5 % at 2.0 mol% of Bi2O3, confirming that the
enhancement of the emission intensity of Er3+ ions was realized by incorporation of bismuth.
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ACKNOWLEDGMENTS
This work was partially supported by National Research Foundation through the research programs
(No. 2008-0061843, No. 20100020794), the New Growth Engine Industry Project of the Ministry of
Knowledge Economy, the Gwangju Institute of Science and Technology Top Brand Project (Photonics
2020), and the Brain Korea-21 Information Technology project, the Ministry of Education, Science and
Technology, South Korea.
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7
2241-2245, (2011).
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Table 1. The composition of the glass samples (in mol%)
Host glass
54SiO2-10B2O3-15Al2O3-10Na2O-8ZnO-1Ga2O3-2In2O3
Dopant
Er2O3
Yb2O3
Bi2O3
SBA-A
SBA-B
SBA-C
SBA-D
1
1
1
1
1
1
1
1
0
0.5
1
2
Figure Captions.
Fig. 1. Measured absorption spectrum of the SBA-A glass and absorption spectra sorely by bismuth
ions in the SBA-B, C, and D glasses (inset)
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Fig. 2. (a) Emission spectra of the SBA-(A, B, C, D) glasses upon pumping at 805 and 980 nm and (b)
the corresponding peak intensity at 1538 nm of Er3+ ions with the bismuth concentration.
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Fig. 3. (a) Effect of Bi2O3 concentration on the lifetime of the emissions at 1183 and 1538 nm excited
at 980 nm and the measured decay curves (inset) and (b) lifetime of the 1020 nm emission of Yb3+ ions
and energy transfer efficiency from Yb3+ (2F5/2) to Er3+ (4I13/2) ions with respect to the bismuth
concentration.
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