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Tm3+ co-doped ZrF4-BaF2-YF3-AlF3 fluoride glass for efficient 2.9 μm mid-infrared laser applications
Journal Pre-proof 3+ 3+ Investigation of Dy /Tm co-doped ZrF4-BaF2-YF3-AlF3 fluoride glass for efficient 2.9�μm mid-infrared laser applications Haiyan Zhao, Shijie Jia, Xin Wang, Ruicong Wang, Xiaosong Lu, Yaxian Fan, Masaki Tokurakawa, Gilberto Brambilla, Shunbin Wang, Pengfei Wang PII:
S0925-8388(19)34000-9
DOI:
https://doi.org/10.1016/j.jallcom.2019.152754
Reference:
JALCOM 152754
To appear in:
Journal of Alloys and Compounds
Received Date: 29 May 2019 Revised Date:
17 October 2019
Accepted Date: 21 October 2019
Please cite this article as: H. Zhao, S. Jia, X. Wang, R. Wang, X. Lu, Y. Fan, M. Tokurakawa, G. 3+ 3+ Brambilla, S. Wang, P. Wang, Investigation of Dy /Tm co-doped ZrF4-BaF2-YF3-AlF3 fluoride glass for efficient 2.9�μm mid-infrared laser applications, Journal of Alloys and Compounds (2019), doi: https:// doi.org/10.1016/j.jallcom.2019.152754. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier B.V.
Investigation of Dy3+/Tm3+ co-doped
1 2
ZrF4-BaF2-YF3-AlF3 fluoride glass for efficient 2.9 µm
3
mid-infrared laser applications
4 Haiyan Zhao1, Shijie Jia1, Xin Wang1, Ruicong Wang1, Xiaosong Lu1, Yaxian
5 6
Fan1,2, Masaki Tokurakawa3, Gilberto Brambilla4, Shunbin Wang1,*, and Pengfei
7
Wang1,5,*
8 9
1
Key Laboratory of In-fiber Integrated Optics of Ministry of Education, College of Science,
10 11
Harbin Engineering University, Harbin 150001, China 2
Academy of Marine Information Technology, Guilin University of Electronic Technology,
12 13
Beihai, 536000, China 3
Institute for Laser Science, University of Electro-Communications, Chofugaoka Chofu
14 15
Tokyo 182-8585, Japan 4
Optoelectronics Research Centre, University of Southampton, Southampton SO17 1BJ,
16 17
United Kingdom 5
Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and
18
Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen,
19
518060, China
20
*[email protected]
21
*[email protected]
1 2
Abstract:
3
Different doping concentrations of Dy3+/Tm3+ in ZrF4-BaF2-YF3-AlF3 (ZBYA) fluoride glass
4
samples were prepared by the melt-quenching method. Spectroscopic properties were analyzed
5
through absorption (from 200 to 3300 nm) and emission spectra (from 1200 to 3200 nm). The
6
spontaneous radiative transition probability, branching ratio and radiative lifetime of various
7
energy levels transition were calculated based on the Judd-Ofelt theory. The emission
8
cross-section value of the 1 mol% Dy3+/1 mol% Tm3+ co-doped ZBYA sample at 2.9 µm were
9
calculated as 3.79 10-21 cm2. Near- and mid-IR emission spectra of Dy3+/Tm3+ co-doped
10
ZBYA-fluoride glass under the excitation of 808 nm laser diode were investigated and discussed.
11
Analysis of the emission spectra and the energy transition process of Dy3+/Tm3+ co-doped glass
12
indicated that the introduction of Tm3+ ions can effectively improve the mid-infrared fluorescence
13
intensity of Dy3+ ions, thus the Dy3+/Tm3+ co-doped ZBYA-fluoride glass can be an excellent
14
candidate material for 2.9 µm mid-infrared laser applications.
15 16
Introduction
17
Mid-infrared fiber lasers (in the wavelength range λ~2-5 µm) have attracted much attention for
18
their wide range of applications in molecular spectroscopy, medical treatment, environment
19
detection, sensors and military defense as they operate in the transparent atmospheric transmission
20
window and cover many important molecular characteristic lines [1]. So far, mid-infrared fiber
21
lasers have been achieved only in fluoride fibers such as ZBLAN [2], fluoroaluminate [3] and
22
fluoroindate [4-6]. Among them, ZBLAN fibers have shown excellent lasing performance: in
23
2018, Yigit Ozan Aydin et al demonstrated a λ~2.82 µm laser in a 7 mol% doped Er:ZBLAN fiber
24
pumped by a high power λ~976 nm laser diode, producing an output power up to 41.6 W [7].
25
Generally, the fluorozirconate glass has the advantages of wide transparency window (λ~0.3-7
26
µm), low phonon energy (580 cm-1) and high rare earth solubility [8-11]. The low phonon energy
27
reduces the multi-phonons non-radiative relaxation probability and therefore increases the
1
emission efficiency between rare earth ion transition levels. In the past two decades, the spectral
2
properties of ZBLAN (53ZrF4-20BaF2-4LaF3-3AlF3-20NaF3) glass have been extensively studied
3
making ZBLAN the main host material for mid-infrared fiber lasers [12-15]. However, its poor
4
thermal and chemical properties, including low glass transition temperature (Tg~267 oC) and
5
predisposition to deliquesce (for the existence of large Na content), limit its applications in high
6
power fiber lasers. ZrF4-BaF2-YF3-AlF3 (ZBYA) glass has been proposed as a fluorozirconate
7
glass alternative to ZBLAN, because of its better thermal and chemical stability [16, 17]. In 2016,
8
Feifei Huang et al investigated the energy transfer mechanisms of Er3+/Pr3+ co-doped ZBYA glass.
9
By comparison, the emission intensity of 2.7 µm of Er3+/Pr3+ co-doped ZBYA glass is stronger
10
than that in Er3+ single-doped samples due to the depletion effect of Pr3+ ions on the population of
11
terminal laser level Er3+: 4I13/2 [18]. In order to improve the λ~ 2.7 µm emission, Huang et al also
12
investigated the fluorescence properties and energy transfer mechanism of Ho3+/Er3+, Er3+/Tm3+
13
co-doped ZBYA glass [19]. These results showed the better chemical and thermal properties of
14
ZBYA-fluoride glass and favourable emission characteristics in the λ~ 2.7 µm wavelength region.
15
Dy3+ ion is another type of rare earth ion that can be used for obtaining mid-infrared emissions at
16
λ~ 2.9 µm due to the transition 6H13/2 → 6H15/2 [20], which is longer and wider than that obtained
17
from Er: 4I11/2 → 4I13/2 and Ho: 5I6→5I7 [21]. However, the mid-infrared fluorescence performance
18
of Dy3+ ions is associated with a weak absorption in the near-infrared band near λ~ 808 nm, λ~
19
912 nm and λ~ 1100 nm, which leads to a low absorption efficiency under the excitation of
20
common commercial NIR LD lasers. An efficient method to improve Dy3+ ions mid-infrared
21
fluorescence efficiency relies on the introduction of relevant sensitizing ions through energy
22
transfer processes [22]. The 3H4 level of Tm3+ has a strong absorption near λ~ 808 nm, while the
23
Tm3+: 3F4 level has similar spectroscopy properties to the Dy3+: 6H11/2 level [23, 24]. Energy
24
transfer between Tm3+ and Dy3+ ions can occur in Tm3+/Dy3+ co-doped materials, thus improving
25
the mid-infrared emissions of Dy3+ ions [22].
26
In this letter, we report the mid-infrared emission performance of different doping concentrations
27
of Dy3+/Tm3+ in ZBYA glasses.
28
Experiments
1
Dy3+/Tm3+ co-doped ZBYA glass samples were prepared from high-purity ZrF4, BaF2, YF3, AlF3,
2
DyF3 and TmF3 powder precursors. The molar compositions of the investigated glasses were
3
50ZrF4-33BaF2-(9-x)YF3-7AlF3-1TmF3-xDyF3
4
and50ZrF4-33BaF2-(9-x)YF3-7AlF3-1DyF3-xTmF3 (x=0.2, 0.5, 1, 2, 3). The raw material batches
5
were weighed with a fine electronic balance, mixed in an agate mortar, put in a platinum crucible
6
and melted in an electric furnace at 850 oC in a glove box. The melts were poured onto a preheated
7
copper plate and annealed in a furnace around the glass transition temperature for 180 min.
8
Finally, the obtained glass samples were cut and polished for measurements. Transmission spectra
9
were measured with a Perkin-Elemer Lambda 900 UV spectrophotometer in the range λ~ 200 -
10
3300 nm and a Perkin Elmer FT-IR spectrometer in the range λ~ 3300 - 10000 nm. Raman spectra
11
were measured by using a Horiba LabRAM HR Evolution spectrometer. Near- and mid-infrared
12
fluorescence spectra were measured using a combination of the Zolix Omni-λ3015 infrared
13
monochromator (InSb detector cooled with liquid nitrogen) and the SCITEC Model 420
14
dual-phase lock-in amplifier. The excitation source was a λ~ 808 nm diode laser with a power
15
setting of 1.6 W. All of the measurements were carried out at room temperature.
16
Result and discussion
17
Fig.1 (a) shows the absorption spectrum of un-doped ZBYA glass in the λ~ 200-10000 nm band.
18
The transmittance at λ~1000-6000 nm is as high as 90%, and the infrared cutoff wavelength is
19
around λ~ 9000 nm. The figure shows that there is a small OH- absorption near λ~ 3 µm. The
20
absorption coefficient αOH- of OH- groups in the 20 mm×12 mm×9 mm ZBYA glass can be
21
calculated using the following equation [25]:
(x=0.2,
0.5,
1,
2,
3)
22
(1)
23
where d is the glass thickness, Tb is the maximum transmittance of the glass, and T is the
24
transmittance at the central wavelength of the OH- absorption peak. αOH- in the ZBYA sample is
1
~0.0098 cm-1, is much lower than that in ZBLAN (~0.11cm-1) [26], gallate (~0.15 cm-1) [25],
2
tellurite (~0.6 cm-1) [27], fluorotellurite (~1.09 cm-1) [28], fluoroaluminate (~0.41 cm-1) [29] and
3
fluorinate (~0.06 cm-1) glasses [30]. As the residual OH- groups in the glass matrix can participate
4
in the energy transfer process of rare earth ions and reduce the emission efficiency, a ZBYA glass
5
with ultra-low OH- is an attractive candidate for 3 µm laser material application [31].
6
Fig.1 (b) shows the Raman spectrum of the ZBYA-fluoride glass sample. An obvious Raman shift
7
peak at 580 cm-1 signs the ZBYA maximum phonon energy. The ZBYA phonon energy is similar
8
to that of ZBLAN (580 cm-1), and lower than that of fluoroaluminate glass and oxide glass hosts
9
[32]: an advantage for achieving lasing at λ~ 2.9 µm.
10 11 12
Fig. 1 (a) Absorption spectrum of the 1.5 mm thick un-doped ZBYA glass in the range λ~ 200-10000 nm. Insets: zoom of the OH- absorption at λ~ 3.0 µm. (b) Raman spectrum of the ZBYA-fluoride glass sample.
13 14
Fig. 2 presents the absorption spectra of Dy3+ -doped and Dy3+ / Tm3+ co-doped ZBYA glasses.
15
The transitions from the 6H15/2 to the higher 6H13/2, 6H11/2, 6H9/2+6F11/2, 6H7/2+6F9/2, 6F7/2, 6F5/2 levels
16
correspond to the absorption bands centered at λ~ 2900 nm, 1700 nm, 1300 nm, 1094 nm, 908 nm
17
and 804 nm, respectively. Compared with the Dy3+-doped sample, the Dy3+/Tm3+ co-doped sample
18
has a significantly higher absorption around λ~ 1700 nm and 800 nm because the Dy3+: 6H15/2 →
1
6
2
those two absorption bands, and the absorption intensity is superimposed. As the concentration of
3
Tm3+ ions increases, the absorption at λ~800 nm increases correspondingly.
4 5 6
H11/2, 6H15/2 → 6F5/2 transition and the Tm3+: 3H6 → 3F4, 3H6 → 3H4 transitions are expanded at
Fig. 2 Absorption spectra of Dy3+ single-doped and Dy3+ / Tm3+ co-doped in ZBYA glasses in the range λ~ 200-3200 nm.
7 8
The relevant spectral parameters of the Dy3+/Tm3+ co-doped ZBYA glass can be calculated from
9
the Judd-Ofelt (J-O) theory [33]. The J-O intensity parameters Ωt (t=2, 4, 6) are commonly used to
10
analyze the symmetry of the glass matrix, the covalency of the rare earth ions and the anion bonds
11
[34]. Generally, Ω2 is determined by the glass matrix structure (such as symmetry around the
12
ligand and order) and is proportional to the covalency between the coordination anions and rare
13
earth ions. The larger is Ω2, the lower is the symmetry around the rare earth ion and the higher is
14
covalency. Ω2 of ZBYA is small, similar to that of the ZBLAN and fluoroaluminate glasses, but
15
smaller than that of chalcohalide and tellurite glasses, indicating that the sample has high
16
symmetry and strong ionicity of the coordination field in the environment. While both Ω4 and Ω6
1
are related to the local basicity of the ligands in the glass. Ω6 is mainly affected by the overlap of
2
the 4f and 5d orbitals of the rare earth ions, and its value increases for increasing densities. As Ω6
3
is high, the emission bandwidth of rare earth ions and the probability of spontaneous radiation
4
increases [35]. Table 1 shows the Judd-Ofelt intensity parameters Ωt (t=2, 4, 6) in various glass
5
hosts.
6
Table 1. Calculated J-O intensity parameters Ωt (t=2, 4, 6) of Dy3+ in various glass hosts. Ωt (10-20 cm2)
Ω2
Ω4
Ω6
Fluoroaluminate[36]
2.7
0.86
1.89
ZBLAN[37]
3.29
1.56
2.48
Chalcohalide[38]
11.82
3.35
1.56
Tellurite[39]
6.85
1.75
1.75
ZBYA(this work)
3.13
0.33
0.43
7 8
Table 2 lists the spontaneous radiation transitions probability (A), fluorescence branching ratio (β)
9
and radiative lifetime (τrad) for Dy3+ energy level transitions in the ZBYA glass sample. As
10
expected, the spontaneous-emission probabilities for the Dy3+: 6H13/2 → 6H15/2 transition is 17.59
11
s-1, which is lower than that recorded in ZBLA (19.5 s-1) [40] and ZBLAY (45.92 s-1) [41].
12
Generally, higher spontaneous-emission probability provides a better opportunity to obtain lasing
13
[42]. The lifetime of the Dy3+: 6H13/2 energy level in ZBYA glass is calculated to be as long as 56.8
14
ms, favorable for achieving efficient 2.9 µm lasing.
15
Table 2. Radiative parameters for various selected excited levels of Dy3+ in ZBYA glass
Transition
Wavelength(nm)
A (s-1)
β (%)
τrad (ms)
6
1325
20.1
85.24
42.4
→ 6H13/2
2390
3.2
13.57
→ 6H11/2
5410
0.28
1.18
6
1760
44.3
94.1
→ 6H13/2
4290
2.8
5.9
6
2864
17.59
100
H9/2+6F11/2 → 6H15/2
H11/2 → 6H15/2
H13/2 → 6H15/2
21.2
56.8
1 2
Assuming that the time to establish thermal equilibrium in the energy level multi-configuration is
3
less than its radiation lifetime, according to the McCumber theory [43], the relationship between
4
the absorption cross section σabs and the emission cross section σemi is:
5
(2)
6
where h, ν, K, and T represent the Planck constant, photon frequency, Boltzmann constant, and
7
room temperature, respectively. ε is the temperature-dependent excitation energy whose value is
8
equal to the energy corresponding to the peak frequency of the absorption spectrum.
9
The absorption cross section can be calculated directly from the measured absorption spectrum:
10
(3)
11
where N is the concentration of rare earth ions, d is the optical path - e.g. the thickness of the
12
sample - and D(λ) is the optical density, which is derived from the absorption spectrum.
13
The emission cross section σemi and the absorption cross section σabs of the Dy3+: 6H13/2 → 6H15/2
14
transition in the 1 mol% Dy3+/1 mol% Tm3+ co-doped sample is presented in Fig. 3(a). The peak
1
value of σemi at λ~2.9 µm is 3.79 10-21 cm2, similar to that in fluoroaluminate glass (~3.96 10-21
2
cm2) [44], while lower than that in ZBLAY (~1.17 10-20 cm2) [41] and tellurite glasses
3
(~2.82 10-20 cm2) [45].
4
The gain cross-section G(λ) as function of the wavelength was calculated from:
5
(4)
6
where P is population inversion parameter, which is related to the concentration ratio of Dy3+ in
7
the 6H11/2 and 6H13/2 level. The gain coefficients with various P ranging from 0 to 1 are presented
8
in Fig.3 (b), and positive gain can be obtained in the range of λ~2800-3000 nm when P>0.4.
9 10 11 12
Fig. 3 (a) Absorption cross-section and emission cross section of 6H13/2 → 6H15/2 transition in 1 mol% Dy3+/1 mol% Tm3+ co-doped sample; (b) Gain coefficient spectra for the 6H13/2 → 6H15/2 transition in the 1 mol% Dy3+/1 mol% Tm3+ co-doped sample.
13 14
The Near-IR fluorescence spectra of Dy3+/Tm3+ co-doped ZBYA glasses in the range λ~1150-1350
15
nm is given in Fig. 4. The fluorescence peak at λ~1260 nm corresponds to the transition of Tm3+:
16
3
17
nm decreases as the concentration of Dy3+ increases or the concentration of Tm3+ decreases. Since
18
the lifetime of the Tm3+: 3H5 level is far shorter than that of the 3H4 level, the energy transfer rate
H5 → 3H6. When the Tm3+ concentration is fixed at 1 mol%, the fluorescence intensity at λ~1260
1
from Tm3+: 3H5 to other levels of Dy3+ ions is extremely small [46]. Therefore, the decrease in the
2
population on 3H5 is mainly due the energy transfer processes from the 3H4 metastable level of
3
Tm3+ to other levels of Dy3+, leading to the depopulation of 3H5.
4 5 6
Fig. 4 Near-infrared fluorescence spectra at λ~1260 nm of the Dy3+/Tm3+-doped ZBYA glasses excited at λ~808 nm when the pump power is set to 1.6 W.
7 8
Fig. 5 shows the strong emissions near λ~1470 nm and λ~1800 nm, which are attributed to the
9
radiative transitions of Tm3+: 3H4 → 3F4 and 3H5 → 3H6, respectively. For fixed Tm3+ doping
10
concentration, the fluorescence intensity at λ~1470 nm and λ~1800 nm gradually decreases as the
11
concentration of Dy3+ increases, which can explain the existence of energy transfer between Tm3+:
12
3
13
When the Dy3+ doping concentration is maintained at 1 mol% and the concentration of Tm3+ ions
14
increases, the emission intensity at λ~1470 nm and λ~1800 nm increases, while when the
15
concentration of Tm3+ is 2 mol%, the emission intensity of λ~1470 nm shows a weakening trend.
16
This is most likely due to the well-known cross relaxation and migration processes of Tm3+
17
(3H4+3H5→2•3F4), which becomes obvious the evident as the concentration of Tm3+ ions
18
increasing [47]. These processes reduce the number of electrons on the Tm3+: 3H4 energy level,
H4 → Dy3+: 6F5/2, Tm3+: 3F4 → Dy3+: 6H11/2, due to their similar energy levels.
1
2 3 4
and lead to the weakening of the λ~1470 nm fluorescence.
Fig.5 Near-infrared fluorescence spectra at λ~1470 nm and λ~1800 nm of the Dy3+/Tm3+-doped ZBYA glasses excited at λ~808 nm when the pump power is set to 1.6 W.
5 6
Fig. 6 shows the fluorescence spectra at λ~2.9 µm, attributed to the Dy3+: 6H13/2 → 6H15/2
7
transition. At the fixed Tm3+ concentration of 1 mol%, the fluorescence intensity increases with
8
increasing Dy3+ doping content from 0.2 to 3 mol% (Fig. 6(a)), thus indicating an efficient energy
9
transfer between the Tm3+: 3F4 and Dy3+: 6H13/2 levels. When the Dy3+ doping concentration is
10
fixed, the same effect occurs as the Tm3+ concentration increases (Fig. 6(b)). The introduction of
11
Tm3+ ions increases the absorption rate of Dy3+ ions and also improves the pumping absorption
12
efficiency, thereby effectively increasing the fluorescence intensity at λ~2.9 µm.
13
1 2
Fig.6 Luminescence spectra of Dy3+ ions at the λ~2.9 µm wavelength in different doping concentrations of the Dy3+/Tm3+-doped ZBYA glasses excited at λ~808 nm when the pump power is set to 1.6 W.
3 4
Fig. 7 shows the energy transfer processes between Tm3+ and Dy3+. Under λ~808 nm laser
5
pumping, the electrons of the Tm3+:3H6 ground state are excited to the 3H4 excited state, and then
6
transition radiatively to the
7
Simultaneously, the minority of Tm3+ ions in the 3H4 level relax to the 3H5 level through
8
multi-phonon relaxation (MPR), and then jump to the 3H6 level to produce λ~1.26 µm
9
near-infrared emission. The electrons of the Dy3+: 6H13/2 level accumulate due to multi-phonon
10
relaxation (MPR) of the upper level, then transition to the ground state 6H15/2, resulting in the
11
λ~2.9 µm mid-infrared emission. The electron in the excited state 3F4 level returns to the ground
12
state, producing the λ~1.8 µm emission. The energy transfers (ET) Tm3+: 3H4 → Dy3+: 6F5/2, Tm3+:
13
3
14
depopulated by the well-known cross relaxation (CR) 3H6 + 3H4 → 3F4 + 3F4. After the Tm3+: 3F4
15
level is populated, electrons of the Tm3+: 3F4 level can be transferred to the Dy3+: 6H11/2 level. In
16
this paper, the change of infrared fluorescence spectra also confirmed the existence of these
17
energy transfer processes.
18
3
F4 level, resulting in a λ~1.47 µm near-infrared emission.
F4 → Dy3+: 6H11/2 are signed as ET1, ET2, respectively. Besides, the Tm3+: 3H4 level can be
1
Fig. 7. Energy transfer processes between Tm3+ and Dy3+ ions in ZBYA glasses.
2 3
Conclusion
4
In conclusion, we investigated the λ~2.9 µm emission and energy transfer mechanism of
5
Dy3+/Tm3+ co-doped ZBYA glasses. Combined with the measured fluorescence spectra at
6
λ~1260 nm, λ~1470 nm, λ~1.8 µm and λ~2.9 µm, the energy transfer processes between Dy3+
7
and Tm3+ ions are analyzed in detail. The strong λ~2.9 µm mid-infrared emission from the
8
Dy3+/Tm3+ co-doped ZBYA glasses was ascribed to the occurrence of the energy transfer process
9
of Tm3+: 3F4 → Dy3+: 6H11/2. Our results show that Dy3+/Tm3+ co-doped ZBYA glass is a
10
potential gain medium for λ~2.9 µm laser application, it lays the foundation for our future
11
preparation of ZBYA glass fiber mid-infrared laser.
12 13
Acknowledgments:
14
This work was supported by the National Natural Science Foundation of China (NSFC) under
15
grant 61575050; National Key R&D Program of China under grant 2016YFE0126500; The
16
fundamental research funds for the central universities (HEUCFG201841); Key Program for
17
Natural Science Foundation of Heilongjiang Province of China under grant ZD2016012; Open
18
Fund of the State Key Laboratory on Integrated Optoelectronics (IOSKL2016KF03); this work
19
was also supported by the 111 project (B13015) to the Harbin Engineering University.
20
References:
21 22 23
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Investigation of Dy3+/Tm3+ co-doped ZrF4-BaF2 -YF3 -AlF3 fluoride glass for efficient 2.9 µm mid-infrared laser applications
Haiyan Zhao 1, Shijie Jia 1, Xin Wang 1, Ruicong Wang 1 , Xiaosong Lu 1, Yaxian Fan 2 , Masaki Tokurakawa 3, Gilberto Brambilla 4, Shunbin Wang 1,*, and Pengfei Wang 1,5,* 1Key Laboratory of In-fiber Integrated Optics of Ministry of Education, College of Science, Harbin Engineering University, Harbin 150001, China 2Academy of Marine Information Technology, Guilin University of Electronic Technology, Beihai, 536000, China 3Institute for Laser Science, University of Electro-Communications, Chofugaoka Chofu Tokyo 182-8585, Japan 4Optoelectronics Research Centre, University of Southampton, Southampton SO17 1BJ, United Kingdom 5Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen, 518060, China *[email protected] *[email protected]
Keywords: ZBYA fluoride glass, mid-infrared laser, Dy3+/Tm3+ co-doped
Energy transfer processes between Dy3+ and Tm3+ ions in ZrF4-BaF2-YF3-AlF3 (ZBYA) fluoride glass samples were investigated in details. The transmittance of ZBYA glass at λ~1000-6000 nm is as high as 90%, with an infrared cutoff wavelength at around λ~9000 nm. αOH- in the ZBYA sample is as low as ~0.0098 cm-1, which is ascribed to the chemical dehydrating process (F-+OH-→O2-+HF ↑) and longtime physical dehydrating process in ultra-dry pure nitrogen atmosphere. The introduction of Tm3+ ions improve the mid-infrared emission intensity of Dy3+ ions in ZBYA glass, which is ascribed to the energy transfer process of Tm3+: 3F4 → Dy3+:6H11/2. This results can be applied in mid-infrared laser.
Declaration of interests
√The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
S0925-8388(19)34000-9
DOI:
https://doi.org/10.1016/j.jallcom.2019.152754
Reference:
JALCOM 152754
To appear in:
Journal of Alloys and Compounds
Received Date: 29 May 2019 Revised Date:
17 October 2019
Accepted Date: 21 October 2019
Please cite this article as: H. Zhao, S. Jia, X. Wang, R. Wang, X. Lu, Y. Fan, M. Tokurakawa, G. 3+ 3+ Brambilla, S. Wang, P. Wang, Investigation of Dy /Tm co-doped ZrF4-BaF2-YF3-AlF3 fluoride glass for efficient 2.9�μm mid-infrared laser applications, Journal of Alloys and Compounds (2019), doi: https:// doi.org/10.1016/j.jallcom.2019.152754. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier B.V.
Investigation of Dy3+/Tm3+ co-doped
1 2
ZrF4-BaF2-YF3-AlF3 fluoride glass for efficient 2.9 µm
3
mid-infrared laser applications
4 Haiyan Zhao1, Shijie Jia1, Xin Wang1, Ruicong Wang1, Xiaosong Lu1, Yaxian
5 6
Fan1,2, Masaki Tokurakawa3, Gilberto Brambilla4, Shunbin Wang1,*, and Pengfei
7
Wang1,5,*
8 9
1
Key Laboratory of In-fiber Integrated Optics of Ministry of Education, College of Science,
10 11
Harbin Engineering University, Harbin 150001, China 2
Academy of Marine Information Technology, Guilin University of Electronic Technology,
12 13
Beihai, 536000, China 3
Institute for Laser Science, University of Electro-Communications, Chofugaoka Chofu
14 15
Tokyo 182-8585, Japan 4
Optoelectronics Research Centre, University of Southampton, Southampton SO17 1BJ,
16 17
United Kingdom 5
Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and
18
Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen,
19
518060, China
20
*[email protected]
21
*[email protected]
1 2
Abstract:
3
Different doping concentrations of Dy3+/Tm3+ in ZrF4-BaF2-YF3-AlF3 (ZBYA) fluoride glass
4
samples were prepared by the melt-quenching method. Spectroscopic properties were analyzed
5
through absorption (from 200 to 3300 nm) and emission spectra (from 1200 to 3200 nm). The
6
spontaneous radiative transition probability, branching ratio and radiative lifetime of various
7
energy levels transition were calculated based on the Judd-Ofelt theory. The emission
8
cross-section value of the 1 mol% Dy3+/1 mol% Tm3+ co-doped ZBYA sample at 2.9 µm were
9
calculated as 3.79 10-21 cm2. Near- and mid-IR emission spectra of Dy3+/Tm3+ co-doped
10
ZBYA-fluoride glass under the excitation of 808 nm laser diode were investigated and discussed.
11
Analysis of the emission spectra and the energy transition process of Dy3+/Tm3+ co-doped glass
12
indicated that the introduction of Tm3+ ions can effectively improve the mid-infrared fluorescence
13
intensity of Dy3+ ions, thus the Dy3+/Tm3+ co-doped ZBYA-fluoride glass can be an excellent
14
candidate material for 2.9 µm mid-infrared laser applications.
15 16
Introduction
17
Mid-infrared fiber lasers (in the wavelength range λ~2-5 µm) have attracted much attention for
18
their wide range of applications in molecular spectroscopy, medical treatment, environment
19
detection, sensors and military defense as they operate in the transparent atmospheric transmission
20
window and cover many important molecular characteristic lines [1]. So far, mid-infrared fiber
21
lasers have been achieved only in fluoride fibers such as ZBLAN [2], fluoroaluminate [3] and
22
fluoroindate [4-6]. Among them, ZBLAN fibers have shown excellent lasing performance: in
23
2018, Yigit Ozan Aydin et al demonstrated a λ~2.82 µm laser in a 7 mol% doped Er:ZBLAN fiber
24
pumped by a high power λ~976 nm laser diode, producing an output power up to 41.6 W [7].
25
Generally, the fluorozirconate glass has the advantages of wide transparency window (λ~0.3-7
26
µm), low phonon energy (580 cm-1) and high rare earth solubility [8-11]. The low phonon energy
27
reduces the multi-phonons non-radiative relaxation probability and therefore increases the
1
emission efficiency between rare earth ion transition levels. In the past two decades, the spectral
2
properties of ZBLAN (53ZrF4-20BaF2-4LaF3-3AlF3-20NaF3) glass have been extensively studied
3
making ZBLAN the main host material for mid-infrared fiber lasers [12-15]. However, its poor
4
thermal and chemical properties, including low glass transition temperature (Tg~267 oC) and
5
predisposition to deliquesce (for the existence of large Na content), limit its applications in high
6
power fiber lasers. ZrF4-BaF2-YF3-AlF3 (ZBYA) glass has been proposed as a fluorozirconate
7
glass alternative to ZBLAN, because of its better thermal and chemical stability [16, 17]. In 2016,
8
Feifei Huang et al investigated the energy transfer mechanisms of Er3+/Pr3+ co-doped ZBYA glass.
9
By comparison, the emission intensity of 2.7 µm of Er3+/Pr3+ co-doped ZBYA glass is stronger
10
than that in Er3+ single-doped samples due to the depletion effect of Pr3+ ions on the population of
11
terminal laser level Er3+: 4I13/2 [18]. In order to improve the λ~ 2.7 µm emission, Huang et al also
12
investigated the fluorescence properties and energy transfer mechanism of Ho3+/Er3+, Er3+/Tm3+
13
co-doped ZBYA glass [19]. These results showed the better chemical and thermal properties of
14
ZBYA-fluoride glass and favourable emission characteristics in the λ~ 2.7 µm wavelength region.
15
Dy3+ ion is another type of rare earth ion that can be used for obtaining mid-infrared emissions at
16
λ~ 2.9 µm due to the transition 6H13/2 → 6H15/2 [20], which is longer and wider than that obtained
17
from Er: 4I11/2 → 4I13/2 and Ho: 5I6→5I7 [21]. However, the mid-infrared fluorescence performance
18
of Dy3+ ions is associated with a weak absorption in the near-infrared band near λ~ 808 nm, λ~
19
912 nm and λ~ 1100 nm, which leads to a low absorption efficiency under the excitation of
20
common commercial NIR LD lasers. An efficient method to improve Dy3+ ions mid-infrared
21
fluorescence efficiency relies on the introduction of relevant sensitizing ions through energy
22
transfer processes [22]. The 3H4 level of Tm3+ has a strong absorption near λ~ 808 nm, while the
23
Tm3+: 3F4 level has similar spectroscopy properties to the Dy3+: 6H11/2 level [23, 24]. Energy
24
transfer between Tm3+ and Dy3+ ions can occur in Tm3+/Dy3+ co-doped materials, thus improving
25
the mid-infrared emissions of Dy3+ ions [22].
26
In this letter, we report the mid-infrared emission performance of different doping concentrations
27
of Dy3+/Tm3+ in ZBYA glasses.
28
Experiments
1
Dy3+/Tm3+ co-doped ZBYA glass samples were prepared from high-purity ZrF4, BaF2, YF3, AlF3,
2
DyF3 and TmF3 powder precursors. The molar compositions of the investigated glasses were
3
50ZrF4-33BaF2-(9-x)YF3-7AlF3-1TmF3-xDyF3
4
and50ZrF4-33BaF2-(9-x)YF3-7AlF3-1DyF3-xTmF3 (x=0.2, 0.5, 1, 2, 3). The raw material batches
5
were weighed with a fine electronic balance, mixed in an agate mortar, put in a platinum crucible
6
and melted in an electric furnace at 850 oC in a glove box. The melts were poured onto a preheated
7
copper plate and annealed in a furnace around the glass transition temperature for 180 min.
8
Finally, the obtained glass samples were cut and polished for measurements. Transmission spectra
9
were measured with a Perkin-Elemer Lambda 900 UV spectrophotometer in the range λ~ 200 -
10
3300 nm and a Perkin Elmer FT-IR spectrometer in the range λ~ 3300 - 10000 nm. Raman spectra
11
were measured by using a Horiba LabRAM HR Evolution spectrometer. Near- and mid-infrared
12
fluorescence spectra were measured using a combination of the Zolix Omni-λ3015 infrared
13
monochromator (InSb detector cooled with liquid nitrogen) and the SCITEC Model 420
14
dual-phase lock-in amplifier. The excitation source was a λ~ 808 nm diode laser with a power
15
setting of 1.6 W. All of the measurements were carried out at room temperature.
16
Result and discussion
17
Fig.1 (a) shows the absorption spectrum of un-doped ZBYA glass in the λ~ 200-10000 nm band.
18
The transmittance at λ~1000-6000 nm is as high as 90%, and the infrared cutoff wavelength is
19
around λ~ 9000 nm. The figure shows that there is a small OH- absorption near λ~ 3 µm. The
20
absorption coefficient αOH- of OH- groups in the 20 mm×12 mm×9 mm ZBYA glass can be
21
calculated using the following equation [25]:
(x=0.2,
0.5,
1,
2,
3)
22
(1)
23
where d is the glass thickness, Tb is the maximum transmittance of the glass, and T is the
24
transmittance at the central wavelength of the OH- absorption peak. αOH- in the ZBYA sample is
1
~0.0098 cm-1, is much lower than that in ZBLAN (~0.11cm-1) [26], gallate (~0.15 cm-1) [25],
2
tellurite (~0.6 cm-1) [27], fluorotellurite (~1.09 cm-1) [28], fluoroaluminate (~0.41 cm-1) [29] and
3
fluorinate (~0.06 cm-1) glasses [30]. As the residual OH- groups in the glass matrix can participate
4
in the energy transfer process of rare earth ions and reduce the emission efficiency, a ZBYA glass
5
with ultra-low OH- is an attractive candidate for 3 µm laser material application [31].
6
Fig.1 (b) shows the Raman spectrum of the ZBYA-fluoride glass sample. An obvious Raman shift
7
peak at 580 cm-1 signs the ZBYA maximum phonon energy. The ZBYA phonon energy is similar
8
to that of ZBLAN (580 cm-1), and lower than that of fluoroaluminate glass and oxide glass hosts
9
[32]: an advantage for achieving lasing at λ~ 2.9 µm.
10 11 12
Fig. 1 (a) Absorption spectrum of the 1.5 mm thick un-doped ZBYA glass in the range λ~ 200-10000 nm. Insets: zoom of the OH- absorption at λ~ 3.0 µm. (b) Raman spectrum of the ZBYA-fluoride glass sample.
13 14
Fig. 2 presents the absorption spectra of Dy3+ -doped and Dy3+ / Tm3+ co-doped ZBYA glasses.
15
The transitions from the 6H15/2 to the higher 6H13/2, 6H11/2, 6H9/2+6F11/2, 6H7/2+6F9/2, 6F7/2, 6F5/2 levels
16
correspond to the absorption bands centered at λ~ 2900 nm, 1700 nm, 1300 nm, 1094 nm, 908 nm
17
and 804 nm, respectively. Compared with the Dy3+-doped sample, the Dy3+/Tm3+ co-doped sample
18
has a significantly higher absorption around λ~ 1700 nm and 800 nm because the Dy3+: 6H15/2 →
1
6
2
those two absorption bands, and the absorption intensity is superimposed. As the concentration of
3
Tm3+ ions increases, the absorption at λ~800 nm increases correspondingly.
4 5 6
H11/2, 6H15/2 → 6F5/2 transition and the Tm3+: 3H6 → 3F4, 3H6 → 3H4 transitions are expanded at
Fig. 2 Absorption spectra of Dy3+ single-doped and Dy3+ / Tm3+ co-doped in ZBYA glasses in the range λ~ 200-3200 nm.
7 8
The relevant spectral parameters of the Dy3+/Tm3+ co-doped ZBYA glass can be calculated from
9
the Judd-Ofelt (J-O) theory [33]. The J-O intensity parameters Ωt (t=2, 4, 6) are commonly used to
10
analyze the symmetry of the glass matrix, the covalency of the rare earth ions and the anion bonds
11
[34]. Generally, Ω2 is determined by the glass matrix structure (such as symmetry around the
12
ligand and order) and is proportional to the covalency between the coordination anions and rare
13
earth ions. The larger is Ω2, the lower is the symmetry around the rare earth ion and the higher is
14
covalency. Ω2 of ZBYA is small, similar to that of the ZBLAN and fluoroaluminate glasses, but
15
smaller than that of chalcohalide and tellurite glasses, indicating that the sample has high
16
symmetry and strong ionicity of the coordination field in the environment. While both Ω4 and Ω6
1
are related to the local basicity of the ligands in the glass. Ω6 is mainly affected by the overlap of
2
the 4f and 5d orbitals of the rare earth ions, and its value increases for increasing densities. As Ω6
3
is high, the emission bandwidth of rare earth ions and the probability of spontaneous radiation
4
increases [35]. Table 1 shows the Judd-Ofelt intensity parameters Ωt (t=2, 4, 6) in various glass
5
hosts.
6
Table 1. Calculated J-O intensity parameters Ωt (t=2, 4, 6) of Dy3+ in various glass hosts. Ωt (10-20 cm2)
Ω2
Ω4
Ω6
Fluoroaluminate[36]
2.7
0.86
1.89
ZBLAN[37]
3.29
1.56
2.48
Chalcohalide[38]
11.82
3.35
1.56
Tellurite[39]
6.85
1.75
1.75
ZBYA(this work)
3.13
0.33
0.43
7 8
Table 2 lists the spontaneous radiation transitions probability (A), fluorescence branching ratio (β)
9
and radiative lifetime (τrad) for Dy3+ energy level transitions in the ZBYA glass sample. As
10
expected, the spontaneous-emission probabilities for the Dy3+: 6H13/2 → 6H15/2 transition is 17.59
11
s-1, which is lower than that recorded in ZBLA (19.5 s-1) [40] and ZBLAY (45.92 s-1) [41].
12
Generally, higher spontaneous-emission probability provides a better opportunity to obtain lasing
13
[42]. The lifetime of the Dy3+: 6H13/2 energy level in ZBYA glass is calculated to be as long as 56.8
14
ms, favorable for achieving efficient 2.9 µm lasing.
15
Table 2. Radiative parameters for various selected excited levels of Dy3+ in ZBYA glass
Transition
Wavelength(nm)
A (s-1)
β (%)
τrad (ms)
6
1325
20.1
85.24
42.4
→ 6H13/2
2390
3.2
13.57
→ 6H11/2
5410
0.28
1.18
6
1760
44.3
94.1
→ 6H13/2
4290
2.8
5.9
6
2864
17.59
100
H9/2+6F11/2 → 6H15/2
H11/2 → 6H15/2
H13/2 → 6H15/2
21.2
56.8
1 2
Assuming that the time to establish thermal equilibrium in the energy level multi-configuration is
3
less than its radiation lifetime, according to the McCumber theory [43], the relationship between
4
the absorption cross section σabs and the emission cross section σemi is:
5
(2)
6
where h, ν, K, and T represent the Planck constant, photon frequency, Boltzmann constant, and
7
room temperature, respectively. ε is the temperature-dependent excitation energy whose value is
8
equal to the energy corresponding to the peak frequency of the absorption spectrum.
9
The absorption cross section can be calculated directly from the measured absorption spectrum:
10
(3)
11
where N is the concentration of rare earth ions, d is the optical path - e.g. the thickness of the
12
sample - and D(λ) is the optical density, which is derived from the absorption spectrum.
13
The emission cross section σemi and the absorption cross section σabs of the Dy3+: 6H13/2 → 6H15/2
14
transition in the 1 mol% Dy3+/1 mol% Tm3+ co-doped sample is presented in Fig. 3(a). The peak
1
value of σemi at λ~2.9 µm is 3.79 10-21 cm2, similar to that in fluoroaluminate glass (~3.96 10-21
2
cm2) [44], while lower than that in ZBLAY (~1.17 10-20 cm2) [41] and tellurite glasses
3
(~2.82 10-20 cm2) [45].
4
The gain cross-section G(λ) as function of the wavelength was calculated from:
5
(4)
6
where P is population inversion parameter, which is related to the concentration ratio of Dy3+ in
7
the 6H11/2 and 6H13/2 level. The gain coefficients with various P ranging from 0 to 1 are presented
8
in Fig.3 (b), and positive gain can be obtained in the range of λ~2800-3000 nm when P>0.4.
9 10 11 12
Fig. 3 (a) Absorption cross-section and emission cross section of 6H13/2 → 6H15/2 transition in 1 mol% Dy3+/1 mol% Tm3+ co-doped sample; (b) Gain coefficient spectra for the 6H13/2 → 6H15/2 transition in the 1 mol% Dy3+/1 mol% Tm3+ co-doped sample.
13 14
The Near-IR fluorescence spectra of Dy3+/Tm3+ co-doped ZBYA glasses in the range λ~1150-1350
15
nm is given in Fig. 4. The fluorescence peak at λ~1260 nm corresponds to the transition of Tm3+:
16
3
17
nm decreases as the concentration of Dy3+ increases or the concentration of Tm3+ decreases. Since
18
the lifetime of the Tm3+: 3H5 level is far shorter than that of the 3H4 level, the energy transfer rate
H5 → 3H6. When the Tm3+ concentration is fixed at 1 mol%, the fluorescence intensity at λ~1260
1
from Tm3+: 3H5 to other levels of Dy3+ ions is extremely small [46]. Therefore, the decrease in the
2
population on 3H5 is mainly due the energy transfer processes from the 3H4 metastable level of
3
Tm3+ to other levels of Dy3+, leading to the depopulation of 3H5.
4 5 6
Fig. 4 Near-infrared fluorescence spectra at λ~1260 nm of the Dy3+/Tm3+-doped ZBYA glasses excited at λ~808 nm when the pump power is set to 1.6 W.
7 8
Fig. 5 shows the strong emissions near λ~1470 nm and λ~1800 nm, which are attributed to the
9
radiative transitions of Tm3+: 3H4 → 3F4 and 3H5 → 3H6, respectively. For fixed Tm3+ doping
10
concentration, the fluorescence intensity at λ~1470 nm and λ~1800 nm gradually decreases as the
11
concentration of Dy3+ increases, which can explain the existence of energy transfer between Tm3+:
12
3
13
When the Dy3+ doping concentration is maintained at 1 mol% and the concentration of Tm3+ ions
14
increases, the emission intensity at λ~1470 nm and λ~1800 nm increases, while when the
15
concentration of Tm3+ is 2 mol%, the emission intensity of λ~1470 nm shows a weakening trend.
16
This is most likely due to the well-known cross relaxation and migration processes of Tm3+
17
(3H4+3H5→2•3F4), which becomes obvious the evident as the concentration of Tm3+ ions
18
increasing [47]. These processes reduce the number of electrons on the Tm3+: 3H4 energy level,
H4 → Dy3+: 6F5/2, Tm3+: 3F4 → Dy3+: 6H11/2, due to their similar energy levels.
1
2 3 4
and lead to the weakening of the λ~1470 nm fluorescence.
Fig.5 Near-infrared fluorescence spectra at λ~1470 nm and λ~1800 nm of the Dy3+/Tm3+-doped ZBYA glasses excited at λ~808 nm when the pump power is set to 1.6 W.
5 6
Fig. 6 shows the fluorescence spectra at λ~2.9 µm, attributed to the Dy3+: 6H13/2 → 6H15/2
7
transition. At the fixed Tm3+ concentration of 1 mol%, the fluorescence intensity increases with
8
increasing Dy3+ doping content from 0.2 to 3 mol% (Fig. 6(a)), thus indicating an efficient energy
9
transfer between the Tm3+: 3F4 and Dy3+: 6H13/2 levels. When the Dy3+ doping concentration is
10
fixed, the same effect occurs as the Tm3+ concentration increases (Fig. 6(b)). The introduction of
11
Tm3+ ions increases the absorption rate of Dy3+ ions and also improves the pumping absorption
12
efficiency, thereby effectively increasing the fluorescence intensity at λ~2.9 µm.
13
1 2
Fig.6 Luminescence spectra of Dy3+ ions at the λ~2.9 µm wavelength in different doping concentrations of the Dy3+/Tm3+-doped ZBYA glasses excited at λ~808 nm when the pump power is set to 1.6 W.
3 4
Fig. 7 shows the energy transfer processes between Tm3+ and Dy3+. Under λ~808 nm laser
5
pumping, the electrons of the Tm3+:3H6 ground state are excited to the 3H4 excited state, and then
6
transition radiatively to the
7
Simultaneously, the minority of Tm3+ ions in the 3H4 level relax to the 3H5 level through
8
multi-phonon relaxation (MPR), and then jump to the 3H6 level to produce λ~1.26 µm
9
near-infrared emission. The electrons of the Dy3+: 6H13/2 level accumulate due to multi-phonon
10
relaxation (MPR) of the upper level, then transition to the ground state 6H15/2, resulting in the
11
λ~2.9 µm mid-infrared emission. The electron in the excited state 3F4 level returns to the ground
12
state, producing the λ~1.8 µm emission. The energy transfers (ET) Tm3+: 3H4 → Dy3+: 6F5/2, Tm3+:
13
3
14
depopulated by the well-known cross relaxation (CR) 3H6 + 3H4 → 3F4 + 3F4. After the Tm3+: 3F4
15
level is populated, electrons of the Tm3+: 3F4 level can be transferred to the Dy3+: 6H11/2 level. In
16
this paper, the change of infrared fluorescence spectra also confirmed the existence of these
17
energy transfer processes.
18
3
F4 level, resulting in a λ~1.47 µm near-infrared emission.
F4 → Dy3+: 6H11/2 are signed as ET1, ET2, respectively. Besides, the Tm3+: 3H4 level can be
1
Fig. 7. Energy transfer processes between Tm3+ and Dy3+ ions in ZBYA glasses.
2 3
Conclusion
4
In conclusion, we investigated the λ~2.9 µm emission and energy transfer mechanism of
5
Dy3+/Tm3+ co-doped ZBYA glasses. Combined with the measured fluorescence spectra at
6
λ~1260 nm, λ~1470 nm, λ~1.8 µm and λ~2.9 µm, the energy transfer processes between Dy3+
7
and Tm3+ ions are analyzed in detail. The strong λ~2.9 µm mid-infrared emission from the
8
Dy3+/Tm3+ co-doped ZBYA glasses was ascribed to the occurrence of the energy transfer process
9
of Tm3+: 3F4 → Dy3+: 6H11/2. Our results show that Dy3+/Tm3+ co-doped ZBYA glass is a
10
potential gain medium for λ~2.9 µm laser application, it lays the foundation for our future
11
preparation of ZBYA glass fiber mid-infrared laser.
12 13
Acknowledgments:
14
This work was supported by the National Natural Science Foundation of China (NSFC) under
15
grant 61575050; National Key R&D Program of China under grant 2016YFE0126500; The
16
fundamental research funds for the central universities (HEUCFG201841); Key Program for
17
Natural Science Foundation of Heilongjiang Province of China under grant ZD2016012; Open
18
Fund of the State Key Laboratory on Integrated Optoelectronics (IOSKL2016KF03); this work
19
was also supported by the 111 project (B13015) to the Harbin Engineering University.
20
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Investigation of Dy3+/Tm3+ co-doped ZrF4-BaF2 -YF3 -AlF3 fluoride glass for efficient 2.9 µm mid-infrared laser applications
Haiyan Zhao 1, Shijie Jia 1, Xin Wang 1, Ruicong Wang 1 , Xiaosong Lu 1, Yaxian Fan 2 , Masaki Tokurakawa 3, Gilberto Brambilla 4, Shunbin Wang 1,*, and Pengfei Wang 1,5,* 1Key Laboratory of In-fiber Integrated Optics of Ministry of Education, College of Science, Harbin Engineering University, Harbin 150001, China 2Academy of Marine Information Technology, Guilin University of Electronic Technology, Beihai, 536000, China 3Institute for Laser Science, University of Electro-Communications, Chofugaoka Chofu Tokyo 182-8585, Japan 4Optoelectronics Research Centre, University of Southampton, Southampton SO17 1BJ, United Kingdom 5Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen, 518060, China *[email protected] *[email protected]
Keywords: ZBYA fluoride glass, mid-infrared laser, Dy3+/Tm3+ co-doped
Energy transfer processes between Dy3+ and Tm3+ ions in ZrF4-BaF2-YF3-AlF3 (ZBYA) fluoride glass samples were investigated in details. The transmittance of ZBYA glass at λ~1000-6000 nm is as high as 90%, with an infrared cutoff wavelength at around λ~9000 nm. αOH- in the ZBYA sample is as low as ~0.0098 cm-1, which is ascribed to the chemical dehydrating process (F-+OH-→O2-+HF ↑) and longtime physical dehydrating process in ultra-dry pure nitrogen atmosphere. The introduction of Tm3+ ions improve the mid-infrared emission intensity of Dy3+ ions in ZBYA glass, which is ascribed to the energy transfer process of Tm3+: 3F4 → Dy3+:6H11/2. This results can be applied in mid-infrared laser.
Declaration of interests
√The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: