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Er3+- and Pr3+-doped Ga-Sb-S chalcogenide glasses were prepared by the traditional melt-quenching method, and their optical properties in the infrared range were investigated. In order to enhance the mid infrared emissions at 2740 nm of Er3+, Pr3+ was introduced into the glass system. Under 808 nm excitation, the emission of 2740 nm was significantly enhanced in the co-doped sample while the emission of 1550 nm was oppositely reduced. Fluorescence decay results indicated that the lifetime of Er3+: 4I13/2 at 1550 nm was evidently decreased in the co-doped sample. The mechanism of the energy transfer process between Er3+ and Pr3+ ions were investigated in this work.
© 2016 Optical Society of America
1. Introduction
Laser operating in the mid-infrared region has attracted considerable attention for applications, such as in medicine, eye-safe laser radar and chemical sensing, remote sensing, medical surgery, and military counter measures, et al. [1–3]. Mid-infrared emission can be obtained from several active rare-earth (RE) ions dispersed in crystalloid or glass [4, 5]. Compared to the crystals, glass is easier to synthesize and shape. Thus, an efficient and low cost fabrication method for them can be achieved.
Recent reports about rare earth doped luminescent material at mid-infrared region have mainly focused on chalcogenide glasses due to their lower phonon energy and lower optical attenuation at infrared region than oxyfluorotellurite glasses. In addition, the chalcogenide glasses exhibit superior thermal stability and have the ability to operate at high power. These characteristics are preferable advantages for the production of infrared laser materials [6, 7]. Reisfeld et al. [8] reported different types of RE ion-doped spectra of Ga-La-S and Al-La-S chalcogenide glass in 1982, and confirmed the feasibility of infrared emission from chalcogenide glasses. Then, photoluminescence (PL) emission in the mid-infrared region from RE ions embedded in chalcogenide glasses has been extensively investigated [9–12]. However, the RE ions are easy to be gathered in chalcogenide glass matrix leading to the energy quenching effect. The lower solution of RE ions exhibits the lower efficiency of infrared emission which limited their applications in the infrared optics. Researchers have focused large effort on the growing of the infrared emission efficiency. Among them, some of these chalcogenide glasses for host media like Ge-Ga-S, Ga-Ga-Sb-S, Ge-As-S, and Ga-La-S glass systems are preferred, because the addition of Ga into chalcogenide glassy networks can improve the solubility of RE3+ ions to promote the formation of Ga-tetrahedral clusters [13–15]. This process provides a comprehensive atomistic structural model for RE-doped chalcogenide glasses. Furthermore, an appropriate amount of Ga can also enhance the chemical and thermal stability of the glasses [16–18].
Previously, Barnier [19] first reported the Ga-Sb-S chalcogenide glasses in 1993 and discussed the glass formation region and quasi-binary phase diagram of Ga2S3-Sb2S3. Compared with most chalcogenide glass systems based on Ge- or As-containing glass formers, the component of the Ga-Sb-S glass by Barnier contains large-scale Ga element with aforementioned advantages. Ga-Sb-S glass can be synthesized by conventional vacuum melt-quenching method. Recently, Zhang et al. [20] reported that the mid-infrared emission from Dy3+-doped Ga-Sb-S chalcogenide glasses exhibited a much lower phonon energy than that in most Ge- and As- based chalcogenide glasses [21]. However, it is still a challenge for chalcogenide glasses to be developed in practice because the infrared emission efficiency cannot meet the demand of device application. Another way to improve the luminescence intensity usually observed in oxide glasses is adjusting the energy transition between rare earth ions, which can be realized in chalcogenide glasses. In this article, Er3+ ion was introduced as dopant for mid-infrared generation, because its appropriate absorption peak matches well the emission waveband of the present available low-cost high-power diode laser operating near 808 nm [22]. Herein, co-doping with other different rare earth Pr3+ ions was employed to investigate the mid-infrared emission properties of Er3+ in Ga-riched Ga-Sb-S chalcogenide glass systems. The present work is important to explore the feasibility of implementing mid-infrared lasers with chalcogenide glass.
2. Experiment
Glass samples with different compositions (mol%) of Ga8Sb32S60-Erx-Pry (x = 0, 0.2; y = 0. 0.1) were prepared by a conventional melt-quenching technique. First, high-purity elements of Ga (99.9999%), Sb (99.9999%), S (99.9999%), and Er (99.99%) were weighed in a glove box filled with nitrogen and then loaded into a pre-cleaned quartz ampoule (12 mm inner diameter). Then, the elements were melted in a vacuum quartz tube at 950 °C for 15 h and annealed at 230 °C for 24 h. Finally, the formed samples were cut and optically polished to 2 mm thickness for spectroscopic measurements.
The thermal properties were determined using a TA Q2000 differential scanning calorimeter (DSC) equipped with an intercooler and thermal gravity (TG) at a heating rate of 10 °C/min. A piece of glass with typical weight about 10 mg was sealed into an aluminum pan for the measurement. The error of the characteristic temperatures was about ± 1°C. X-ray diffraction (XRD) measurements of powder sample were performed on a Germany Bruker D2 diffractometer. The diffraction patterns were scanned over the 2θ range 10–70° with a 0.1° step. The optical absorption spectra of the polished glass discs were recorded using an American PerkinElmer Lambda 950 spectrophotometer in the spectral range of 750–2300 nm. PL in the infrared region was measured using an FLS 980 fluorescence spectrometer with liquid-nitrogen-cooled InSb detector. A continuous wave diode laser operating at wavelength of 808 nm and power of 0.5 W was used as excitation source. Decay curves were measured using a digital oscilloscope with an electronic chopper at excitation of 808 nm. Lifetime was determined and calculated from the 1/e decay time of the fitted decay curves. All measurements were performed at room temperature.
3. Results and discussion
3.1 XRD and DSC measurement
The homogeneity of prepared glasses can be confirmed by XRD pattern and DSC curves. As can be seen, the samples have approximately single-phase composition, and the absence of sharp peaks confirm the amorphous nature of the materials formed in Fig. 1. This result indicated that the prepared samples presented on the uniform glassy state with no obvious crystallization. However, the small halos at the low diffraction angle in the diffractograms of the bulk materials are due to the polymeric nature of the materials, corresponding to S related polymeric rings. The size of this halo is affected by factors such as the preparation technique, mixing in the bulk material, etc.
Figure 2 exhibited the DSC measurement of rear earth ions doped glasses, and the glass transition temperature Tg and crystallization temperature Tx determined from the DSC curves are presented in Table 1. It can be clearly seen that no obvious exothermic peak was observed in the curves between Tg and Tx. It indicated that the relative homogeneous glassy materials without obvious phase separation are obtained in our work. The ΔT ( = Tx–Tg) is about 110 °C, indicating that they have good thermal stability for optical applications.
Table 1. Characteristic temperatures of the rare-earth-doped Ga–Sb–S glasses
3.2 Absorption spectroscopy
Figure 3 shows the absorption spectra of the glass samples single- or co-doped with Er3+and Pr3+ at room temperature from 750 nm to 2300 nm. The absorption bands are assigned as excited states of Er3+ and Pr3+ ions on the basis of their energy level distributions [23]. Absorption transition of the Er3+-doped glass sample are centered at 808, 980, and 1550 nm. By contrast, the Pr3+-doped sample exhibits absorption transition centered at 1500, 1600, and 2050 nm. It is noted that absorption band superposition occurred during the co-doping of Er3+ and Pr3+ ion in the glass. These absorption bands are assigned to the transitions from the Er3+:4I15/2 and Pr3+:3H4 ground state to the excited states of Er3+ and Pr3+.
According to the above absorption spectra, the cross section of the ground state absorption can be determined from the Er3+-and Pr3+- doped glass samples using the following relation [24]:
where lg(I0 / I) is the absorbance, L is the thickness of the glass sample (cm), and N is the RE concentration per cubic centimeter in the glass. The maximum absorption cross sections of Er3+: 4I11/2 and 4I13/2 are 0.57 × 10−20 and 1.5 × 10−20 cm2 at 987 and 1540 nm. The maximum absorption cross-sections of Pr3+ corresponding to 1G4, 3F4, and 3F3 are calculated as 0.14 × 10−20, 2.2 × 10−20, and 4.1 × 10−20 cm2 at 1030, 1488, and 1600 nm. The full absorption cross-sections curves near the main spectra at 980 and 1550 nm of Er3+ and Pr3+ dopants in the Ga-Sb-S chalcogenide glass are shown in Fig. 4. The absorption cross sections of Er3+ and Pr3+ remarkably overlapped around 1550 nm. The energy transfer theory developed by Föster–Dexter indicates that the energy transfer rate for the dipole–dipole interaction mechanism is relevant to the overlapping of the cross sections [25, 26]. The possible energy transfer process between Er3+ and Pr3+ may occur.3.3 Fluorescence spectra and lifetime
The infrared PL spectra of Er3+-doped and Er3+/Pr3+-doped Ga-Sb-S chalcogenide glasses are measured under 808 nm laser excitation, and the results are shown in Fig. 5. Three emission bands in the Er3+-doped glass were centered at 1550, 1710, and 2740 nm. These emissions can be attributed to the transitions of Er3+: 4I13/2-4I15/2, Er3+: 4I9/2-4I13/2, and 4I11/2-4I13/2, respectively. Apparently, not any relevant infrared emissions are observed in Pr3+ -doped glass. The changes that co-doping with Pr3+ ions resulted in the significant reduction in emission intensity of 1550 nm, while the intensity of the 2740 nm emission was significantly enhanced with the addition of Pr3+ ions. The emission centered at 1710 nm was almost unchanged before and after co-doping conditions, which means different energy transitions occurred. Figure 6 presents the energy level schemes of Er3+ and Pr3+ in the Ga-Sb-S chalcogenide glass [27, 28]. As excited by the 808 nm laser source, RE ions of Er3+ on the ground state can be excited to the upper energy state of 4I9/2 and back to the ground state through different transitions. With these different energy transitions, the emissions at 1550, 1710, and 2740 nm are formed. Meanwhile, the ET1 and ET2 energy process were the possible transitions and interaction in the co-doped sample. ET1 represents the energy transfer process from Er3+: 4I11/2 to Pr3+: 1G4 (Er3+: 4I11/2 + Pr3+: 3H4 = Er3+: 4I15/2 + Pr3+: 1G4), whereas ET2 is the energy transfer from Er3+: 4I13/2 to Pr3+: 1G4 (Er3+: 4I13/2 + Pr3+: 3H4 = Er3+: 4I15/2 + Pr3+: 3F3, 4). Both energy transitions occurred in the same process when excited by 808 nm laser excitation, of which similar transitions has been found in germanate glasses [29]. However, ET2 was much more efficient than ET1, because the oscillator strength of the former energy transfer was extremely larger than the latter, which can also be defined by the bigger absorption cross-section in Fig. 4. The theory of energy transfer rate developed by Föster–Dexter [30, 31] shows that the energy transfer rate is proportional to the oscillator strength and spectral overlap. Therefore, Pr3+ ions could efficiently quench Er3+: 4I13/2 level by energy transfer and enhance 2740 nm emission.
Fig. 5 Mid-infrared emission spectra from Er3+- and Er3+/Pr3+-doped Ga-Sb-S chalcogenide glasses excited at 808 nm
The energy transfer mechanism between Er3+ and Pr3+ was analyzed in combination with fluorescence decays spectra in Fig. 7. The emission decay curves for 4I13/2-4I15/2 transition in the Er3+-doped and Er3+/Pr3+-doped Ga-Sb-S chalcogenide glass were measured under pulsed 808 nm excitation. The fluorescence decay data for these glass samples were fitted to a single-exponential function. The decay time of Er3+: 4I13/2 level decreased from 2.19 ms to 0.85 ms after Pr3+ was co-doped in the glass. The efficiency of energy transfer process was calculated using the lifetime values with the following equation [32, 33]:
Fig. 7 Fluorescence decays for 4I13/2-4I15/2 transition of Er3+- and Er3+/Pr3+-doped samples at 808 nm laser excitation.
where τEr and τEr/Pr are the lifetimes of Er3+: 4I13/2 level measured at 1550 nm in Er3+-doped and Er3+/Pr3+-doped sampples, respectively. The value of ηET reached 71% for Er3+/Pr3+ -doped Ga-Sb-S chalcogenide glass. This result suggests that Pr3+ ions can be used effectively to depopulate Er3+: 4I13/2. The quenched Er3+: 4I13/2 lifetime also identified the energy transfer process from Er3+: 4I13/2 to Pr3+:3F4 and 3F3 [34].
The experimental and analytical results reveal that Pr3+ can enhance the 2740 nm emission of Er3+ ions by energy transfer from Er3+: 4I13/2 to Pr3+: 3F3,4 in the co-doped glass sample. Meanwhile, the 1550 nm emission was oppositely quenched in this energy transfer process. The phenomenon has been reported in oxide and fluoride glasses, but detailed explanation has not been provided [29, 35]. In general, the active ions are the acceptor ions, whereas the sensitizing ions are donors. Sensitizing ions usually have large absorption cross sections, making them acquire laser energy effectively. Then the emissions from active ions were enhanced by the energy transfer from sensitizer ions. However, in the Er3+/Pr3+ co-doped system, Pr3+ did not contribute for the Er3+ ions emission by raising the absorption efficiency of laser energy, but largely depopulated the energy level of Er3+: 4I13/2 by the energy transfer process ET2. Then the population inversion was realized in the energy level of Er3+: 4I11/2 and the appreciable reabsorption by 4I13/2 energy level corresponding to 2740 nm was weakened when the glass was co-doped with Pr3+ ions, subsequently explaining the enhancement of emission at 2740 nm.
4. Conclusions
The infrared emission from Er3+-doped and Er3+/Pr3+ co-doped Ga-Sb-S glasses pumped with a 808 nm laser diode were studied. It is found that Pr3+ addition can greatly enhance the mid-infrared emission at 2740 nm of Er3+ ions in the co-doped sample, which is ascribed to the energy transfer between Pr3+ and Er3+ ions and shortening lifetime of lower lasing level Er3+: 4I13/2 state with the addition of Pr3+ ions. The fast quenching emission at 1550 nm can be dominated by the more effective energy transfer process of ET2 than ET1. Importantly, the calculated energy transfer efficiency was determined to be approximately 71%, which provides a feasibility to improve the weak mid-infrared emission in chalcogenide glasses. The excellent properties imply that Er3+/Pr3+ co-doped Ga-Sb-S chalcogenide glass can be a candidate as an efficient gain media in the 2740 nm glass fiber laser system.
Funding
Natural National Science Foundation of China (NSFC) (61605093); Ningbo Natural Science Foundation (NNSF) (No. 2015A610079); Open Foundation of State Key Laboratory of Infrared Physics (Grant No. M201510); Magna Fund sponsored by K. C. Wong in Ningbo University.
Acknowledgments
The authors thank the relevant measurements by Key Laboratory of Advanced Materials of Yunnan Province.
References and links
1. F. K. Tittel, D. Richter, and A. Fried, “Mid-infrared laser applications in spectroscopy, ” in Solid-State Mid-Infrared Laser Sources, Dr. Claus, E. Ascheron. (Springer, 2003).
2. P. Werle, F. Slemr, K. Maurer, R. Kormann, R. Mücke, and B. Jänker, “Near- and mid-infrared laser-optical sensors for gas analysis,” Opt. Lasers Eng. 37(2–3), 101–114 (2002). [CrossRef]
3. R. Kaufmann, A. Hartmann, and R. Hibst, “Cutting and skin-ablative properties of pulsed mid-infrared laser surgery,” J. Dermatol. Surg. Oncol. 20(2), 112–118 (1994). [CrossRef] [PubMed]
4. A. B. Seddon, Z. Tang, D. Furniss, S. Sujecki, and T. M. Benson, “Progress in rare-earth-doped mid-infrared fiber lasers,” Opt. Express 18(25), 26704–26719 (2010). [CrossRef] [PubMed]
5. I. T. Sorokina and K. L. Vodopyanov, Solid-state Mid-Infrared Laser Sources (Springer Science & Business Media, 2003).
6. H. Guo, L. U. Min, G. Tao, L. Feng, and B. Peng, “Research progress of rare earth ions doped chalcogenide glasses for mid-infrared luminescence,” J. Chin. Ceram. Soc. 37(12), 2151–2156 (2009).
7. Ł. Sójka, Z. Tang, H. Zhu, E. Bereś-Pawlik, D. Furniss, A. B. Seddon, T. M. Benson, and S. Sujecki, “Study of mid-infrared laser action in chalcogenide rare earth doped glass with Dy3+, Pr3+and Tb3+,” Opt. Mater. Express 2(11), 1632–1640 (2012). [CrossRef]
8. R. Reisfeld, “Chalcogenide glasses doped by rare-earths-structure and optical-properties,” in Annales de chimie-science des materiaux, (masson editeur, 1982).
9. S. Dai, B. Peng, X. Wang, X. Shen, Q. Nie, and T. Xu, “Research development of chalcogenide glass materials emitting 3–5 m fluorescence,” Guangzi Xuebao 37(SUPPL), 239–243 (2008).
10. Ł. Sojka, Z. Tang, H. Sakr, D. Furniss, T. Benson, A. Seddon, E. Barney, E. Beres–Pawlik, and S. Sujecki, “Spectroscopy of mid-infrared (4.8µm) photoluminescence in Tb3+ doped chalcogenide glass and fibre,” in 2015 17th International Conference on Transparent Optical Networks (ICTON), (IEEE, 2015), pp. 1–3.
11. Z. Tang, D. Furniss, M. Fay, H. Sakr, L. Sójka, N. Neate, N. Weston, S. Sujecki, T. M. Benson, and A. B. Seddon, “Mid-infrared photoluminescence in small-core fiber of praseodymium-ion doped selenide-based chalcogenide glass,” Opt. Mater. Express 5(4), 870–886 (2015). [CrossRef]
12. T. H. Lee, S. I. Simdyankin, J. Hegedus, J. Heo, and S. R. Elliott, “Spatial distribution of rare-earth ions and GaS4 tetrahedra in chalcogenide glasses studied via laser spectroscopy and ab initio molecular dynamics simulation,” Phys. Rev. B 81(10), 104204 (2010). [CrossRef]
13. J. Heo, J. M. Yoon, and S. Y. Ryou, “Raman Spectroscopic Analysis on the Solubility Mechanism of La3+ in GeS2–Ga2S3 Glasses,” J. Non-Cryst. Solids 238(1-2), 115–123 (1998). [CrossRef]
14. R. Golovchak, Y. Shpotyuk, V. Nazabal, C. Boussard-Pledel, B. Bureau, J. Cebulski, and H. Jain, “Study of Ga incorporation in glassy arsenic selenides by high-resolution XPS and EXAFS,” J. Chem. Phys. 142(18), 184501 (2015). [CrossRef] [PubMed]
15. M. E. Pollard, K. J. Knight, G. J. Parker, D. W. Hewak, and M. D. B. Charlton, “Fabrication of photonic crystals in rare earth doped chalcogenide glass films for enhanced upconversion,” Proc. SPIE 8257, 223–239 (2012). [CrossRef]
16. A. Yang, M. Zhang, L. Lei, Y. Wang, B. Zhang, Z. Yang, and D. Tang, “Ga–Sb–S Chalcogenide Glasses for Mid–Infrared Applications,” J. Am. Ceram. Soc. 99(1), 12–15 (2016). [CrossRef]
17. H. Guo, X. Zheng, X. Zhao, G. Gao, Y. Gong, and S. Gu, “Composition dependence of thermally induced second-harmonic generation in chalcohalide glasses,” J. Mater. Sci. 42(16), 6549–6554 (2007). [CrossRef]
18. S. Barnier, M. Guittard, C. Julien, and A. Chilouet, “Etude de l’environnement de l’antimoine dans les verres gallium-antimoine-soufre en liaison avec le diagramme de Phase et les spectres d’absorption infrarouge,” Mater. Res. Bull. 28(5), 399–405 (1993). [CrossRef]
19. M. Zhang, A. Yang, Y. Peng, B. Zhang, H. Ren, W. Guo, Y. Yang, C. Zhai, Y. Wang, Z. Yang, and D. Tang, “Dy3+ -doped Ga–Sb–S chalcogenide glasses for mid-infrared lasers,” Mater. Res. Bull. 70, 55–59 (2015). [CrossRef]
20. G. Li, T. Xu, S. Dai, T. Zhang, Q. Zhang, and Q. Jiao, “Optical Properties and Thermal Stability of Infrared Chalcogenide Glass Ga2S3–Sb2S3,” J. Chin. Ceram. Soc. 44(6), 832–837 (2016).
21. T. Wei, Y. Tian, F. Chen, M. Cai, J. Zhang, X. Jing, F. Wang, Q. Zhang, and S. Xu, “Mid-infrared fluorescence, energy transfer process and rate equation analysis in Er3+ doped germanate glass,” Sci. Rep. 4(25), 6060 (2014). [CrossRef] [PubMed]
22. S. L. Kang, D. D. Chen, Q. W. Pan, J. R. Qiu, and G. P. Dong, “2.7 μm emission in Er3+–doped transparent tellurite glass ceramics,” Opt. Mater. Express 6(6), 1861–1870 (2016). [CrossRef]
23. W. T. Carnall, P. R. Fields, and K. Rajnak, “Electronic Energy Levels in the Trivalent Lanthanide Aquo Ions. I. Pr3+, Nd3+, Pm3+, Sm3+, Dy3+, Ho3+, Er3+, and Tm3+,” J. Chem. Phys. 49(10), 4424–4442 (1968). [CrossRef]
24. D. E. McCumber, “Theory of Phonon Terminated Optical Masers,” Phys. Rev. 134(2A), A299–A306 (1964). [CrossRef]
25. D. F. D. Sousa, J. A. Sampaio, L. A. O. Nunes, M. L. Baesso, A. C. Bento, and L. C. M. Miranda, “Energy transfer and the 2.8 μm emission of Er3+- and Yb3+-doped low silica content calcium aluminate glasses,” Phys. Rev. B 62(5), 3176–3180 (2000). [CrossRef]
26. E. Pecoraro, D. F. D. Sousa, R. Lebullenger, A. C. Hernandes, and L. A. O. Nunes, “Evaluation of the energy transfer rate for the Yb3+: Pr3+ system in lead fluoroindogallate glasses,” J. Appl. Phys. 86(6), 3144–3148 (1999). [CrossRef]
27. S. H. Park, D. C. Lee, J. Heo, and D. W. Shin, “Energy transfer between Er3+ and Pr3+ in chalcogenide glasses for dual-wavelength fiber-optic amplifiers,” J. Appl. Phys. 91(11), 9072–9077 (2002). [CrossRef]
28. V. Moizan, V. Nazabal, J. Troles, P. Houizot, J. L. Adam, J. L. Doualan, R. Moncorgé, F. Smektala, G. Gadret, S. Pitois, and G. Canat, “Er3+ -doped gegasbs glasses for mid-IR fibre laser application: synthesis and rare earth spectroscopy,” Opt. Mater. 31(1), 39–46 (2008). [CrossRef]
29. X. Li, X. Liu, L. Zhang, L. Hu, and J. Zhang, “Emission enhancement in Er3+/Pr3+-codoped germanate glasses and their use as a 2.7–mm lasermaterial,” Chin. Opt. Lett. 11(12), 121601 (2013). [CrossRef]
30. T. Förster, “Zwischenmolekulare energiewanderung und fluoreszenz,” Ann. Phys–berlin. 437(1-2), 55–75 (1948). [CrossRef]
31. D. L. Dexter, “A theory of sensitized luminescence in solids,” J. Chem. Phys. 21(5), 836–850 (1953). [CrossRef]
32. J. Heo, W. Y. Cho, and W. J. Chung, “Sensitizing effect of Tm3+ on 2.9 μm emission from Dy3+ -doped Ge25Ga5S70 glass,” J. Non-Cryst. Solids 212(s2–3), 151–156 (1997).
33. Y. Tian, R. Xu, L. Hu, and J. Zhang, “2.7 μm fluorescence radiative dynamics and energy transfer between Er3+ and Tm3+ ions in fluoride glass under 800 nm and 980 nm excitation,” J. Quant. Spectrosc. Ra 113(1), 87–95 (2012). [CrossRef]
34. P. S. Golding, S. D. Jackson, T. A. King, and M. Pollnau, “Energy transfer processes in Er3+ -doped and Er3+, Pr3+ -codoped ZBLAN glasses,” Phys. Rev. B 62(2), 856–864 (2000). [CrossRef]
35. G. X. Bai, J. Ding, L. L. Tao, K. F. Li, L. L. Hu, and Y. H. Tsang, “Efficient 2.7 micron emission from Er3+/Pr3+ codoped oxyfluorotellurite glass,” J. Non-Cryst. Solids 358(23), 3403–3406 (2012). [CrossRef]
