Superbroadband near-infrared emission and energy transfer in Pr 3 +-Er 3 + codoped fluorotellurite glasses

We report the first demonstration of superbroadband emission extending from 1.30 to 1.68 μm in praseodymium(Pr)-erbium(Er) codoped fluorotellurite glasses under 488 nm excitation. This superbroad near-infrared emission is contributed by the Pr: D2→G4 and Er: I13/2→I15/2 transitions which lead to emissions located at 1.48 and 1.53 μm, respectively. The quenching of the Pr emission resulted from the cross relaxation [D2, H4]→[G4, F3,4] was effectively compensated by the codoping of Er. The results suggest that, other than the heavy-metal and transition-metal elements of active bismuth (Bi), nickel (Ni), chromium (Cr), etc., Pr-Er codoped system is a promising alternative for the broadband near-infrared emission covering the expanded low-loss window. ©2012 Optical Society of America OCIS codes: (160.5690) Rare-earth-doped materials; (300.6280) Spectroscopy, fluorescence and luminescence; (230.2285) Fiber devices and optical amplifiers. References and links 1. G. A. Thomas, B. I. Shraiman, P. F. Glodis, and M. J. Stephen, “Towards the clarity limit in optical fibre,” Nature 404(6775), 262–264 (2000). 2. S. Kasap, “Optoelectronics” in The Optics Encyclopedia edited by T. Brown, K. Creath, H. Kogelnik, M. A. Kriss, J. Schmit, and M. J. Weber (Wiley-VCH, 2004), vol. 4, pp. 2237–2284. 3. K. Murata, Y. Fujimoto, T. Kanabe, H. Fujita, and M. Nakatsuka, “Bi-doped SiO2 as a new laser material for an intense laser,” Fusion Eng. Des. 44(1–4), 437–439 (1999). 4. M. Peng, J. Qiu, D. Chen, X. Meng, and C. Zhu, “Superbroadband 1310 nm emission from bismuth and tantalum codoped germanium oxide glasses,” Opt. Lett. 30(18), 2433–2435 (2005). 5. I. A. Bufetov and E. M. Dianov, “Bi-doped fiber lasers,” Laser Phys. Lett. 6(7), 487–504 (2009). 6. V. G. Truong, L. Bigot, A. Lerouge, M. Douay, and I. Razdobreev, “Study of thermal stability and luminescence quenching properties of bismuth-doped silicate glasses for fiber laser applications,” Appl. Phys. Lett. 92(4), 041908 (2008). 7. M. Y. Sharonov, A. B. Bykov, V. Petricevic, and R. R. Alfano, “Spectroscopic study of optical centers formed in Bi-, Pb-, Sb-, Sn-, Te-, and In-doped germanate glasses,” Opt. Lett. 33(18), 2131–2133 (2008). 8. T. Suzuki, G. S. Murugan, and Y. Ohishi, “Optical properties of transparent Li2O-Ga2O3-SiO2 glass-ceramics embedding Ni-doped nanocrystals,” Appl. Phys. Lett. 86(13), 131903 (2005). 9. Y. C. Huang, Y. K. Lu, J. C. Chen, Y. C. Hsu, Y. M. Huang, S. L. Huang, and W. H. Cheng, “Broadband emission from Cr-doped fibers fabricated by drawing tower,” Opt. Express 14(19), 8492–8497 (2006). 10. M. Peng, G. Dong, L. Wondraczek, L. Zhang, N. Zhang, and J. Qiu, “Discussion on the origin of NIR emission from Bi-doped materials,” J. Non-Cryst. Solids 357(11–13), 2241–2245 (2011). 11. See, for example, Rare-Earth-Doped Fiber Lasers and Amplifiers (Second Edition, Revised and Expanded) edited by M. J. F. Digonnet (Marcel Dekker, 2009), and references therein. 12. B. Zhou, H. Lin, and E. Y. B. Pun, “Tm-doped tellurite glasses for fiber amplifiers in broadband optical communication at 1.20 μm wavelength region,” Opt. Express 18(18), 18805–18810 (2010). 13. B. Zhou, H. Lin, B. J. Chen, and E. Y. B. Pun, “Superbroadband near-infrared emission in Tm-Bi codoped sodium-germanium-gallate glasses,” Opt. Express 19(7), 6514–6523 (2011). 14. D. R. Simons, A. J. Faber, and H. de Waal, “Pr-doped GeSx-based glasses for fiber amplifiers at 1.3 μm,” Opt. Lett. 20(5), 468–470 (1995). #159575 $15.00 USD Received 9 Dec 2011; revised 23 Mar 2012; accepted 29 Mar 2012; published 14 May 2012 (C) 2012 OSA 21 May 2012 / Vol. 20, No. 11 / OPTICS EXPRESS 12205 15. Y. G. Choi, K. H. Kim, B. J. Park, and J. Heo, “1.6 μm emission from Pr: (F3, F4)→H4 transition in Prand Pr/Er-doped selenide glasses,” Appl. Phys. Lett. 78(19), 1249–1251 (2001). 16. B. Zhou and E. Y. B. Pun, “Superbroadband near-IR emission from praseodymium-doped bismuth gallate glasses,” Opt. Lett. 36(15), 2958–2960 (2011). 17. J. Dong, Y. Q. Wei, A. Wonfor, R. V. Penty, I. H. White, J. Lousteau, G. Jose, and A. Jha, “Dual-pumped tellurite fiber amplifier and tunable laser using Er/Ce codoping scheme,” IEEE Photon. Technol. Lett. 23(11), 736–738 (2011). 18. B. R. Judd, “Optical absorption intensities of rare-earth ions,” Phys. Rev. 127(3), 750–761 (1962). 19. G. S. Ofelt, “Intensities of crystal spectra of rare-earth ions,” J. Chem. Phys. 37(3), 511–520 (1962). 20. R. T. Génova, I. R. Martin, U. R. Rodriguez-Mendoza, F. Lahoz, A. D. Lozano-Gorrin, P. Nunez, J. GonzalezPlatas, and V. Lavin, “Optical intensities of Pr ions in transparent oxyfluoride glass and glass-ceramic. Applications of the standard and modified Judd-Ofelt theories,” J. Alloy. Comp. 380(1–2), 167–172 (2004). 21. L. R. Moorthy, M. Jayasimhadri, A. Radhapathy, and R. V. S. S. N. Ravikumar, “Lasing properties of Pr-doped tellurofluorophosphate glasses,” Mater. Chem. Phys. 93(2–3), 455–460 (2005). 22. V. Nazabal, S. Todoroki, A. Nukui, T. Matsumoto, S. Suehara, T. Hondo, T. Araki, S. Inoue, C. Rivero, and T. Cardinal, “Oxyfluoride tellurite glasses doped by erbium: thermal analysis, structural organization and spectral properties,” J. Non-Cryst. Solids 325(1–3), 85–102 (2003). 23. S. Dai, J. Zhang, C. Yu, G. Zhou, G. Wang, and L. Hu, “Effect of hydroxyl groups on nonradiative decay of Er: I13/2→I15/2 transition in zinc tellurite glasses,” Mater. Lett. 59(18), 2333–2336 (2005). 24. P. S. Golding, S. D. Jackson, T. A. King, and M. Pollnau, “Energy transfer processes in Er-doped and Er, Pr-codoped ZBLAN glasses,” Phys. Rev. B 62(2), 856–864 (2000). 25. S. H. Park, D. C. Lee, J. Heo, and D. W. Shin, “Energy transfer between Er and Pr in chalcogenide glasses for dual-wavelength fiber-optic amplifiers,” J. Appl. Phys. 91(11), 9072–9077 (2002). 26. Y. Ohishi, T. Kanamori, J. Temmyo, M. Wada, M. Yamada, M. Shimizu, K. Yoshino, H. Hanafusa, M. Horiguchi, and S. Takahashi, “Laser diode pumped Pr-doped and Pr-Yb-codoped fluoride fiber amplifiers operating at 1.3 μm,” Electron. Lett. 27(22), 1995–1996 (1991). 27. X. Zhu and R. Jain, “Watt-level Er-doped and Er-Pr-codoped ZBLAN fiber amplifiers at the 2.7-2.8 microm wavelength range,” Opt. Lett. 33(14), 1578–1580 (2008). 28. T. Schweizer, D. W. Hewak, B. N. Samson, and D. N. Payne, “Spectroscopic data of the 1.8-, 2.9-, and 4.3-μm transitions in dysprosium-doped gallium lanthanum sulfide glass,” Opt. Lett. 21(19), 1594–1596 (1996). 29. D. Yang, E. Y. B. Pun, B. Chen, and H. Lin, “Radiative transitions and optical gains in Er/Yb codoped acidresistant ion exchanged germanate glass channel waveguides,” J. Opt. Soc. Am. B 26(2), 357–363 (2009). 30. A. Jha, S. Shen, and M. Naftaly, “Structural origin of spectral broadening of 1.5-μm emission in Er-doped tellurite glass,” Phys. Rev. B 62(10), 6215–6227 (2000).


Introduction
Development of superbroadband near-infrared luminescence sources for broadband optical amplifiers and tunable lasers covering entirely the expanded low-loss telecommunication window (~1.2-1.7 μm) attracts considerable attention, in particular, after the progress made in the production of hydroxyl (OH -)-free silica fibers (dry optical fibers) [1,2].Previous investigations were focused on the bismuth (Bi) [3][4][5][6], and then an extension to other heavy metal (HM) and transition metal (TM) ions, such as nickel (Ni), chromium (Cr), lead (Pb), etc. [7][8][9].However, the bandwidth and peak wavelength of the broadband emissions from HM/TM ions depend sensitively on the host matrix and the excitation wavelength, and also the luminescence origin for some of them requires further studies [10].To date, there has been little work reports on the superbroadband luminescence from rare earth (RE) doped systems, although they play crucial roles as optical amplifiers and laser sources in telecommunication systems [11].Typical RE emissions/amplifications cover only separate C-, L-, S-, E-, and Obands.Thus, novel host matrix, dual-pump configurations, nanostructures, and REs codoping schemes have been investigated to further improve the bandwidth and the quantum efficiency [11].Recently, broadband emissions located at 1.20 and 1.47 μm were observed in thulium (Tm 3+ )-doped glasses [12,13], and a broader emission band from 1.0 to 1.7 μm was obtained using Tm-Bi codoping scheme by taking advantage of the Bi 1.3 μm emission [13].
Praseodymium (Pr 3+ ) shows promising to achieve some novel near-infrared emissions due to the rich multiple energy levels.Apart from the well-known 1.3 μm emission ( 1 G 4 → 3 H 5 transition) [14], an emission around 1.6 μm from the 3 F 3,4 → 3 H 4 transition was also observed in Pr 3+ -doped selenide glass [15].We recently observed superbroadband near-infrared luminescence in Pr 3+ -doped bismuth gallate glass [16].However, the low transmission of bismuth gallate glass in the blue region resulted in a depression of the pump efficiency using blue light, at which Pr 3+ possesses intense absorption bands.In addition, the Pr 3+ near-infrared emission, especially at the longer wavelength side, was seriously quenched by the cross relaxation [ 1 D 2 , 3 H 4 ]→[ 1 G 4 , 3 F 3,4 ] because of the intense ground-state absorption 3 F 3,4 ← 3 H 4 which is overlapped with the Pr 3+ emission.
In the present work, we propose Pr 3+ -Er 3+ codoping scheme to achieve the superbroadband near-infrared emission for the first time to our best knowledge.Efficient Er 3+ 1.53 μm emissions/amplifications have already been demonstrated under 488 nm excitation (into the absorption band Er 3+ : 4 F 7/2 ← 4 I 15/2 ) [11].Fluorotellurite glasses were selected as host because of their broad transmission window, good mechanical properties and chemical durability, and optical amplification and laser operation have been achieved in tellurite glass fibers [17].
The refractive index of the glass samples was measured using a Metricon 2010 prism coupler.The Raman spectrum of undoped glass sample was measured using a HORIBA Jobin Yvon HR800 Raman spectrometer with a 488 nm laser excitation source.The absorption spectra were recorded using a Perkin Elmer UV-VIS-NIR Lambda 19 double beam spectrophotometer.The visible and infrared emission spectra were recorded using an Edinburgh Instruments FLSP920 spectrofluorometer.The wavelengths of excitation sources were tuned from a continuous xenon lamp by a monochromator.The excitation spectra were recorded using the same setup with a continuous wavelength xenon lamp as the excitation source.The emission decay curves were recorded using the same setup with a flash xenon lamp as the excitation source.All the measurements were carried out at room temperature.Figure 1 shows the absorption spectra of Pr 3+ -, Er 3+ -singly doped and Pr 3+ -Er 3+ codoped samples.All the absorption bands observed are due to the electronic transitions from the ground-state to the respective excited states as indicated in Fig. 1.The transparency at the blue wavelength region is much higher than bismuth gallate glass, which would allow efficient pumping with blue light sources.It is interesting to observe that both Pr 3+ and Er 3+ possess absorptions around 488 nm [see inset (a) of Fig. 1]; they correspond to the Pr 3+ : 3 P 0 ← 3 H 4 and Er 3+ : 4 F 7/2 ← 4 I 15/2 transitions, respectively.This resonant energy-level matching makes it possible to achieve the superbroadband emission in the Pr 3+ -Er 3+ codoping scheme by pumping with a single-wavelength light source.This is in agreement with the excitation spectra, as shown in inset (b) of Fig. 1.Using the absorption spectra, Judd-Ofelt analysis was performed [18,19].The values of intensity parameters Ω t (t = 2, 4, 6) are calculated to be (3.57,6.60, 5.18) × 10 −20 cm 2 , and (5.62, 1.12, 1.78) × 10 −20 cm 2 for Pr 3+ -and Er 3+ -singly doped samples, respectively, using a least-squares fitting of the experimental and theoretical electric dipole oscillator strengths.The larger Ω 2 value of Pr 3+ in fluorotellurite than those other fluoride contained oxide glasses indicates a stronger asymmetry and covalent environment of Pr 3+ in fluorotellurite glass [20,21].A similar result is also obtained for Er 3+ -doping, in which the value of Ω 2 is larger than those ZnF 2 contained tellurite glasses [22].The spontaneous transition properties of Pr 3+ and Er 3+ are listed in Table 1.The spontaneous transition probability of Pr 3+ : 1 D 2 → 1 G 4 is 880.1 s -1 (with branch ratio of 11.1%), which is comparable to that of Pr 3+ in bismuth gallate glass [16].Regarding the Er 3+ : 4 I 13/2 → 4 I 15/2 , the spontaneous transition probability (454.1 s -1 ) is larger than that in ZnF 2 contained and oxide-based tellurite glasses [22,23].Fig. 2. Normalized near-infrared emission spectra of Er 3+ -doped and Pr 3+ -Er 3+ codoped samples with respect to the Er 3+ 1.53 μm emission.Inset shows the normalized emission spectra with respect to the Pr 3+ emission at 1.42 μm wavelength.The excitation wavelength is 488 nm.

Results and discussion
Figure 2 compares the near-infrared emissions of Pr 3+ -Er 3+ codoped samples under 488 nm excitation for different Pr 3+ concentrations.Compared with the narrower Er 3+ 1.53 μm emission band (Er 3+ : 4 I 13/2 → 4 I 15/2 transition), the emission in Pr 3+ -Er 3+ codoped samples shows an obvious extension and enhancement in the short wavelength side, resulting in a superbroad emission band at 1.3-1.68μm range.The broad emission at short wavelength region is contributed by the Pr 3+ : 1 D 2 → 1 G 4 transition, which leads to a broad near-infrared emission band under blue excitation.This is in agreement with the Pr 3+ -doped bismuth gallate glass [16].Figure 2 inset shows the normalized emissions of the Pr 3+ -Er 3+ codoped samples with different Er 3+ concentrations.The composite near-infrared emission at the longer wavelength side is enhanced by incorporation of Er 3+ .The emission observed at 1.23 μm is due to the Er 3+ : 4 S 3/2 → 4 I 11/2 transition, which shows a relative increasing trend with the increase of Pr 3+ .

Conclusions
Superbroadband near-infrared emission covering the expanded low-loss telecommunication window was achieved in Pr 3+ -Er 3+ codoped fluorotellurite glasses under 488 nm excitation.Er 3+ is demonstrated to be a good candidate to compensate the quenching of Pr 3+ near-infrared emission resulted from the cross relaxation process [ 1 D 2 , 3 H 4 ]→[ 1 G 4 , 3 F 3,4 ].The results confirm that Pr 3+ -Er 3+ codoped fluorotellurite glass is promising for the superbroadband amplified spontaneous emission sources, optical amplification, and tunable lasers applications.Further investigations and experiments are underway.