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Role of PbO substitution by PbF2 on structural behavior and luminescence of rare earth-doped lead borate glass
Journal of Alloys and Compounds 451 (2008) 220–222
Role of PbO substitution by PbF2 on structural behavior and luminescence of rare earth-doped lead borate glass W.A. Pisarski a,∗ , G. Dominiak-Dzik b , W. Ryba-Romanowski b , J. Pisarska c a
University of Silesia, Institute of Materials Science, Bankowa 12, 40-007 Katowice, Poland b Institute of Low Temperature and Structure Research, Wrocław, Poland c Silesian University of Technology, Department of Materials Science, Katowice, Poland Available online 18 April 2007
Abstract Structural behavior and luminescence properties of rare earth ions (Pr3+ , Eu3+ , Er3+ ) in oxide and oxyfluoride lead borate glasses have been studied using X-ray diffraction and spectroscopic methods. Substitution of PbO by PbF2 results in decreasing of the number of tetrahedral BO4 units, which was observed for Pr3+ and Eu3+ ions in lead borate glasses using infrared spectroscopy. In contrast to oxyfluoride lead borate glasses, several diffraction lines due to crystalline ErBO3 phase were identified for Er-doped oxide sample. Luminescence spectra for rare earth ions in lead borate based glasses have been analyzed, where PbO was totally substituted by PbF2 . © 2007 Elsevier B.V. All rights reserved. Keywords: Lead borate glass; Rare earth ions; Structure; Luminescence
1. Introduction
2. Experimental techniques
Oxide and oxyfluoride lead borate systems doped with rare earth ions belong to heavy metal glass family, which contain unique properties in relation to practical application for photonics and electrochemical devices such as solid-state lasers, optical amplifiers and advanced batteries. Some interesting optical [1–3] and structural [3–5] properties present lead borate glasses containing rare earth ions. Quite large glass-forming region and wide transparency from the UV–vis to the nearinfrared spectral range as well as a large variety of structural groups existing in compositional-dependent lead borate glasses are promising for structural and optical investigations. In our study, we demonstrate the recent results obtained for rare earth ions in lead borate glasses, where PbO was totally substituted by PbF2 . Rare earths as an optically active ions were limited to Pr3+ , Eu3+ and Er3+ ions. Structural behavior and luminescence properties have been examined using X-ray diffraction, FT-IR transmission and luminescence spectroscopy.
Multicomponent rare earth-doped lead borate glasses with chemical composition (in wt.%): 72PbO–18B2 O3 –6Al2 O3 –3WO3 –1Ln2 O3 (where Ln = Pr, Eu, Er) were prepared. Lead oxide was totally substituted by PbF2 in order to obtain oxyfluoride samples. Anhydrous oxides and lead fluoride (99.99% purity, Aldrich) were used as starting materials. Homogeneous mixture was heated in a protective atmosphere of dried argon. Glasses were melted at 850 ◦ C in Pt crucibles, then poured into preheated copper moulds and annealed below the glass transition temperature. After this procedure, the samples were slowly cooled to the room temperature. Transparent glassy plates were obtained in thickness of about 2 mm. The X-ray diffraction analysis was carried out using INEL diffractometer with Cu K␣ radiation in 2θ ranges 0–120◦ . The IR transmission spectra in the frequency region 400–4000 cm−1 were stored on BRUKER FT-IR spectrometer using the KBr pellet disc technique. The luminescence of the samples has been excited by a Continuum Surelite Optical Parametric Oscillator (OPO), pumped by a third harmonic of a Nd:YAG laser. The luminescence was dispersed by a 1-m double grating monochromator and detected with a photomultiplier with S-20 spectral response. The luminescence spectra were recorded using a Stanford SRS 250 boxcar integrator controlled by a computer. Luminescence decay curves were recorded and stored by a Tektronix TDS 3052 oscilloscope. All measurements were carried out at room temperature.
3. Results and discussion 3.1. Structural behavior ∗
Corresponding author. E-mail address: [email protected] (W.A. Pisarski).
0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2007.04.182
An existence of structurally different borate groups in PbO–B2 O3 based glasses is favorable to be investigated by spec-
W.A. Pisarski et al. / Journal of Alloys and Compounds 451 (2008) 220–222
221
Fig. 2. X-ray diffraction patterns recorded for oxide and oxyfluoride lead borate glasses doped with Er3+ ions. Fig. 1. FT-IR transmission spectra recorded for oxide and oxyfluoride lead borate glasses doped with Ln3+ ions (where Ln = Pr or Eu).
troscopic techniques. The multicomponent lead borate glasses consist of various structural units like boroxol rings, penta-, tri-, di- and meta-borate groups with bridging or non-bridging oxygen ions. Structural conversion from three-coordinated to four-coordinated boron atoms has been observed in the optical glasses based on PbO–B2 O3 . In this case, the influence of total substitution of PbO by PbF2 on structural behavior of rare earth-doped lead borate glass has been analyzed using infrared spectroscopy. Fig. 1 presents IR transmission spectra for Lndoped lead borate glasses (Ln = Pr, Eu) without (a) and with (b) PbF2 . Three characteristic groups of bands are associated to BO3 bending (650–700 cm−1 ) and vibrations of tetrahedral BO4 (850–1050 cm−1 ) and trigonal BO3 (∼1300 cm−1 ) units, respectively. Two important effects can be observed. First, the infrared bands are shifted to longer wavelengths (lower frequency region), when PbO was totally replaced by PbF2 . Second, the intensity of the infrared band in 850–1050 cm−1 spectral region decreases. It suggests that number of BO4 units is reduced
with substitution of PbO by PbF2 and so-called BO4 → BO3 back conversion appears. Quite different situation has been observed for Er-doped lead borate system. In contrast to Ln-doped lead borate glasses (where Ln = Pr, Eu), Er-doped sample has semi-crystalline nature. Fig. 2 presents X-ray diffraction patterns recorded for oxide and oxyfluoride lead borate system containing erbium ions. Several diffraction lines due to crystalline ErBO3 phase have been identified using X-ray diffraction analysis [6]. The size of the ErBO3 crystallites is greater than 0.1 m, whereas the crystallized fraction close to 4.3% has been estimated. 3.2. Luminescence Luminescence spectra recorded for the oxide and oxyfluoride lead borate glasses containing Pr3+ [7–9], Eu3+ [10–12] and Er3+ [13–15] ions have been investigated in detail. Fig. 3 shows luminescence spectra for Pr3+ , Eu3+ and Er3+ ions in lead borate glasses, where lead oxide was totally substituted
Fig. 3. Luminescence spectra recorded for oxide and oxyfluoride lead borate glasses doped with rare earth ions.
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Table 1 Spectroscopic parameters for rare earth ions in oxide and oxyfluoride lead borate glasses Ln
Transition
PbF2 (wt.%)
Pr
1 D –3 H 2 4
0 72
Eu
5 D –7 F 0 2
0 72
Er
4I 4 13/2 – I15/2
0 72
λp (nm)
λ (nm)
τ m (ms)
604 599
23.5 18
0.012 0.016
612.5 612.5
11.6 10.6
1.650 1.850
99 62
0.400 0.820
1531 1533
by PbF2 . The spectra were recorded under the same experimental conditions. Luminescence bands are associated to (a) 1 D –3 H transition of Pr3+ , (b) 5 D –7 F transition of Eu3+ and 2 4 0 2 (c) 4 I13/2 –4 I15/2 transition of Er3+ , respectively. Luminescence band due to 1 D2 –3 H4 transition of Pr3+ ions is shifted in direction to shorter wavelengths, when PbO was replaced by PbF2 [9]. The luminescence intensity variations for Eu3+ [12] and Er3+ [15] ions in lead borate glasses have been analyzed in our previous works. Substitution of PbO by PbF2 in glass composition strongly influences the bonding character between rare earth and surrounding ligands. As a consequence, it modifies coordination sphere of luminescent ions. It is interesting to see how these modifications influence luminescence properties of Pr3+ , Eu3+ and Er3+ ions in lead borate glass systems. The selected spectroscopic parameters like peak emission wavelength, emission linewidth and measured lifetime for excited states of rare earth ions have been evaluated. The results are given in Table 1. In all cases, the luminescence linewidth decreases, when lead oxide is substituted by lead fluoride. It results in the replacement of oxygen with fluorine in coordination sphere of rare earth ions. The luminescence lifetimes for 1 D2 state of Pr3+ and 5 D0 state of Eu3+ slightly increase with substitution PbO by PbF2 . The values of 1 D2 lifetimes of Pr3+ ions for oxide and oxyfluoride lead borate glass systems are comparable to that one obtained for borate crystals exhibiting non-linear optical (NLO) properties [16]. In contrast to them, the discrepancy between 4 I13/2 luminescence lifetimes of Er3+ ions in the oxide and oxyfluoride lead borate glasses is significant. Total substitution of PbO by PbF2 results in two-fold increase of 4 I13/2 lifetime from 400 to 820 s. Especially, quite intensive and relatively long-lived NIR luminescence at 1.53 m obtained for Er3+ ions in oxyfluoride lead borate glasses is demanded for broadband optical amplifiers [17].
4. Conclusions The structural and optical aspects for selected rare earth ions in lead borate glasses have been analyzed, where PbO was totally substituted by PbF2 . Luminescence spectra for rare earth ions (Pr, Eu, Er) in multicomponent oxide and oxyfluoride lead borate glasses have been registered, which correspond to 1 D2 –3 H4 transition of Pr3+ , 5 D0 –7 F2 transition of Eu3+ and 4 I13/2 –4 I15/2 transition of Er3+ ions, respectively. In all cases luminescence linewidth decreases, when PbO was totally substituted by PbF2 . The replacement of PbO by PbF2 results also in decreasing of the number of tetrahedral BO4 units, which was observed for Pr3+ and Eu3+ ions in lead borate glasses using infrared spectroscopy. The structural investigations using X-ray diffraction indicate that glass-forming region for Er-doped lead borates strongly depends on PbO and/or PbF2 content. References [1] A. Speghini, M. Peruffo, M. Casarin, D. Ajo, M. Bettinelli, J. Alloys Compd. 300–301 (2000) 174. [2] C.K. Jayasankar, V. Venkatramu, S. Surendra Babu, P. Babu, J. Alloys Compd. 374 (2004) 22. [3] G. Lakshminarayana, S. Buddhudu, Physica B 373 (2006) 100. [4] H. Ushida, Y. Iwadate, T. Hattori, S. Nishiyama, K. Fukushima, Y. Ikeda, M. Yamaguchi, M. Misawa, T. Fukunaga, T. Nakazawa, S. Jitsukawa, J. Alloys Compd. 374 (2004) 167. [5] J. Pisarska, W.A. Pisarski, J. Optoelectron. Adv. Mater. 7 (2005) 2667. [6] W.A. Pisarski, T. Goryczka, B. Wodecka-Du´s, M. Pło´nska, J. Pisarska, Mater. Sci. Eng. B 122 (2005) 94. [7] P. Srivastava, S.B. Rai, D.K. Rai, J. Alloys Compd. 368 (2004) 1. [8] W.A. Pisarski, J. Pisarska, G. Dominiak-Dzik, W. Ryba-Romanowski, J. Phys.: Condens. Matter 16 (2004) 6171. [9] G. Dominiak-Dzik, W. Ryba-Romanowski, J. Pisarska, W.A. Pisarski, J. Lumin. 122–123 (2007) 62. [10] V. Venkatramu, D. Navarro-Urrios, P. Babu, C.K. Jayasankar, V. Lavin, J. Non-Cryst. Solids 351 (2005) 929. [11] V. Venkatramu, P. Babu, C.K. Jayasankar, Spectrochim. Acta A 63 (2006) 276. [12] W.A. Pisarski, J. Pisarska, M. M˛aczka, W. Ryba-Romanowski, J. Mol. Struct. 792–793 (2006) 207. [13] Q. Chen, M. Ferraris, D. Milanese, Y. Menke, E. Monchiero, G. Perrone, J. Non-Cryst. Solids 324 (2003) 12. [14] L.R.P. Kassab, L.C. Courrol, R. Seragioli, N.U. Wetter, S.H. Tatumi, L. Gomes, J. Non-Cryst. Solids 348 (2004) 94. [15] W.A. Pisarski, J. Mater. Sci.: Mater. Electron. 17 (2006) 245. [16] M. Malinowski, M. Kowalska, R. Piramidowicz, T. Łukasiewicz, M. ´ Swirkowicz, Majchrowski, J. Alloys Compd. 323–324 (2001) 214. [17] W.A. Pisarski, J. Pisarska, G. Dominiak-Dzik, 17th International Conference on Photonics in Europe. World of Photonics Congress 2005. European Conference on Lasers and Electro-Optics CLEO/EUROPE-EQEC 2005, Munich, Germany, 2005.
Role of PbO substitution by PbF2 on structural behavior and luminescence of rare earth-doped lead borate glass W.A. Pisarski a,∗ , G. Dominiak-Dzik b , W. Ryba-Romanowski b , J. Pisarska c a
University of Silesia, Institute of Materials Science, Bankowa 12, 40-007 Katowice, Poland b Institute of Low Temperature and Structure Research, Wrocław, Poland c Silesian University of Technology, Department of Materials Science, Katowice, Poland Available online 18 April 2007
Abstract Structural behavior and luminescence properties of rare earth ions (Pr3+ , Eu3+ , Er3+ ) in oxide and oxyfluoride lead borate glasses have been studied using X-ray diffraction and spectroscopic methods. Substitution of PbO by PbF2 results in decreasing of the number of tetrahedral BO4 units, which was observed for Pr3+ and Eu3+ ions in lead borate glasses using infrared spectroscopy. In contrast to oxyfluoride lead borate glasses, several diffraction lines due to crystalline ErBO3 phase were identified for Er-doped oxide sample. Luminescence spectra for rare earth ions in lead borate based glasses have been analyzed, where PbO was totally substituted by PbF2 . © 2007 Elsevier B.V. All rights reserved. Keywords: Lead borate glass; Rare earth ions; Structure; Luminescence
1. Introduction
2. Experimental techniques
Oxide and oxyfluoride lead borate systems doped with rare earth ions belong to heavy metal glass family, which contain unique properties in relation to practical application for photonics and electrochemical devices such as solid-state lasers, optical amplifiers and advanced batteries. Some interesting optical [1–3] and structural [3–5] properties present lead borate glasses containing rare earth ions. Quite large glass-forming region and wide transparency from the UV–vis to the nearinfrared spectral range as well as a large variety of structural groups existing in compositional-dependent lead borate glasses are promising for structural and optical investigations. In our study, we demonstrate the recent results obtained for rare earth ions in lead borate glasses, where PbO was totally substituted by PbF2 . Rare earths as an optically active ions were limited to Pr3+ , Eu3+ and Er3+ ions. Structural behavior and luminescence properties have been examined using X-ray diffraction, FT-IR transmission and luminescence spectroscopy.
Multicomponent rare earth-doped lead borate glasses with chemical composition (in wt.%): 72PbO–18B2 O3 –6Al2 O3 –3WO3 –1Ln2 O3 (where Ln = Pr, Eu, Er) were prepared. Lead oxide was totally substituted by PbF2 in order to obtain oxyfluoride samples. Anhydrous oxides and lead fluoride (99.99% purity, Aldrich) were used as starting materials. Homogeneous mixture was heated in a protective atmosphere of dried argon. Glasses were melted at 850 ◦ C in Pt crucibles, then poured into preheated copper moulds and annealed below the glass transition temperature. After this procedure, the samples were slowly cooled to the room temperature. Transparent glassy plates were obtained in thickness of about 2 mm. The X-ray diffraction analysis was carried out using INEL diffractometer with Cu K␣ radiation in 2θ ranges 0–120◦ . The IR transmission spectra in the frequency region 400–4000 cm−1 were stored on BRUKER FT-IR spectrometer using the KBr pellet disc technique. The luminescence of the samples has been excited by a Continuum Surelite Optical Parametric Oscillator (OPO), pumped by a third harmonic of a Nd:YAG laser. The luminescence was dispersed by a 1-m double grating monochromator and detected with a photomultiplier with S-20 spectral response. The luminescence spectra were recorded using a Stanford SRS 250 boxcar integrator controlled by a computer. Luminescence decay curves were recorded and stored by a Tektronix TDS 3052 oscilloscope. All measurements were carried out at room temperature.
3. Results and discussion 3.1. Structural behavior ∗
Corresponding author. E-mail address: [email protected] (W.A. Pisarski).
0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2007.04.182
An existence of structurally different borate groups in PbO–B2 O3 based glasses is favorable to be investigated by spec-
W.A. Pisarski et al. / Journal of Alloys and Compounds 451 (2008) 220–222
221
Fig. 2. X-ray diffraction patterns recorded for oxide and oxyfluoride lead borate glasses doped with Er3+ ions. Fig. 1. FT-IR transmission spectra recorded for oxide and oxyfluoride lead borate glasses doped with Ln3+ ions (where Ln = Pr or Eu).
troscopic techniques. The multicomponent lead borate glasses consist of various structural units like boroxol rings, penta-, tri-, di- and meta-borate groups with bridging or non-bridging oxygen ions. Structural conversion from three-coordinated to four-coordinated boron atoms has been observed in the optical glasses based on PbO–B2 O3 . In this case, the influence of total substitution of PbO by PbF2 on structural behavior of rare earth-doped lead borate glass has been analyzed using infrared spectroscopy. Fig. 1 presents IR transmission spectra for Lndoped lead borate glasses (Ln = Pr, Eu) without (a) and with (b) PbF2 . Three characteristic groups of bands are associated to BO3 bending (650–700 cm−1 ) and vibrations of tetrahedral BO4 (850–1050 cm−1 ) and trigonal BO3 (∼1300 cm−1 ) units, respectively. Two important effects can be observed. First, the infrared bands are shifted to longer wavelengths (lower frequency region), when PbO was totally replaced by PbF2 . Second, the intensity of the infrared band in 850–1050 cm−1 spectral region decreases. It suggests that number of BO4 units is reduced
with substitution of PbO by PbF2 and so-called BO4 → BO3 back conversion appears. Quite different situation has been observed for Er-doped lead borate system. In contrast to Ln-doped lead borate glasses (where Ln = Pr, Eu), Er-doped sample has semi-crystalline nature. Fig. 2 presents X-ray diffraction patterns recorded for oxide and oxyfluoride lead borate system containing erbium ions. Several diffraction lines due to crystalline ErBO3 phase have been identified using X-ray diffraction analysis [6]. The size of the ErBO3 crystallites is greater than 0.1 m, whereas the crystallized fraction close to 4.3% has been estimated. 3.2. Luminescence Luminescence spectra recorded for the oxide and oxyfluoride lead borate glasses containing Pr3+ [7–9], Eu3+ [10–12] and Er3+ [13–15] ions have been investigated in detail. Fig. 3 shows luminescence spectra for Pr3+ , Eu3+ and Er3+ ions in lead borate glasses, where lead oxide was totally substituted
Fig. 3. Luminescence spectra recorded for oxide and oxyfluoride lead borate glasses doped with rare earth ions.
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Table 1 Spectroscopic parameters for rare earth ions in oxide and oxyfluoride lead borate glasses Ln
Transition
PbF2 (wt.%)
Pr
1 D –3 H 2 4
0 72
Eu
5 D –7 F 0 2
0 72
Er
4I 4 13/2 – I15/2
0 72
λp (nm)
λ (nm)
τ m (ms)
604 599
23.5 18
0.012 0.016
612.5 612.5
11.6 10.6
1.650 1.850
99 62
0.400 0.820
1531 1533
by PbF2 . The spectra were recorded under the same experimental conditions. Luminescence bands are associated to (a) 1 D –3 H transition of Pr3+ , (b) 5 D –7 F transition of Eu3+ and 2 4 0 2 (c) 4 I13/2 –4 I15/2 transition of Er3+ , respectively. Luminescence band due to 1 D2 –3 H4 transition of Pr3+ ions is shifted in direction to shorter wavelengths, when PbO was replaced by PbF2 [9]. The luminescence intensity variations for Eu3+ [12] and Er3+ [15] ions in lead borate glasses have been analyzed in our previous works. Substitution of PbO by PbF2 in glass composition strongly influences the bonding character between rare earth and surrounding ligands. As a consequence, it modifies coordination sphere of luminescent ions. It is interesting to see how these modifications influence luminescence properties of Pr3+ , Eu3+ and Er3+ ions in lead borate glass systems. The selected spectroscopic parameters like peak emission wavelength, emission linewidth and measured lifetime for excited states of rare earth ions have been evaluated. The results are given in Table 1. In all cases, the luminescence linewidth decreases, when lead oxide is substituted by lead fluoride. It results in the replacement of oxygen with fluorine in coordination sphere of rare earth ions. The luminescence lifetimes for 1 D2 state of Pr3+ and 5 D0 state of Eu3+ slightly increase with substitution PbO by PbF2 . The values of 1 D2 lifetimes of Pr3+ ions for oxide and oxyfluoride lead borate glass systems are comparable to that one obtained for borate crystals exhibiting non-linear optical (NLO) properties [16]. In contrast to them, the discrepancy between 4 I13/2 luminescence lifetimes of Er3+ ions in the oxide and oxyfluoride lead borate glasses is significant. Total substitution of PbO by PbF2 results in two-fold increase of 4 I13/2 lifetime from 400 to 820 s. Especially, quite intensive and relatively long-lived NIR luminescence at 1.53 m obtained for Er3+ ions in oxyfluoride lead borate glasses is demanded for broadband optical amplifiers [17].
4. Conclusions The structural and optical aspects for selected rare earth ions in lead borate glasses have been analyzed, where PbO was totally substituted by PbF2 . Luminescence spectra for rare earth ions (Pr, Eu, Er) in multicomponent oxide and oxyfluoride lead borate glasses have been registered, which correspond to 1 D2 –3 H4 transition of Pr3+ , 5 D0 –7 F2 transition of Eu3+ and 4 I13/2 –4 I15/2 transition of Er3+ ions, respectively. In all cases luminescence linewidth decreases, when PbO was totally substituted by PbF2 . The replacement of PbO by PbF2 results also in decreasing of the number of tetrahedral BO4 units, which was observed for Pr3+ and Eu3+ ions in lead borate glasses using infrared spectroscopy. The structural investigations using X-ray diffraction indicate that glass-forming region for Er-doped lead borates strongly depends on PbO and/or PbF2 content. References [1] A. Speghini, M. Peruffo, M. Casarin, D. Ajo, M. Bettinelli, J. Alloys Compd. 300–301 (2000) 174. [2] C.K. Jayasankar, V. Venkatramu, S. Surendra Babu, P. Babu, J. Alloys Compd. 374 (2004) 22. [3] G. Lakshminarayana, S. Buddhudu, Physica B 373 (2006) 100. [4] H. Ushida, Y. Iwadate, T. Hattori, S. Nishiyama, K. Fukushima, Y. Ikeda, M. Yamaguchi, M. Misawa, T. Fukunaga, T. Nakazawa, S. Jitsukawa, J. Alloys Compd. 374 (2004) 167. [5] J. Pisarska, W.A. Pisarski, J. Optoelectron. Adv. Mater. 7 (2005) 2667. [6] W.A. Pisarski, T. Goryczka, B. Wodecka-Du´s, M. Pło´nska, J. Pisarska, Mater. Sci. Eng. B 122 (2005) 94. [7] P. Srivastava, S.B. Rai, D.K. Rai, J. Alloys Compd. 368 (2004) 1. [8] W.A. Pisarski, J. Pisarska, G. Dominiak-Dzik, W. Ryba-Romanowski, J. Phys.: Condens. Matter 16 (2004) 6171. [9] G. Dominiak-Dzik, W. Ryba-Romanowski, J. Pisarska, W.A. Pisarski, J. Lumin. 122–123 (2007) 62. [10] V. Venkatramu, D. Navarro-Urrios, P. Babu, C.K. Jayasankar, V. Lavin, J. Non-Cryst. Solids 351 (2005) 929. [11] V. Venkatramu, P. Babu, C.K. Jayasankar, Spectrochim. Acta A 63 (2006) 276. [12] W.A. Pisarski, J. Pisarska, M. M˛aczka, W. Ryba-Romanowski, J. Mol. Struct. 792–793 (2006) 207. [13] Q. Chen, M. Ferraris, D. Milanese, Y. Menke, E. Monchiero, G. Perrone, J. Non-Cryst. Solids 324 (2003) 12. [14] L.R.P. Kassab, L.C. Courrol, R. Seragioli, N.U. Wetter, S.H. Tatumi, L. Gomes, J. Non-Cryst. Solids 348 (2004) 94. [15] W.A. Pisarski, J. Mater. Sci.: Mater. Electron. 17 (2006) 245. [16] M. Malinowski, M. Kowalska, R. Piramidowicz, T. Łukasiewicz, M. ´ Swirkowicz, Majchrowski, J. Alloys Compd. 323–324 (2001) 214. [17] W.A. Pisarski, J. Pisarska, G. Dominiak-Dzik, 17th International Conference on Photonics in Europe. World of Photonics Congress 2005. European Conference on Lasers and Electro-Optics CLEO/EUROPE-EQEC 2005, Munich, Germany, 2005.