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Spectroscopic properties of trivalent europium and terbium ions in modificated polyethylene phthalate with aza-aromatic acids
JOURNAL OF
LUMINESCENCE ELSEWIER
Journal
of Luminescence
72-74
(1997) 487-489
Spectroscopic properties of trivalent europium and terbium ions in modificated polyethylene phthalate with aza-aromatic acids P.N.M. dos Anjos *, W.M. de Azevedo, G.F. de Si, O.L. Malta Department0 de Quimica Fundamental - UFPE. Ac. Luiz Freire. s/n, Cidade Unirersitbria, Recife PE. CEP: 50670-901. Brazil
Abstract
We have measured the emission spectra and lifetimes for Eu(II1) and Tb(II1) ions in polyethylene phthalate doped with some N-hetero-aromatics acids, which were pyrazine-2-carboxylic, pyridine-2-carboxylic, pyridine-3-carboxylic acids and amine-3-substituted acids. From the results we have found that pyrazine-2-carboxylic acid enhances both europium and terbium luminescence, while the other acids increase the polymer luminescence. This points out that these acids are less effective in transferring energy to Eu(III) and Tb(II1) excited states than the first one. Keywords:
Eu; Tb; Energy transfer; Polyethylene phthalate
1. Introduction
We have recently used ternary complexes of europium and terbium with pyrazine-2-carboxylic acid for doping a polyester matrix, namely polyethylene phthalate (PEP), obtained by condensation reaction between phthalic acid and ethylene glycol [l]. We found that these complexes maintained their luminescent properties and strongly interacts with matrix states [2]. To investigate the influence of doped polymer on rare-earth ion luminescence, we have synthesized the same polyester with europium and terbium chlorides and the N-aromatic acids that are used as ligand in complexes [3]. These were the following: amine-3-pyrazine-2-carboxylic acid (APZ), amine-3-pyridine-2carboxylic acid (APR), pyridine-2-carboxylic acid (picolinic acid) (HPR), pyridine-3-carboxylic acid *Corresponding [email protected].
author.
0022-2313/97/$17.00 Published PII SOO22-2313(96)00209-8
Fax:
55-81-271-8442;
by Elsevier Science B.V
e-mail:
(nicotinic acid) (HNC) and pyrazine-2-carboxylic acid (HPZ). These acids have been used for synthesizing complexes because they act like an antenna [4]. They absorb ultraviolet radiation efficiently through allowed electronic transitions and then transfer energy nonradiatively to excited ion states, whereby enabling emission of visible radiation from lower excited states. This mechanism can become less effective when there are other ways for deactivating the excited states [S], such as vibrational modes of coordinated ligands.
2. Experimental The synthesis of polyethylene phthalate has been described in Ref. [l]. Here we have modified the procedure slightly to allow for the doping to proceed with aza-aromatic acids. The preparation mixture were (percentage in weight): phthalic acid (59%) and ethyleneglycol(29%) and glycerol (9%),
488
P.N.M. dos Anjos et al. /Journal
of Luminescence
rare-earth chlorides (1%) and aromatic acid (1%). We have used a Laser Science model VSL-337ND nitrogen laser ffr exciting the samples at wavelength 3370 A. The emission spectra were
72-74 (1997) 487-489
measured at room temperature using a Jobin Yvon double monochromator model UlOOO Ramanor coupled to a water-cooled RCA C310340-02 photo multiplier. Lifetime measurements were performed
6000 5000 Wavelength (A)
8000 SObO Wavelength (A) Fig. 1. Emisson spectra of the doped each graphic, the sequence of doping
PEP matrices with N-aromatic acids is (near axis) PEP, HPZ
acids and (bottom)
Europium
, HPR, HNC, APZ and APR.
and (top) Terbium
chlorides.
For
P.N.M. dos Anjos et al. 1 Journal of Luminescence 72-74 (1997) 487-489
using a Hamamatsu lP28S air-cooled photo multiplier coupled to Princeton Applied ResearcOh EG&G Box-car system. The 5D0 + ‘Ij’* (at 6170 A, for Eu(III)), and ‘D4 --) ‘FS (at 5450 A, for Tb(II1)) transitions were chosen to measure lifetimes.
3. Results and discussion Emission spectra of PEP with Eu(II1) and Tb(II1) chlorides are shown in Fig. 1. We can distinguish two set of bands. One is regarded with the Eu(II1) and Tb(II1) electronic transitions from states ‘Do and 5D4, respectively, to the multiplet ‘F, (J = 0,1,2,3,4,5,6). The other one corresponds to transitions occurring from PEP excited states. In this set we have observed two wide0bands, approximately centered at 4200 and 4900 A. One band can be assigned to singlet-singlet transition and the other one to triplet-singlet transition [6]. Two pathways would be possible for energy emission. One would be fluorescence and phosphorescence of PEP matrix. The other would be via 5D0 or 5D4 states of Eu(II1) or Tb(II1) ions, respectively, after radiativeless energy transfer from excited states of the PEP matrix. We have analyzed the emission spectra dividing the rare-earth emission intensity by PEP emission intensity. This parameter roughly estimates the relation between the two path for energy transference with reference to the N-aromatic acids. We obtained the following ratios. Eu(II1): 0.43 for PEP not doped, 1.53 for PEP with HPZ, 0.19 for PEP with APZ, 0.27 for PEP with APR, 0.23 for PEP with HPR and 0.55 for PEP with HNC. We found the following values for PEP with Tb(II1): 0.57 for PEP not doped, 5.48 for PEP with HPZ, 0.51 for PEP with HPR, 0.44 for PEP with HNC, 0.66 for PEP with APR and for PEP with APZ. In addition, lifetimes for Eu(II1) emission at each case were: 611 ps for PEP, 758 ps for PEP with HPZ, 683 ps for PEP with HPR, 508~s for PEP with HNC, 629 ~LSfor PEP with APR and 583 ps for PEP with APZ. Whereas for Tb(III), lifetimes were the following: 1300~~sfor PEP, 1492~s for PEP with HPZ, 1240 ps for PEP with HPR, 1096 ps for PEP with
489
HNC, 1270 ps for PEP with APR and 838 ps for PEP with APZ. The values cited above show that only HPZ acid significantly enhanced both rare-earth emission and lifetime with regard to PEP emission. While for APR, HPR and APZ acids the ratios and lifetime were lower than that for undoped PEP. For Eu(III), PEP with HNC acid had a ratio slightly greater. For Tb(II1) HPR, HNC and APZ acids reduced both ratio and lifetimes. For PEP-doped with APR the ratio was slightly greater. We have considered from these features that only HPZ acid becomes more effective than the energy transfer to rare-earth excited states while the other acids have the opposite effect. This can happen because doping alters the electronic structure of polymer bringing them near resonance with rare-earth excited states. In addition, the lifetimes indicate that doping can significantly change the coordination sites, depending on whether the Eu(II1) and Tb(II1) transitions become more permissible or not; of them one has been found in similar situations at coordination complexes [7].
Acknowledgements
The authors are grateful to the CNPq, FACEPE and FINEP (Brazilian agencies) for financial supports.
References [l] W.M. de Azevedo, P.N.M. dos Anjos, O.L. Malta and G.F. de SB, J. Alloys Comp. 180 (1992) 125-130. [Z] W.M. de Azevedo, P.N.M. dos Anjos, O.L. Malta and G.F. de SB, J. Lumin. 60&61 (1994) 493-496. [3] G.F. de S& L.H.A. Nunes, Z.-M. Wang and G.R. Choppin, J. Alloys Comp. 196 (1993) 17-23. [4] N. Sabatinni, M. Guardigli and J.-M. Lehn, Chem. Rev. 123 (1993) 201-228. [5] R.F. Cozens; Electric Properties of Polymers (Academic Press New York, 1982) pp. 93-125. [6] J.P. LaFemina and G. Arjavalingam, J. Chem. Phys. 95 (1991) 984-988. [7] O.L. Malta, J. Phys. Chem. Solids 56 (1995) 1053-1062.
LUMINESCENCE ELSEWIER
Journal
of Luminescence
72-74
(1997) 487-489
Spectroscopic properties of trivalent europium and terbium ions in modificated polyethylene phthalate with aza-aromatic acids P.N.M. dos Anjos *, W.M. de Azevedo, G.F. de Si, O.L. Malta Department0 de Quimica Fundamental - UFPE. Ac. Luiz Freire. s/n, Cidade Unirersitbria, Recife PE. CEP: 50670-901. Brazil
Abstract
We have measured the emission spectra and lifetimes for Eu(II1) and Tb(II1) ions in polyethylene phthalate doped with some N-hetero-aromatics acids, which were pyrazine-2-carboxylic, pyridine-2-carboxylic, pyridine-3-carboxylic acids and amine-3-substituted acids. From the results we have found that pyrazine-2-carboxylic acid enhances both europium and terbium luminescence, while the other acids increase the polymer luminescence. This points out that these acids are less effective in transferring energy to Eu(III) and Tb(II1) excited states than the first one. Keywords:
Eu; Tb; Energy transfer; Polyethylene phthalate
1. Introduction
We have recently used ternary complexes of europium and terbium with pyrazine-2-carboxylic acid for doping a polyester matrix, namely polyethylene phthalate (PEP), obtained by condensation reaction between phthalic acid and ethylene glycol [l]. We found that these complexes maintained their luminescent properties and strongly interacts with matrix states [2]. To investigate the influence of doped polymer on rare-earth ion luminescence, we have synthesized the same polyester with europium and terbium chlorides and the N-aromatic acids that are used as ligand in complexes [3]. These were the following: amine-3-pyrazine-2-carboxylic acid (APZ), amine-3-pyridine-2carboxylic acid (APR), pyridine-2-carboxylic acid (picolinic acid) (HPR), pyridine-3-carboxylic acid *Corresponding [email protected].
author.
0022-2313/97/$17.00 Published PII SOO22-2313(96)00209-8
Fax:
55-81-271-8442;
by Elsevier Science B.V
e-mail:
(nicotinic acid) (HNC) and pyrazine-2-carboxylic acid (HPZ). These acids have been used for synthesizing complexes because they act like an antenna [4]. They absorb ultraviolet radiation efficiently through allowed electronic transitions and then transfer energy nonradiatively to excited ion states, whereby enabling emission of visible radiation from lower excited states. This mechanism can become less effective when there are other ways for deactivating the excited states [S], such as vibrational modes of coordinated ligands.
2. Experimental The synthesis of polyethylene phthalate has been described in Ref. [l]. Here we have modified the procedure slightly to allow for the doping to proceed with aza-aromatic acids. The preparation mixture were (percentage in weight): phthalic acid (59%) and ethyleneglycol(29%) and glycerol (9%),
488
P.N.M. dos Anjos et al. /Journal
of Luminescence
rare-earth chlorides (1%) and aromatic acid (1%). We have used a Laser Science model VSL-337ND nitrogen laser ffr exciting the samples at wavelength 3370 A. The emission spectra were
72-74 (1997) 487-489
measured at room temperature using a Jobin Yvon double monochromator model UlOOO Ramanor coupled to a water-cooled RCA C310340-02 photo multiplier. Lifetime measurements were performed
6000 5000 Wavelength (A)
8000 SObO Wavelength (A) Fig. 1. Emisson spectra of the doped each graphic, the sequence of doping
PEP matrices with N-aromatic acids is (near axis) PEP, HPZ
acids and (bottom)
Europium
, HPR, HNC, APZ and APR.
and (top) Terbium
chlorides.
For
P.N.M. dos Anjos et al. 1 Journal of Luminescence 72-74 (1997) 487-489
using a Hamamatsu lP28S air-cooled photo multiplier coupled to Princeton Applied ResearcOh EG&G Box-car system. The 5D0 + ‘Ij’* (at 6170 A, for Eu(III)), and ‘D4 --) ‘FS (at 5450 A, for Tb(II1)) transitions were chosen to measure lifetimes.
3. Results and discussion Emission spectra of PEP with Eu(II1) and Tb(II1) chlorides are shown in Fig. 1. We can distinguish two set of bands. One is regarded with the Eu(II1) and Tb(II1) electronic transitions from states ‘Do and 5D4, respectively, to the multiplet ‘F, (J = 0,1,2,3,4,5,6). The other one corresponds to transitions occurring from PEP excited states. In this set we have observed two wide0bands, approximately centered at 4200 and 4900 A. One band can be assigned to singlet-singlet transition and the other one to triplet-singlet transition [6]. Two pathways would be possible for energy emission. One would be fluorescence and phosphorescence of PEP matrix. The other would be via 5D0 or 5D4 states of Eu(II1) or Tb(II1) ions, respectively, after radiativeless energy transfer from excited states of the PEP matrix. We have analyzed the emission spectra dividing the rare-earth emission intensity by PEP emission intensity. This parameter roughly estimates the relation between the two path for energy transference with reference to the N-aromatic acids. We obtained the following ratios. Eu(II1): 0.43 for PEP not doped, 1.53 for PEP with HPZ, 0.19 for PEP with APZ, 0.27 for PEP with APR, 0.23 for PEP with HPR and 0.55 for PEP with HNC. We found the following values for PEP with Tb(II1): 0.57 for PEP not doped, 5.48 for PEP with HPZ, 0.51 for PEP with HPR, 0.44 for PEP with HNC, 0.66 for PEP with APR and for PEP with APZ. In addition, lifetimes for Eu(II1) emission at each case were: 611 ps for PEP, 758 ps for PEP with HPZ, 683 ps for PEP with HPR, 508~s for PEP with HNC, 629 ~LSfor PEP with APR and 583 ps for PEP with APZ. Whereas for Tb(III), lifetimes were the following: 1300~~sfor PEP, 1492~s for PEP with HPZ, 1240 ps for PEP with HPR, 1096 ps for PEP with
489
HNC, 1270 ps for PEP with APR and 838 ps for PEP with APZ. The values cited above show that only HPZ acid significantly enhanced both rare-earth emission and lifetime with regard to PEP emission. While for APR, HPR and APZ acids the ratios and lifetime were lower than that for undoped PEP. For Eu(III), PEP with HNC acid had a ratio slightly greater. For Tb(II1) HPR, HNC and APZ acids reduced both ratio and lifetimes. For PEP-doped with APR the ratio was slightly greater. We have considered from these features that only HPZ acid becomes more effective than the energy transfer to rare-earth excited states while the other acids have the opposite effect. This can happen because doping alters the electronic structure of polymer bringing them near resonance with rare-earth excited states. In addition, the lifetimes indicate that doping can significantly change the coordination sites, depending on whether the Eu(II1) and Tb(II1) transitions become more permissible or not; of them one has been found in similar situations at coordination complexes [7].
Acknowledgements
The authors are grateful to the CNPq, FACEPE and FINEP (Brazilian agencies) for financial supports.
References [l] W.M. de Azevedo, P.N.M. dos Anjos, O.L. Malta and G.F. de SB, J. Alloys Comp. 180 (1992) 125-130. [Z] W.M. de Azevedo, P.N.M. dos Anjos, O.L. Malta and G.F. de SB, J. Lumin. 60&61 (1994) 493-496. [3] G.F. de S& L.H.A. Nunes, Z.-M. Wang and G.R. Choppin, J. Alloys Comp. 196 (1993) 17-23. [4] N. Sabatinni, M. Guardigli and J.-M. Lehn, Chem. Rev. 123 (1993) 201-228. [5] R.F. Cozens; Electric Properties of Polymers (Academic Press New York, 1982) pp. 93-125. [6] J.P. LaFemina and G. Arjavalingam, J. Chem. Phys. 95 (1991) 984-988. [7] O.L. Malta, J. Phys. Chem. Solids 56 (1995) 1053-1062.