Vol. 32, No. 4 (2020) Synthesis and Photo-Physical Properties of Europium(III) and Terbium(III) Complexes with Thiosemicarbazones 957
7.0×103
6.0×103
5.0×103
4.0×103
3.0×103
2.0×103
1.0×103
0
6.0×103
5.0×103
4.0×103
3.0×103
2.0×103
1.0×103
0
(a)
(b)
1050 1070 1090 1110 1130 1150 1170 1190 1210 1230
1050 1070 1090 1110 1130 1150 1170 1190 1210 1230
Time (µs)
Time (µs)
Fig. 6. Luminescence decay curve of (a) [Eu(L3)Cl(H2O)2] (b) [Tb(L3)OAc(H2O)2]
On the other hand, the excitation spectra of terbium(III)
complex [Tb(L3)OAc(H2O)2] exhibits the most intense exci-
tical and spectral data reveal that the Schiff base coordinates
to the central Ln(III) by its two azomethine nitrogen atoms
and two oxygen atoms of water molecule. Europium(III) and
terbium(III) complexes exhibit characteristic luminescence in
red and green regions, respectively.
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5
tation peak at 395 nm which corresponds to the F6 → L10
excited level transition of Tb3+. The emission spectrum of the
Tb(III) complex exhibits five emission bands at 485, 549, 592,
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7
656 and 678 nm corresponding to the 5D4 → F6, 5D4 → F5, 5D4
→ F4, 5D4 → F2 and 5D4 → F1 electronic transitions, respectively
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7
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ACKNOWLEDGEMENTS
(Fig. 5a-b). 5D4 → F5 transition is most intense and practically
7
The authors are thankful to STIC Cochin, IIT madras for
providing the necessary spectral and analytical data. The
authors are also thankful to University Grant Commission,
New Delhi, India for financial assistance.
unaffected by the symmetry of the crystalline field surrounding
the emissive centre exhibits the strong green emission. The
less intense emission peak centered at 656 nm is attributed
7
to 5D4 → F2 which is known to be moderately sensitive to the
surrounding site. Furthermore, this emission spectra of the
europium and terbium complexes shows a high background
which can be ascribed as the characteristic fluorescence for
the ligand L. It is shown that the energy of H2L ligand transfers
to Eu3+ and Tb3+ totally. This property of emission spectrum is
similar to that of the reported complexes [45]. The appearance
of weak characteristics emission of Eu(III) and Tb(III) ions
and the fluorescence of the ligand L may be due to the compe-
tition between the ligand fluorescence process and the energy
transfer process from the lowest triplet state level of the ligand
to the excited state level of the ligand to the excited state of
Eu(III) and Tb(III). Through intersystem crossing, the efficient
energy transfer from the triplet state of the ligands crossed to
reach the emissive level of the central lanthanides cation is
achieved only when the prepared complexes are in crystalline
or solid form. The two water molecule presented in the coordi-
nation sphere seem to play less important role in quenching
the luminescent emission of the lanthanide cation since they
are equally present in the luminescent prepared complexes.
The quantum yield and luminescence life times of both
europium(III) and terbium(III) complexes were investigated.
The quantum yields of [Eu(L3)Cl(H2O)2] and [Tb(L3)OAc(H2O)2]
complexes were found to be 0.49 and 0.53, respectively. Lumine-
scence decay curves obtained at room temperature by moni-
CONFLICT OF INTEREST
The authors declare that there is no conflict of interests
regarding the publication of this article.
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Conclusion
In this work, new Eu(III) and Tb(III) complexes of thio-
semicarbazones are synthesized and characterized. The analy-
Vishwakarma, Ananya
