abstract
In this work, we report a theoretical and experimental investigation of the energy transfer mechanism in two isotypical 2D coordination polymers, (infinity)[(Tb1-xEux)(DPA)(HDPA)], where H(2)DPA is pyridine 2,6-dicarboxylic acid and x = 0.05 or 0.50. Emission spectra of (infinity)[(Tb0.95Eu0.05)(DPA)(HDPA)] and (infinity)[(Tb0.5Eu0.5)(DPA)(HDPA)], (I) and (2), show that the high quenching effect on Tb3+ emission caused by Eu3+ ion indicates an efficient Tb3+-> Eu3+ energy transfer (ET). The k(ET) of Tb3+-> Eu3+ ET and rise rates (k(r)) of Eu3+ as a function of temperature for (1) are on the same order of magnitude, indicating that the sensitization of the Eu3+5D0 level is highly fed by ET from the D-5(4) level of Tb3+ ion. The eta(ET) and R-0 values vary in the 67-79% and 7.15 to 7.93 angstrom ranges. Hence, Tb3+ is enabled to transfer efficiently to Eu3+ that can occupy the possible sites at 6.32 and 6.75 angstrom. For (2), the ET processes occur on average with eta(ET) and R-0 of 97% and 31 angstrom, respectively. Consequently, Tb3+ ion is enabled to transfer energy to Eu3+ localized at different layers. The theoretical model developed by Malta was implemented aiming to insert more insights about the dominant mechanisms involved in the ET between lanthanides ions. Calculated single Tb3+-> Eu3+ ETs are three orders of magnitude inferior to those experimentally; however, it can be explained by the theoretical model that does not consider the role of phonon assistance in the Ln(3+)-> Ln(3+) ET processes. In addition, the Tb3+-> Eu3+ ET processes are predominantly governed by dipole-dipole (d-d) and dipole-quadrupole (d-q) mechanisms.
keywords
COOPERATIVE OPTICAL TRANSITIONS; DOPED INORGANIC MATERIALS; LIGAND-FIELD PARAMETERS; SPECTROSCOPIC PROPERTIES; COORDINATION POLYMERS; UP-CONVERSION; SENSITIZED LUMINESCENCE; EU3+ COMPLEXES; GLASS-CERAMICS; TB3+
subject category
Chemistry; Science & Technology - Other Topics; Materials Science
authors
Rodrigues, MO; Dutra, JDL; Nunes, LAO; de Sa, GF; de Azevedo, WM; Silva, P; Paz, FAA; Freire, RO; Junior, SA
our authors
Filipe Alexandre Almeida Paz
Principal Researcheracknowledgements
We gratefully acknowledge CNPq (INCT/INAMI and RH-INCT/INAMI), PRONEX-FACEPE-CNPq (APQ-0859-1.06/08), and FCT (PTDC/QUI-QUI/098098/2008-FCOMP-01-0124-FEDER-010785) and PhD scholarship No. SFRH/BD/46601/2008 for its financial support and CETENE and LNLS (proposal D10A-XRD2-10164) for providing the facilities. We also wish to thank Prof. Dr. Petrus Santa Cruz for providing the SPECTRA LUX Software. This software is freely available via e-mail: petrus@pq.cnpq.br.