A site selective luminescence excitation and Raman scattering study of Eu(CF3SO3)3-PPO; ion association and ionic exchange rate

Abstract

The luminescence of Eu3+ in a salt–polymer complex, poly(propylene oxide) containing Eu(CF3SO3)3 salt, was studied using broad band and site-selective excitation. Two distinctly different types of local structure around Eu3+ were detected. To investigate and compare the local structure around the SO3CF−3 anions with that around the Eu3+ cations, a Raman scattering study of the SO3 symmetric stretch vibration was performed in the same system. The vibrational data clearly reveal that also the anions are subject to two types of local environment. It is found that neither of the two states can be attributed to ‘‘free’’ (completely solvated) ions, which implies the existence of two different anion–cation configurations. Temperature and concentration dependent studies of the site-selective Eu3+ luminescence and the SO3 vibrational spectrum show that the relative amount of ions in the two states is, within the experimental accuracy, constant. However at elevated temperatures there is a rapid exchange between the two states not found at lower temperatures. The characteristic time scale for the ionic exchange is found to be closely related to the structural relaxation time of the polymer segmental mobility. The findings support the idea that ionic diffusion in salt–polymer complexes is assisted by the local polymer chain mobility which is used in models to explain polymer electrolyte performance.

Optical investigation of the emission lines for Eu3+ and Tb3+ ions in the GaN powder host

“…The latter may for instance be due to vibrational excitations and then result in vibrational transitions. Moreover an external field causes Stark splitting of the (2J+1)-fold degenerate levels, the number of splitting lines being dependent on the symmetry of the field [10,11].…”

Cation concentration and local ligand field of polyether–salt complexes

“…In the case of polymer electrolytes modified by europium salts, the Eu ϩ3 near surroundings were investigated using the luminescence features of the trivalent cation; indeed, these europium electrolytes are strongly luminescent from 14 K up to room temperature, [6][7][8][9][10][11][12] with lifetimes on the order of 1 ms at low temperatures. 7,13 The observed 5 D 0,1 → 7 F 0 -4 emission lines of PEO, modified by EuBr 3 , PEO n EuBr 3 , with the number n of ether oxygens in the polymer chain per Eu 3ϩ cation ranging from 80 to 3, have previously been used for determining the average Eu 3ϩ -nearest ligands distance as lying between 2.3 and 2.7 Å, 9,10 and the associated local symmetry group as being C 2 .…”

White light emission ofEu3+-based hybrid xerogels

“…While in the 7 F 1 manifold the three Stark levels are well defined, there is some uncertainly in the identification and energy assignment of the lower-energy split component of the 7 -based oxide glasses and has been also reported for other polymer-based materials modified by europium salts. 17,22 The previously reported local coordination of Eu 3ϩ in POE and POP electrolytes is approximately a C 2v site symmetry. 15,18,19 This same local geometry has also been proposed for EuCl 3 incorporated in POE oligomers.…”

“…Both vibrational and electronic spectroscopic techniques are relevant tools for gaining some insight about the structural molecular characteristics of those amorphous regions. These techniques have been frequently used in various polymer-salt complexes to investigate several aspects of their molecular characteristics, such as, for instance, the conformation of the polymer chains, [5][6][7] the anionic and cationic environments, [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] the vibrational modes of polymer-cation coordination, [9][10][11]24 and ether oxygen-metal ion stretching motions. 10,11,22 In the case of polymer electrolytes incorporating lan-thanide salts, since the first initial reports indicating that trivalent cations were also soluble in POE and poly͑oxypro-pylene͒, POP, 13,14 several papers have been published during this decade showing that the ion-polymer chain interactions can be investigated using the cation emission features, [14][15][16][17][18][19][20][21][22][23][24] and the active vibrational modes of the anions.…”