3. Results and discussion
In the following text the term ‘pH in MeCN medium’ implies
the aqueous solution of BA/Eu3þ–BA prepared at a pH, from which
5 mL was taken and dissolved in 0.5 mL of MeCN. Also the terms
‘uncomplexed Eu3þ’ and ‘complexed Eu3þ’ refer to Eu3þ species in
MeCN/water medium without and with benzoate ion, respectively.
3.1. Luminescence enhancement studies of Eu3þ–BA in MeCN
To begin with, luminescence intensity of complexed Eu3þ in
MeCN was measured as a function of BA concentration and pH of
the aqueous solution. Maximum luminescence intensity was
found over 3 104
–7 104 M of BA concentration and pH 4.5.
Therefore in the luminescence enhancement studies, concentration
of BA and pH of the solution was maintained at 5 104 M
and 4.5, respectively. The excitation and emission spectra of
various Eu3þ ion species recorded in different medium are shown
in Figs. 1 and 2 respectively. The excitation and emission spectra of
Eu3þ–BA recorded in MeCN medium are shown in Figs. 1c and 2c,
respectively. For comparison, spectra recorded in aqueous medium
for uncomplexed Eu3þ (Figs. 1a and 2a) and Eu3þ–BA complex (900 μs) of the Eu3þ–BA system in MeCN corroborates the fact
that a strong complex is formed by substituting water molecules
from the first coordination sphere of Eu3þ.