Luminescence study of lanthanide(III) ions in non-aqueous solutions containing azide ions

Abstract

Luminescence lifetime and intensity measurements of lanthanide(III) ions, Ln3+ (Eu, Gd and Tb), in non-aqueous solutions containing azide ions (N3−) have been performed to study the quenching effect of N3− using time-resolved laser-induced luminescence spectroscopy and conventional luminescence spectroscopy. The luminescence Stern–Volmer quenching constants KsvΦ and azide non-radiative decay constants kN3 of the excited Eu(III) ion in the presence of N3− were measured in N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methylformamide (NMF), formamide (FA) and methanol (MeOH). The obtained quenching effect of the Ln3+ luminescence by azide in the non-aqueous solvents shows the order: Gd>Eu>Tb, which does not obey the energy gap law, ΔE, between the emitting and the ground state of the Ln3+ ion (Gd>Tb>Eu). The anomaly in the quenching pattern observed in the case of Eu3+ can be attributed to its partial reduction to Eu2+, additionally to the energy transfer from excited state of Eu3+ to N3−. The values of quenching rate constants kN3measured for Eu3+ in various solutions depend on the acceptor number (AN) of the solvents used.