The distinctive luminescence of lanthanide ions has long been a challenge for the spectroscopist. Methods to counter the extremely low absorption coefficients and luminescence quantum yields have concentrated on
Protective ligands to reduce vibrational quenching effects by XH moieties (X = O, N,).
Deuterated solvents (also to reduce quenching effects of XH).
Antenna chromophores for enhanced absorption (with later energy-transfer to, and luminescence by, the lanthanide).
Luminescence from these systems comprises a number of sharp and well-resolved bands with characteristically long lifetimes, roughly 106 103 s, depending upon the degree of quenching. With an integrated phosphorimeter, the SpexFluoroMax-P allows convenient time-gated measurement of lanthanide systems. In this Application Note, two lanthanide complexes comprising an encapsulating complex with benzophenone antenna chromophore (L, see Fig. 1) and europium (Eu) or terbium (Tb) ions are investigated using time-gated spectroscopy with the FluoroMax-P.
Experiment & Results
An excitation source (xenon lamp) flashes (~ 3 s pulse-width). Detection of the samples luminescence occurs within a time-window after the flash, according to a chosen delay time and detection-window size. Acquisition of a spectrum corresponding to any desired time-slice during the luminescence decay is possible. Luminescence lifetime measurements are made by recording the intensity of a specific wavelength with a chosen detection-window size and incremented delay time (Fig. 2).
The individual spectra of Tb-L and Eu-L complexes are shown in Figs. 3 and 4. The resulting luminescence spectrum from a mixture of Tb-L and