Speciation analyses by laser fluorescence spectroscopy
Time resolved laser fluorescence spectroscopy (TRLFS) is the analytical technique which observes de-excitation processes of excited fluorophore created by short-pulsed laser. TRLFS data of a fluorescent metal ion includes shape of emission spectrum its temporal decay These information reflects the number of allowed transitions and their probabilities competitive non-fluorescent de-excitation pathways Thus, the spectral shape will change when a fluorescence metal coordinates with a ligand and changes its energy levels and/or associated transition probabilities due to variation of the symmetry around it. Similarly, fluorescence decay lifetime will vary when a ligand around the central metal ion is displaced by another ligand, as de-excitation pathways change. We can use these changes in TRLFS data to probe reactions with a fluorescent metal ion and estimate its structural information. As good approximation, For instance, Eu3+, a chemical homologue of trivalent actinides such as Am3+ and Cm3+, has the energy diagram as in Figure 1 and the emission spectrum as in Figure 2. Its decay lifetime is around 110 μsec. Three major peaks in Figure 2 corresponds to the transitions from the 5D0 states to the 7F1，7F2，and 7F4 states. Upon complexation with acetate ligand, the spectrum changes in Figure 3. Particularly, the peak around 620 nm due to so-called hyper-sensitive transition, 5D0 → 7F2, is significantly enhanced. An overtone of OH vibration of water molecule provides an efficient pathway for excited Eu3+; the […]