( t 486 and540 nm. Figure 2 shows fluo...)Phosphorescence lifetime measured using the SPEX phosphorimeter

t 486 and 540 nm. Figure 2 shows fluorescence from a solution of peptide + fluorescein dye, also with and without delay. With a 50-s delay, all fluorescence from the peptide + fluorescein vanishes. Taken together, Figures 1 and 2 show that the phosphorescent species is Tb.

Figure 3 (on back) combines all three species, as a plot of peptide-terbium complex with and without 0.67-M fluorescein, without and with a 50-s delay between excitation with a xenon flash lamp. Again, the spurious fluorescence at 363 nm is removed by delaying the sample window for 50 s. Curves 3-b and 3-c directly compare fluoresceincontaining and fluorescein-lacking solutions, showing fluorescein phosphorescence at 511 nm caused by energy transfer from the complex to the fluorescein.

Figure 4 shows phosphorescence-decay curves of peptide with terbium ion alone (τ = 3.8 ms), and in the presence of fluorescein (τ = 3.0 ms). The faster phosphorescence decay in the presence of fluorescein (curve 4-b) confirms energy-transfer from the peptide-Tb donor to the fluorescein acceptor.

Similar experiments can be performed with the FLUOROMAX-P spectrofluorometer, containing an integrated phosphorimeter along with CW lamp.

Conclusions
Use of a SPEX phosphorimeter, including gated delay of signal-acquisition, can reveal extra information about the physical and chemical properties of materials.

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