Determination of Atomic and Molecular Excited-State Lifetimes Using an Optoelectronic Cross-Correlation Method

Abstract

A new optoelectronic cross-correlation technique has been used to measure excited-state lifetimes of several organic fluorophores in solution and of sodium atoms in both air-acetylene and methane-air flames. Capable of time resolution in the picosecond range, the new method was validated by the excellent agreement between measured and literature values for fluorescence lifetimes of the organic species. Lifetime values for Na atoms in flames are among the most precise ever reported and agree closely with values calculated from the known flame gas composition, temperature, and the quenching cross-sections of the two dominant quenching species in the flame, N2 and CO2. From the Na excited-state lifetimes (0.72 ± 0.07 ns for air-acetylene and 0.48 ± 0.08 ns for methane-air flames), quantum efficiencies for atomic fluorescence were calculated.