Journal of Physical Chemistry A, Vol.112, No.42, 10502-10508, 2008
Parametric Investigation of Laser-Induced Fluorescence of Solid-State Uranyl Compounds
The combination of remote/standoff sensing and laser-induced fluorescence (LIF) spectroscopy shows potential for detection of uranyl (UO22+) compounds. Uranyl compounds exhibit characteristic emission in the 450-600 urn (22200 to 16700 cm(-1)) spectral region when excited by wavelengths in the ultraviolet or in the short-wavelength portion of the visible spectrum. We report a parametric study of the effects of excitation wavelength [including 532 nm (18797 cm(-1)), 355 nm (28169 cm(-1)), and 266 mu (37594 cm(-1))] and excitation laser power on solid-state uranium compounds. The uranium compounds investigated include uranyl nitrate, uranyl sulfate, uranyl oxalate, uranium dioxide, triuranium octaoxide, uranyl acetate, uranyl formate, zinc uranyl acetate, and uranyl phosphate. We observed the characteristic uranyl fluorescence spectrum from the uranium compounds except for uranium oxide compounds (which do not contain the uranyl moiety) and for uranyl formate, which has a low fluorescence quantum yield. Relative uranyl fluorescence intensity is greatest for 355 nm excitation, and the order of decreasing fluorescence intensity with excitation wavelength (relative intensity/laser output) is 355 nm > 266 nm > 532 nm. For 532 nm excitation, the emission spectrum is produced by two-photon excitation. Uranyl fluorescence intensity increases linearly with increasing laser power, but the rate of fluorescence intensity increase is different for different emission bands.