Exploring the Multidimensionality of High-Resolution Photoluminescence Spectroscopy to Face Environmental Challenges

Academic Research Topics in Environmental Measurement and Monitoring
Oral Presentation

Prepared by

Contact Information: [email protected]; 407-823-4162


ABSTRACT

The multidimensional nature of photoluminescence phenomena provides fluorescence and phosphorescence techniques with unique potential for the analysis of polycyclic aromatic compounds in environmental matrixes. The simplicity of experimental procedures makes room-temperature photoluminescence techniques the most popular approaches. The main limitation of room-temperature techniques is the broad nature of excitation and emission spectra. Reducing the sample temperature offers several advantages. Luminescence quantum yields often increase, and the complications of oxygen quenching and energy transfer are eliminated. Temperature effects on luminescence are specially pronounced in the so-called line-narrowing photoluminescence techniques, where the sample matrix is frozen to 77K or below.
This presentation will highlight significant improvements made to line-narrowing photoluminescence techniques. The complications of traditional low-temperature methodology were eliminated by using a cryogenic fiber optic probe with the distal end frozen directly into the sample matrix. It is possible now to routinely perform measurements at liquid nitrogen (77K) and helium (4.2K) temperatures; frozen samples are prepared in a matter of seconds. The full dimensionality of photoluminescence is obtained with the aid of a pulsed tunable dye laser for sample excitation, a spectrograph and an intensifier-charged coupled device (ICCD). Because of the spectrograph and the ICCD, wavelength time matrices (WTMs) and time-resolved excitation-emission matrices (TREEMs) are efficiently recorded in short analysis time.
Emphasis will be given to the environmental analysis of high molecular weight polycyclic aromatic hydrocarbons (HMW-PAHs). Similar chromatographic behaviors and almost identical mass fragmentation patterns make separation and identification of HMW-PAHs via GC-MS and HPLC-MS difficult. Since the carcinogenic properties of those pollutants differ significantly within isomers of the same molecular weight, it is of paramount importance to determine the most toxic isomers even if they are present at much lower concentrations than their less toxic isomers.