Solid-surface luminescence interactions

Applications and Interactions in Solid-Surface Luminescence Analysis... 

Solid-surface room-temperature phosphorescence (RTF) is a relatively new technique which has been used for organic trace analysis in several fields. However, the fundamental interactions needed for RTF are only partly understood. To clarify some of the interactions required for strong RTF, organic compounds adsorbed on several surfaces are being studied. Fluorescence quantum yield values, phosphorescence quantum yield values, and phosphorescence lifetime values were obtained for model compounds adsorbed on sodiiun acetate-sodium chloride mixtures and on a-cyclodextrin-sodium chloride mixtures. With the data obtained, the triplet formation efficiency and some of the rate constants related to the luminescence processes were calculated. This information clarified several of the interactions responsible for RTF from organic compounds adsorbed on sodium acetate-sodium chloride and a-cyclodextrin-sodium chloride mixtures. Work with silica gel chromatoplates has involved studying the effects of moisture, gases, and various solvents on the fluorescence and phosphorescence intensities. The net result of the study has been to improve the experimental conditions for enhanced sensitivity and selectivity in solid-surface luminescence analysis. 

Interactions in Solid-Surface Luminescence Temperature Variation. Solid-surface luminescence analysis, especially solid-surface RTF, is being used more extensively in organic trace analysis than in the past because of its simplicity, selectivity, and sensitivity (,1,2). However, the interactions needed for strong luminescence signals are not well understood. In order to understand some of the interactions in solid-surface luminescence we recently developed a method for the determination of room-temperature fluorescence and phosphorescence quantum yields for compounds adsorbed on solid surfaces (27). In addition, we have been investigating the RTF and RTF properties of the anion of p-aminobenzoic acid adsorbed on sodium acetate as a model system. Sodium acetate and the anion of p-aminobenzoic acid have essentially no luminescence impurities. Also, the overall system is somewhat easier to study than compounds adsorbed on other surfaces, such as filter paper, because sodium acetate is more simple chemically. 

Solid-surface luminescence analysis is a useful approach for organic trace analysis because of its simplicity, sensitivity, and selectivity. It will continue to be used in environmental analysis and other areas not only for the reasons mentioned above but also because it is readily adaptable to field work. By developing a fundamental understanding of the interactions responsible for strong RTF and RTF signals, the advantages and disadvantages of the luminescence approach will be more specifically defined in the future. 

Luminescence probing techniques have demonstrated their versatility in characterizing the environment found on, the mobility and accessibility allowed at, and the reactivity occurring at gas-solid and liquid-solid interfaces. Pyrene can be used to monitor the interactive nature of the silica surface, and 1-AP and PCA faithfully distinguish the silanol functionality present at the silica gel surface. MCB silica gel possesses a higher relative geminal silanol concentration compared to the FS-662 silica gel ... 

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