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Special Topic 3.3 Phosphorescence excitation spectra

The more convenient method of phosphorescence excitation was introduced by Kearns in 1965. Because emission spectroscopy is much more sensitive than absorption, particularly for phosphorescence that can efficiently be separated from stray light and fluorescence, the determination of singlet triplet absorption spectra by monitoring the resulting phosphorescence emission has often been successful with comparatively little effort. [Pg.90]

Recent developments of pulsed light sources, optical components, fast and sensitive detectors and electronic equipment for data collection and analysis have permitted the construction of numerous instruments, often commercially available, for the collection of luminescence data with excellent resolution in time, spectral distribution and space. The sensitivity has reached the ultimate level that allows the characterization of such properties for single molecules (see Section 3.13). Only an overview of some of these techniques is given here. [Pg.91]

Ultrashort fluorescence lifetimes are best determined by photon upconversion. An excellent description of the technique for non-specialists wishing to set up an experiment is in preparation as part of a current IUPAC project on ultrafast intense laser chemistry .181 The time resolution is basically limited by the temporal width of the laser pulses that are being used. An intense gate pulse at frequency vq is mixed with the fluorescence at a frequency vp in a nonlinear optical crystal (Special Topic 3.1), to create a short pulse at the sum frequency i j. The gate pulse thus represents a time window for the fluorescence [Pg.91]

6 Absorption and Emission Spectroscopy with Polarized Light [Pg.92]

The orientation of transition moments in the molecular framework can be predicted by quantum mechanical calculations (Sections 2.1.4 and 4.4). Experimentally, the direction of transition moments can be assessed by studying the absorption of linearly polarized light by samples in which the molecules are preferentially oriented. Complete orientation is available in single crystals. However, optical measurements on single crystals are demanding and rarely practicable, not least because extremely thin crystals are required for absorption studies. [Pg.92]


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