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AMORAN: sensor for intrinsic fluorescence measurements of PET
Fluorescence is the property of absorbing radiation and emitting instantaneously a radiation, which is shifted (compared to the absorption) to longer wavelengths. The figure illustrates the changes of a molecule's energy levels and the spectra of absorption (excitation) and fluorescence.
PET provides a special fluorescence emission, only occurring in singular dimers (see figure left). These dimers are only present in amorphous regions, in any state of deformation.
Energy levels (left) and spectrum (right) of intrinsic fluorescence or PET dimers.
The fibre is illuminated with UV radiation polarized either parallel and perpendicular to its axis. The fluorescence radiation is analysed either parallel and perpendicular to the fibre axis.
The measured four intensities are:
I33: intensity of the fluorescence
light polarizer and analyser are parallel to sample axis (3),
I31: polarizer parallel, analyser perpendicular to draw axis,
I13: polarizer perpendicular, analyser parallel to draw axis,
I11: polarizer and analyser perpendicular to draw axis.
the orientation values are calculated by:
and r is the emission anisotropy.
Biaxial material is characterized by the intensity ratios RTD and RMD:
Further information about the measurement principle and the application of this sensor is available in the literature.
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