Question

What interferences are encountered in UV fluorescence?

Why is phosphorescence not used as extensively as fluorescence for analytical measurements?

Answer 1

Ans 1: Fluorescence is the process by which a molecule absorbs a photon of light exciting an electron to a higher energy state. This electron often relaxes through internal conversion or through vibrational relaxation down to the lowest vibrational level of the excited state and then a photon of a longer wavelength (lower energy) is emitted. This shift in the energy of the emitted photon relative to excited photon is called a Stokes Shift. Exceptions to this decrease in energy of the emission relative to the excitation can be found in the case of multiphoton excitation.

There are two main mechanisms by which a compound can directly interfere with a UV fluorescent: quenching and autofluorescence.

Ans 2: phosphorescence is not extensively used as fluorescence because unlike fluorescence, phosphorescence does not re-emit immediately as it absorbs. fluorescence takes around 10^-9 to 10^-7 sec while phosphorescence takes around 10^-3 to 10^2 sec. The slower time scales of the re-emission of phosphorescence are associated with "forbidden" energy state transitions in quantum mechanics. As these transitions occur very slowly in certain materials, absorbed radiation is re-emitted at a lower intensity for up to several hours after the original excitation. therefore phosphorescence is not a suitable property for analytical measurement.