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Abstract Luminescence is the emission of light from any substance, and occurs from electronically excited states. Luminescence is formally divided into two categories—fluorescence and phosphorescence—depending on the nature of the excited state. In excited singlet states, the electron in the excited orbital is paired (by opposite spin) to the second electron in the ground- state orbital. Consequently, return to the ground state is spin allowed and occurs rapidly by emission of a photon. The emission rates of fluorescence are typically108 s–1, so that a typical fluorescence lifetime is near 10 ns (10.0 x 10–9 s). Photoluminescence is a type of optical spectroscopy in which a molecule is promoted to an electronically excited state by absorption of ultraviolet, visible, or near infrared radiation. The emitted light is detected. Photoluminescence processes are subdivided into fluorescence and phosphorescence [Wehry E. L., 1993]. The key characteristic of fluorescence spectrometry is its high sensitivity. |