7. Which of the following description about various forms of light emission is NOT correct? (4%)
(A) Fluorescence and phosphorescence signals are typically measured at a 90° angle to the excitation beam.
(B) In fluorescence spectra, the emitted radiation usually has a longer wavelength than the excitation radiation; this
difference is called the Stokes shift.
(C)The average lifetime of an excited triplet state is orders of magnitude shorter than that of an excited singlet state.
(D)Chemiluminescence occurs when a chemical reaction generates an electronically excited species; this excited
molecular species then emits light as it relaxes to the ground state.
(E)Chemiluminescence is usually measured without selecting a specific wavelength for detection.
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