I think, the question should by:
When does quenching occur in a chemiluminescence reaction?
Quenching is a process that decreases the fluorescence intensity of any compound while chemiluminescence refers to emission of cold light due to a chemical reaction. Quenching of fluorophore occurs in a chemiluminescence reaction when the fluorescence of the fluorophore is quenched that leads to the decrease in the intensity of the fluorescence.
In terms of energy transfer, quenching occurs when loss of excitation energy of the molecule takes place in a chemiluminescence reaction.
