Nonluminescence

Nonluminescence is the absence of luminescent emission from a substance under excitation. It describes materials or conditions in which light is not emitted through luminescent processes such as fluorescence, phosphorescence, chemiluminescence, or bioluminescence. By definition, luminescence involves light produced by mechanisms other than heat, so nonluminescence is effectively the lack of such light emission under specified stimuli.

Causes of nonluminescence include a very low quantum yield, rapid nonradiative decay that dissipates energy as heat, or electronic structures that do not permit radiative transitions within the detectable range. Some materials have energy gaps or selection rules that prevent photon emission, or they may require activator ions or sensitizers to become luminescent. In solids, defects, dopant concentrations, or structural factors can also suppress emission. It is important to note that nonluminescence can be conditional: a material might emit under certain wavelengths, temperatures, or chemical environments but not under others.

In practice, many common substances are nonluminescent under ordinary laboratory conditions; for example, plain glasses and many polymers show little to no detectable emission. In luminescence research, nonluminescent materials serve as controls or references, while others may be rendered luminescent through doping, sensitization, or changes in excitation.

Measurement and reporting typically rely on emission spectra, intensity, and decay lifetimes. If no detectable emission is observed above background under specified excitation, the material is described as nonluminescent for that setup. Note that nonluminescence does not imply total darkness; such materials may still absorb or scatter light.