Which term most specifically denotes emission of light immediately during exposure to radiation?

• A. Luminescence
• B. Fluorescence
• C. Phosphorescence
• D. Selective Absorption

Answer: (B)

Emission of light while the exciting radiation is still present is fluorescence. In fluorescence, the atoms absorb energy and electrons jump to higher energy levels, then return to their ground state almost immediately, emitting photons in the process. This happens so quickly (typically nanoseconds) that the light appears to flash right as the radiation is applied and ceases as soon as the excitation stops.

Luminescence is the broad category that covers any light emission not due to heat, including fluorescence and phosphorescence. Phosphorescence, by contrast, continues to glow after the excitation source is removed because some electrons stay in longer-lived excited states and decay later. Selective absorption, on the other hand, is about absorbing specific wavelengths of light rather than emitting light, so it isn’t the process described.