Final answer:
The main difference between phosphorescent and fluorescent materials is the duration of light emission after the excitation source has been removed. Fluorescent materials emit light nearly instantaneously, while phosphorescent materials have a delayed light emission because of electrons transitioning to metastable states with longer lifetimes.
Step-by-step explanation:
The major difference between phosphorescent and fluorescent materials is a) The emission of light after the removal of the excitation source. While both types of materials are capable of transforming nonvisible electromagnetic radiation into visible light, the mechanisms and timeframes in which they release this energy differ substantially.
Fluorescence occurs when a material absorbs light at one wavelength (excitation wavelength) and almost immediately re-emits light at a longer wavelength (emission wavelength). The process typically involves electrons being excited from a ground state to an excited state and returning to the ground state, releasing energy in the form of light with very short lifetimes, typically about 10-8 seconds.
In contrast, phosphorescence involves electrons being excited to metastable states that have significantly longer lifetimes, sometimes ranging from milliseconds to minutes or hours. This delay is due to the electrons transitioning to energy levels with quantum numbers that greatly differ from those of available lower levels. As a result, phosphorescent materials can continue to emit light long after the excitation source has been removed.