The primary distinction between fluorescence and phosphorescence lies in the nature of the light emission after excitation. Fluorescence involves the emission of light that ceases almost immediately upon removing the excitation source, whereas phosphorescence involves light emission that persists even after the excitation source is removed.
Regarding LEDs (light-emitting diodes), they operate on a different principle altogether. LEDs are based on electroluminescence, which is the process of light emission resulting from the recombination of charge carriers (electrons and holes) within a semiconductor material. This recombination releases energy in the form of photons, producing light.
LEDs do not rely on either fluorescence or phosphorescence processes. Instead, they generate light through a phenomenon known as radiative recombination. When a voltage is applied across the LED, electrons and holes combine at the junction of two different semiconductor materials, releasing energy in the form of photons. This process is immediate and does not involve the delayed emission characteristic of phosphorescence.
Therefore, when discussing LEDs, it is more accurate to describe their light emission as a result of electroluminescence rather than fluorescence or phosphorescence.