Fotoluminenssi

Fotoluminenssi, also known as photoluminescence, is a process where a substance absorbs photons (light) and then re-emits photons. This emission typically occurs at a longer wavelength than the absorbed light. The absorbed photons excite electrons within the material to higher energy levels. As these electrons return to their ground state, they release energy in the form of photons, which we perceive as emitted light.

There are two primary types of photoluminescence: fluorescence and phosphorescence. Fluorescence is a rapid emission process that occurs almost instantaneously after excitation, typically within nanoseconds. Once the excitation source is removed, the fluorescence stops. Phosphorescence, on the other hand, involves a slower emission process. Excited electrons can become trapped in metastable states, leading to a delayed emission of light that can persist for seconds, minutes, or even hours after the excitation source is removed. This lingering glow is what we commonly refer to as phosphorescence.

The phenomenon of photoluminescence has numerous applications. It is utilized in fluorescent dyes and pigments for markers and displays, in fluorescent lighting where a mercury vapor lamp excites a phosphor coating, and in scientific research for imaging and sensing. Phosphorescent materials are found in glow-in-the-dark toys, safety signs, and watch dials. The specific wavelengths of absorption and emission, as well as the duration of the emitted light, are characteristic properties of different photoluminescent materials and are key to their respective applications.