Photoluminescence

Photoluminescence is a process in which a substance absorbs photons and then re-emits them. Most photoluminescent events, including those materials known as phosphors, are typically very fast, on the order of 10 nanoseconds. However, slower instances, such as phosphorescence, can take up to minutes or hours at low temperature to re-emit the absorbed radiation.

Mechanism

Photoluminescence involves absorption of photons followed by the re-emission of photons. This process can be divided into four key steps: absorption, impurity trapping, recombination, and emission.

In the absorption step, a photon is absorbed and creates a photoexcited electron and a hole. The impurity trapping step involves the movement of the excited electron and the hole towards each other. In the recombination step, the electron and the hole recombine. Finally, in the emission step, a photon is emitted.

Types of Photoluminescence

There are two main types of photoluminescence: Fluorescence and Phosphorescence. Fluorescence is the immediate emission of radiation after excitation, while phosphorescence is a type of photoluminescence where the energy from the absorbed photon undergoes intersystem crossing into a higher triplet state and slowly decays back to the lower singlet state.

Applications

Photoluminescence is used in a wide range of applications, including LED technology, solar cells, and Bioimaging. In LEDs, photoluminescence is used to convert high-energy blue light into lower-energy green and red light. In solar cells, photoluminescence can be used to determine material quality. In bioimaging, photoluminescent probes can be used to image biological structures and processes.

See Also

• Luminescence
• Photophysics
• Quantum dot