Views:237 Author:Site Editor Publish Time: 2020-04-08 Origin:Site
Photoluminescence refers to the luminous phenomenon produced by exciting light-emitting materials with ultraviolet, visible or infrared light. It roughly goes through three main processes: absorption, energy transfer and light emission. The absorption and emission of light between transitions between energy levels pass through excited states. Energy transfer is due to the motion of the excited state.
The energy of the excitation light radiation can be directly absorbed by the luminescent center (activator or impurity), or it can be absorbed by the matrix of the luminescent material. In the first case, the light-emitting center absorbs energy and transitions to a higher energy level, and then transitions back to a lower energy level or a ground state energy level to emit light. The study of the energy spectrum properties of these excited states involves the interaction between the impurity center and the lattice, which can be analyzed by the crystal field theory. As the effect of the crystal field is strengthened, both the absorption spectrum and the emission spectrum are changed from broad to narrow, and the temperature effect is also changed from weak to strong, which makes part of the excitation energy become the character vibration energy, and the luminous efficiency decreases.
Photoluminescent materials are divided into light emitting materials for fluorescent lamps, light emitting materials for plasma display panels (PDP), long afterglow light emitting materials, and up conversion light emitting materials.
Light-emitting diode (LED) is a solid light source, which has the advantages of energy saving, environmental protection, full solidification and long life. It is one of the important ways for humans to resolve the energy crisis in the 21st century. White LED uses its power saving (1/8 of incandescent, 1/2 of fluorescent), small size, low heat generation, low voltage or low current start, long life (more than 120000h), fast response, shock resistance, shock resistance. The advantages of recyclability, pollution-free, flat packaging, and easy development into thin and short products have been rapidly developed. White LED is widely used in a variety of lighting fields such as urban landscape lighting, liquid crystal display backlight, indoor and outdoor general lighting, etc. It is considered as a new generation of green lighting light source that replaces incandescent and fluorescent lamps.
Long afterglow luminescent material is a kind of photoluminescence material that can store the energy of external light irradiation under natural light or artificial light source, and then slowly release it in the form of visible light at a certain temperature (referring to room temperature). Long afterglow luminescent materials are called light storage materials or noctilucent materials. Long afterglow luminescent materials have important applications in low-light display, lighting, special environments (transportation, aerospace, navigation, printing and dyeing, textiles, art, etc.).
An up-conversion luminescent material is a luminescent material that absorbs low-energy light radiation and emits high-energy light radiation. Up-transfer luminescence refers to the phenomenon in which two or more low-energy photons are converted into one high-energy photon. The luminescence mechanism of the up-conversion luminescent material is due to the coupling effect of two-photon or multi-photon; its characteristic is that the absorbed photon energy is lower than the emitted photon energy, this phenomenon violates Stokes' law, so this kind of the material is also called anti-Stokes luminescent material. Upconverting luminescent materials in some documents specifically refer to materials that convert infrared light into visible light.
The most common application of photoluminescence is fluorescent lamps. It emits visible light by the ultraviolet light generated by the gas discharge in the lamp tube exciting the luminescent powder on the tube wall. Its efficiency is about 5 times that of incandescent lamps. In addition, the photoluminescence of "black light lamps" and other monochromatic lamps are widely used in printing, reproduction, medical, plant growth, insect trapping and decoration technologies. The up-converting material can convert infrared light into visible light and can be used to detect infrared light, such as the light field of an infrared laser.
Photoluminescence is a non-destructive and highly sensitive analytical method. It can provide information about the structure, composition, and environmental atomic arrangement of the material. The application of laser makes this kind of analysis method penetrate into the fields of micro area, selective excitation and transient process, and also makes it an important research method. It is now widely used in physics, materials science, chemistry, and molecular biology.