Luminescence is a kind of light emission of non thermal radiation of matter, and its duration is much longer than the vibration period of light (巴巴巴巴巴巴巴巴巴巴巴巴巴.Luminescence is different from the thermal radiation of incandescent objects such as incandescent lamps.The basic properties of thermal radiation do not vary with the properties of the heating body, while luminescence reflects the characteristics of the material.
Luminescence is a result of the interaction between external factors (photoelectric radiation, etc.) and matter.Once the external action stops, the luminescence will also stop, but there is a duration that is much longer than the vibration period of light (10-14 seconds).This feature was pointed out by Vavilov, a Soviet scientist. It can distinguish light emission from other types of light emission, such as scattering and reflection.
The shortest luminous duration known is longer than 10-12 seconds, and the longest is several hours.[1]
According to intensificationenergyThe methods can be divided into the following situations:
① Photoluminescence the phenomenon of luminescence caused by an object excited by external light.Its light emission wavelength is generally greater than or equal to the excitation light wavelength.Medical x-ray machine uses x-ray to excite phosphor and produce visible light.
② Electroluminescence the phenomenon of light emission in which electric energy is directly converted into light energy.In the past, it was called electroluminescence, such as the luminescence generated by discharge.Fluorescent lamp is the combination of electroluminescence and photoluminescence: the mercury atom in the lamp is excited by the discharge of two electrodes, and the ultraviolet ray emitted by the mercury atom is received and converted into visible light by the phosphor on the tube wall.Television screens are also electroluminescent.
③ Radioluminescence the emission of light by a radioactive substance.On a clock or instrumentLuminous paintIt is the use of emitting light.They contain phosphor and radioactive material tritium or radium.
④ Chemiluminescence luminescence caused by chemical reaction.The energy released by some chemical reactions, especially the oxidation reaction, can excite electrons.For light-emitting molecules, this can produce chemiluminescence, such as the chemiluminescence of compound Luminol.
⑤ Bioluminescence - a special form of luminescence occurring in organisms.Such as fireflies.The luminous efficiency can reach 100%.[2]
application area
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The main application fields of luminescence are light sources, display devices, detector devices and optoelectronic devices.In addition, it can also be used for trace analysis in inorganic chemistry and analysis of organic molecules such as proteins and nucleic acids;It can be used for medical diagnosis;It is also used in petroleum, paper making, food, metal processing and other industries and agriculture.Polanyi, the 1986 Nobel Prize winner, used infrared chemiluminescence to analyze the structure and properties of newly formed molecules.
For inorganic insulators or semi insulators, the structure of the luminescence center and the possible lattice sites occupied by activator ions can be analyzed by their luminescence spectra.Luminescence can also vividly show the process of energy transmission.
There are various pigments in the chloroplasts of plants. Their luminescence is used to study how the light energy absorbed by plants is transferred and transformed into chemical energy to supply water andcarbon dioxideUsed in combination.
The luminescence of pure semiconductors can provide information about their energy band structure and properties, and the luminescence can also show various elemental excitation spectra.The photoluminescence spectrum of GaAs is shown in the figure. The exciton absorption is shown by two dotted lines.According to the theory, exciton and photon can couple to generate polariton, which has two states with small energy difference.This has been confirmed experimentally that they appear on both sides of the exciton absorption line (arrow).Luminescence can also provide the structural details of donor or acceptor energy levels, that is, some excited states before their ionization, as well as various composite luminescence spectra.Overheating luminescence provides information about the distribution and scattering of overheated electrons.This is very important for semiconductor devices with high speed response.
energyEfficiency - refers toluminescenceThe ratio of the energy input from the excitation source to the energy input from the excitation source;
luminosityEfficiency - refers toluminescenceThe ratio of the luminosity of and the input luminosity of the excitation source.
Concept of light
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lightIt is a kind ofelectromagnetic waveSubstance in form.Electromagnetic waves have a wide wavelength range, including radio wavesinfrared、visible light, UVX-ray, cosmic rays, etc.Among them, electromagnetic waves with a wavelength of 380nm~780nm can causevisionReaction, so calledvisible light。Light is reversible.
be inground stateElectron absorption in molecules ofenergy(Electrical, thermal, chemical andLight energyAnd so on) are excited to the excited state. These electrons in the excited state usually return to the ground state in the form of radiative transition or non radiative transition.
Radiation free transition: vibration relaxation (VR), internal conversion (IC), inter system transition (ISC), etc.
fluorescenceIs excited bySinglet stateMinimum vibrationErgosphereIt is generated by the interlayer transition of each vibration energy to the ground state;andphosphorescenceIt is produced by the transition between the lowest vibrational energy layer of the excited triplet state and the vibrational energy layers of the ground state.
visible light
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(1) Visible light has the following characteristics
(A) The visible light wavelength range is limited and only covers the wholeelectromagnetic waveA tiny fraction of the spectrum.
(B) Different wavelengths of light present different colors, from long to short wavelengths, showing red, orange, yellow, green, green, blue, and purple respectively.
(C) SinglewavelengthAnd the light whose spectral width is less than 5nmMonochromatic light。Light containing two or more wavelength components is calledCompound lightThe compound light makes the human eye produce mixed colors.Because it cannot act asMonochromatic lightAppears inspectrumSo it is also calledNonspectral light。
Through a large number of experiments, people found thatMonochromatic lightMost colors in nature can be obtained by mixing in a certain proportion.The three monochromatic lights with this characteristic are calledTribasic colour light, and this discovery is also summarized as the three primary color theorem, the main contents of which are as follows:
Most colors in nature can be determined byTricolorMixed in a certain proportion;On the contrary, these colors can also be decomposed into three primary colors;
TricolorThey must be mutually independent, that is, none of the primary colors can be obtained by mixing the other two primary colors;
The hue and saturation of mixed colors are determined byTricolorThe mixing proportion of;
