Fluorescent material refers to a kind of material that can emit some visible light after being irradiated by electron beam or light (ray) with specific frequency. For example, it is often seen at the crime scene that Luminol reagent, which is used to test blood stains, reacts with iron (- said to be heme) in the blood and emits blue fluorescence when irradiated with ultraviolet light.
Fluorescence is the radiation emitted when a substance is inactivated from the excited state to a low energy state with the same multiplicity. The most common is to absorb ultraviolet light and emit visible light. The most basic condition for a compound to produce fluorescence is that the energy absorbed when it undergoes a multiplicity invariant transition is less than the energy required to break the weakest chemical bond. The compound structure must have fluorescent groups such as=C=0, - N=O, - N=N,=C=N,=C=S, etc.
For molecules with fluorescence characteristics, after absorbing the energy of the incident light, an electronic transition occurs. The excited electrons can release their energy to the ground state through various ways. Without emitting any radiation, they transition to the excited state with slightly lower energy and the same spin multiplicity, and then release energy to the ground state in the form of luminescence, so we can see fluorescence.
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Luminous paint: a kind of material that can give off light in the dark. It can be divided into self luminous type and light storing type. The basic composition of self luminous luminous material in the middle is radioactive material, which does not need to absorb energy from the outside, and can emit light continuously. Radioactivity may cause a hazard to human body (depending on the composition), so its application is greatly limited; Light storing luminous materials rarely use radioactive materials, mainly by absorbing external light energy and slowly releasing it, and must store enough light energy to ensure continuous luminescence for a period of time. The use is basically unrestricted, but the brightness is not as good as that of self luminous materials.
Reflective material: This material is widely used in various traffic signs. At present, traffic signs can be divided into two types: Type - is completely reflective material, that is, to achieve warning purposes by reflecting the incident light back; Another type is photoluminescence, which can not only reflect light, but also emit photons when exposed to light. It looks more eye-catching than ordinary reflective materials, such as chalcogenide materials. These usually do not produce radiation harmful to human body, but whether it has chemical toxicity depends on the specific analysis of specific components.
Fluorescent stick and fluorescent key chain: The fluorescent stick that must be used in festival parties and various concerts is mainly composed of three substances: peroxide, ester compound and fluorescent dye. Shake it for a few times or shake it for a few times. The peroxide reacts with the ester compound, and then transfers the energy after the reaction to the fluorescent dye. Finally, the dye emits fluorescence. The whole process will not emit radiation harmful to the human body. Although the fluorescent rod will not emit harmful rays, the liquid inside is edible, and contact with skin, especially eyes, should be avoided as far as possible. A similar principle applies to fluorescent keychains.
Fluorescent brightener: In order to make the paper look white, some businesses will add fluorescent brightener, or fluorescent bleach, which is a complex organic compound. This whitening agent absorbs ultraviolet light and emits blue light, which is complementary to the yellow light of the paper to form white, so as to achieve whitening effect. It is widely used in paper making, textile, detergent and other fields. This substance does not produce harmful radiation to humans, but may be chemically toxic.
Fluorescent lamp: the fluorescent tube is filled with argon mixed gas and mercury vapor. The discharge of the lamp tube electrode makes mercury emit light in the ultraviolet band. The phosphorous fluorescent paint on the inner surface of the lamp tube absorbs ultraviolet light and emits fluorescence of different colors depending on the proportion of phosphorous components. The phosphorous fluorescent paint on the inner surface of the lamp tube absorbs most of the ultraviolet light during the lighting process. Under normal circumstances, qualified fluorescent lamps are used. Even if there are some tiny cracks on the fluorescent paint coating, the health risk of using fluorescent lamps will not be increased.
Natural fluorescence: the luminescence of fireflies, in short, is a series of complex biochemical reactions catalyzed by fluorescein, and the product of the reaction is the light on their farts.