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Electromagnetic radiation excitation

This excitation method includes infrared, visible light, ultraviolet light, x-rays and gamma rays. They use appropriate materials to absorb these energies and then partially emit them in the form of visible light. This energy source is most widely used in exciting luminescence, and its emission wavelength is generally longer than the wavelength of absorbed radiation (Stokes' law). For example, the most convenient way to excite phosphors is to use the ultraviolet radiation generated by certain gas discharges. For example, discharges in mercury vapor and argon can convert more than 50% of electrical energy into ultraviolet radiation of 253.7 nanometers and 185.0 nanometers. By selecting appropriate phosphors to convert this ultraviolet light into visible light, an effective conversion of electrical energy into white light can be obtained. This is the basic principle of fluorescent lamps. In the past three decades, the efficiency of producing white light using this method has been improved to about 80 lumens/watt, which is higher than any light source that relies on increasing the temperature of the incandescent body to emit light.

Although the high-voltage arc of mercury can produce a higher proportion of visible light, it also emits a portion of ultraviolet light close to 365 nanometers, so it is necessary to use this part of the emission with various different luminescent materials. Red-emitting phosphors are usually used to make up for the lack of red light in the visible spectrum of mercury. Some metal halide lamps have a wider linear spectrum than lamps using mercury alone, so phosphors can also be used to take advantage of the ultraviolet radiation emitted by mercury and other metals.

Radioactive substances emit very short wavelength X-rays and gamma rays, which can excite a variety of materials to emit light. However, because their penetration is too strong, the energy that can be absorbed by the appropriate thickness of the phosphor screen is reduced, so the light output is small and can only be used as an indicator light source, such as radiology, material testing, nuclear research, etc.

Under strong excitation and high-precision controlled optical conditions, some crystalline phosphors that normally have linear emission can emit the same wavelength as a very strong and narrow coherent light beam, rather than the general messy and diffuse light emission. This is the role of lasers, which are generally not used as fluorescence, but to a large extent this is just a matter of definition.

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