First of all, you may want to review the previous class about ultraviolet UV, as shown in Figure 1 is the spectrum of electromagnetic waves, from the shortest gamma rays to the longest radio waves are electromagnetic waves, and light is one kind of electromagnetic waves, ultraviolet UV is between 200 nm to 410 nm band of electromagnetic waves, according to light quantum theory, waves. The shorter the light, the stronger the energy, the more destructive it is to organisms. Ultraviolet (UV) light is such a light. Our sun has this band in its spectrum. But because of the protection of the earth's atmosphere, especially the ozone layer of the atmosphere, which absorbs ultraviolet (UV) light from the sun's spectrum, the destructive power is so great. The electromagnetic wave did not enter our living environment, so that all things could thrive and thrive on the earth.

According to the size of the UV energy, in fact, is the different wavelength, we divided the UV into three kinds, they are:

UVA (320~410nm)
UVB (280nm~320nm)
UVC (200nm~280nm)

So the question is, how do we get UV light in addition to the UV light in the solar spectrum?

The first method is to find an atom. The energy difference between the excited state and the ground state of his electrons is just in the ultraviolet range. We know that the transition of electrons in the atomic orbital will do the energy conversion in the form of electromagnetic waves. Fortunately, we have such elements in our periodic table that meet this requirement.

But unfortunately, this element is harmful to the human or earth environment mercury, commonly known as mercury, mercury lamp or commonly known as mercury lamp is ultraviolet disinfection, solidification and exposure of the most mainstream products, even fluorescent lamps and energy-saving lamps are one of the largest applications of mercury lamp, the principle of this lamp is simple, cathode ray tube out High-energy electrons excite the atoms of mercury vapor in an excited state, and the excited electrons return to the ground state to emit ultraviolet light. If red, green and blue RGB phosphor is coated on the outside, it is a fluorescent lamp or energy-saving lamp.

The second method is to use the semiconductor luminescence principle to make UV-band light sources. It is known that the band gap between aluminum nitride and gallium nitride or InGaN semiconductor materials falls between the blue and ultraviolet bands, but how to grow such materials can never be solved. So the idea lasted until the early 1990s, until a series of breakthroughs by the Nobel Prize-winning team of Dr. Hirohiro Nakazaki and Professor Hirohiro Tanabe of Nagoya University and Dr. Hirohiro Nakazaki started the GaN era, as shown in Figure 3, using the mix change of Al, In, Ga, N materials, I They can make ultraviolet and visible light at different wavelengths. (It doesn't matter if we don't understand it here, just remember that we humans can create shoulder-to-shoulder ultraviolet light by mixing some materials.)