UV violet LEDs are receiving extensive attention from lighting equipment manufacturers and LCD manufacturers. Because by using ultraviolet light in combination with fluorescent materials that can convert ultraviolet light into red (R), green (G), and blue (B), respectively, it is possible to realize white LEDs with strong color reproducibility. At present, most of the commercially available white LEDs use blue LEDs and phosphor materials that convert blue light into yellow light, and the red light component is weak. A faint orange color appears when white light shines on a red substance. If you want to use it for backlighting, you have to think about a color filter. But if it is a UV violet LED, these problems can be solved. However, since the luminous efficiency of UV violet LEDs is about half lower than that of products using blue LEDs, brightness has become a major issue for UV LEDs.

After the above technology was published, it became clear how to produce white LEDs with the same brightness as blue LEDs.

Chip size and packaging are critical in development

    In order to solve the performance deterioration phenomenon of LED due to ultraviolet light, the method of not using resin material is adopted in the packaging process. By packing the LED chip into a metal package, it is directly sealed with a metal cover without using any packaging material. This approach has previously been used in GaN-based blue-violet semiconductor lasers. Because the epoxy resin material previously used as a packaging material is prone to the deterioration of the resin performance under the action of ultraviolet light, the transparency is reduced, and the brightness of the LED is also reduced.

    In addition, there is another feature that cannot be ignored. That is to set the UV LED light emission wavelength to 380nm. In products with a wavelength of 405nm, UV LEDs with higher output power already exist. For example, the output power of the Uv violet LED industrial sample supplied by Cree Company of the United States is 250mW. However, considering the currently used fluorescent materials, the RGB conversion efficiency of the 380nm wavelength LED is higher.

    The "21st Century Lighting Project", which includes Yamaguchi University and other institutions, is exploring the feasibility of using 400nm wavelength ultraviolet LEDs. Because "light with a wavelength of 380nm will face a limit sooner or later when improving the luminous efficiency of white LEDs manufactured using ultraviolet LEDs" (Tagguchi Masao, professor of the University's Faculty of Engineering and project leader of the "21st Century Lighting Project").