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Our project aims at developing LEDs for UV emission for various applications, including in particular phototherapy at 310 nm, and sterilization of water and food at 275 nm. Such UV LEDs are alternatives to the existing Hg lamps, which are often criticized for the toxicity of Hg, but also for their slow turn on. Hence, the major impact in the long term is economic and social. As detailed hereafter, the UV market is large and growing. In developed countries, alternative solutions exist and their replacement by nitride based UV diodes will be motivated by a financial payback so that the main impact can be described in economic terms. In underdeveloped countries however, the situation is quite different, in particular for the water sterilization at 275 nm. There is currently no good solution for this problem and the consequences are dramatic. In that case, the impact is clearly a social one and it can be of vital importance.
The UV market is worth $ 200M, mainly due to UV curing but with an increasing part due to phototherapy and sterilization. The market forecast indicates that applications at 365 nm (curing) dominate the market but applications at 310 nm (phototherapy) and at 275 nm (sterilization) are emerging and will dominate the market in five years time. While LEDs at 365 nm can be obtained without TJ and a low operating voltage, LEDs at 310 and 275nm will require a TJ to operate at low voltage.
UV C (275 nm) is very efficient in eliminating bacteria in water. Safe drinking water and basic sanitation is of crucial importance for health, especially among children. Water-related diseases are the most common cause of illness and death among the poor in developing countries. According to the World Health Organization, 1.6 million deaths of children per year can be attributed to unsafe water, poor sanitation, and lack of hygiene. The WHO/UNICEF Joint Monitoring Program evaluated that meeting the Millennium Development Goals Target 10 (i.e. halve, by 2015, the proportion of people without sustainable access to safe water and basic sanitation) would avoid 470 000 deaths per year. Developed countries have succeeded in purifying and distributing drinking water. In France, this process started in the XXth century. In 1930, 23% of the cities only had drinking water, and the process of building a complete drinking water distribution system was achieved in the 80’s. The last step of purifying process was, and still is, the addition of chlorine. While efficient, it has some drawbacks. First, the concentration must remain small if the water is to be drunk. Second, and this partially results from the first point, it takes a certain time for eliminating bacteria (about 2 hours). Third, it requires providing chlorine to water plants. Fourth, water smells chlorine at various degrees. Although these drawbacks have been accepted for decades, some cities are now changing technology and start to use UV. As an example of an ordinary city moving towards UV technology, Modane switched to UV beginning of 2016. For an annual water consumption of 240 000 m3, a UV system worth 60 k€ has been installed, and the payback will be reached in the long term by saving on the chlorine. Current systems are using Hg lamps, which are quite efficient: from 25 to 40% efficacy at 254 nm for low pressure lamps. They have a lifetime of about 8000h, i.e. one year. Their limited lifetime is one motivation for replacing them by UV LEDs. The second motivation is the hazard related to the Hg vapors. The third one is the evolution in the legislation and the banishment of Hg lamps for lighting. When Hg lamps will stop being used for lighting, developing them for the sole market of water treatment may become problematic. Hence, UV LEDs are likely to take advantage of this opportunity to penetrate the water treatment market.
