Ultraviolet light gives you a tan, is used in the lithography process to produce many computer components, and cannot be seen by the human eye. It is also very hard to produce efficiently because of its small wavelength. To directly produce UV light would require the source is the size of the wavelength, which is just very hard to work with. Researchers at the University of Michigan have found a way to get around this requirement using a nonlinear process.
In optics, a nonlinear material is one which does not emit the same light that enters it. Instead it produces a different harmonic of light. Going up by one harmonic means if the source light is 800 nm (near-infrared), the resulting light would be 400 nm (violet). In this case the wavelength is actually a fourth, instead of a half. This allows a much simpler, more efficient, and cheaper infrared light source to be used to produce UV light.