There is disclosed a composition for converting electromagnetic energy to ultraviolet C (UVC) radiation or radiation of a shorter wavelength, the composition comprising at least one phosphor capable of converting an initial electromagnetic energy (A) to an electromagnetic energy (B) comprising UVC radiation or radiation of a shorter wavelength, and an organic or inorganic media containing said phosphor. There is also a method of sterilizing an article by exposing it to UVC radiation or radiation of a shorter wavelength for a time sufficient to deactivate or kill at least one microorganism and/or for a time sufficient to inhibit abnormal cell growth within the body, when said composition is in an implantable medical device. A method of coating an article with such compositions is also disclosed.