Abstract: A UV screening composition comprising particles which are capable of absorbing UV light so that electrons and positively charged holes are formed within the particles, characterised in that the particles are adapted to minimise migration to the surface of the particles of the electrons and/or the positively charged holes when said particles are exposed to UV light in an aqueous environment.

Abstract: Compounds having the formula Z2O3:Zx+ where Z is a rare earth metal and x is from 2 to 4, and nanoparticles thereof together with a process for their production and their uses are disclosed.

Abstract: The light emitter is fabricated from a silicon substrate (2) that has a layer of porous silicon (3) on its upper surface. A hole transporter (4) is applied to the upper surface of the porous silicon (2) and penetrates the channels (3′) formed within the porous silicon. An upper semitransparent p-type material such as NiO is used as the upper contact (5) to the hole transporter and a further contact is formed on the base of the silicon wafer (2). The penetration of the hole transporter into the interstices between the silicon particles significantly improves the efficiency of the light emitter by up to two orders of magnitude. The light emitter is particularly suited to use in VLSI and display applications.