Ultraviolet light screening compositions

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.

1 . 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.  
     
     
         2 . A composition according to  claim 1  wherein the particles contain luminescence trap sites and/or killer sites.  
     
     
         3 . A composition according to  claim 2  wherein the particles are reduced zinc oxide particles.  
     
     
         4 . A composition according to  claim 2  wherein the particles comprise a host lattice incorporating a second component to provide luminescence trap sites and/or killer sites.  
     
     
         5 . A composition according to  claim 4  wherein the host lattice is a metal oxide selected from zinc oxide and titanium dioxide.  
     
     
         6 . A composition according to  claim 4  wherein the second component is selected from a metal such as nickel, iron, chromium, copper, tin, aluminium, lead, silver, zirconium, manganese, zinc, cobalt, gallium niobium, vanadium, antimony, tantalum, strontium, calcium, magnesium, barium, molybdenum and silicon ions.  
     
     
         7 . A composition according to  claim 4  wherein the second component is selected from iron, chromium, manganese and gallium ions the 3+ state.  
     
     
         8 . A composition according to  claim 4  wherein the particles comprise a titanium dioxide host lattice doped with manganese ions in the 3+ state.  
     
     
         9 . A composition according to  claim 4  wherein the second component is present in an amount of from about 0.1 to 1%.  
     
     
         10 . A composition according to  claim 1  wherein the particles comprise a population of coated nanoparticles of a metal oxide.  
     
     
         11 . A composition according to  claim 10  wherein the metal oxide is titanium dioxide.  
     
     
         12 . A composition according to  claim 10  wherein the coating is selected from trioctylphosphine oxide and sodium hexametaphosphate.  
     
     
         13 . A composition according to  claim 1  wherein the size of the particles is from 1 to 200 nm.  
     
     
         14 . A composition according to  claim 1  wherein the particles have an outer coating.  
     
     
         15 . A method for preparing a composition as defined in  claim 1  which comprises associating the particles with a carrier.  
     
     
         16 . A particle as defined in  claim 4  which comprises a host lattice incorporating a second component to provide luminescence trap sites and/or killer sites.  
     
     
         17 . A particle as defined in  claim 10  which comprises a population of coated nanoparticles of a metal oxide.  
     
     
         18 . A method for preparing a particle as defined in  claim 16  which comprises combining a host lattice with a second component to provide luminescence trap sites and/or killer sites.  
     
     
         19 . A method for preparing a particle as defined in  claim 17  which comprises combining a population of coated nanoparticles of a metal oxide to form a larger particle.  
     
     
         20 . A composition according to  claim 1  wherein said composition is for topical application.  
     
     
         21 . A composition according to  claim 20  wherein said composition is a sunscreen.