Abstract: A surface treatment material useful in making coatings to be applied to fomitic surfaces to inhibit the proliferation of microorganisms, especially bacteria, comprises a photocatalytic component consisting of a metal oxide catalyst together with a metal dopant acting as an upconversion luminescence agent, for example based upon ErCl3, TiO2, Er(NO3)3/TiO2, NdCl3/TiO2, Nd(NO3)3/TiO2, GdCl3/TiO2, Gd(NO3)/TiO2, and optionally including other metals, especially a transition metal such as silver, provides antimicrobial activity in the dark, and enhanced antibacterial activity when exposed to wavelengths in the range of 350 to 790 nm, and thus finds utility in the healthcare, leisure and food industries.