A particulate lanthanide-doped material comprising an inorganic host phosphor and a lanthanide ion dopant. With the lanthanide-doped material being in an oxidized state, photoluminescence is suppressed. Photoluminescence of the material can be activated by the presence of a reducing substance that reduces the lanthanide-doped material in a redox interaction. The lanthanide-doped material can be used for biodetection (e.g. detecting the presence of microorganisms in a sample). This could have numerous applications, such as detecting the presence of contaminating microorganisms in a sample (e.g. in a food or cosmetic product).