A getter device including a substrate formed of a first getter material having a composition for gettering a first gas species, and a second getter material contacting an external surface of the substrate and having a composition for gettering a second gas species. The substrate has internal porosity connected to openings at its external surface, and the second getter material covers at least a portion of the external surface of the substrate but is absent from at least part of the internal porosity within the substrate so that the first getter material is exposed within the internal porosity for gettering the first gas species. According to a second aspect, a substrate is formed of a material transparent to radiation, and a film of getter material is deposited on the substrate to be sufficiently thin and/or porous so that the film is also transparent to the radiation transmitted through the substrate.