A Double‐Band Emitter with Ultranarrow‐Band Blue and Narrow‐Band Green Luminescence

Understanding the origin and mechanisms of luminescence is a crucial point when it comes to the development of new phosphors with targeted luminescence properties. Herein, a new phosphor belonging to the substance class of alkali metal lithosilicates with the generalized sum formula Cs(4−x−y−z)Rb(x)Na(y)Li(z)[Li(3)SiO(4)](4):Eu(2+) is reported. Single crystals of the cyan‐emitting UCr(4)C(4)‐type phosphor show a peculiar double‐band luminescence with one ultranarrow emission band at 473 nm and a narrow emission band at 531 nm under excitation with UV light (λ (exc)=408 nm). Regarding occupation of the channels by the light metal ions, investigations of single‐crystal XRD data led to the assumption that domain formation with distinct lithium‐ and sodium‐filled channels occurs. Depending on which of these channels hosts the activator ion Eu(2+), a green or blue emission results. The herein‐presented results shed new light on the luminescence process in the well‐studied UCr(4)C(4)‐type alkali metal lithosilicate phosphors.