Discovery of New Narrow-Band Phosphors with the UCr4C4-Related Type Structure by Alkali Cation Effect

Narrow‐band luminescence materials used in white light‐emitting diodes (WLEDs) have demonstrated a great potential to increase the maximum accessible color gamut, improve the color rendition, or enhance the visual luminous efficacy for illumination and display devices. So far, the discovery of narrow‐band rare earth doped phosphors for emerging applications remains challenging owing to the limited systems in use and the broadening effect of 4f–5d transition. Here, two narrow‐band cyan‐emitting phosphors with the UCr₄C₄‐related type structure, RbNa₂K(Li₃SiO₄)₄:Eu²⁺ (RNKLSO:Eu²⁺) and CsNa₂K(Li₃SiO₄)₄:Eu²⁺ (CNKLSO:Eu²⁺), are reported. The narrow‐band emission results from the highly condensed network and a cube‐like site for the activator (Eu²⁺). The emission peak assignments are investigated, and the variations of luminescence behavior with compositional changes of alkali cations are elaborated in detail. RNKLSO:8% Eu²⁺ (95%@250 °C of the integrated emission intensity at 25 °C) shows better thermal stability than that of CNKLSO:8% Eu²⁺ (79%@250 °C), which can be explained by the thermally activated crossover process represented in the configurational coordinate diagram. The optical properties of the as‐fabricated WLEDs are studied and demonstrate potential with tunable properties for the full spectrum phosphor‐converted LEDs. These findings in UCr₄C₄‐type phases help shedding light on new avenues for fabricating new and totally unexpected narrow‐emitting phosphors with versatile applications.