Multiple site occupancy induced a novel broadband Ca8(Al12O24)(WO4)2: Eu2+ blue phosphor for pc-converted WLEDs

A series of novel broadband blue-emitting Ca ₈ (Al ₁₂ O ₂₄ )(WO ₄ ) ₂ : x mol% Eu ²⁺ (0.1 ≤  x  ≤ 2.5) phosphors were synthesized by the solid-state method. Based on the crystal structure and the Rietveld refinement results of XRD, the Ca ₈ (Al ₁₂ O ₂₄ )(WO ₄ ) ₂ : Eu ²⁺ phosphors were proven to be a pure-phase material. The Ca ₈ (Al ₁₂ O ₂₄ )(WO ₄ ) ₂ host with the larger bandgap energy can provide a satisfactory bandgap environment for the Eu ²⁺ ions. Under 325 nm excitation, the Ca ₈ (Al ₁₂ O ₂₄ )(WO ₄ ) ₂ : Eu ²⁺ exhibits a broad blue-emitting band in the range of 380–550 nm, resulting from the 4f ⁶ 5d ¹ →4f ⁷ transition of Eu ²⁺ . As the concentration of Eu ²⁺ increases, the emission peak of Ca ₈ (Al ₁₂ O ₂₄ )(W O ₄ ) ₂ : Eu ²⁺ undergoes a redshift, originating from the decrease in the 5d orbital energy level caused by the transformation of Eu ²⁺ from a lower to a higher coordination number. Simultaneously, the concentration quenching causes the emission intensity of samples to initial increase and subsequent decrease, with the optimal doping concentration of Eu ²⁺ being 0.3 mol%. The concentration quenching mechanism has been confirmed to be the electric dipole-dipole interaction. Additionally, the Ca ₈ (Al ₁₂ O ₂₄ )(WO ₄ ) ₂ : 0.3 mol%Eu ²⁺ shows bright blue light (0.150, 0.054), and higher color purity (92.0%) and a low CCT (1754.7 K) These results manifest that novel blue broadband Ca ₈ (Al ₁₂ O ₂₄ ) (WO ₄ ) ₂ : Eu ²⁺ phosphors have potential application prospects in pc-WLED lighting driven by ultraviolet excitation.