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

Abstract A series of novel broadband blue-emitting Ca₈(Al₁₂O₂₄)(WO₄)₂: x mol% Eu²⁺ (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 Ca₈(Al₁₂O₂₄)(WO₄)₂: Eu²⁺ phosphors were proven to be a pure-phase material. The Ca₈(Al₁₂O₂₄)(WO₄)₂ host with the larger bandgap energy can provide a satisfactory bandgap environment for the Eu²⁺ ions. Under 325 nm excitation, the Ca₈(Al₁₂O₂₄)(WO₄)₂: Eu²⁺ exhibits a broad blue-emitting band in the range of 380–550 nm, resulting from the 4f⁶5d¹→4f⁷ transition of Eu²⁺. As the concentration of Eu²⁺ increases, the emission peak of Ca₈(Al₁₂O₂₄)(W O₄)₂: Eu²⁺ undergoes a redshift, originating from the decrease in the 5d orbital energy level caused by the transformation of Eu²⁺ 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 Eu²⁺ being 0.3 mol%. The concentration quenching mechanism has been confirmed to be the electric dipole-dipole interaction. Additionally, the Ca₈(Al₁₂O₂₄)(WO₄)₂: 0.3 mol%Eu²⁺ 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 Ca₈(Al₁₂O₂₄) (WO₄)₂: Eu²⁺ phosphors have potential application prospects in pc-WLED lighting driven by ultraviolet excitation.