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

A series of novel broadband blue-emitting Ca₈(Al₁₂O₂₄)(WO₄)₂: x% Eu²⁺ (0.1≤x≤2.5) phosphors were synthesized via the solid-state method. The analysis of crystal structure and the X-ray diffraction confirms that the Ca₈(Al₁₂O₂₄)(WO₄)₂: Eu²⁺ phosphors are phase-pure and crystallize in the orthorhombic system with space group Aba2. The wide bandgap energy of the Ca₈(Al₁₂O₂₄)(WO₄)₂ host provides a suitable bandgap environment for 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)(WO₄)₂: Eu²⁺ undergoes a redshift, originating from the site competition by Eu²⁺ doping. Concurrently, due to concentration quenching, the emission intensity initially increases and subsequent decreases, reaching a maximum at an optimal Eu²⁺ doping concentration of 0.3%. The concentration quenching mechanism was confirmed to be electric dipole-dipole interaction. Additionally, the optimally doped Ca₈(Al₁₂O₂₄)(WO₄)₂: 0.3% Eu²⁺ phosphor exhibits bright blue emission with CIE coordinates of (0.150, 0.054) and high color purity of 92.0%. These results demonstrate that this novel type of blue broadband Ca₈(Al₁₂O₂₄)(WO₄)₂: Eu²⁺ phosphor has great potential in the field of optical applications under excitation of near-ultraviolet light.