Manipulating the redistribution of single dopant via crystal-site engineering approach in Ba4Gd3(K1-xNax)3(PO4)6F2:Eu2+ phosphors for warm white light emitting diodes

Highlights: • Ba₄Gd₃(K_1-xNa_x)₃(PO₄)₆F₂:Eu²⁺ (0 ≤ x ≤ 1.0) solid solutions are successfully prepared. • Na-substitution triggers an anisotropic lattice shrinkage along the c-axis. • Na-substitution triggers migration of Eu²⁺ from M(1) and Gd(2) sites to A(3) sites. • The relative emission intensity can be regulated by increasing Na doping content. • The Ba₄Gd₃Na₃(PO₄)₆F₂:Eu²⁺ phosphor converted WLED exhibits quite CRI (R_a = 90.2). Manipulating the redistribution of single dopant among multiple crystallographic sites can optimize and design luminescence materials for single-doped warm white phosphor with high color rendering. However, successful cases are barely reported, because the substitution of all sites and the warm white emitting of multiemission bands cannot be guaranteed. Herein, we synthesized a series of Ba₄Gd₃(K_1-xNa_x)₃(PO₄)₆F₂:Eu²⁺ (0 ≤ x ≤ 1.0) solid solutions via crystal-site engineering approach to manipulate the redistribution of Eu²⁺ dopant for tunable photoluminescence property. Na⁺ ions preferentially substitution in the A and B columns along the c-axis direction gives rise to the anisotropic lattice shrinkage. The multiemission bands of Ba₄Gd₃(K_1-xNa_x)₃(PO₄)₆F₂:Eu²⁺ phosphors almost cover the whole visible light range because Eu²⁺ dopant can occupy the M(1), Gd(2) and A(3) sites. The Na-substitution results in a redistribution of Eu²⁺ dopants among different cation sites, and induces a continuous increase of the relative emission intensities at longer wavelength with increasing Na⁺ doping content. Moreover, the unique optical feature enables the single-phased Ba₄Gd₃Na₃(PO₄)₆F₂:Eu²⁺ phosphor converted WLED to exhibit quite high color rendering index (R_a = 90.2) and moderate correlated color temperature (CCT = 4125 K). The manipulating the redistribution of single dopant via crystal-site engineering approach reported here can not only carve out a new avenue for warm WLEDs, but also be applied to develop novel potential phosphors for practical optical application.