Structure-luminescence correlation studies in Dy /Eu doped A2P2O7 (A = Ca/Sr/Ba and Zn) phosphors for white light generation

Structure-luminescence correlation in Dy/Eu doped pyrophosphate materials (A₂P₂O₇; A = Ca, Sr, Ba, Zn) is investigated, unveiling novel strategies for white light generation. The Hubbard corrected density functional theory (DFT+U) calculations reveal that Dy³⁺ doping reduces the coordination number and metal-oxygen bond lengths. The local lattice distortions enhance the asymmetric crystal field, favoring ⁴F_9/2 → ⁶H_15/2, ⁶H_13/2 transitions corresponding to blue and yellow emissions following the $4f\to 5d\to 4f$ energy transfer pathway. The luminescence mechanism confirms that Eu²⁺ exhibits stronger hybridization with oxygen, yielding blue-green emission through the $f-d$ transition, while Eu³⁺ contributes red-orange emission via $f-f$ transitions. The Eu doped systems are more resistant to lattice strain than Dy doped ones, and structurally more perturbed due to smaller ionic radii and stronger Coulomb interactions. These findings predict the oxidation state variations based on structural constraints and offer deep insight into the electronic structure and luminescence behavior of pyrophosphate phosphors.