Near-ultraviolet excited Tm³⁺ and Dy³⁺ ions co-doped barium lanthanum silica oxide phosphors for white-light applications

Nowadays, trivalent rare-earth ions activated inorganic luminescent materials have been widely investigated owing to their important applications in solid-state lighting field. Tm³⁺ and Dy³⁺ ions single- or co-doped Ba₃La₆(SiO₄)₆ (BLSO) phosphor materials for white light application were synthesized by a citrate-based sol-gel method. The prepared samples were examined by X-ray diffraction (XRD), scanning electron microscopy and Fourier-transform infrared spectroscopy to analyze the phase purity, surface morphology and existence of functional groups, respectively. The XRD pattern confirmed that the BLSO host lattice exhibited a hexagonal crystal structure with P6₃/m (176) space group, which is well indexed with standard JCPDS data. From photoluminescence results, the BLSO:Tm³⁺ phosphors exhibited purplish blue emission at 453 nm (¹D₂→³F₄) and the BLSO:Dy³⁺ phosphors showed predominant yellow emission at 575 nm (⁴F_9/2 → ⁶H_13/2) compared to their shoulder blue emission at 479 nm (⁴F_9/2 → ⁶H_15/2), indicating that the Dy³⁺ ions occupied lattice sites with low inversion symmetry. The determined Commission Internationale de I'Eclairage (CIE) (0.3391, 0.3302) values for the Tm³⁺/Dy³⁺ co-doped BLSO phosphors were near to the standard sun light CIE values (0.33, 0.33) under near-ultraviolet (364 nm) excitation. The energy transfer process from Dy³⁺ to Tm³⁺ ions was discussed and it was proved by their corresponding decay curves. Additionally, thermal study was carried out for the optimized phosphor and it maintained superior thermal PL properties.