Synergistic Effect of Tb³⁺ Doping and Facial Oxygen Vacancies in NaLi₂PO₄: A Promising Phosphor for pc-WLEDs.

Phosphor-converted white light-emitting diodes (pc-WLEDs) have emerged as globally dominant energy-efficient lighting sources. In this work, a novel orthophosphate phosphor Tb3+@NaLi2PO4 have been synthesized and evaluated for cost-effective and durable pc-WLED applications. High-temperature solid-state diffusion synthesis was found an appropriate process for the controlled generation of facial oxygen vacancies (Vₒ) which can modulate the optical properties of the host lattice significantly. Phase purity and morphological features were confirmed through X-ray diffraction (XRD) and scanning electron microscopy (SEM), while elemental composition and chemical states were analysed via X-ray photoelectron spectroscopy (XPS). A notable reduction in the optical band gap of NaLi₂PO₄ has been observed which was attributed due to Tb³⁺ incorporation and oxygen vacancy formation. It was validated through UV–visible spectroscopy and density functional theory (DFT) both experimentally and theoretically. Photoluminescence (PL) analysis revealed the characteristics emissions of Tb³⁺ ion at 5D₃ → 7F and 5D₄ → 7F under the excitation wavelength of 280 nm. The chromaticity of the emitted light was strongly depended on dopant concentration, 1 mol% doping of Tb³⁺ ions yielded to optimal Commission Internationale de l’Éclairage (CIE) coordinates for pc-WLED performance. These findings highlight the structural–optical interplay in Tb3+@NaLi2PO4 orthophosphate and underscore its potential as a promising phosphor for next-generation solid-state lighting.