Synthesis of novel Ce3+ doped NaLi2PO4 UV-A emitting phosphor

Abstract

Ce³⁺ doped NaLi₂PO₄ orthophosphate material was successfully synthesized via the solid-state diffusion method. The phase purity of synthesized phosphor was confirmed by Powder X-ray Diffraction (PXRD). Elemental analysis and surface morphology of phosphor material were analyzed by Field Emission Scanning Electron Microscope (FE-SEM) and Energy Dispersive X-Ray Spectroscopy (EDX) respectively. In addition, chemical states and their elemental bonding of material were investigated by X-ray Photoelectron Spectroscopy (XPS). Whereas Diffuse Reflectance Spectra (DRS) is utilized to examine the optical energy band gap of NaLi₂PO₄ and NaLi₂PO₄:Ce³⁺ phosphors. First principle study was employed to explain the energy band gap deviation between the theoretical and experimental results of phosphors. Fluorescence properties of NaLi₂PO₄:Ce³⁺ phosphor (0.0 to 0.3 mol %) were studied at excitation wavelength of 277 nm. NaLi₂PO₄:Ce³⁺phosphor exhibited intense emission peaks centred at 335 and 360 nm due to spin orbit splitting of ²F_5/2 and ²F_7/2. Beyond the optimal limit of dopant ions, non-radiative energy transfer phenomena occurred due to dipole–dipole interaction between the acceptor and the donor. Minimum stokes shift between the excitation and emission bands of phosphor leads it to persistent UV emission. These properties of NaLi₂PO₄:Ce³⁺ phosphor predicts its possible use in the development of UV-A phosphor LEDs.