Spectral Investigation of Enhanced Orange Emission in Eu³⁺ Activated LaPO₄ Nanophosphors Through Codoping With Na⁺ and Bi³⁺ Ions

Lanthanum phosphate is a well-known potential host for rare earth activators for phosphor-converted white LED application. Na⁺ and Bi³⁺ codoped Eu³⁺ activated LaPO₄ nanophosphor is successfully synthesized using citrate-based hydrothermal method at ambient condition and confirmed by XRD, EDS and XPS analysis. The excitation spectra of the sample exhibit sharp f-f characteristics peak of Eu³⁺ at 393 nm that is found to be the most dominant. The comparative photoluminescence studies of La_1-xPO₄:xEu³⁺(x = 0.10), La_1-x-y PO₄:xEu³⁺, yNa⁺(x = 0.10, y = 0.05), and La_1-x-y-zPO₄:xEu³⁺, yNa⁺, zBi³⁺ (x = 0.10, y = z = 0.05) reveal a progressive enhancement of the orange emission from Eu³⁺ as Na⁺ and (Na⁺, Bi³⁺) ions are incorporated into the LaPO₄ matrix. The dominance of ⁵D₀-⁷F₁ magnetic dipole transition contributing a major part of orange luminescence of the nanophosphors and the symmetric site occupancy of Eu³⁺ was justified from the observed trend of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msub><mml:mi>Ω</mml:mi> <mml:mn>4</mml:mn></mml:msub> <mml:mo>></mml:mo> <mml:msub><mml:mi>Ω</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:mrow> <mml:annotation>$$ {\varOmega}_4>{\varOmega}_2 $$</mml:annotation></mml:semantics> </mml:math> in the Judd-Ofelt intensity parameters. The CIE studies confirm the improvement in color purity of emission from 32.5% to 90.6% due to the presence of Na⁺ and Bi³⁺ions.