Spectral Investigation of Enhanced Orange Emission in Eu Activated LaPO Nanophosphors Through Codoping With Na and Bi Ions.

Lanthanum phosphate is a well-known potential host for rare earth activators for phosphor-converted white LED application. Na and Bi codoped Eu activated LaPO 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 Eu at 393 nm that is found to be the most dominant. The comparative photoluminescence studies of LaPO:xEu(x = 0.10), La PO:xEu, yNa(x = 0.10, y = 0.05), and LaPO:xEu, yNa, zBi (x = 0.10, y = z = 0.05) reveal a progressive enhancement of the orange emission from Eu as Na and (Na, Bi) ions are incorporated into the LaPO matrix. The dominance of D-F magnetic dipole transition contributing a major part of orange luminescence of the nanophosphors and the symmetric site occupancy of Eu was justified from the observed trend of 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 Biions.