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 La1-xPO4:xEu(3+)(x = 0.10), La1-x-y PO4:xEu(3+), yNa(+)(x = 0.10, y = 0.05), and La1-x-y-zPO4:xEu(3+), yNa(+), zBi(3+) (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 D-5(0)-F-7(1) 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 Omega(4 )> Omega(2) 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 Bi(3+)ions.