White Light Emission from NaCaPO4:Dy3+ Phosphor for Ultraviolet-Based White Light-Emitting Diodes

Trivalent dysprosium (Dy3+)-doped NaCaPO4 phosphors were synthesized by using a conventional solid-state reaction technique. The phase and the structure of the as-prepared powders were characterized by using X-ray diffraction analysis and revealed that the pure NaCaPO4 formed with orthorhombic structure. The photoluminescence excitation and emission spectra were measured to characterize the luminescent properties of NaCaPO4:Dy3+ phosphors. Sharp emission peaks were observed at 482 nm (blue) and 575 nm (yellow) upon 367 nm excitation, which are attributed to the characteristic F-4(9/2) -> H-6(J) (J = 15/2 and 13/2) transitions of trivalent Dy3+ ions, respectively. The suitable control of the blue/yellow intensity ratio is expected to realize a white luminescent system. The lifetime of F-4(9/2) level was measured by exciting Dy3+ ions at 355 nm excitation. The chromaticity coordinates were calculated from the emission spectra and analyzed with Commission International de I'Eclairage (CIE) programs and diagrams. The CIE color coordinates fall in the white light region under different ultraviolet (UV) excitations. These results indicate that NaCaPO4:Dy3+ phosphor could be a potential candidate for UV-based white light-emitting diodes.