Properties–structure relationship research on LiCaPO4:Eu2+ as blue phosphor for NUV LED application

• Pure phase blue phosphors of LiCaPO4:Eu2+ with a hexagonal structure were first prepared via solid-state method.
• The crystallographic site of Eu2+ ion in the LiCaPO4 lattice was identified as 8-fold Ca2+ site.
• The phosphor exhibits excellent thermal stability and the corresponding mechanism was thermal assisted ionization.
• Bright and high color purity blue LED prototype based on LiCaPO4:Eu2+ phosphor was fabricated.

Blue-emitting phosphors of Eu2+-activated LiCaPO4 with a hexagonal structure were prepared via a conventional solid-state method. The XRD, PL spectra and thermal quenching were applied to characterize the phosphors. The crystallographic site of Eu2+ ion in the LiCaPO4 lattice was identified and discussed. The optimized LiCaPO4:0.03Eu2+ exhibits the bright greenish-blue emission with CIE coordinates of (0.119, 0.155) and a quantum efficiency of 52%. The critical energy-transfer distance was confirmed as ∼18 Å by both calculated crystal structure method and experimental spectral method. The thermal stability of LiCaPO4:Eu2+ was evaluated by temperature-dependent PL spectra, and the thermal quenching mechanism was found to be thermal assisted ionization. Prototype blue LEDs with high color purity and good current stability were fabricated.

The graphical abstract shows the excitation and emission spectrum of LiCaPO4:Eu2+, and the CIE coordinates of LiCaPO4:Eu2+. The inset shows the photo of blue LED prepared by LiCaPO4:Eu2+ and NUV chip. It indicates that this phosphor can be excited by UV light and emit strong greenish-blue light.Figure optionsDownload as PowerPoint slide