Electronic structure and photoluminescence properties of yellow-emitting Ca10Na(PO4)7: Eu2+ phosphor for white light-emitting diodes

The yellow-emitting Ca10Na(PO4)7:Eu2+ phosphors were synthesized by conventional high-temperature solid-state reaction method. The phosphors were well characterized by powder X-ray diffraction, FT-IR spectra and diffuse reflectance spectra. DFT calculation results showed that Ca10Na(PO4)7 had an indirect bandgap with a bandgap energy of about 3.82 eV. Ca10Na(PO4)7:Eu2+ showed a yellow emission band peaking at 550 nm under 350 nm excitation. The broad emission bandwidth (about 138 nm) of Ca10Na(PO4)7:Eu2+ is favorable for white LEDs conversion phosphors. The optimal doping concentration of Eu2+ ions in Ca10Na(PO4)7:Eu2+ phosphor was about 8 mol%. This study demonstrated that the energy transfer among the nearest-neighbor ions was the main mechanism of concentration quenching of Ca10Na(PO4)7:Eu2+ phosphor. These results indicate that Ca10Na(PO4)7:Eu2+ may be potentially useful as a UV radiation-converting phosphor for white LEDs.