Sr3Ce(PO4)3:Eu2+: a broadband yellow-emitting phosphor for near ultraviolet-pumped white light-emitting devices

Abstract

We have synthesized and investigated a series of yellow-emitting Sr₃Ce(PO₄)₃:Eu²⁺ phosphors, showing an extreme broadband at around 535 nm (with a FWHM of ca. 200 nm/6760 cm⁻¹) and a large Stoke shift (ca. 8265 cm⁻¹), which is attributed to the 4f–5d transition of Eu²⁺ without the contribution from Ce³⁺ emission under excitation at long wavelengths (>370 nm). However, such broadband Eu²⁺ emission is rather surprising, considering that there is only one cation site for the Eu²⁺ luminescent center. Herein, we investigated the crystal structure by performing X-ray Rietveld refinement on the synchrotron X-ray diffraction data, and demonstrate that both cation and anion sites in Sr₃Ce(PO₄)₃ are disordered in the host lattice. These unusual structural characters generate a variety of distinct Eu²⁺ sites, which is verified by decay lifetime analysis and electron paramagnetic resonance spectra, and thus result in astonishing broadband yellow-emission. Moreover, a white LED device with a color-rendering index of 86.5, a color temperature of 5996 K, and chromaticity coordinates of (0.32, 0.38) was obtained by combining a 405 nm near-UV LED chip and the phosphor blends of yellow-emitting Sr₃Ce(PO₄)₃:Eu²⁺ and the commercial blue-emitting BaMgA₁₀O₁₇:Eu²⁺ phosphor. These results indicate that the as-prepared yellow-emitting Sr₃Ce(PO₄)₃:Eu²⁺ phosphor has potential applications in the dual-color-phosphor-converted WLEDs.