摘要
We have synthesized and investigated a series of yellow-emitting Sr <sub>3</sub> Ce(PO <sub>4</sub> ) <sub>3</sub> :Eu <sup>2+</sup> phosphors, showing an extreme broadband at around 535 nm (with a FWHM of ca. 200 nm/6760 cm <sup>-1</sup> ) and a large Stoke shift (ca. 8265 cm <sup>-1</sup> ), which is attributed to the 4f-5d transition of Eu <sup>2+</sup> without the contribution from Ce <sup>3+</sup> emission under excitation at long wavelengths (>370 nm). However, such broadband Eu <sup>2+</sup> emission is rather surprising, considering that there is only one cation site for the Eu <sup>2+</sup> 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 Sr <sub>3</sub> Ce(PO <sub>4</sub> ) <sub>3</sub> are disordered in the host lattice. These unusual structural characters generate a variety of distinct Eu <sup>2+</sup> 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 Sr <sub>3</sub> Ce(PO <sub>4</sub> ) <sub>3</sub> :Eu <sup>2+</sup> and the commercial blue-emitting BaMgA <sub>10</sub> O <sub>17</sub> :Eu <sup>2+</sup> phosphor. These results indicate that the as-prepared yellow-emitting Sr <sub>3</sub> Ce(PO <sub>4</sub> ) <sub>3</sub> :Eu <sup>2+</sup> phosphor has potential applications in the dual-color-phosphor-converted WLEDs.