New Yellow-Emitting Whitlockite-type Structure Sr<sub>1.75</sub>Ca<sub>1.25</sub>(PO<sub>4</sub>)<sub>2</sub>:Eu<sup>2+</sup> Phosphor for Near-UV Pumped White Light-Emitting Devices
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Abstract
New compound discovery
is of interest in the field of inorganic solid-state chemistry. In
this work, a whitlockite-type structure Sr<sub>1.75</sub>Ca<sub>1.25</sub>(PO<sub>4</sub>)<sub>2</sub> newly found by composition design
in the Sr<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>–Ca<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub> join was reported. Crystal structure
and luminescence properties of Sr<sub>1.75</sub>Ca<sub>1.25</sub>(PO<sub>4</sub>)<sub>2</sub>:Eu<sup>2+</sup> were investigated, and the yellow-emitting
phosphor was further employed in fabricating near-ultraviolet-pumped
white light-emitting diodes (w-LEDs). The structure and crystallographic
site occupancy of Eu<sup>2+</sup> in the host were identified via
X-ray powder diffraction refinement using Rietveld method. The Sr<sub>1.75</sub>Ca<sub>1.25</sub>(PO<sub>4</sub>)<sub>2</sub>:Eu<sup>2+</sup> phosphors absorb in the UV–vis spectral region of 250–430
nm and exhibit an intense asymmetric broadband emission peaking at
518 nm under λ<sub>ex</sub> = 365 nm which is ascribed to the
5d–4f allowed transition of Eu<sup>2+</sup>. The luminescence
properties and mechanism are also investigated as a function of Eu<sup>2+</sup> concentration. A white LED device which is obtained by combining
a 370 nm UV chip with commercial blue phosphor and the present yellow
phosphor has been fabricated and exhibit good application properties
