Ca<sub>9–<i>y</i></sub>Mg<sub><i>y</i></sub>NaGd<sub>0.667</sub>(PO<sub>4</sub>)<sub>7</sub>:Eu<sup>2+</sup>: A Single Eu<sup>2+</sup>-Doped F

The multi-cationic site occupation\ncontrol of rare earth doped\nphosphor materials is one of the key factors in achieving single-phase\nfull-spectrum emission. In this work, the site distribution of Eu<sup>2+</sup> in Ca<sub>9</sub>NaGd<sub>0.667</sub>(PO<sub>4</sub>)<sub>7</sub> (CNGP):<i>x</i>%Eu<sup>2+</sup> phosphors with\nmulti-cationic sites was determined. Under 385 nm excitation, CNGP:<i>x</i>%Eu<sup>2+</sup> samples exhibited a cyan emission composed\nof three sub-Gaussian components. The CNGP:1.5%Eu<sup>2+</sup> phosphor\nwas structurally modified through the partial substitution of Mg<sup>2+</sup> for Ca<sup>2+</sup> according to the crystallographic site\nengineering theory, and corresponding luminescent properties had been\nadjusted. When the concentration of Mg<sup>2+</sup> changed, the Ca<sub>9–<i>y</i></sub>Mg<sub><i>y</i></sub>NaGd<sub>0.667</sub>(PO<sub>4</sub>)<sub>7</sub>:1.5%Eu<sup>2+</sup> (CNGPE:<i>y</i>Mg<sup>2+</sup>) phosphors exhibited a tunable emission\nfrom cyan to orange and achieved white light emission at <i>y</i> = 0.6. Based on the change of the crystal field environment, the\nmechanism of Mg<sup>2+</sup> substitution affecting the luminescence\ncharacteristics of CNGP:<i>x</i>%Eu<sup>2+</sup> phosphors\nwas researched in detail. The light-emitting diode device consisted\nof a CNGPE:0.6Mg<sup>2+</sup> phosphor and a 385 nm chip and had a\nhigh color rendering index (CRI = 91.9), low correlated color temperature\n(CCT = 4852 K), and excellent color stability. The optical performance\nof this device makes it promising to be used in full spectrum lighting.