Ca_9–<i>y</i>Mg_<i>y</i>NaGd_0.667(PO₄)₇:Eu²⁺: A Single Eu²⁺-Doped Full-Spectrum White Light Emission Phosphor with High Color Rendering Index

The multi-cationic site occupation control of rare earth doped phosphor materials is one of the key factors in achieving single-phase full-spectrum emission. In this work, the site distribution of Eu²⁺ in Ca₉NaGd_0.667(PO₄)₇ (CNGP):<i>x</i>%Eu²⁺ phosphors with multi-cationic sites was determined. Under 385 nm excitation, CNGP:<i>x</i>%Eu²⁺ samples exhibited a cyan emission composed of three sub-Gaussian components. The CNGP:1.5%Eu²⁺ phosphor was structurally modified through the partial substitution of Mg²⁺ for Ca²⁺ according to the crystallographic site engineering theory, and corresponding luminescent properties had been adjusted. When the concentration of Mg²⁺ changed, the Ca_9-<i>y</i>Mg_<i>y</i>NaGd_0.667(PO₄)₇:1.5%Eu²⁺ (CNGPE:<i>y</i>Mg²⁺) phosphors exhibited a tunable emission from cyan to orange and achieved white light emission at <i>y</i> = 0.6. Based on the change of the crystal field environment, the mechanism of Mg²⁺ substitution affecting the luminescence characteristics of CNGP:<i>x</i>%Eu²⁺ phosphors was researched in detail. The light-emitting diode device consisted of a CNGPE:0.6Mg²⁺ phosphor and a 385 nm chip and had a high color rendering index (CRI = 91.9), low correlated color temperature (CCT = 4852 K), and excellent color stability. The optical performance of this device makes it promising to be used in full spectrum lighting.