Photoluminescence\nTuning of Stable CaYGaO<sub>4</sub>: Bi/Eu via Compositional Modulation\nand Crystallographic Site Engineering\nfor nUV wLEDs

The olivine-based gallate CaYGaO<sub>4</sub> (CYG) with\nunique\ncationic ordering, rich lattice sites, and self-photoluminescence\n(PL) is suitable for application as a host of phosphor. However, research\nin this area is still in its early stages, especially in high-quality\nfull-spectrum white lighting. Herein, novel CYG: Bi<sup>3+</sup>/Eu<sup>3+</sup> with a controllable PL property is designed based on energy\ntransfer and superposition of emissions from blue self-PL, blue PL\nof Bi<sup>3+</sup>, and red-PL of Eu<sup>3+</sup>. Intriguingly, PL\nintensity and quantum efficiency could be enhanced via codoping Li<sup>+</sup>/Zn<sup>2+</sup> separately/simultaneously because of their\ntwo intentional functions as both charge balancer and flux. Unlike\nself- and Eu<sup>3+</sup> PL, Bi<sup>3+</sup> PL is quite sensitive\nto the lattice environment owing to its exposed 6s<sup>2</sup> electronic\nconfiguration and is tuned via codoping Sr<sup>2+</sup> to regulate\nthe nephelauxetic effect and crystal field splitting concurrently\naround Bi<sup>3+</sup>. Meanwhile, for further regulating the PL of\nBi<sup>3+</sup> and obtaining “warm” white light, La<sup>3+</sup> is codoped into the phosphor via crystallographic site engineering\nto control the substitution trends of Bi<sup>3+</sup> at distinct\nlattice sites. Finally, as a proof-of-concept, a full-spectrum phosphor-converted\nwhite-light-emitting diode device under nUV pumping with remarkable\ncolor rendering index (<i>R</i><sub>a</sub>), high luminous\nefficiency, and chemical/thermal stability is achieved by utilizing\nthe individual CYG:Bi/Eu/Li/Zn/Sr/La phosphor via a remote “capping”\npackaging method.