Photoluminescence Tuning of Stable CaYGaO4: Bi/Eu via Compositional Modulation and Crystallographic Site Engineering for nUV wLEDs

The olivine-based gallate CaYGaO₄ (CYG) with unique cationic ordering, rich lattice sites, and self-photoluminescence (PL) is suitable for application as a host of phosphor. However, research in this area is still in its early stages, especially in high-quality full-spectrum white lighting. Herein, novel CYG: Bi³⁺/Eu³⁺ with a controllable PL property is designed based on energy transfer and superposition of emissions from blue self-PL, blue PL of Bi³⁺, and red-PL of Eu³⁺. Intriguingly, PL intensity and quantum efficiency could be enhanced via codoping Li⁺/Zn²⁺ separately/simultaneously because of their two intentional functions as both charge balancer and flux. Unlike self- and Eu³⁺ PL, Bi³⁺ PL is quite sensitive to the lattice environment owing to its exposed 6s² electronic configuration and is tuned via codoping Sr²⁺ to regulate the nephelauxetic effect and crystal field splitting concurrently around Bi³⁺. Meanwhile, for further regulating the PL of Bi³⁺ and obtaining "warm" white light, La³⁺ is codoped into the phosphor via crystallographic site engineering to control the substitution trends of Bi³⁺ at distinct lattice sites. Finally, as a proof-of-concept, a full-spectrum phosphor-converted white-light-emitting diode device under nUV pumping with remarkable color rendering index (R_a), high luminous efficiency, and chemical/thermal stability is achieved by utilizing the individual CYG:Bi/Eu/Li/Zn/Sr/La phosphor via a remote "capping" packaging method.