Waste to wealth: transforming Eu²⁺/Eu³⁺ co-activation from weak link to strength for advanced multifunctional...

Conventional Eu²⁺/Eu³⁺ co-activated phosphors are often excluded from high-quality lighting applications due to challenges such as disparate thermal quenching between the two valence states and resultant poor color rendering. To overcome these limitations, this work proposes a general crystal field engineering strategy, rather than focusing solely on optimizing a single phosphor. Using β-Sr(Ca)P₂O₆:Eu^2+/3+ as a model system, we demonstrate that Ca²⁺ substitution for Sr²⁺ effectively modifies the local crystal field, thereby achieving optimization of the luminescent performance. Spectroscopic and crystallographic analyses indicate that the substitution of Ca²⁺ for Sr²⁺ results in the decrease of unit cell parameters and the shortening of (Ca,Sr)-O bonds, inducing significant crystal field splitting and scattering effect. Simultaneously, this substitution enhances the rigidity of the host structure and reduces the electron-phonon coupling, leading to markedly emission spectrum redshift and improved thermal stability. The phosphor enables multifunctional applications, including high-CRI full-spectrum w-LEDs and plant-growth-enhancing red-blue dual-emission LEDs, demonstrating its dual value for agricultural lighting and high-quality solid-state lighting. More importantly, the crystal field engineering strategy illustrated here offers a universal route to regulate the local environment and enhance the performance of various Eu²⁺/Eu³⁺ co-activated phosphors, highlighting its broad potential beyond the current material system for both agricultural and high-quality solid-state lighting.