Li+ induced enhancements in Eu3+→Eu2+ reduction and photoluminescence properties of Eu-doped KAlSi2O6 phosphors for WLED applications

Abstract

WLEDs have revolutionized modern lighting technologies, but the exploration of high-quality NUV-excited phosphors remains a significant challenge. Herein, we propose a Li⁺ co-doping strategy to regulate Eu valence states and enhance luminescence properties in silicate-based phosphors. A series of [K_1-xLi_x]AlSi₂O₆: 0.02Eu (x = 0–0.08) phosphors are successfully synthesized via a solid-state reaction method. XRD and XPS analyses reveal that Li⁺ ions preferentially occupy the K⁺ sites in the KAlSi₂O₆ lattice, weakening K-O bonding energy and facilitating the Eu³⁺→Eu²⁺ reduction. Under 365 nm excitation, KAlSi₂O₆: 0.02Eu exhibits a broad Eu²⁺-related emission band (400–600 nm) and two narrow Eu³⁺-related peaks (593 and 612 nm). Incorporation of Li⁺ ions quenches Eu³⁺ emissions and enhances Eu²⁺ emission, peaking at x = 0.06. Moreover, [K_0.94Li_0.06]AlSi₂O₆: 0.02Eu demonstrates excellent thermal stability (85.45 % at 423 K) with negligible chromaticity shift (ΔE = ∼0.0022 in 293–463 K), attributed to its high structural rigidity and single emitting center. A WLED fabricated with [K_0.94Li_0.06]AlSi₂O₆: 0.02Eu achieves a high color rendering index (R_a = 90.4) and a moderate correlated color temperature (CCT = 4536 K). These findings not only highlight the potential of [K_0.94Li_0.06]AlSi₂O₆: 0.02Eu as a blue phosphor for human-centric WLEDs, but also provide a strategy for enhancing Eu³⁺→Eu²⁺ reduction efficiency in silicates.