Tailoring of White Luminescence in a NaLi3 SiO4 :Eu2+ Phosphor Containing Broad-Band Defect-Induced Charge-Transfer Emission

Abstract

Single-component materials with white-light emission are ideal for lighting applications. However, it is very challenging to achieve white luminescence in single-dopant activated solid phosphors. Herein, white NaLi₃ Si_{1- x} O₄ :Eu²⁺ materials are designed via defect engineering and synthesized by reducing the Si content (0.15 ≤ x ≤ 0.25). Stochiometric NaLi₃ SiO₄ :Eu²⁺ exhibits a narrow-band blue emission at 469 nm, ascribed to the 5d → 4f transition of Eu²⁺ at highly symmetric cuboid Na sites, while samples with Si content reduced by 15-25% display white emission with two peaks at 472 nm and 585 nm. The newly appeared broadband yellow peak arises from charge-transfer transitions involving Eu²⁺ and nearby defects, as verified by an unusual bandwidth, a large Stokes shift, and a long decay time. A single-component white light-emitting diode device is fabricated by employing a white phosphor to demonstrate a color-rendering index of 82.9. This result provides a new design strategy for single-component white-light materials with broad-band defect-induced charge-transfer emission.

Keywords: charge-transfer emission; light-emitting diodes; white luminescence.