Structural confinement helps achieve more accurate energy transfer: studies on garnet structural NYGlG:Tb3+,Eu3+ phosphors†

Abstract

In the quest to enhance the performance of white light-emitting diodes (WLEDs), the development of efficient red phosphors is essential. To address this issue, a series of co-doped garnet-type phosphors, NaY₂Ga₂InGe₂O₁₂:Tb³⁺,Eu³⁺ (NYGIG:Tb³⁺,Eu³⁺), were synthesized, utilizing structural confinement to achieve more precise energy transfer and improve luminescence performance. Comprehensive characterization techniques, including powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and elemental mapping, confirmed the structural and compositional features of the phosphors. Na⁺ ions occupy one-third of the eight-coordinated sites in NYGIG, separating Tb³⁺ and Eu³⁺ ions, which improves the precision of energy transfer. Statistical results demonstrate that Na⁺ increases the formation probability of Tb³⁺–Eu³⁺ pairs to 7%, effectively preventing the formation of long Tb³⁺–Tb³⁺ and Eu³⁺–Eu³⁺ chains while the probability of forming a Tb³⁺–Eu³⁺ pair is merely 3.12% in traditional garnets. When the Tb³⁺ doping concentration is 50%, the energy transfer efficiency reaches 95% at an optimal Eu³⁺ doping concentration of 7%. Moreover, the NYGIG:0.5Tb³⁺,0.07Eu³⁺ phosphor achieves a quantum yield of 70.4% and maintains strong luminescence intensity at elevated temperatures, retaining over 85% of its room temperature luminescence intensity at 425 K. The electroluminescence (EL) spectrum of the assembled WLED, powered using a 365 nm near-UV chip, shows balanced white light output with a high color rendering index (CRI ∼ 87) and CIE coordinates of (0.402, 0.380). These findings underscore the significant potential of NYGIG:Tb³⁺,Eu³⁺ phosphors for advancing highly efficient WLED technologies.