A multi-centre activated single-phase white light phosphor with high efficiency for near-UV based WLEDs

Abstract

Single-phase white light phosphors for phosphor-converted white light-emitting diodes (pc-WLEDs) have become a hot spot and attracted considerable attention. However, the unsatisfactory luminous efficiency and colour rendering index of this kind of device hinder their large-scale applications in the field of lighting. Herein, a novel multi-centre activated single-phase white light phosphor, Gd₂Sr₃B₄O₁₂:Ce³⁺,Tb³⁺,Sm³⁺, has been designed and prepared. The crystal structures of the host and the doped samples are characterized with XRD and Rietveld refinements. The band gap of the host calculated with the density functional theory is consistent with the value obtained from the UV-Vis reflection spectrum. Benefiting from the energy transfer paths of Ce³⁺–Tb³⁺, Ce³⁺–Sm³⁺ and Tb³⁺–Sm³⁺, which are quantitatively evaluated with photoluminescence spectra and decay curves, the intensities of the characteristic emission peaks of the three dopants are found to be closely interlocked and the emission colour of the phosphors can be precisely tuned by adjusting the relative ratio of the three ions. Under the excitation of near-UV light, the two phosphors of Gd₂Sr₃B₄O₁₂:0.03Ce³⁺,0.18Tb³⁺,0.05Sm³⁺ and Gd₂Sr₃B₄O₁₂:0.03Ce³⁺,0.22Tb³⁺,0.07Sm³⁺ emit white light with CIE coordinates of (0.32, 0.35) and (0.34, 0.34), and the quantum efficiencies are 46.8% and 34.9%, respectively. The temperature-dependent photoluminescence spectra of the phosphors show that the quenching temperature (T_50%) is as high as 450 K. Finally, WLED devices with maximal colour rendering index of 87.5 are obtained by fabricating the two single-phase white light phosphors with 365 nm LED chips. The balanced and preferable comprehensive performances of Gd₂Sr₃B₄O₁₂:Ce³⁺,Tb³⁺,Sm³⁺ demonstrate that the as-prepared single-phase white light phosphor can be a promising candidate for fabricating near-UV chip-based WLEDs.