Electronic structure, colour-tunable emission and energy transfer in Li3Ba2Y3(WO4)8:Bi3+,Eu3+ phosphors for white light-emitting diodes†

Abstract

Solid-state phosphor-converted white light-emitting diodes (pc-WLEDs) are the leading trend of the lighting industry in the 21st century. To pursue high quality WLED lighting, the development of highly efficient phosphors with tunable luminescence has become a hot research topic. Herein, we reported for the first time on Bi³⁺/Eu³⁺-doped Li₃Ba₂Y₃(WO₄)₈ phosphors that exhibited tunable emission and high energy transfer efficiency of 89.90% from Bi³⁺ to Eu³⁺. The phase purity, microstructure, electronic structure and photoluminescence properties of these phosphors were studied in detail. Bi³⁺ and Eu³⁺ were effectively doped in Li₃Ba₂Y₃(WO₄)₈ with an optical bandgap of 3.81 eV. The band structure and density of states were quantitatively evaluated by density functional theory simulation. At an excitation wavelength of 342 nm, the Bi³⁺-doped phosphor achieved yellow-green emission. By alloying Eu³⁺ into Li₃Ba₂Y₃(WO₄)₈:Bi³⁺, the luminescence gradually turned red due to the energy transfer from Bi³⁺ to Eu³⁺. Moreover, the activation energy of the prepared phosphor was 0.1897 eV, demonstrating excellent thermal stability. Eventually, by combining Li₃Ba₂Y₃(WO₄)₈:4%Bi³⁺,4%Eu³⁺ and a blue-emitting BAM:Eu²⁺ phosphor with a 365 nm ultraviolet chip, a WLED device with a high colour rendering index (R_a) of 78.7, chromaticity coordinates of (0.3401, 0.3131) and correlated colour temperature of 5080 K was successfully achieved. This work provided new insights into the design and development of color-tunable phosphors for white LEDs.