Novel red-emitting SrBi2B4O10:Eu3+ phosphors: Synthesis, crystal structure and luminescence

The novel red-emitting Sr(Bi_1–xEu_x)₂B₄O₁₀ (x = 0.05, 0.10, 0.15, 0.20, 0.25, 0.30) phosphors were obtained by solid state reactions. Emission and excitation spectra of the Sr(Bi_1–xEu_x)₂B₄O₁₀ phosphors were investigated. The most intense band for all samples of the concentration series is in the region of 611 nm at excitation 392 nm. Distribution of the Eu³⁺ ions over cation sites was refined for x = 0.15, 0.20 and 0.30 from single-crystal X-ray diffraction data. In the SrBi_1.70Eu_0.30B₄O₁₀ and SrBi_1.60Eu_0.40B₄O₁₀ crystal structures, the Eu³⁺ ions occupy only the Bi2 site, then, the Eu³⁺ ions occupy 57 % of the Bi1 site and 3 % of the Bi2 site in the SrBi_1.40Eu_0.60B₄O₁₀ crystal structure. The asymmetry ratio is determined as the ratio of the integral intensity of radiative transitions ⁵D₀–⁷F₂ to ⁵D₀–⁷F₁ for Eu³⁺ ions. This means that the local environment of europium ions does not change or changes insignificantly. The optimal concentration is x = 0.25. It was shown by absorption spectroscopy, that the optical band gap for this sample is equal to 3.69 ± 0.01 eV. It has been demonstrated that if Eu³⁺ ions occupy the Bi1 and Bi2 sites, the R_c is considerably decreased, resulting in a change of energy migration in the crystal structures from one-dimensional to two-dimensional. The CIE chromaticity coordinates for the Sr(Bi_1–xEu_x)₂B₄O₁₀ phosphors were found to be (0.64, 0.35), which are in close proximity to the NTSC standard values of (0.67, 0.33) for commercial red phosphors. The obtained results show that the Sr(Bi_1–xEu_x)₂B₄O₁₀ phosphors are promising candidates for solid state lighting application.