Novel CaBi2B4O10:Eu3+ red phosphor: Synthesis, crystal structure, luminescence and thermal expansion

Abstract

The europium doped calcium bismuth borates, CaBi2B4O10:xEu3+ (x = 0–0.3), were prepared using high-temperature solid state synthesis. The crystal structure of the CaBi2B4O10 was solved and refined from single crystal X-ray diffraction data to R1 = 0.029. The CaBi2B4O10 crystallizes in triclinic space group P1‾, a = 6.6665 (1), b = 6.8277 (1), c = 9.5478 (1) Å, α = 94.2420 (8)°, β = 108.5210 (8)°, γ = 101.2840 (8)°, V = 399.76 (1), Z = 2. This compound is isotypical to SrBi2B4O10. Crystal structure contains [B4O9]6– isolated tetraborate groups (4 B:3Δ□: ˂2Δ□˃Δ), Bi–O chains and interstitial Sr atoms. Tetraborate group consists of the triborate ring [B3O7]5– and branched BO3 triangle. Thermal expansion of CaBi2B4O10 was studied by powder HTXRD. The thermal expansion is highly anisotropic (α11 = 14.9 (7), α22 = 2.8 (1), α33 = 7.2 (4), αV = 25 (1) × 10−6 °C−1 at 25 °C). Maximal thermal expansion occurs between the planes of triborate ring and branched BO3 triangle. These solid solutions show an efficient red emission (λmax = 611 nm) when excited by UV-light (λex = 392 nm). The optimal europium doping concentration in CaBi2B4O10 host was found to be 10 at.% due to the area of miscibility of CaBi2-xEuxB4O10 (x = 0–0.225) solid solutions.