Controllable synthesis of bifunctional material Ca2Ti2O6:Eu3+ and its comparative study on luminescence and photocatalytic properties with CaTiO3:Eu3+

Pure pyrochlore Ca₂Ti₂O₆, perovskite CaTiO₃, and their mixed crystalline phases with different proportions were controllably synthesized via a solvothermal method, followed by a subsequent calcination process. RIR (reference intensity ratio) data of Ca₂Ti₂O₆ were first obtained by X-ray diffraction (XRD), which can be used to quantitatively analyze the phase composition. When Eu³⁺ is doped into these calcium titanium oxides, they can be used as luminescent and photocatalytic materials. The structure, luminescence, and photocatalytic properties of pure pyrochlore Ca₂Ti₂O₆:Eu³⁺ and perovskite CaTiO₃:Eu³⁺ were comparatively studied in detail. The relative intensities of the excitation peaks and the emission peaks in Ca₂Ti₂O₆:Eu³⁺ and CaTiO₃:Eu³⁺ are different, which is attributed to the different symmetries of Eu³⁺ inhabiting the two kinds of lattices. In addition, although the luminescence intensity of CaTiO₃:3%Eu³⁺ is higher than that of Ca₂Ti₂O₆:3%Eu³⁺ under excitation at 394 nm, the luminescence intensity of Ca₂Ti₂O₆:3%Eu³⁺ is superior to that of CaTiO₃:3%Eu³⁺ under excitation at 464 nm and 533 nm. Photocatalytic experiments show that Ca₂Ti₂O₆:3%Eu³⁺ has better photocatalytic performance than CaTiO₃:3%Eu³⁺, which is mainly due to its smaller crystallite size, higher specific surface area and pyrochlore structure. In addition, biphase (Ca₂Ti₂O₆–CaTiO₃):3%Eu³⁺ has the best photocatalytic activity compared with the single phase Ca₂Ti₂O₆:3%Eu³⁺ and CaTiO₃:3%Eu³⁺, owing to the presence of heterojunctions that significantly reduced the band gap. It is anticipated that the discovery of this bifunctional Ca₂Ti₂O₆:Eu³⁺ would expand the application of rare earth-doped calcium titanium oxide materials.