Luminescence and photocatalytic properties of bifunctional materials CaTi2O4(OH)2:Eu3+ and [CaTi2O4(OH)2–CaTiO3]:Eu3+

Abstract

CaTi2O4(OH)2:Eu3+, CaTiO3:Eu3+ and [CaTi2O4(OH)2–CaTiO3]:Eu3+ were synthesized by a solvothermal method without the help of templates or surfactants. And their structures, luminescence properties, and photocatalytic properties were systematically studied. The RIR (reference intensity ratio) data of CaTi2O4(OH)2 were first investigated via X-ray diffraction (XRD), thus the ratios of each phase in the (m%CaTi2O4(OH)2-n%CaTiO3):3%Eu3+ biphasic mixture was determined. The bandgap value of CaTi2O4(OH)2:3%Eu3+ is 0.28 eV less than that of CaTiO3:3%Eu3+. The specific surface area of CaTi2O4(OH)2 is 8.2 times larger than that of CaTiO3. Compared with CaTiO3:Eu3+, the CaTi2O4(OH)2:Eu3+ showed stronger luminescence intensity. The Judd-Ofelt theory analysis show that the Eu3+ ions in CaTi2O4(OH)2:Eu3+ have low local symmetry, high Eu–O bonds covalence and low ligands electron density. The photocatalytic properties of CaTi2O4(OH)2:y%Eu3+, CaTiO3:x%Eu3+ and [62.2%CaTi2O4(OH)2-37.8%CaTiO3]:3% Eu3+ were comparatively studied in detail. The band-gap value of [62.2 % CaTi2O4(OH)2–37.8%CaTiO3]:3%Eu3+ is significantly reduced due to the presence of heterojunctions compared to CaTi2O4(OH)2:y%Eu3+ and CaTiO3: x%Eu3+. The built-in electric potential at heterojunction interface will guide electrons and holes to move in opposite directions, therefore [CaTi2O4(OH)2–CaTiO3]:Eu3+ has excellent photocatalytic activity.