Eu³⁺-doped Y₂O₃ hexagonal prisms: Shape-controlled synthesis and tailored luminescence properties

In this work, Eu³⁺ doped Y₂O₃ hexagonal prisms were synthesized by a novel two-phase approach, which involves water at the bottom as aqueous phase and oleylamine in the above as oil phase. With this unique reaction system, precursors of hexagonal prisms Y₄O(OH)₉(NO₃) were first obtained by simply varying the volume ratio of water to oleylamine. Time-dependent experiments were systematically performed to reveal the growth mechanism of the precursor. After subsequent heat treatment, these precursors transformed to Y₂O₃ hexagonal prisms with controlled diameters and aspect ratios varying from 4 to 19. Such a transformation is preceded via a topotactic process, as indicated by TG-DTA and mass spectra. Eventually, all Eu³⁺ doped Y₂O₃ hexagonal prisms were found to exhibit an intensive red emission at 611 nm, which corresponds to ⁵D₀→⁷F₂ transition of Eu³⁺. With varying the aspect ratio of hexagonal prisms and increasing Eu³⁺ concentration in Y₂O₃, an optimum external quantum efficiency was achieved. - Graphical abstract: In this work, Eu³⁺ doped Y₂O₃ hexagonal prisms with controlled aspect ratio from 4.4 to 19.3 were synthesized by transformation of the precursor Y₄O(OH)₉(NO₃) hexagonal prisms from a novel two-phase reaction system. The growth mechanism of the precursor has been systematically investigated, and a topotactic phase transformation from precursors to cubic Y₂O₃ is for the first time put forward. By the size controlling and aspect ratio adjusting, the luminescence emission intensity as well as external quantum efficiency of Eu³⁺ doped Y₂O₃ hexagonal prisms is further tailored to show an optimum. - Highlights: • Eu³⁺ doped Y₂O₃ hexagonal prisms were synthesized by a novel two-phase approach. • Inheriting mechanism of prisms morphology from Y₄O(OH)₉(NO₃) to Y₂O₃ was discussed. • Aspect ratio of prisms was tailored by the volume ratio of water to oleylamine. • Luminescence properties were optimized by adjusting aspect ratio of prisms