Hydrothermal synthesis and improved luminescent properties of nanosheet-based rare earth orthoborates lantern-like assemblies

Hexagonal vaterite-type LuBO3:Tb3+/Eu3+ lantern-like phosphors have been successfully prepared by a simple hydrothermal process directly without sintering treatment. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction, photoluminescence, low-voltage cathodoluminescence, and kinetic decays were used to characterize as-prepared phosphors, which present complex lantern-like 3D assemblies that are composed of nanosheets with thickness of about 23 nm and high crystallinity in spite of the moderate reaction temperature of 210 °C. The reaction mechanism and the self-assembly evolution process have been proposed. The pH, temperature, time, and ethylene glycol play critical roles in the formation of this specific hierarchical and complex 3D structure. Under UV excitation and low-voltage electron beam excitation, vaterite-type LuBO3:Tb3+ samples showed the characteristic green emission of Tb3+ corresponding to 5 D 4 → 7 F 5 transitions; vaterite-type LuBO3:Eu3+ particles exhibited a strong red emission corresponding to primary group electric dipole transition 5 D 0 → 7 F 2 with much higher R/O values (chromatically redder fluorescence, increase of 29 %) compared with samples by conventional solid-state reaction, which have potential applications in fluorescent lamps and field emission displays.