Shape-Controllable Synthesis and Morphology-Dependent Luminescence Properties of GaOOH:Dy³⁺ and β-Ga₂O₃:Dy³⁺

Dy³⁺-doped gallium oxide hydroxides (GaOOH:Dy³⁺) with various morphologies (submicrospindles, submicroellipsoids, 3D hierarchical microspheres) were synthesized by a facile soft-chemical method. After annealing at 1000 °C, the GaOOH:Dy³⁺ precursor was easily converted to β-Ga₂O₃:Dy³⁺ phosphors which kept their original morphologies. The as-prepared GaOOH:Dy³⁺ and β-Ga₂O₃:Dy³⁺ products were characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), low- to high-resolution transmission electron microscopy (TEM), selected area electron diffraction (SAED), photoluminescence (PL) spectra, cathodoluminescence (CL) spectra, and quantum yield (QY). With an increase in pH from 4 to 9, the morphology of GaOOH:Dy³⁺ varied from submicrospindles to 3D hierarchical microspheres of self-assembled nanoparticles. A possible mechanism for the formation of various morphologies of GaOOH:Dy³⁺ and β-Ga₂O₃:Dy³⁺ was proposed. Under ultraviolet and low-voltage electron beam excitation, the pure β-Ga₂O₃ samples exhibit a blue emission with a maximum at 438 nm originating from the GaO₆ groups, while the β-Ga₂O₃:Dy³⁺ samples show the characteristic emission of Dy³⁺ corresponding to ⁴F_9/2 → ⁶H_{15/2, 13/2} transitions due to an efficient energy transfer from β-Ga₂O₃ to Dy³⁺. A simple model was proposed to explain the energy transfer process and luminescence mechanism. Furthermore, the dependence of luminescence intensity on the morphology has been investigated in detail. Under 257 nm UV and electron beam excitation, the β-Ga₂O₃:Dy³⁺ phosphor with a submicroellipsoid shape shows the highest relative emission intensity and quantum yield compared with other morphologies, and the obtained phosphors have potential applications in the areas of fluorescent lamps and field emission displays (FEDs).