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 degrees C, the GaOOH:Dy3+ precursor was easily converted to beta-Ga2O3:Dy3+ phosphors which kept their original morphologies. The as-prepared GaOOH:Dy3+ and beta-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 beta-Ga2O3:Dy3+ was proposed. Under ultraviolet and low-voltage electron beam excitation, the pure beta-Ga2O3 samples exhibit a blue emission with a maximum at 438 nm originating from the GaO6 groups, while the beta-Ga2O3:Dy3+ samples show the characteristic emission of Dy3+ corresponding to F-4(9/2) -> H-6(15/2), (13/2) transitions due to an efficient energy transfer from beta-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 beta-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).