Nearly monodisperse YBO₃ architectures with various shapes have been prepared on a large scale by a facile, effective, and environmentally friendly hydrothermal process using Y(OH)₃ as a precursor. X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL) and cathodoluminescence (CL) spectra were used to characterize the samples. The shape and size of these as-prepared YBO₃ architectures can be tuned effectively by controlling the reaction conditions, such as reaction time, and the molar ratio of H₃BO₃/Y(OH)₃. As a typical morphology, the possible formation mechanism for YBO₃ monodisperse flower-like microstructures is presented in detail. To extend this method, other LnBO₃ (Ln = Dy, Ho, Er) architectures with well-defined shape and dimensionality can also be achieved by adjusting different rare-earth hydroxides precursors. Under UV excitation and low-voltage electron beam excitation, YBO₃: 5 mol % Eu³⁺ sample exhibits a strong red emission lines of Eu³⁺ corresponding to ⁵D₀ → ⁷F_J (J = 0–4) transitions. When doped with 5 mol % Tb³⁺ ions, the emission lines of Tb³⁺ corresponding to ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3) transitions with ⁵D₄ → ⁷F₅ (green emission at 542 nm) being the most prominent group have been observed. This work sheds some light on the design of a well-defined complex nanostructure, and the luminescent properties have potential applications in fluorescent lamps and field emission displays.