Monoclinic YW2O6(OH)3 : Eu with 3D hierarchical superstructures, namely, micro-waxberry and micro-flower, have been selectively synthesized via an efficient surfactant- and template-free hydrothermal process for the first time. Morphology modulation can be easily realized simply by changing the pH value of the precursor medium. X-Ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution TEM (HRTEM), energy-dispersive X-ray (EDX) spectrometry and photoluminescence (PL) spectra were employed to characterize the as-obtained products. A possible formation mechanism of the YW2O6(OH)3 : Eu hierarchical architectures was proposed on the basis of time-dependent experiments. Comparative experiments indicated that pure and well-crystallized YW2O6(OH)3 : Eu could be obtained only in an appropriate pH range of 2–3. An investigation on the PL properties of two YW2O6(OH)3 : Eu samples with waxberry-like and flower-like microstructures revealed that the optical properties were strongly correlated with the crystallinity and morphology. Both samples exhibited red emissions with a high color purity. More importantly, micro-waxberry displayed a stronger emission and possessed a much higher R/O value than micro-flower, implying an improvement of color purity. Through fine adjustment of the pH value of the initial solution from 3 to 2, not only was better crystallinity obtained, but also the enhanced red color purity could be realized. The possible reasons responsible for this improvement were discussed.
