Template-free synthesis of highly uniform α-GaOOH spindles and conversion to α-Ga₂O₃ and β-Ga ₂O₃

Monodispersed single crystalline α-GaOOH spindles have been prepared via a simple wet-chemical route at 60 °C, in which GaCl₃ was used as the gallium source and ammonia as the alkali. The α-GaOOH spindles obtained at pH values of 10.0 and 11.0 have a hierarchical layered nanostructure and are comprised of many nanoplatelets. The investigation of the products formed at early growth stages indicates that the spindles are formed by a self-assembly process via oriented attachment. During this process, the pH value and the ammonia molecule have great influence on the morphology of the final products. Smooth prism-like α-GaOOH crystals were obtained at a lower pH value of 8.0 when ammonia was used or when ammonia was replaced by ethylenediamine at pH values of 8.0 and 10.0. The single-phase α-Ga ₂O₃ and β-Ga₂O₃ spindles can be obtained by thermal treatment of the α-GaOOH spindles at 600 and 900 °C, respectively. The morphological characteristics of the pristine α-GaOOH spindles are well maintained in the oxide products in terms of good dispersion, size uniformity and layered nanostructure. The β-Ga ₂O₃ spindle product exhibits a strong blue luminescence emission under the excitation wavelength of 250 nm.