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This paper presents a facile hydrothermal route to synthesize monodispersive and single-crystalline BaHfO(3) hollow micro- and nanospheres in a concentrated basic environment. The hollow spheres were size tunable from submicrometer to nanoscale by simply adjusting the base concentration at a suitable temperature. The base concentration played the key role on forming BaHfO(3) hollow spheres. Detailed investigations on base concentration, reaction temperature, and duration indicated that the formation of BaHfO(3) hollow spheres was driven by Ostwald ripening process. Because of the abundance of defects, the as-prepared BaHfO(3) hollow nanospheres exhibited a blue light emission under UV-light excitation at room temperature. Calcination led to the photoluminescence declination due to the decrease of defects.

BaZrO3, SrZrO3 and SrHfO3 hollow microparticles were prepared by a reflux method. The concentrated KOH solution used initiated a grain nucleation process to reduce particle sizes, and afforded a high reaction temperature to promote the hollowing process.

Based on the theory of sol-gel science, perovskite SrHfO(3) hollow cuboidal particles with tunable sizes were rationally synthesized by templateless hydrothermal reactions in KOH solutions. The concentrated KOH solution not only elevated the supersaturation of the reactants to promote the grain growth of SrHfO(3) but also controlled the aggregated particle sizes by compressing the electrical double layers of the primary particulates. The following Ostwald ripening process produced hollow particles with sizes ranging from submicrometer to hundred nanometre. The HRTEM image and SAED pattern revealed the single crystal nature of each hollow cuboidal nanoshell. The KOH concentration and reaction time related experiments confirmed that the formation of SrHfO(3) hollow cuboidal nanoshell was driven by the Ostwald ripening process and followed our assumption. The particles experienced solid, core-shell and hollow morphologies as the reaction proceeded. Also, the formation of SrHfO(3) hollow cuboidal nanoshells favored high reaction temperature which initiated and accelerated the ripening process. The as-prepared hollow cuboidal nanoshells displayed blue light emission under UV laser excitation at room temperature. After calcination, the photoluminescence intensity declined due to the improvement of crystallinity.