Evidence for a non-epitaxial growth-detachment mechanism in seed-mediated glycothermal synthesis of colloidal garnet nanoparticles

Seed-mediated synthesis of nanoparticles typically results in hetero-epitaxial growth, which eventually leads to larger nanoparticles with core-shell morphology. Counter intuitively, a seed-mediated glycothermal synthesis of large-lanthanide gallium/aluminum garnets nanoparticles (NPs) (Ln₃(Ga/Al)₅O₁₂, Ln = Lanthanide, e.g., Tb/Gd/Eu) using undoped YAG (Yttrium Aluminum Garnet, Y₃Al₅O₁₂) NPs as seeds, yielded highly dispersed colloidal garnets NPs of interest with no discernible core-shell features. Moreover, most of them are physically separate from the seeds. Based on the time-dependent evolution of physico-chemical and optical characterizations of the materials during reaction, along with DFT modeling, we offer a first insight into the mechanistic aspects of this non epitaxial NP formation. Growth of an amorphous Ln-(Al/Ga)-based material on top of the seed ligand is predicted computationally and confirmed experimentally, followed by detachment of the garnet NPs of interest away from the ligand-protected seeds once garnet crystallization occurs. This novel mechanism could be leveraged to overcome high formation barriers and enable seed-mediated synthesis of colloidal garnet nanoparticles with large lanthanides, or even beyond, without core-shell structure.