Control of Polymorph Formation in LaVO₄ Nanoparticles Synthesized by Aqueous Coprecipitation

Lanthanum orthovanadate crystallizes in tetragonal and monoclinic phases showing structure-dependent optical and catalytic properties, exhibiting potential for optical thermometry and peroxidase-mimicking catalysis. Although template conversion strategies enable formation of m-LaVO₄ via colloidal synthesis, phase selection in aqueous routes is still a challenge because kinetically stable t-LaVO₄ is often the main product at 1 atm and 25 °C. In this study, we adapted a simple aqueous colloidal precipitation route for controlling morphology and structure of LaVO₄ colloids. A kinetic study was performed by XRD and by in situ luminescence monitoring Eu³⁺ emissions. A progressive increase in the monoclinic fraction with the aging of the reaction mixture, indicated a time-dependent structural transformation towards the thermodynamically favored polymorph from hydroxide-rich kinetic intermediates. The results indicate that hydroxide concentration and aging time are determining factors in the phase selection of LaVO₄ via coprecipitation. The proposed route constitutes a simple alternative for obtaining nanoparticles in an aqueous medium.