PVP-mediated synthesis of MPO4 (M = Y, Er) hollow mesocrystal cubes via a ripening process

Abstract

YPO₄ and ErPO₄ hollow mesocrystal cubes were successfully synthesized using PVP as additive to modify the crystallization of YPO₄ and ErPO₄. The time-dependent TEM images revealed that the as-formed nanocubes covered in PVP self-assembled into big mesocrystal cubes via oriented attachment firstly, followed by the ripening process to form a yolk–shell mesocrystal structure and finally hollow mesocrystal cubes. Usually, the ripening process promotes the transformation from the mesocrystal to the single crystal, but in our case, the mesocrystal remains, which is confirmed by TEM, SEM and SAED. PVP plays a key role for the formation of hollow mesocrystal cubes. BET measurements show that the shells of the hollow cubes are porous with a pore size of 36–37 nm. The shapes of the YPO₄ can be varied from cubes to cuboids by adjusting reaction temperatures. By doping, YPO₄:Eu and YPO₄:Tb hollow mesocrystal cubes are also synthesized, which display red and green emissions under ultraviolet excitation.