New synthetic strategies for luminescent YVO4:Ln3+ (Ln = Pr, Sm, Eu, Tb, Dy, Ho, Er) with mesoporous cell-like nanostructure

Abstract

A series of single-crystalline Ln3+-doped YVO4 (Ln = Pr, Sm, Eu, Tb, Dy, Ho, Er) nanoparticles with mesoporous cell-like nanostructure were prepared via initiating homogeneous precipitation followed by a hydrothermal treatment. All synthetic samples with mesoporous cell-like nanostructure showed a slight variation of crystallite size, ranging from 15 to 17 nm. TEM analysis demonstrated that the diameter of the internal mesoporous structure is about 2∼10 nm. The calculated unit cell volume showed a linear increase trend with increasing the ionic radius of the doped Ln3+ ions. Under UV irradiation, the characteristic emission of rare earth ions can be clearly observed for YVO4:Ln3+ (Ln = Dy, Eu, Sm, Er, Ho) samples. Moreover, the mesoporous cell-like nanostructure has exhibited an enhanced optical property compared with the nanoparticles without mesoporous nanostructure. However, for Ln = Tb and Pr, the characteristic emission of rare earth ions is difficult to observe, even quenching. Furthermore, the bandgap energy Eg showed an obvious red-shift, reducing to 3.67 ± 0.08 eV for YVO4:Eu3+ nanoparticles. The band gap reduction of YVO4:Ln3+ samples possessed the sequence: Eu3+ > Dy3+ > Sm3+ > Er3+ > Ho3+ whereas the band gaps of the YVO4:Ln3+ (Ln = Tb, Pr) samples remained unchanged, almost equal to the YVO4 host. Moreover, due to the tendency to be oxidized to the tetravalent state in Tb3+ and Pr3+ ions, an intervalence charge transfer (IVCT) transition occurs in these two ions, which contributes to quench the luminescence of YVO4:Ln3+ (Ln = Tb, Pr).