Template-free synthesis, growth mechanism and photoluminescent properties of Ln(OH)3 and Ln2O3 nanorods (Ln: lanthanide ion)

Uniform and well-defined single-crystalline Ln(OH)3 and La(OH)3:Eu3+ (Ln: lanthanide ion) nanorods were successfully synthesized by a large-scale and facile hydrothermal method only using Ln(NO3)3·6H2O as lanthanide source and H2O2 as controller without any surfactant or template. The as-formed product via the hydrothermal process, La(OH)3:Eu3+, could transform to hexagonal La2O3:Eu3+ with the same morphology by a postannealing process. The above mentioned samples were characterized by means of X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and photoluminescence (PL) spectra. By tuning the hydrothermal treatment time, a morphological evolution between the nanoparticles and nanorods was observed. Furthermore the growth mechanism and the morphological evolution of different shapes were investigated. Unlike traditional synthesis of Ln(OH)3, H2O2 does not leave any impurity in the reaction system and makes the process very simple to obtain and separate the nanoparticles, nanomultipods and nanorods morphology. The La2O3:Eu3+ nanorods exhibit a strong red emission corresponding to 5D0 → 7F2 transition (625 nm) of Eu3+ under UV light excitation (282 nm), which have potential applications in fluorescent devices.