Synthesis, characterization, shape-preserved transformation, and optical properties of La(OH)3, La2O2CO3, and La2O3 nanorods

A simple method to directly synthesize stable and crystalline pure phase La(OH)₃ nanorods, with a diameter of around 15 nm and lengths in the range of 120-200 nm, was developed using cationic surfactant (cetyltrimethylammonium bromide, CTAB). The obtained La(OH)₃ nanorods can be successfully converted to La₂O₂CO₃ and La₂O₃ nanorods via calcination under appropriate conditions. Analytical methods such as X-ray diffraction (XRD) spectra, Fourier transformed infrared (FTIR) spectrum, differential scanning calorimetry and thermogravimetric analysis (DSC-TGA), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM) were employed to characterize the morphology and microstructure of the final products. The results reveal that La(OH)₃ nanorods were shape-preserved and transformed to La₂O₂CO₃ nanorods at 400 °C for 2 h and to La₂O₃ nanorods at 800 °C for 2 h, respectively. TEM images indicate that the as-obtained La₂O₂CO₃ and La₂O₃ entirely consist of uniform nanorods in high yield with diameters of about 15 nm and 23 nm, lengths of 200-300 nm and 300-500 nm, respectively. The formation mechanism of the La(OH)₃, La₂O₂CO₃ and La₂O₃ nanorods was investigated. Room-temperature photoluminescence (RTPL) properties were investigated under the excitation of 275 nm. The ⁵D₃ → ⁷F_j (j = 2-6) emission peaks at the wavelength below 500 nm were found in the RTPL spectra.