Microwave approach for the synthesis of rhabdophane-type lanthanide orthophosphate (Ln = La, Ce, Nd, Sm, Eu, Gd and Tb) nanorods under solvothermal conditions

Rhabdophane-type hexagonal lanthanide orthophosphate, LnPO₄ · nH₂O (Ln = La, Ce, Nd, Sm, Eu, Gd and Tb, n = 0 to 0.6), and body-centered tetragonal ErPO₄ · nH₂O nanowires/nanorods have been successfully synthesized in high yield (>95%) by simple microwave heating of an aqueous solution of Ln(III) nitrate and NH ₄H₂PO₄ in the pH range 1.8-2.2. The reaction was conducted in a simple domestic microwave oven. The structure, morphology, composition and physical properties of the as-prepared products have been characterized by powder X-ray diffraction, low resolution transmission electron microscopy, high resolution transmission electron microscopy, selected area electron diffraction, thermogravimetric analysis, differential scanning calorimetry, infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy. The length and width of the resulting lanthanide orthophosphate nanowires/nanorods are in the range 70-2200 nm and 6-130 nm, respectively. A possible mechanism for the formation of LnPO₄ · nH₂O nanowires/nanorods is briefly discussed.