Low-temperature synthesis of NaRE(WO) films anion exchange from layered rare-earth hydroxides (LRHs) films, phase/morphology evolution and photoluminescence

Films of alkaline lanthanide tungstates, NaRE(WO 4 ) 2 (RE = La-Ho, and Y), were hydrothermally synthesized via an anion exchange using electrodeposited layered rare-earth hydroxide (RE 2 (OH) 5 NO 3 · n H 2 O) films as precursor templates in the presence of excess Na 2 WO 4 at pH ∼ 10 and 100 °C, without further heat treatment. The crystal structures and photoluminescence of the materials were characterized by XRD, FT-IR, FE-SEM, TEM, and PLE/PL spectroscopy techniques. The evolution of the phase composition and particle morphology from La 2 (OH) 5 NO 3 · n H 2 O to NaLa(WO 4 ) 2 was unveiled by varying the reaction time. With the successful synthesis of NaRE(WO 4 ) 2 for the wide range of REs, the effects of lanthanide contraction on the structural features and morphology of the NaRE(WO 4 ) 2 films were also clarified. Additionally, the photoluminescence of the NaEu(WO 4 ) 2 and NaTb(WO 4 ) 2 films were investigated, and they exhibited strongly red and green emissions, respectively. To the best of our knowledge, the layered rare-earth hydroxides have not been utilized as precursors to synthesize NaRE(WO 4 ) 2 films, and this work might have wide implications for the generation of other types of inorganic functional films. LRH films were prepared via electrodeposition within 10 minutes, and they were used as precursor templates to produce NaRE(WO 4 ) 2 films at pH ∼ 10. The obtained NaEu(WO 4 ) 2 and NaTb(WO 4 ) 2 films exhibit enhanced photoluminescence.