Low-temperature synthesis of NaRE(WO 4 ) 2 films via 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.