Photoluminescent Films of MoO₄^–2 Exchanged Layered Rare-Earth Hydroxides for Solid-State Lighting

With the advancement of solid-state lighting technology, the design and preparation of fluorescence conversion films have become increasingly important. RE 2 (OH) 5 NO 3 · n H 2 O is a popular building block in constructing multifunctional films. In this paper, an electrodeposition method is developed to prepare RE 2 (OH) 5 NO 3 · n H 2 O films within 10 min, avoiding the problems of long-time consumption and low yield of the available four-step method. The study of anion exchange of RE 2 (OH) 5 NO 3 · n H 2 O found that the higher concentration difference between the anion source Na 2 MoO 4 and RE 2 (OH) 5 NO 3 · n H 2 O promotes the exchange of interlayer NO 3 – and ligands (hydroxyl and water) in the [RE 2 (OH) 5 (H 2 O) n ] + main layer with MoO 4 2–, and forms tetragonal-structured NaRE(MoO 4 ) 2 film at pH ∼7 and 150 °C. Due to the fluorescence quenching groups in RE 2 (OH) 5 NO 3 ·nH 2 O structure were exchanged by MoO 4 2–, the intensity of Eu 3+ emission ( 5 D 0 → 7 F 2 ) for NaEu(MoO 4 ) 2 film is ∼10 times that of Eu 2 (OH) 5 NO 3 ·nH 2 O film under excitation at 394 nm. In addition, the films exhibit multicolor luminescence and long fluorescence lifetime by doping activators (Eu 3+ and Tb 3+ ) into the NaLa(MoO 4 ) 2 lattice and adjusting the molar ratio of activators, making them promising color-conversion films for solid-state lighting. This work offers a new concept for the design and fabrication of NaRE(MoO 4 ) 2 films, and it might be extended to other kinds of functional films.