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

Abstract

With the advancement of solid-state lighting technology, the design and preparation of fluorescence conversion films have become increasingly important. RE2(OH)5NO3·nH2O is a popular building block in constructing multifunctional films. In this paper, an electrodeposition method is developed to prepare RE2(OH)5NO3·nH2O 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 RE2(OH)5NO3·nH2O found that the higher concentration difference between the anion source Na2MoO4 and RE2(OH)5NO3·nH2O promotes the exchange of interlayer NO3 – and ligands (hydroxyl and water) in the [RE2(OH)5(H2O) n ]+ main layer with MoO4 2–, and forms tetragonal-structured NaRE(MoO4)2 film at pH ∼7 and 150 °C. Due to the fluorescence quenching groups in RE2(OH)5NO3·nH2O structure were exchanged by MoO4 2–, the intensity of Eu3+ emission (5D0 → 7F2) for NaEu(MoO4)2 film is ∼10 times that of Eu2(OH)5NO3·nH2O film under excitation at 394 nm. In addition, the films exhibit multicolor luminescence and long fluorescence lifetime by doping activators (Eu3+ and Tb3+) into the NaLa(MoO4)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(MoO4)2 films, and it might be extended to other kinds of functional films.