Anion-Exchange Behavior and Optical Properties of Ternary Y/Gd/Eu Layered Rare-Earth Hydroxides

Self-assembly layered rare-earth hydroxide (LRH) nanosheets of ternary Y/Gd/Eu system were synthesized by a chemical precipitation route at freezing temperature. The anion-exchange behavior and optical properties of the LRHs were studied. The results show that at the SO42-/Ln(3+) molar ratio (R) of 0.25, the SO42- almost replaces the NO3- located in the interlayer of the LRH via anion exchange; however, the photoluminescence (PL) intensity decreases. Gd3+ substitution for Y3+ significantly changes the coordination environment of Eu3+, leading to different intensities for the splitting bands of D-5(0)-> F-7(J) transition peaking at similar to 590 and 595 nm. Sulfate exchange inhibits surface diffusion and inter-particle sintering during calcination, and thus well-dispersed oxide powders that exhibit typical Eu3+ red emission are obtained. The Gd3+ addition sensitizes Eu3+ emission to enhance the PL intensity of the phosphors. Improved PL intensity and external quantum efficiency and decreased fluorescence lifetime are observed at higher calcination temperatures.