In Situ and Ex Situ Luminescence Investigation of Rare Earth Layered Double Hydroxides Intercalated with Mellitate Anion

This work reports the preparation by co-precipitation method of [Zn2Al0.95:Ln0.05(OH)6](HMA)0.21·(H2O)x, where x = 1.0–1.7 and Ln3+: Sm3+, Eu3+, Gd3+, Tb3+ and Dy3+, doped trivalent lanthanide ions (Ln3+) intercalated with mellitate (HMA5−) anions in the interlayer gallery. The results indicate that the Ln3+ ions and the organic anion are effectively introduced into the material without significantly losing the structural properties of the layered double hydroxydes (LDH). In situ measurements reveal slight changes in the luminescent properties assigned to the nucleation and growth processes of the LDH. Ex situ experiments show that the photophysical properties also changed after the drying process, indicating significant interactions of the mellitate anion in the materials. LDH-HMA:Eu3+ and LDH-HMA:Tb3+ exhibit high luminescence intensity in the red and green spectral regions due to the 5D0→7F0-6 and 5D4→7F6-0 transitions, respectively. The LDH-HMA doped with different ratios Eu3+/Tb3+ presenting emission colors from red to green are also investigated. Surprisingly, the unexpected afterglow blue luminescence from the LDH-HMA doped with Gd3+ ion is ascribed to the phosphorescence T→S0 transition. Finally, obtaining three red, green and blue luminophores based on the same type of material represents an effective strategy toward white-light emission realized by mixing three different LDHs materials based on Ln3+ ions.