Preparation And Luminescent Properties Of Doped And Coated Rare Earth Complex

Rare earth complexes and some core-shell structured complexes with enhanced optical and thermal stabilities have been prepared successfully. The as-prepared products were characterized by element analysis, Fourier transform infrared (IR), X-ray diffraction (XRD), thermogravimetry-differential thermal analysis (TG-DTA), UV-Vis spectra, scanning electron microscope (SEM), transmission electron microscope (TEM), photoluminescence (PL), and energy-dispersive X-ray spectroscopy (EDS), respectively. The results are as follows.1. Three new complexes of rare earth Eu³⁺ with benzoic acid (HBA), p-phthalic acid (p-Phth) and trimesic acid (HTMA) were prepared by precipitation methods. The results of UV spectra and PL spectra indicate that the photoluminescence of the complexes originate from the"Antenna Effect". The energy match of the lowest triplet state energies of ligand to the excited states of lanthanide ion is mostly factor of the emission intensity of the complex.2. Three series of doped rare earth complexes (Eu_1-xRE_x)₂(p-Phth)₃ (RE=Y, La, Gd ) were synthesized by precipitation method. The compositions and structures of the complexes were confirmed using element analysis, FT-IR, and XRD. Remarkable enhancement of the PL intensities was observed from the Eu³⁺ complexes co-doped with Y³⁺, La³⁺ and Gd³⁺. The influence of the three ions follows the order Y³⁺>Gd³⁺>La³⁺. Since the excited state levels of doped ions (Y³⁺, La³⁺ and Gd³⁺) are higher than the triplet state level of ligand, thus the energy the ligand absorbs can not be transferred to the doped ions, but transmitting to the central ion by the bridge structure of the ligand; On the other hand, the doping concentration of Eu³⁺ ions will be decreased by co-doping with Y³⁺, La³⁺ and Gd³⁺ ions, which prevents the quenching of its luminescence. It has been known that luminescence and quenching are the two contrary behaviors in the luminescent process. As a result, the incorporation of inert rare earth ions into Eu complex enhances its PL intensity and reduces its cost.3. Two kinds of ternary complexes containing europium with H2(p-Phth) as the first ligand, and phen , Bipy as the second ligand were synthesized. The compositions, morphologies, and other properties were investigated using elemental analysis, IR, SEM, UV, TG-DTA, and PL, respectively. The effect of the second ligands (phen, Bipy) was also analyzed thoroughly. The second ligands were proposed to replace part of crystal water and increase the conjugate plane of the complex system, resulting in enhancing the rigid structure and promoting the absorption of energy. The ligands phen and Bipy not only effectively transfer the absorbed energy to Eu³⁺ ion, but also act as a good energy transmission channel between the first ligand and Eu³⁺ ion, which enhance the PL intensity of the complexes.4. Core-shell structures of RE2(p-Phth)3/SiO2 (RE=Eu,Tb) materials were fabricated through the hydrolysis of tetraethyl-orthosilicate (TEOS) with NH3·H2O as the catalyzer in the alcohol solution containing pre-synthesized rare earth complex. It is found that the coating of SiO2 around the rare earth complexes significantly decreases the energy loss on their particles surface, accelerates energy transition, and enhances the luminescent intensity. Compared with those of uncoated Eu and Tb complexes, the PL intensities of SiO2 coated materials increase by about 70% and 32%, respectively. Moreover, the SiO2 shell also enhances the luminescent and thermal stabilities of the complexes, which greatly improves the practical applications of the complexes.