Lanthanide molecular-based hybrids covalently bonded with silica: Photoluminescence and control of micromorphology

The syntheses of modified 5-bromonicotinic acid by (3-aminopropyl)triethoxysilane and the preparation of their corresponding organic–inorganic molecular-based hybrid material with the two components equipped with covalent bonds are described. The organic moiety is a derivative of 5-bromonicotinic acid which is applied to coordinate to RE3+ and further introduced into silica matrices by Si–O bonds after hydrolysis and polycondensation processes. Judd–Ofelt theory proves that covalency increases along with increasing reciprocal energy difference between the 4fN and 4fN-15d1configurations. Ultraviolet absorption, phosphorescence and luminescence spectra were utilized to characterize the photophysical properties of the obtained hybrid material and the above spectroscopic data reveal that the triplet energy of modified 5-bromonicotinic acid matches with the emissive energy level of RE3+. In this way, the intramolecular energy transfer process took place within these molecular-based hybrids and strong green, red or blue emissions of RE3+ have been acquired. Scanning electronic microscope presents no phase separation phenomenon appear and the different crystal structures of lanthanide complex precursor molecules have influence on the microstructure and micromorphology of corresponding molecular hybrids.