Structural and photoluminescence characterization of mesoporous silicon-phosphates

Two different types of mesoporous silicon-phosphate supports using different surfactants (a mixture of (CH3)3C13H27NBr with an organophosphorus coupling molecule (HO-PO(i-C3H7)2) and with a co-surfactant ((C2H5)3(C6H5)PCl), respectively) were synthesized. Trivalent europium (Eu) ions were immobilized via ion-exchange on these supports. The resulting materials were characterized using nitrogen adsorption isotherms at −196 °C, thermogravimetric analysis, SEM, TEM, FT-IR, PXRD, CP/MAS. and 31P NMR, DR-UV–vis as well as steady-state and time-resolved photoluminescence spectroscopy. The results evidenced that the co-polymerization of silicon and phosphorous yielded a unique morphology in these materials. Following calcination at 450 and 900 °C europium-exchanged silicon-phosphates with great surface area (BET = 600–705 m2 g−1) and 3.4 nm sized mesopores were obtained. The differences among the optical properties of the non-calcined europium materials such as the emission lifetimes, local environment at the europium sites or the relative contribution of the upper excited levels to the total photoluminescence were assigned to the surfactants used in the synthesis. Calcination of the silicon-phosphates at higher temperatures than 450 °C did not induce major changes in the structural properties; in contrast, photoluminescence properties of europium were markedly improved in terms of intensity and average lifetime.