Microstructural comparison between PMMA-SiO 2 and PMMA-TiO 2 hybrid systems using Eu 3+ as ion-probe luminescence

Organic-inorganic Eu 3+ -doped PMMA-SiO 2 and PMMA-TiO 2 hybrid systems were synthesized by sol-gel. The doping ions were used as ion-probe luminescence to analyze the differences in the microstructure of the hybrid matrices. The local symmetry environment of the Eu 3+ ions in the hybrid matrices was described by the asymmetry parameter (R), defined as the intensity ratio of the 5 D 0  →  7 F 2 / 5 D 0  →  7 F 1 transitions. The photoluminescence of PMMA-SiO 2 with quenched emission and lower R is consistent with a symmetric, hydrated environment surrounding the Eu 3+ ions. Meanwhile, the higher value of R and the higher emission intensity, observed for PMMA-TiO 2, reveal a lower symmetric environment of the Eu 3+ ions. Furthermore, the emission and excitation bands of the 5 D 0 − 7 F 0 transition shows a red shift in the PMMA-TiO 2 spectra, indicating higher Eu-O covalence degree. The calculated values of the Judd-Ofelt parameters are in agreement with the higher Eu-O covalence degree in this hybrid material.