Morphology and Optical Properties of SiO2-Based Composite Thin Films with Immobilized Terbium(III) Complex with a Biscoumarin Derivative

The complex of Tb(III) with the biscoumarin derivative 3,3 '-[(4-hydroxyphenyl)methyl)]bis-(4-hydroxy-2H-1-benzopyran-2-one), Tb(C25H15O7)(3)center dot 5H(2)O, was successfully immobilized by a simple technique in transparent SiO2-based matrix. The films and monoliths obtained were studied by IR spectroscopy, fluorescent spectroscopy, and microscopy. The micromorphology of the films was studied by atomic force microscopy, proving their homogeneity. The 3-D surface of the films is very complex geometrically and appears relatively smooth, with very fine nano-asperities spread on the surface due to the preparation process. A detailed surface description of the surface morphology at nanometer scale using statistical parameters, according to ISO 25178-2: 2012, was made. The presence of the Tb(III) complex in the films and monoliths was proven by the characteristic emission bands of the Tb(III) ions. The lifetime of the immobilized Tb(III) complex was determined, showing better protection of the SiO2 matrix in the monoliths than with the films.