Local heterogeneity for a Eu3+-doped glass evidenced by time-resolved fluorescence spectroscopy coupled to scanning near-field optical microscopy

Abstract : Time-resolved fluorescence spectroscopy (TRFS) was applied to an aluminate glass sample doped with Eu3+ cation as a fluorescent probe of chemical environment and local symmetry. Conventional far field experiments revealed the presence of two different phases an amorphous phase featured by a highly disordered environment surrounding the Eu3+ cation and a more ordered polycrystalline phase that shows a significant increase of the Eu3+ fluorescence decay time compared to the amorphous phase. Near-field fluorescence spectra and decay kinetics were performed in the frontier region between the two phases using a home-built scanning near-field optical microscope (SNOM). SNOM-TRFS experiments confirmed the presence of local heterogeneities in this part of the glass at a sub-micrometric spatial scale. Polycrystalline sites were featured by an important shear-force interaction with the probing fiber optic tip, a longer fluorescence decay time and a higher Stark splitting of the 5D07FJ (J = 1 to 4) electronic transitions of the Eu3+ cations.