Optical properties of silica sol-gel materials singly- and doubly-doped with Eu3+and Gd3+ ions

Abstract

In present work, the optical and structural properties of silica sol-gel glasses and glass-ceramic materials singly- and doubly-doped with Eu3+ and Gd3+ ions were investigated. The optical properties of studied systems were determined based on absorption, excitation and emission spectra as well as luminescence decay analysis. Conducted studies clearly indicated a significant enhancement of visible emission originated from Eu3+ ions as a result of changing the excitation mechanism, via Gd3+→Eu3+ energy transfer. The luminescence intensity R-ratio was analyzed before and after heat-treatment process upon excitation at γex=393 nm and γex=273 nm. Moreover, the influence of excitation wavelength on luminescence decay time of the 5D0 excited state was also analyzed. The Gd3+→Eu3+ energy transfer efficiencies for precursor and annealed samples were calculated based on luminescence lifetime of the 6P7/2 level of Gd3+ ions. The X-ray diffraction measurements were conducted to verify the nature of obtained sol-gel materials. In result, the formation of orthorhombic GdF3 nanocrystal phase dispersed in amorphous silica glass host was identified after annealing. Obtained results clearly indicated an incorporation of Eu3+ activators into formed GdF3 nanocrystals. Thus, conducted heat-treatment process led to considerable changes in surrounding environment around Eu3+ ions. Actually, it was found that energy transfer phenomenon and heat-treatment process were responsible for significant improvement of Eu3+ luminescence in studied sol-gel samples.