Optical properties of silica sol-gel materials singly- and doubly-doped with Eu^3＋and Gd^3＋ ions

In present work, the optical and structural properties of silica sol-gel glasses and glass-ceramic materials singly- and dou- bly-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 enhance- ment 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 λex=393 nm and λex=273 nm. Moreover, the influence of excitation wavelength on luminescence decay time of the 5D0 excited state was also analyzed. The GdS＋-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 re- sult, 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 en- ergy transfer phenomenon and heat-treatment process were responsible for significant improvement of Eu3＋ luminescence in stud- ied sol-gel samples.

Photoluminescence and energy transfer in transparent glass-ceramics based on GdF3:RE3+（RE=Tb,Eu）nanocrystals

In the present work,the transparent oxyfluoride glass-ceramic samples containing GdF3:RE^3+(RE=Tb,Eu)nanocrystals(nGCs)were fabricated via controlled heat-treatment of precursor xerogels prepared using a sol-gel method.The formation of GdF3 nanocrystalline phase from gadolinium(III)trifluoroacetate was verified based on XRD measurements.The average crystal sizes calculated from Scherrer formula were estimated to^10 nm as well as^6 nm for Tb^3+-and Eu^3+-doped samples,respectively.The optical behavior of prepared sol-gel samples was evaluated based on photoluminescence excitation(PLE)and emission spectra(PL)as well as luminescence decay analysis.Obtained samples exhibit the 5D4→7FJ(J=6-3,Tb3+)and the 5D0→7FJ(J=0-4,Eu3+)emission bands recorded within the visible spectral area under excitation at near-UV(393 nm(Eu^3+),351,369,378 nm(Tb^3+))as well as middle-UV illumination(273 nm(Gd3+)).Additionally,based on recorded decay curves,the luminescence lifetimes(τm)for the 5D4(Tb^3+)and the 5D0(Eu3+)excited states were also evaluated.In general,recorded luminescence spectra and double-exponential character of decay curves for nGCs indicate a successful migration of Tb^3+and Eu^3+dopant ions from amorphous silicate framework to lowphonon energy GdF3 nanocrystal phase.