Structure and luminescent properties of oxyfluoride glass-ceramics with YF3:Eu3+ nanocrystals derived by sol-gel method

In this paper, the transparent oxyfluoride glass-ceramic materials containing YF3:Eu3+ nanocrystals were fabricated via controlled ceramization of precursor xerogels at relatively low temperature T = 350 degrees C. The formation of YF3 nanocrystalline phase from Y(CF3COO)(3) was verified based on X-ray diffraction (XRD) measurements as well as high-resolution transmittance electron microscopy (HR-TEM). Based on IR-ATR spectroscopy the functional groups inside sol-gel structures were identified. The optical properties of Eu3+ ions in fabricated sol-gel samples were investigated based on photoluminescence excitation and emission spectra as well as luminescence decay analysis of the D-5(0) excited level. Upon excitation at near-UV illumination, lambda(exc) = 393 nm, the series of 4f(6)-4f(6) photoluminescence bands of Eu3+ ions in reddish-orange light area were recorded. The Stark splitting of photoluminescence bands, double-exponential character of decay curves and long-lived emission for fabricated glass-ceramic samples clearly evidenced the partial substitution of Y3+ by optically active Eu3+ ions in precipitated YF3 nanocrystals. Indeed, it was identified that applied annealing conditions resulted in significant, almost 34-fold prolongation of luminescence lifetime from 0.24 ms (Eu3+ ions in xerogel host) up to 8.14 ms (Eu3+ ions incorporated into YF3 nanocrystals). It was also observed a clear correlation between identified phonon energies from IR measurements and luminescence behavior of Eu3+ ions.