Photoluminescence investigation of sol-gel glass-ceramic materials containing SrF2:Eu3+ nanocrystals

Abstract

In the present paper, the nanocrystalline transparent oxyfluoride SrF2:Eu3+ glass-ceramic materials (nGCs) were synthesized via a low-temperature sol-gel method, in which trifluoroacetic acid (TFA) was used as a fluorination reagent. The thermal degradation of precursor xerogels was examined by TG/DSC analysis and the formation of SrF2 nanocrystals inside silicate xerogel host was proved by XRD measurements. Additionally, to verify the structural changes within silicate network during ceramization process, the IR-ATR measurements were also carried out. The optical properties of Eu3+ ions in precursor xerogels and fabricated nGCs were investigated based on photoluminescence excitation (PLE: λem = 611 nm) and emission (PL: λexc = 393 nm) spectra as well as luminescence decay analysis of the 5D0 excited level. It was observed, that for precursor silica xerogels the electric-dipole transition (ED) 5D0 → 7F2 was dominant, meanwhile the magnetic-dipole transition (MD) 5D0 → 7F1 had the greatest intensity for SrF2:Eu3+ nGCs. Thus, the R/O-ratio (R/O = I(5D0 → 7F2)/I(5D0 → 7F1)) was calculated to estimate the symmetry in the local framework around Eu3+ ions. Moreover, the reddish-orange photoluminescence is long-lived (about 30-fold longer) for SrF2:Eu3+ nGCs compared with xerogels. The changes in emission spectra as well as double-exponential character of luminescence decay curves recorded for obtained nGCs indicated the successful migration of optically active Eu3+ ions from amorphous silica framework to low phonon energy SrF2 nanocrystal phase.