Energy transfer and tunable emission in BaGdF5: RE3+ (RE= Ce, Tb, Eu) nano-glass-ceramics

Ce3+ single-doped, Ce3+-Tb3+, Ce3+-Eu3+ and Tb3+-Eu3+ co-doped, and Ce3+-Tb3+-Eu3+ triply-doped nano-glass-ceramics (nGCs), containing cubic 10 nm size BaGdF5 nanocrystals, were synthesized by thermal treatment of precursor sol-gel glasses. The structural characterization was carried out by X-ray diffraction, transmission electron microscopy and energy dispersive X-ray spectroscopy, while the spectroscopic study was performed by excitation and emission spectra, along with lifetime measurements. In the Ce3+ single-doped, and Ce3+-Tb3+, Ce3+-Eu3+ co-doped nGCs, the emission spectra by exciting in the maximum of the UV excitation band of Ce3+ ions (∼ 300 nm) show a UV-violet broad band corresponding to the emission of Ce3+ ions. Additionally, Gd3+ UV, Tb3+ green and Eu3+ red emission peaks are also observed respectively, revealing an energy transfer mechanism from the Ce3+ to these ions. For the Tb3+-Eu3+ co-doped nGCs, efficient energy transfer from Gd3+ host to Tb3+ and Eu3+, and from Tb3+ to Eu3+ ions were also evidenced. Moreover, taking advantage of the Eu3+ properties as structural probe ion, it was found that an important fraction of dopant ions were incorporated to the BaGdF5 nanocrystalline environments. In the Ce3+-Tb3+-Eu3+ triply-doped nGCs, intense and simultaneous UV-violet, green and red emissions were observed under Ce3+ excitation. Moreover, it was shown that the emitted colour can be tuned by varying the Eu3+ doping level and/or the excitation wavelength. After the analysis of nGCs luminescent features, the energy transfer and metal-metal charge transfer mechanisms, responsible of these emissions, are proposed. Results suggest these materials have potential applications as efficient UV to VIS converters.