Does BaYF5 nanocrystals exist? - The BaF2-YF3 solid solution revisited using photoluminescence spectroscopy

During thermolysis of metal trifluoroacetates in high boiling organic solvents the two Ba1−xRExF2+x phases with cubic fluorite-type structure are formed in BaF2-YF3 system. In contrast to previous reports formation of so-called 'BaYF5' nanocrystals was not observed. Besides the X-ray diffraction analysis the samples doped with optically active Eu3+ and Er3+ ions were characterized with photoluminescence spectroscopy and results provided by both methods corroborates each other. Upconversion emission observed under excitation at 980 nm for the Ba1−xYxF2+x phase co-doped with Yb3+ and Er3+ ions is strongly composition dependent. Its intensity increases with increasing of REF3 content for 0.2 < x < 0.45, whereas the opposite trend is evident for x > 0.45 and upconversion emission is totally quenched for x > 0.6. The important outcome of the present study is that compositions other than that with x = 0.5 should be probed to fully benefit from photoluminescence potential of Ba1−xRExF2+x nanofluoride phases activated with lanthanide ions.