Multicolor luminescence properties of Ln7O6F9: RE3+ (Ln = Y, Lu; RE = Pr, Sm and Eu) nano-rods with bifurcation

The uniform 1D nano-rods of RE 3+ doped Ln 7 O 6 F 9 ( Ln  = Y and Lu; RE  = Pr, Sm and Eu) were synthesized through a facile two-step hydrothermal method without extra fluorine source followed by post-heat treatment. The phase formation, morphologies, as well as photoluminescence properties of the materials were investigated. The precursor composition was determined to be Ln (OH) 1.69 F 1.31 using the Fourier transform infrared spectrum (FT-IR), thermal gravimetric and differential scanning calorimetry (TG-DSC). The average lengths of Y 7 O 6 F 9 and Lu 7 O 6 F 9 were about 6.8 and 7.9 μm, respectively, with the average width of about 650 nm. It was interesting that the tip of the nano-rods exhibits a straight line and divergent umbrella shaped bifurcation for Y 7 O 6 F 9 and Lu 7 O 6 F 9 , respectively. Upon ultraviolet excitation, Pr 3+ , Sm 3+ and Eu 3+ ions in Ln 7 O 6 F 9 showed blue, orange and red emissions originating from their characteristic f-f transitions. In addition, the 4 f 1 5 d 1  → 4 f 2 band emissions (340–450 nm) as well as typical 4 f 2  → 4 f 2 line emissions (450–700 nm) of Pr 3+ were observed in Pr 3+ -doped Ln 7 O 6 F 9 . For Sm 3+ -doped Ln 7 O 6 F 9 , only the typical f - f transitions of Sm 3+ were observed with the absence of charge transfer (CT) band. However, the broad excitation bands at 255 nm attributing to the charge transfer transition of Eu 3+ (i.e. O 2−  → Eu 3+ CT) were observed in Eu 3+ -doped Ln 7 O 6 F 9 .