Garnet-type Li 6 Ca(La 0.97 Yb 0.02 RE 0.01 ) 2 Nb 2 O 12 (RE = Ho, Er, Tm) new phosphors were successfully synthesized via solid reaction at 900°C for 5 hours, whose course of phase evolution, macroscopic/local crystal structure and up-/down-conversion (UC/DC) photoluminescence were clarified. Mechanistic study and materials characterization were attained via XRD, Rietveld refinement, DTA/TG, electron microscopy (FE-SEM/TEM), and Raman/reflectance/fluorescence spectroscopies. The phosphors were shown to exhibit UC luminescence dominated by a ~ 553 nm green band ( 5 F 4 / 5 S 2 → 5 I 8 transition) for Ho 3+ , a ~ 568 nm green band ( 4 S 3/2 → 4 I 15/2 transition) for Er 3+ and a ~ 806 nm near-infrared band ( 3 H 4 → 3 H 6 transition) for Tm 3+ under 978 nm laser excitation, with CIE chromaticity coordinates of around (0.31, 0.68), (0.38, 0.60) and (0.17, 0.24), respectively. Analysis of the pump-power dependence of UC intensity indicated that all the emissions involve a two-photon mechanism except for the ~ 486 nm blue emission of Tm 3+ ( 1 G 4 → 3 H 6 ), which requires a three-photon process. The DC luminescence of these phosphors is featured by dominant bands at ~ 553 nm for Ho 3+ (green, 5 F 4 / 5 S 2 → 5 I 8 transition), ~568 nm for Er 3+ (green, 4 S 3/2 → 4 I 15/2 transition) and ~ 464 nm for Tm 3+ (blue, 1 D 2 → 3 F 4 transition). The UC and DC properties were also comparatively discussed.
Guang-Xin Xiang,Guo-Jun Wang,Zhi-Jun Zhang,He Feng,Jing-Tai Zhao,Jiao Wang,Xin-Yuan Sun,Ri-Hua Mao,Yong Wang
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 .
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