Rare-earth borates have attracted considerable attention due to the practical applications in various areas such as solid-state lasers, non-linear optical (NLO) crystal, plasma display panel (PDP), and LED.^1-4 To date, extensive research efforts have been devoted to develop fluorescent materials doped with rare earth (RE³⁺) ions.

In this work, novel rare-earth borate KBaTbB₂O₆ (KBT)was synthesized using a conventional solid-state reaction method. The crystal structure of KBT has been determined by the Rietveld analysis performed with the General Structure Analysis System (GSAS) software,⁵ as shown in Figure 1, and the single crystal growth is still under investigation. The Rietveld refinement demonstrates that KBT is isomorphous with KBaY(BO₃)₂⁶ and crystallizes in the planar trigonal [BO₃]^3- group R-3m with lattice parameters of a = 5.45623(6) Å, c = 17.8629(2) Å, and Z = 3. Crystal structure data are listed in Table 1.

Since Tb³⁺ is introduced into [BO₃]^3- net of the structures, the host sensitization of Tb³⁺ would occur, which gives rise to an efficient luminescence from the Tb³⁺.⁷ By doping rare earth ions such as Eu³⁺ and Ce³⁺ into KBT, the light emitting ions can be enhanced or quenched via the energy transfer process. In this study, a series of novel emission-tunable Ce³⁺/Eu³⁺ solely doped KBT samples were synthesized in form of highly crystalline powders. The photoluminescence properties and energy transfer mechanism are investigated in detail. The weak green emission from Tb³⁺ was enhanced significantly by introduction of sensitizer Ce³⁺ ions, owing to an efficient resonant-type energy transfer from Ce³⁺ to Tb³⁺. Energy transfer also occurred from Tb³⁺ to Eu³⁺ for KBT: Eu³⁺ and tunable emission was obtained by changing the doping concentration of Eu³⁺. The critical energy transfer distance was calculated by the concentration quenching theory. Our investigation has demonstrated that KBT can act as a potential luminescent material for the application of PDP and n-UV LED.

Keywords: KBaTbB₂O₆, Rietveld analysis, luminescence, energy transfer

Figure 1. Experimental (crosses) and calculated (red solid line) XRD patterns and their difference (blue solid line) for the Rietveld fit of KBT XRD pattern by GSAS program. The short vertical lines show the position of Bragg reflections of the calculated pattern.  The inset shows the crystal structure of KBT along the c-axis direction.

Figure 2. PL and PLE spectra of KBT, KBT: Eu ³⁺ and KBT: Ce³⁺.The insets show the CIE chromaticity coordinates for KBT, KBT: Eu ³⁺ and KBT: Ce³⁺ (from No.1 to No.3)and the corresponding samples under a UV lamp box (254 nm for No.1 and No.2, and 365 nm for No.3).

Table 1. Basic crystallographic and experimental data of KBT based on Rietveld refinement.

References

(1) Guo, R.; Wu, Y.; Fu, P.; Jing, F. Opt. Commun. 2005, 244, 321-325.

(2) Mills, A. Inorg. Chem. 1962, 1, 960-961.

(3) Zeng, X.; Im, S.-J.; Jang, S.-H.; Kim, Y.-M.; Park, H.-B.; Son, S.-H.; Hatanaka, H.; Kim, G.-Y.; Kim, S.-G. J. Lumin. 2006, 121, 1-6.

(4) Xia, Z. G.; Zhuang, J.; Liao, L. Inorg. Chem. 2012, 51, 7202-7209.

(5) Larson, A. C.; Von Dreele, R. B. GSAS Generalized Structure Analysis System, Laur, 86-748, Los Alamos National Laboratory: Los Alamos, NM, 1994.

(6) Gao, J. H.; Song, L. M.; Hu, X. Y.; Zhang, D. K. Solid State Sci. 2011, 13, 115-119.

(7) Han, L.; Wang, Y.; Wang, Y.; Zhang, J.; Tao, Y. J. Alloy. Compd. 2012, 551, 485-489.

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