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76 Handbook on the Physics and Chemistry of Rare Earths FIG. 74 1 0.5 0 450 y=0.20 y=0.12 y=0.30 y=0.08 y=0.04 y=0.01 500 550 600 650 Wavelength (nm) Dependence of the emission spectra on the (Y0.98xCe0.02Tby)2Si3O3N4 (0.01 y Redrawn from Zhu, J., Qin, S., Xia, Z., Liu, Q., 2015. Synthesis and color-tunable emission studies of Y2Si3O3N4:Ce3+,Tb3+ phosphors. Ceram. Int. 41, 12633–12637. Zeng et al., 2015). Ba3RNa(PO4)3F crystallizes in a hexagonal structure with space group P6 (Fig. 75). There are three kinds of Ba2+ sites, denoted Ba1, Ba2, and Ba3, the environments of which are as shown in Fig. 75 (Mathew et al., 1979). Ba1 and Ba2 have both sevenfold coordination with five oxygen and two fluorine atoms, whereas Ba3 has sixfold oxygen coordination. The Ba1 site is occupied by Ba2+ and La3+, and Ba2 and Ba3 sites are occupied by Ba2+ and Na+, all the sites being disordered. The average Ba–X bond distances for each Ba site are as follows: Ba1–O is 0.2683 nm, Ba1–F is 0.2436 nm; Ba2–O is 0.2749 nm, Ba2–F is 0.2823 nm; Ba3–O is 0.2550 nm (Jiao et al., 2013). Ba3LaNa(PO4)3F:Eu2+ has two broad excitation band ranging from 330 to 450 nm with a maximum at 400 nm due to Eu2+ (Fig. 76), which matches well with the emission of near-UV LED chips (360–410 nm). Under 400 nm exci- tation, the emission spectrum has an intense blue emission band with a peak at 465nm attributed to the 5d!4f transition of Eu2+. The highest emission intensity is obtained at a composition of (Ba0.98Eu0.02)3LaNa(PO4)3F. Fig. 77A shows the excitation and emission spectra of Ba3(La0.90Tb0.10) Na(PO4)3F and (Ba0.99Eu0.01)3(La0.88Tb0.12)Na(PO4)3F. The excitation spec- trum of Ba3(La0.90Tb0.10)Na(PO4)3F consists of a strong broad band in the range 200–250 nm, which corresponds to the 4f8 ! 4f75d1 transition of Tb3+. Some small peaks between 280 and 500 nm can be assigned to the 4f–4f tran- sitions. The emission peaks at 490, 543, 581, and 619 nm correspond to the transition from the 5D4 excited level to 7F6, 7F5, 7F4, and 7F3 ground levels of Tb3+, respectively. The three additional peaks observed at 380, 410, and 430 nm are assigned to the 5D3 ! 7FJ transitions. 0.30). Relative intensity (a.u.)PDF Image | HANDBOOK ON THE PHYSICS AND CHEMISTRY OF RARE EARTHS
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