Point Defects and Photoluminescence of Green Phosphors Ca(1-1.5x) WO4: Tb-x(3+) and Ca(1-2x) WO4 : Tb-x(3+), Tb Na-x(+)

Two types of Tb- and Na-substituted green phosphors Ca(1-1.5x)WO4 : Tb-x(3+) and Ca(1-2x)WO4: Tb-x(3+), Na-x(+) were synthesized with various x values, using a solid-state reaction. The former phosphors contained both substitutional and vacancy point defects, while the later had only substitutional defects. X-ray diffraction results showed that the main diffraction peak, (112), was centered at 2 theta = 28.72 degrees and indicated that there was no basic structural deformation caused by substitutions or vacancies. The photoluminescence emission and photoluminescence excitation spectra revealed the optical properties of trivalent terbium ions, Tb3+. Typical transitions, D-5(3), -> F-7(6), -> F-7(5), -> F-7(4) and 5D4 -> F-7(6), -> F-7(5), -> F-7(4), -> F-7(3), and cross relaxations were observed. Subtle differences in the photoluminescence of green phosphors were observed as a result of the point defects. The FT-IR spectra indicated that some of the ungerade vibrational modes had shifted positions and changed shapes, spreading out over a wide range of frequencies. This change can be attributed to the different masses of Tb3+ and Na+ ions and V-Ca" vacancies compared to Ca2+ ions. The gerade normal modes of the Raman spectra exhibited subtle differences resulting from point defects in Ca(1-1.5x) TbxWO4 and Ca(1-2x) Tb-x NaxWO4.