Two types of Tb- and Na-substituted green phosphors Ca(1-1.5x)WO4: and Ca(1-2x)WO4: weresynthesized with various x values, using a solid-state reaction. The former phosphors contained both substitutional and vacancypoint defects, while the later had only substitutional defects. X-ray diffraction results showed that the main diffraction peak,(112), was centered at 2θ=28.72o and indicated that there was no basic structural deformation caused by substitutions orvacancies. The photoluminescence emission and photoluminescence excitation spectra revealed the optical properties of trivalentterbium ions, Tb3+. Typical transitions, 5D3→7F6, 7F5, 7F4 and 5D4→7F6, 7F5, 7F4, 7F3, and cross relaxations were observed.Subtle differences in the photoluminescence of green phosphors were observed as a result of the point defects. The FT-IRspectra indicated that some of the ungerade vibrational modes had shifted positions and changed shapes, spreading out overa wide range of frequencies. This change can be attributed to the different masses of Tb3+ and Na+ ions and VCa" vacanciescompared to Ca2+ ions. The gerade normal modes of the Raman spectra exhibited subtle differences resulting from point defectsin Ca(1-1.5x)TbxWO4 and Ca(1-2x)TbxNaxWO4.

• Cho, Seon-Woog(Department of Materials Science and Engineering, Silla University)