Investigation on optical band gap, photoluminescence properties and concentration quenching mechanism of Pb TbWO green-emitting phosphors.

A series of monophasic Tb (2, 5, 7, 10 and 15at%) doped PbWO phosphors were successfully prepared via hydrothermal method. X-ray diffraction patterns revealed that the prepared samples possess a high crystallinity with tetragonal scheelite-type structure. FT-IR and Raman analysis exhibited a WO stretching peak of WO group, which is also related to the scheelite structure. UV-visible diffuse reflectance spectra indicated a reduction in the optical band gap with the replacement of Pb by Tb ions. The presence of strong and intense emission peaks characteristic of Tb with the dominant peak at 545nm (green, D→F transition) under UV irradiation at 320nm demonstrated an efficient energy transfer from the host to Tb ions. Using Van Uitert's model, the concentration quenching mechanism between Tb ions in PbWO:Tb phosphor was attributed to a dipole-dipole interaction and the critical distance was determined to be ~12Å. The decay lifetimes and CIE chromaticity co-ordinates of PbWO:Tb phosphors were also investigated in detail. These prepared materials might serve as a potential phosphor for LED applications.