Investigation on optical band gap, photoluminescence properties and concentration quenching mechanism of Pb 1-x Tb 3+ x WO 4 green-emitting phosphors.

A series of monophasic Tb3+ (2, 5, 7, 10 and 15at%) doped PbWO4 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 WO4 2- 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 Pb2+ by Tb3+ ions. The presence of strong and intense emission peaks characteristic of Tb3+ with the dominant peak at 545nm (green,5 D4 →7 F5 transition) under UV irradiation at 320nm demonstrated an efficient energy transfer from the host to Tb3+ ions. Using Van Uitert's model, the concentration quenching mechanism between Tb3+ ions in PbWO4 :Tb3+ 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 PbWO4 :Tb3+ phosphors were also investigated in detail. These prepared materials might serve as a potential phosphor for LED applications.