“…It is revealed from figure 5a that the strongest intensity is observed upon excitation at 270 nm; this result further supported the effective energy transfer from the host lattice to the Tb 3+ ions. The spectra consist of emission peaks originating from the 5 D 3 and 5 D 4 energy states with little background emission from the host lattice; the peaks observed in the range between 400 and 467 nm originate from the 5 D 3 state and can be ascribed to the 5 D 3 -7 F 5 (423 nm), 5 D 3 -7 F 4 (437 nm), 5 D 3 -7 F 3 (45 nm) and 5 D 3 -7 F 2 (467 nm) transitions whereas the peaks centred at 489, 544, 585 and 621 nm originate from the 5 D 4 state and they can be attributed to the 5 D 4 -7 F 6 , 5 D 4 -7 F 5 , 5 D 4 -7 F 4 and 5 D 4 -7 F 3 transitions, respectively [16,31,32]. Figure 5b shows the emission spectra of ZnWO 4 :xTb 3+ (x = 1, 3, 5, 7, 10 and 12 at%) obtained by monitoring the excitation wavelength at 270 nm, this wavelength was chosen because the strongest emission was observed upon excitation at this wavelength.…”