Luminescent properties of Eu3+ in MWO4 (M=Ca, Sr, Ba) matrix

The Eu3+ doped MWO4 (M=Ca, Sr, Ba) phosphors were synthesized via high temperature solid state reaction. The crystal phases of these phosphors were identified by X-ray diffraction. Shifts of the peaks in the structure were observed when Ca2+ sites in the host were completely occupied by the Sr2+ ions or Ba2+ ions. As a result of this replacement, the charge-transfer (CT) band exhibited a blue shift from CaWO4: Eu3+ to SrWO4: Eu3+ and BaWO4: Eu3+. This blue shift could be interpreted with the decreases of the bond covalence between the ligands (L) and the central ion (M) in matrix. In this work, red afterglow originated from the 5D0–7FJ (J=0,1,2,3,4) transitions of Eu3+ could clearly be observed after samples were excited at 254 nm. The thermoluminescence (TL) spectra showed that there were five traps levels in CaWO4: Eu3+ sample and two traps levels in CaWO4: Eu3+ and CaWO4: Eu3+ samples, respectively. The possible explanation of this afterglow phenomenon was also discussed in detail.