Reddish orange long lasting phosphorescence of Sm3+ in Sr2ZnSi2O7:Sm3+ phosphors

Long lasting phosphorescence phosphors with composition of (Sr1-xSmx)2ZnSi2O7 were prepared by conventional high-temperature solid-state method. Their properties were systematically investigated utilizing XRD, photoluminescence, phosphorescence and thermoluminescence spectra. The results showed that these phosphors emitted reddish orange light that corresponds to the characteristic emission due to the 4G5/2→6H5/2, 6H7/2 and 6H9/2 transitions of Sm3+. After the UV light excitation source was switched off, the bright reddish orange long lasting phosphorescence could be observed and it could last for about 30 min in the limit of light perception of dark-adapted human eyes (0.32 mcd/m2). A wide TL band raging from room temperature to 700 K with two dominating peaks at 340 and 602 K appeared in the TL spectrum. The TL curve could be fitted to five TL peaks and the low temperature TL peak at 340 K was found to be responsible for the long lasting phosphorescence. Also, the mechanism was discussed.