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.
Long-lasting phosphorescence (LLP) was observed in Ce-doped Y3Al5O12 phosphors synthesized in reducing atmosphere. The characteristic emission of the 2D-2F5/2 and 2D-2F7/2 transition of Ce3+ in photoluminescence (PL) and LLP spectra was studied. It was interesting that the ratio between the peak areas of 2D-2F5/2 and 2D-2F 7/2 transitions in the PL spectrum was different from the ratio of that in LLP emission spectrum. And the ratios had different change regularities with increased Ce3+ concentration. The possible reason was attributed to the defect in the YAG host,which was affected by increasing the Ce3+ concentration. There were indications that the defect in the Ce3+-doped YAG samples was strongly associated with oxygen vacancy. And the defect levels were studied through thermoluminescence (TL) experiment. The results showed that the trap depth was between 0.6 and 0.65 eV,and the kinetic order of the LLP was 2.
YVO4:Eu nanocrystalline phosphors were successfully prepared at 400 oC in equal moles of NaNO3 and KNO3 molten salts. NaOH concentration and annealing temperature played important roles in phase purity and crystallinity of the nanocrystallines, and the optimum NaOH concentration and annealing temperature were 6:40 and 400 oC, respectively. The nanocrystallines were well crystallized with a cubic morphology in an average grain size of 18 nm. Upon excitation of the vanadate groups at 314 nm, YVO4:Eu nanocrystallines exhibited the characteristic emission of Eu3+, which indicated that there was an energy transfer from vanadate groups to Eu3+. Moreover, the influence of superficial effect, especially the dangling bonds on the structure and luminescent properties of the nanocrystallines was discussed in detail.
