Y <sub> 2 </ Sub> O <sub> 2 </ Sub> S: Ti, Eu New Red Long Afterglow Luminescent Materials Synthesis And Performance

The Y2O2S:Ti,Eu phosphor was successfully synthesized via high temperature sintering method. The effect of the sintering temperature on the shape, crystal structure and luminescence properties of the phosphors was investigated in detail. Based on the results of XRD, SEM and luminescence spectra, it was found that the sample sintered at 1200℃ for 2.5h had a single Y2O2S phase which has space groupof P3ml and the largest grain size with the best luminescence and afterglowperformance. Relatively low sintering temperature led an incomplete growth of grain with the residue Y2O3 phase while the high sintering temperature resulted over-sintering which may destroy the structure of the grain.A series of Y2O2S:0.06Ti,xEu red long afterglow phosphors was synthesized. The effect of the different Eu concentration on the spectra and afterglow property of the phosphor was investigated. The emission spectra was found to be made up of a series sharp emission lines which is the 5DJ(J=0,l) to 7FJ( J=0,1,2,3,4)transition of Eu³+. The excitation spectra were two broad bands and several sharp lines. The highest energy band with a maximum at about 265nm is due to Y2O2S lattice absorption. The lower energy broad band with a maximum at about 345nm is the charge transfer band, which is due to electron transfer from ligands to the central Eu3+ ions. As the x increased, the location and shape of the emission lines remained unchanged while the intensity and sequence changed greatly. Y2O2S:0.06Ti,0.04Eu phosphor has the best luminescence performance. The afterglow result supported that the increasing of Eu concentration had a significant effect on the performance at the first stage. The phosphorescence performance reached the optimization when the molar ratio of Eu ion was x=0.04. According to the XRD result, tiny aberrance rather than the new phase was found as the concentration of Eu ions increased.The result of phosphorescence emission spectra showed an obviously difference between Y2O2S:0.06Ti,xEu and Y2O₂S:Ti phosphor. The phosphorescence emissionspectra of Y2O2S:0.0611,xEu was made up of a broad emission band with the peak at 59Onm which due to the Ti emission and a series sharp emission lines located above 540nm which due to the Eu3+ emission. Nevertheless, Y2O2S:Ti showed a broad emission band with the peak at 590nm while Y2O2S:Eu showed no afterglow. It was found that the afterglow of Eu3+ came from an energy transfer process which was described as following: after the excitation of the light source, the phosphor Y2O2S:Ti produced a broad band phosphorescence with the peak at 590nm. Since the broaden band phosphorescence overlapped with the 7Fo—^Do and 7Fo—?5Di transition absorption lines of Eu3+ ion, the energy was transferred to Eu3+ ion which was excited into 5Do and 5Di excitation state after absorbing the energy from broaden band of Ti traps. Eu3+ ion relaxed from 5Di to 5Do, then return back to the ground state with light emitting. The formula of the decay curve of the phosphor was calculated, which could be described as:I = k *[A *exlh + A, *e^x/hvSince the rare earth ions has an excellent luminescence performance and the phosphor Y2O2S:Ti produces a broad band phosphorescence, it is possible to explore many new kinds of long afterglow phosphors with various colour and excellent luminescence performance through the energy transfer process.