| As a photoluminescent material,the long afterglow luminescent materials have been found a wide application in many fields including some research fields of the advanced science and technology.In this paper,SrZn2(PO4)2 as the host shows the advantages of easy preparation,high chemical stability,cheap raw materials,high thermal stability,and environmental friendliness,while Mn2+is explored as the luminescent center.The preparation of the new yellowish green long persistent phosphor SrZn2(PO4)2:Mn2+is reported,and the luminescent properties of the phosphor are effectively improved by co-doping with other rare earth ions.X-ray powder diffraction(XRD)analysis,scanning electron microscope(SEM),X-ray photoelectron spectroscopies(XPS),excitation-emission spectroscopies,afterglow decay curves,thermoluminescence spectroscopies and electron paramagnetic resonance(EPR)spectroscopies were characterized for the phosphors to systematically investigate the luminescence properties and structural properties of the prepared samples,and to construct and understand the luminescence mechanisms of the materials Some limited innovative results have been achieved in this research.(1)The yellowish green long afterglow luminescent material SrZn2(PO4)2:Mn2+was synthesized by high-temperature solid-phase method in a reducing atmosphere.When the doping concentration of Mn2+falls at the mole fraction of 0.004,the best afterglow performance of the material is obtained.The results show that the ~4T1(~4G)?~6A1(~6S)transition emission of Mn2+is responsible for the yellowish green color of the samples.The XPS analysis and defect equation analysis show that there exist certain intrinsic defects in the materials:(1(1??((5(5(5(5),(1(1??,??44)),(1(1··,(5(5(5(5··4)4),··44)).The doping of Mn2+increases the defect concentration of(1(1··,which is of great help to improve the afterglow performance of the materials.It can be speculated from the EPR analysis that the electron paramagnetic resonance signals in SrZn2(PO4)2 materials are resulted from the trapping of holes from the intrinsic defect oxygen vacancy defects and zinc vacancy defects in the materials.The afterglow characteristics are closely related to the defects in the samples.(1(1··,(5(5(5(5··44)),··44))defects can trap electrons during the excitation process,while(1(1??((5(5(5(5),(1(1??,??44))defects capture holes.The trapped electrons and holes will be released under thermal stimulation,and then t recombine with the characteristic emission of light.(2)The long afterglow luminescent materials of SrZn2(PO4)2:Mn2+,Nd3+were synthesized by high temperature solid-phase method under the reducing atmosphere.and the luminescence properties of Nd3+co-doped SrZn2(PO4)2:Mn2+material and its luminescence mechanism were studied.The analysis of XPS,TL and EPR shows that the inequivalent substitution of Nd3+for Sr2+with the production of·defects significantly enhance the defect concentrations of materials.The best afterglow performance of SrZn2(PO4)2:Mn2+,Nd3+material is obtained with the 0.006 mole fraction of Nd3+.The fluorescence spectra,show that there exist the overlap between some excitation bands of SrZn2(PO4)2:Mn2+and some emission bands of SrZn2(PO4)2:Nd3+,from which it can be speculated that there exist an energy transfer of Nd3+?Mn2+.In SrZn2(PO4)2:Mn2+,Nd3+,Nd3+acts both as a sensitizing ion for the role of an energy transfer and as a defect provider for the increase of the effective defect concentration,resulting in the improvement of the luminescent properties of the materials.(3)The long afterglow luminescent material SrZn2(PO4)2:Mn2+,Er3+was synthesized by high temperature solid-phase method under reducing atmosphere,and its good crystalline properties were characterized by XRD and SEM.XPS analysis and defect equation analysis show that there exist intrinsic defects of(1(1??((5(5(5(5),(11??,??44),(1(1··,(5(5(5(5··44)),··44))in the material and·defects resulted from the inequivalent replacement of Er3+for Sr2+.The analysis of TL spectrum shows that the doping of Er3+results in the movement of TL peaks toward the low temperature and the significant increase of the intensity of the peaks.The best afterglow performance of the material is obtained with the 0.004 mole fraction of Er3+The introduction of Er3+significantly increases the effective trap concentration,enhances the ability of the traps to capture carriers and prolongs the lifetime of hole-electron pairs in the lattice,resulting in the improvement of the afterglow properties of the as-prepared samples. |
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