| The Eu2+was widely used in rare-earth-doped materials. In general, Eu2+was used as luminescent center. The electron configuration of Eu2+ion is4f75s25p65d0and the luminescence of Eu2+is electron transition by4f65dâ†'8S2/7(4f7). The energy level of5d is very sensitive to the change of crystal field due to the naked electronic shell. So, the split of5d energy level is quite different in different matrix crystalline field, and the luminescence wavelength of Eu2+is quite different. The co-doped Re3+ions tend to replace the original Sr2+ions and produce defects around the lattice positions. Such defects with positive charge serve as the traps for the activated electrons from Eu2+photoluminescent. In this work, Sr3Al2O6:Eu2+,Dy3+is synthesized by a high temperature solid state method. The role of Sr/Ca ratio in adjusting the phase structure, the emission colors and decay times of phosphor samples has been investigated. And the mechanism of long persistence also has been discussed, according to the result of thermoluminescence spectra.The long persistent phosphors Sr3Al2O6:Eu0.012+, Dy0.02-x3+, Hox3+(x=0,0.01,0.02) were prepared by a high temperature solid state reaction. All samples show a broad band emission peaking at-510nm, which can be ascribed to Eu2+transition between4f65d1and4f7electron configurations. With the increase of substitution of Ho3+ions for the Dy3+ions in the as-prepared phosphors Sr3Al2O6: Eu0.012+, Dy0.02-x3+, Hox3+(x=0,0.01,0.02), the initial intensity of the afterglow obviously decreases. From the thermoluminescence (TL) curves of the samples, we conclude that codoped Ho3+ions lead to a decline of the trap depth and redistribution of the trap. This may be responsible for the change of afterglow of Sr3Al2O6:Euo.oi2+, Dy0.02-x3+, Hox3+(x=0,0.01,0.02).The long persistent phosphors Sr3-xCaxAl2O6:Eu2+, Dy3+(x=0,1,2,3) were prepared by the high temperature solid state reaction. The structure, photoluminescence, afterglow and thermoluminescence properties were studied. The x-ray diffraction analysis show that all samples have similar structure which is cubic structure Sr3-xCaxAl2O6。 However, with the substitution of Ca2+for Sr2+, the diffraction peaks of these XRD patterns shift to the higher angles, which lead to lattice contraction and a smaller lattice constant. Photoluminescence spectra reveal that all emission spectra are broad band emission. These emissions correspond to Eu2+transition between4f65d1and4f7electron configurations. Emission peaks of Sr3Al2O6:Eu2+, Dy3+and Ca3Al2O6:Eu2+, Dy3+located at510nm and440nm respectively. However, there are two emission peaks in Sr2CaAl2O6: Eu2+, Dy3+and SrCa2Al2O6:Eu2+, Dy3+which located at510nm and440nm respectively. The Results indicate that the Sr/Ca ratio has no influence on the phase structure, but luminescent properties change significantly with the Sr/Ca ratio. The initial intensity and attenuating speed of the afterglow are different in different sample. However, all decay curves conform to the double exponential decay. Result shows that luminescent properties can be adjusted by Sr/Ca ratio. In addition, we also recorded thermo luminescence of all samples. We also find that the initial intensity of afterglow significantly reduced when there are two trap energies in sample, which may be due to electron transfer between trap levels. |
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