Effect Of Host Material Composition On Luminescent Spectra Of Strontium Aluminates Long Persistence Phosphor

Strontium aluminates co-actived by Eu and Dy provides an intense and long persistent phosphorescence at room temperature after being irradiated for short time by sun light or visible light. Due to this effect, it is a new long persistent phosphor of energy-saving, high efficiency, stability and non-pollution. Luminescence of the phosphor is due to 4f-5d electron transition of Eu2+. The inter configuration transition from the 4f65d state to the 8S7/2 is the source of the luminescence, so its luminescent properties are greatly dependent on the lattice environment. Because Eu2+ is surrounded by host ions, mixed states of 4f5d will be split by the crystal field and the luminescent wavelength will be changed. Since Eu2+′s 5d state is comparatively low, luminescent wavelengths lie in the visible range. The change of the surrounding crystal lattice may change the position of 5d, and then the luminescence color of Eu2+ will change.First, a series of strontium aluminates host materials XSrO·YAl2O3 were prepared. Based on XRD chart analysis, with the increase of the ratio of Al/Sr, aluminates rich in strontium changed to that rich in aluminum. In other words, strontium aluminates were found in the order from Sr3Al2O6 to SrAl2O4, and then to SrAl12O19. Then a series of long persistence phosphor powders of strontium aluminates X(Sr0.95Eu0.025Dy0.025O)·YAl2O3 were produced by mixing Al2O3 with SrCO3 with different ratios, adding Eu2+ and Dy3+ with invariable consistency as the activator and co-activator respectively, and H3BO3 as the flux, grading efficiently, under the reducing-atmosphere caused by carbon powder protection, then heating in an electric oven to 1300℃ for 2 hours. Observing by fluorescence spectra, it was found that the excitation spectra were in the range from ultraviolet to visible light and that excitation bands had little change, the emission band shifted from 525nm to 471nm with the increase of the ratio of Al/Sr. when the main crystal lattice of host change from Sr3Al2O6 to SrAl2O4, and then to SrAl12O19, the increase of the crystal lattice symmetry cause the decrease of the crystal filed strength surrounding Eu2+ ion. The different strontium aluminates hosts have different influence on the Eu2+′s 4f65d energy level split, so the lowest position of Eu2+'s 4f65d energy level move from lower to higher, thus the luminescent wavelength blue-shift.A series of luminescent powders were prepared with different consistencies of Eu2+ adding to the SrAl2O4 host. The result means there is no change on the fluorescence spectra bands. But when the concentration is more than 5% concentration quenching will occur. With the concentration of Eu2+ increasing, lattice symmetry increase, electron cloud deformation possibility weaken, and finally the number of luminescent centers reduces. These will result in luminescent concentration quenching.These conclusions may be the foundation for the further research and the development of strontium aluminates long persistent phosphor with high luminescent properties.