Synthesis And Luminescent Properties Of Rare Earth Doped Nano Silico-aluminate Long-lasting Phosphors

In recent years,long afterglow materials activated by rare earth,as a kind of non-polution and environmentally friend materials,have attracted more and more attentions,which have potential applications in some fields,such as traffic,military,safety,electrical appliances,architecture and information storage.However,aluminate-based luminescent materials have some disadvantages:bad moisture resistance and single color etc..Although silicate-based materials have stable structures,its luminescent properties are lower than that of aluminate-based materials.Therefore,it is necessary to investigate new long afterglow materials.Especially,during the preparation of luminescent materials,the low temperature combustion and sol-gel methods can be often used to fabricate high purity materials on lower synthesis temperature,which have good application prospect.In this paper,we successfully prepare strontium aluminosilicate-based long afterglow materials by the low temperature combustion and sol-gel methods,and studythe effects of preparation processes on the luminescent properties.In addition,we systematically investigates the effects of differentsensibilizer and alkali metal doping on luminescence and long afterglow properties.The main contents and conclusions are followed below:(1)Aluminate,silicate basedluminescentmaterials arerespectively prepared by the combustion method.In this experiment,NO3-is oxidant,urea is reducing agent and the boric acid is flux.XRD analysis shows that silicate based material is pure SrAl2O4 and the aluminate basedone is orthorhombic ?-Sr2SiO4.When the doping amount of Eu2+ is 0.04 and 0.03 respectively for the two materials,their luminous intensity attains to the maximum.(2)The luminescent material of Sr2Al2SiO7:Eu3+is prepared by sol-gel method andthe effects of pH on the material structure and luminescent performance are explored.The result shows the diffraction peak intensity of impurity gradually decreases when acid solution becomes neutral slowly and increases instead when the pH continues to go up.The diffraction peak diminishes at pH=6 and the pure Sr2Al2SiO7 is accordingly got.The luminescent intensity firstly declines down and then raises up with the pH increasing and attends the peak at pH=9.(3)The material structure and luminescent performance of Sr2Al2SiO7:Eu2+and Sr2Al2SiO7:Eu2+/Re3+are investigated.It is observed that the auxiliary activatordoesn't change the crystal structure and the position of emission spectrum peak.There is no characteristicspeak of it.This indicates that Eu2+ acts only on the luminous center and the activator affects just the luminescent intensityand afterglow.The luminous intensity of Sri.92Al2SiO7:0.04Eu2+,0.04Nd3+ is the highest and its relative intensity is about 6900.Afterglow of Sr2Al2SiO7:Eu2+/Dy3+and Sr2Al2SiO7:Eu2+/Pr3+ is the best because it still gives out light after holding three hours in the dark.(4)The influences of doped Ca2+andMg2+on long-afterglow material are discussed for Sr1.96-xCaxAl2SiO7:0.04Eu2+(x=0.1?0.2?0.3?0.4?0.5?0.6)and Sr1.96-xMgxAl2SiO7:0.04Eu2+(x=0.1?0.2?0.3).Ca2+goes into Sr2Al2SiO7 matrix and replaces parts of Sr2+.The Ca2+ doped material is composed of regular particles with powder size ranged from 50 nm to 200 nm.Its emission peak emerges inthe wavelength of 512 nm which is typically green light of Eu2+.It has a blue shift to the undoped one.When the concentration of Ca2+ is 0.2,the long-afterglow time is 109 second and three second longer than the undoped one.It is due to that the electron trap depth of the material attains to the best value of 0.77eV and the trap density gets to the maximum value of 3.86×104no cm-3.Thus,moderate amount of Ca2+ dopingcan improve the afterglow performance of Sr2-yAl2SiO7:yEu2+materials.After Mg2+ is doped,the wavelength of emissionis 511 nm.The blue shift appears too.Doped Mg2+ decreases electron trap depth and density and reduces afterglow time.(5)We investigate the imparts of Ca2+?Mg2+ and Eu2+ co-doping on the structure and luminescent properties of Sr2-x-y-zCaxMgyAl2SiO7:zEu2+.The results showed that the crystal structure was not changed,but the luminescent intensity was significantly improved.Ca2+is the main factor to affect the luminescent intensity and Eu2+is the next.When Ca2+ and Mg2+ doping contents are up to 0.2 and 0.1 respectively,the maximum emission intensity located at 469 nm reaches 8500 with Eu2+=0.04.