Study On The Luminescence Properties Of Rare Earth-doped Three-dimensional Ordered Macroporous CeO₂

In recent years,nanometer materials have become a hot topic to the researchers for theirs unique characteristic basing on their nanoscopic length scales.Three dimensionally macroporous(3DOM)materials,as one of the representative of nanometer materials,have been a subject of intensive research due to their potential applications in adsorption,separation,catalysts,sensors and photonic crystals.Further development of porous materials is to expand their application to the desired areas.One of novel applications of 3DOM materials is to combine the feature of porous structure for the storage delivery of specific species with photoluminescence property for simultaneous tracking or monitoring the species,which have been proven to be potential applications in medicine,bio-imaging and even military affairs.In this paper,the Yb3+/Er3+doped CeO2 3DOM was prepared by combining self-assembly method with sol-gel method.The effect of Yb3+ ions concentration on upconversion emission was investigated in the 3DOM CeO2:0.005 Er3+,xYb3+(x=0,0.005,0.02,0.05,0.1).The result showed that,red and green UCemission of the samples was enhanced and decreased with the increasing of Yb3+ ions,respectively which was attributed to the enhancement of cross relaxation of Er3+ ions.At the same time,the effect of propous structure on UC emission of 3DOM CeO2:Er3+,Yb3+was also studied.It is interesting that the relative intensity of the red to the green emission in the 3DOM sample increased in comparison with that of powder sample without propus structure due to the increased non-radiative relaxation from 4I11/2 to 4I13/2 state in the 3DOM materialsIn addition,3DOM CeO2:Er3+,Tm3+,Yb3+with near infrared to near infrared upconversion emission were prepared and the influence of photonic band gap on the upconversion emission was investigated.Comparing with the sample witout photonic band gap,suppression of the blue or red upconversion luminescence were observed in the 3DOM CeO2:Er3+,Tm3+,Yb3+.It is interesting that the near infrared upconversion emissions located at about 803 nm were enhanced due to the inhibition of visible upconversion emission in the 3DOM CeO2:Er3+,Tm3+,Yb3+.The enhancement of near infrared UC emission is caused by the population enhancement of 1G4 level of Tm3+.Finally,the upconversion and the near infrared emission properties of Er3+ions were systematically investigated in the CeO2:Er3+,Yb3+3DOM.Comparing with the reference sample,significant suppression of both the green and red upconversion luminescence of Er3+ions were observed in the 3DOM CeO2:Er3+,Yb3+.It is interesting that the infrared emission located was enhanced due to inhibition of upconversion emission in the the 3DOM CeO2:Er3+,Yb3+.In addition,a new method for near infrared emission enhancement of rare-earth doped inverse opals is reported.3DOM CeO2:Er3+,Yb3+ were prepared.The near infrared emission property depend on the overlapped extend between the excited light and photonic band gap.The near infrared emission at 1540 nm of CeO2:Er3+,Yb3+ inverse opals have been enhanced obviously when the wavelength of the excitation light overlapped with photonic band gaps edge,which is attributed to slow light effect of photonic crystals.