The Nature And Mechanism Of The Luminescence Of Rare Earth Ions To Convert Titanate Anti Opal Photonic Crystal

Upconversion luminescence (UC) is a basic process in excited condensed matters, in which infrared radiation can be capable of converting into visible light. UC luminescence has potential applications in several areas such as color displays, sensors, detection of infrared radiation, and UC lasers. The application of UC emission of rare earth ions is limited due to its low efficiency of energy transfer and excitation state absportion. Photonic crystals are three dimensional periodic dielectric composites in which the distribution of refractive index varies on the visible wavelength scale. Since it is possible for photonic crystal to modulate the photonic state density of materials and the interaction between excitation light and materials, it will lead to the control of physical process and photoelectric properties of photoelectric materials, and it also provides an effective way to control the upconversion luminescence property and process. In this study, the titanate inverse opal photonic crystals doped with rare earth ions were prepared by sol-gel combined with self-assemble method. The upconversion luminescence properties and mechanisms of rare earth ions were investigate under modulation of photonic crystal bandgap.Upconversion light-emitting photonic materials (Y2Ti2O7:Yb3+,Er3+and Y2Ti2O7:Yb3+,Tb3+,Er3+) with inverse opal structure were obtained by the self-assembly technique in combination with a sol-gel method. The effect of the photonic stop-band on the upconversion luminescence of Er3+and Tb3+has been observed in the inverse opals photonic ctrystals. The results showed that the upconversion luminescence of Er3+and Tb3+can be modified by both photonic band gap and band edge. Significant suppression of the upconversion emission was detected if the photonic band-gap overlaps with the rare earth ions emission band, while enhancement of the upconversion emission occurs if the emission band appears at the edge of the band gap.The effect of the photonic stop-band on the upconversion luminescence and mechanism of Er3+have been observed in the inverse opals of Er3+and Yb3+co-doped Bi2Ti2O7. It is interesting that the upconversion emission mechanism of Er3+can be changed by suppression of the green upconversion emission of Er3+, thus the two-photon red upconversion emission changed to the three-photon process.Influence of competition between excited-state absorption and spontaneous emission from intermediate excited state on upconversion emission was investigated in Yb3+, Tb3+inverse opal photonic crystals. The result clearly shows that upconversion emission from Tb3+can be modulated by the photonic crystal. When upconversion emission band from Tb3+intermediate excited state overlaps with the photonic band gap, the short wavelength upconversion emission from upper state of Tb3+is obviously enhanced due to an inhibition of spontaneous emission from the intermediate excited state in the photonic crystal.In this thesis, we fabricated Y2Ti2O7:Yb, Er, Tm upconversion inverse opal photonic crystals with energy transfer between Er3+and Tm3+, and investigated the influence of photonic band gap on the upconversion emission and energy transfer between Tm3+and Er3+. In the upconversion inverse opals, the energy transfer among Tm3+and Er3+is enhanced by suppression of the red (659nm and675nm) upconversion emission of donor Er3+, and thus the blue (475nm and486nm) upconversion emission from acceptor Tm3+is considerably improved.