The Optical Properties Of Rare Earth In Photonic Crystal And Size-dependence Of Ground State Energy Of The Excitons In Rare Earth Oxides

Photonic crystals (PCs) are materials that posses spatial periodicity in their dielectric constants on the order of the wavelength of light. Photonic bandgap(PBG) is the key feature of PCs, it can prohibit light in a certain direction just like the electron move in the semiconductor. Therefore, it is predicted that PCs may replace semiconductor to be the carrier of information and media of transmission and result in another technological revolution. However, there have been a lot of challenges on both the theory of the formation of PBG and the fabrication of PCs.The YBO3:Eu3+inverse opals with photonic stop band (PSB) centering at～680 nm were fabricated by the polystyrene (PS) colloidal templating technique. In the inverse opals, large Lamb shifts (less than1.0 nm) were observed for the first time to our knowledge, which are identical to the theoretical prediction by the pseudogap model. Remarkably, the emissions in the inverse opals first decayed with a much faster power law (t-3) and then followed with a slower exponential process due to the co-existence of the diffusion field and the propagating field in the PCs. The novel spectra] phenomenon observed in this work is significant of understanding the modification of PSB on sharp line emissions.The exciton energies of rare earth oxides (Ln2O3) have rarely been calculated by the theory. Experimentally, the blue-shift of exciton energy in nanocrystals deviates from the traditional size confinement effect. Herein, the dependence of the ground-state energy of an exciton in Y2O3 spheres on particle radius was calculated by using a variational method. In the model, an exciton confined in a sphere surrounded by a dielectric continuum shell was considered. The ground-state energy of exciton comprises kinetic energy, coulomb energy, polarization energy and exciton-phonon interaction energy. The kinetic and coulomb energy were considered by the effective mass and the dielectric continuum and the exciton-phonon interaction energy was given by the intermediate coupling method. The numerical results demonstrate that the present model is roughly in consistent with the experimental results. The confinement effect of the kinetic energy is dominant of the blue-shift of the exciton energy in the region of R<5nm, while confinement effect of the coulomb energy is dominant of the blue-shift of the exciton energy in the region of R>5nm. The polarization energy contributes largely to the exciton energy as the particle size is smaller than～10 nm, while the exciton-phonon interaction energy takes only a little contribution in all the range.