Nhng tin b trong Quang hc, Quang ph và ng dng VI ISSN 1859 - 4271

Advances in Optics, Photonics, Spectroscopy & Applications VI ISSN 1859 - 4271agreement with the last root in the x- and z-direction. Therefore, the energy of Plasmonoscillation for up compounds will be about 10.4, 11.3 and 10.65 eV respectively.The refractive index and the real part of sigma of NaTiO3, BiTiO3 and Bi0.5Na0.5TiO3compounds for the x- and z- directions are shown in figure 6 and figure 7. We see the mentionedsmall difference in these directions, for them which means that this compounds can havebirefractive character at these frequencies. In order to obtain the static refractive index, we usedthe following equation that relates the magnitude of refractive index with dielectric function:( ω) + Reε[ ω]εααααn αα =2We see that doping NaTiO3, BiTiO3 compounds with a small amount of Bi, Na impuresincrease the refractive index.Fig. 6. Refraction index of NaTiO 3 , BiTiO 3 and Bi 0.5 Na 0.5 TiO 3 compounds.Fig. 7. Real part of sigma of NaTiO 3 , BiTiO 3 and Bi 0.5 Na 0.5 TiO 3 compounds.IV. CONCLUSIONThe effect of Bi, Na modification on the band structure, DOS and optical properties ofNaTiO3, BiTiO3 compounds were studied. We showed that incorporation of Bi, Na atoms, evenin small amounts, remarkably changes the <strong>ph</strong>ysical properties of NaTiO3, BiTiO3 compoundsand improves its transparency, which is very important in electro-optic applications. We alsoshowed that Bi-4f, Na-3s orbitals play an important role in decreasing the band gap and otherproperties. In fact, Bi-doped NaTiO3, Na-doped BiTiO3 increases the DOS above the Fermilevel, which can be useful for lasers. We also conclude that substitu<s<strong>trong</strong>>tin</s<strong>trong</strong>>g Bi in NaTiO3 compoundand Na in BiTiO3 will increase the refractive index. We showed that there is a small birefractioneffect in some frequencies. Plasma oscillations and threshold optical absorption of thiscompound were obtained.76