I.V. Kityk

White light emission from Sm3+/Tb3+ codoped oxyfluoride aluminosilicate glasses under UV light excitation

In this paper, we report on the absorption and photoluminescence properties of oxyfluoride aluminosilicate and boro-aluminosilicate glasses codoped with Sm3+ and Tb3+ ions. The differential thermal analysis profiles of these glasses have been obtained to confirm their thermal stability. From the measured absorption spectrum, Judd?Ofelt (J?O) intensity parameters (?2, ?4 and ?6) have been evaluated for the Sm3+ ion. When excited by ultraviolet light these glasses emit a combination of blue, green and orange?red wavelengths forming white light. The ratio of the intensities of orange?red to green emissions can be tuned by varying both the concentration of the Sm3+ ion and the composition of the glass matrix. The excitation and emission spectra have shown a self-quenching effect for the Sm3+ ions and an efficient energy transfer from Tb3+?:?5D4 ? Sm3+?:?4G5/2 was observed which was also confirmed by the decay lifetime measurements.

Photoluminescence of Eu3+-, Tb3+-, Dy3+- and Tm3+-doped transparent GeO2–TiO2–K2O glass ceramics

In this paper, we present the photoluminescence properties of Eu3+-, Tb3+-, Dy3+- and Tm3+-doped potassium–titanium–germanate glasses and glass ceramics. Following the x-ray diffraction measurement, the glass structure was established. Compared to Eu3+-, Tb3+-, Dy3+- and Tm3+-doped glasses, their respective glass ceramics show stronger emissions due to the presence of the K2TiGe3O9 crystalline phase. For Eu3+-doped glass and glass ceramics, five emission bands centered at 578 nm , 592 nm , 614 nm , 653 nm and 702 nm have been observed with 394 nm excitation wavelength. Of them, 614 nm has shown a bright reddish-orange emission. For Tb3+-doped glass and glass ceramic, four emission bands centered at 490 nm , 549 nm , 586 nm and 621 nm have been observed with an excitation at 378 nm wavelength. Of them, 549 nm has shown a bright green emission. With regard to Dy3+:glass and glass ceramic, a blue emission band centered at 485 nm and a bright fluorescent yellow emission at 576 nm have been observed, apart from (665 nm) emission transition with an excitation at 387 nm , 4F7/2) wavelength. Emission bands of (650 nm) and (700 nm) transitions for the Tm3+:glass and glass ceramic, with excitation at (468 nm), have been observed. The stimulated emission cross sections of all the emission bands of Eu3+, Tb3+, Dy3+ and Tm3+:glasses and glass ceramics have been computed based on their measured Δλ (FWHM) and lifetimes (τm).

Electronic band structure of AgCd2GaS4: theory and experiment

We report theoretical calculations of the band structure of AgCd2GaS4 using the full-potential linear augmented plane wave method and experimental measurements of the valence band x-ray photoelectron spectroscopy. We find that the valence band maximum and the conduction band minimum are located at the ? point of the Brillouin zone resulting in a direct energy gap of 1.0?eV compared to our measured experimental value of 2.15?eV. Our analysis of the partial density of states shows that there is a weak covalent interaction between Ag and Ga atoms and between Ag and Cd atoms, and a substantial covalent interaction between Ag and S atoms. Thus the Ga?Ag and Cd?Ag bonds are basically of ionic character, and Ag?S bonds are of covalent character. The theoretical results of the density of states are in agreement with the valence band x-ray photoelectron spectroscopy measurements with respect to spectral peak positions. We have analyzed the calculated density of states and find a strong/weak hybridization between the Ag, Cd, Ga and S states in the valence and conduction bands.

First and second harmonic generation of the optical susceptibilities for the non-centro-symmetric orthorhombic AgCd2GaS4

We present the results of an ab initio theoretical study of the linear and nonlinear optical susceptibilities for the AgCd2GaS4 using the full potential linearized augmented plane wave (FP-LAPW) method as implemented in the WIEN2K code. We have used the Engel–Vosko exchange–correlation potential which is based on the generalized gradient approximation. Our calculations show that the valence band maximum (VBM) and conduction band minimum (CBM) are located at Γ resulting in a direct energy gap. We present calculations of the frequency-dependent complex dielectric function e(ω). Our calculations show that the edge of the optical absorption for e2xx(ω) and e2zz(ω) are located around 2 eV. The linear optical properties show a strong negative uniaxial anisotropy. The optical properties are scissors corrected to match the calculated energy gap with the measured one. The optical properties are analyzed in terms of the calculated electronic structure. The imaginary and real parts of the second-order SHG susceptibility were evaluated. Our calculation shows that χ333(2)(ω) is the dominant component which shows the largest total Reχijk(2)(0) value 2.0 pm V−1.

X-ray diffraction and optical properties of a noncentrosymmetric borate CaBiGaB2O7

Single crystals of the noncentrosymmetric borate CaBiGaB(2)O(7) were synthesized by conventional solid state reaction. The purity of the crystal was checked by x-ray powder diffraction. The optical properties were measured by analyzing the diffuse reflectance data obtained with a Shimadzu UV-3101PC double-beam, double-monochromator spectrophotometer. We find a steep absorption edge confirming its semiconducting nature. The optical band gap obtained by extrapolation of a linearlike absorption edge was roughly 2.9 eV consistent with the observed pale yellow color of the sample. Theoretical calculations based on the structural model built from our measured atomic parameters have been performed using the all-electron full potential linearized augmented plane wave method. The generalized gradient approximation (GGA) of the exchange correlation potential as given by Engel-Vosko GGA is used. The frequency-dependent complex dielectric function was calculated and the origin of some of the spectral peaks is discussed. The linear optical properties show strong uniaxial anisotropy and birefringence that favors large second order susceptibility. Our calculations show that the complex second order nonlinear optical susceptibility tensor chi(322) ((2))(omega) is the dominant component having the largest total Re chi(322) ((2))(0) value of about 1.8 pm/V.

Electronic Band Structure and Optical Properties of Srn+1TinO3n+1 Ruddlesden–Popper Homologous Series

State-of-the-art calculations of electronic band structures, density of states and frequency-dependent optical properties have been reported for Srn+1TinO3n+1 (n=1, 2, 3, ∞) compounds. These materials possess indirect wide energy band gaps. The frequency dependent optical properties of n=1,2,3 compounds show considerable anisotropy and positive birefringence. The conduction band minimum is originates from Ti-d states, while the valence band maximum is governed by O-p states. The bandwidth of the Ti-d states is responsible for the decrease in the energy band gap as n changes from 1 to 2, 3, and ∞. We have analyzed the degree of hybridization on the basis of the ratio of the orbital overlapping within the muffin tin sphere.

1,4-dialkoxy-2,5-bis[2-(thien-2-yl)ethenyl]benzenes as promising materials for laser optical limiters

A new promising organic chromophore for two-photon laser absorption at 1064 nm with 1,4-diethoxy-2,5-bis[2-(5-methylthien-2-yl)ethenyl]benzene (A-C) was synthesized. We have performed evaluations of the two-photon absorption for these chromophores incorporated into the polymer matrices. Following the obtained quantum chemical data, we have performed quantum chemical simulations of the third-order susceptibilities for the investigated chrompophore incorporated into the PMMA matrices. The calculations were done within the three-level model. We have established that the experimentally calculated data are a bit less than theoretically calculated; however, the general tendency of their changes shows a good coincidence. The maximally achieved value of the TPA is equal to about 59.2 cm/GW at wavelength 1064 nm, which, together with their high photothermal stabilities, make them good candidates for optical-limiting processes.

Electronic structure and optical properties of 1T-TiS2 and lithium intercalated 1T-TiS2 for lithium batteries

We report results of first-principles calculations of electronic and optical properties of pristine 1T-TiS(2) and 1T-TiS(2) intercalated with lithium. Calculations have been performed using the full-potential linearized augmented plane wave method based on density functional theory together with the local density approximation for the exchange correlation energy functional. We have calculated the band structure, density of states, and the linear optical properties. We compare our results of the intercalated 1T-LiTiS(2) with the host 1T-TiS(2) to ascertain the effect of Li intercalation on the electronic and optical properties. The Li-s and Li-p bands are very broad and do not contribute much to the density of states. Our calculations show that the electronic and optical properties are influenced significantly when TiS(2) is intercalated with lithium.

Comparison of the Density of States Obtained from the X-ray Photoelectron Spectra with the Electronic Structure Calculations for α-BiB3O6

We report measurements of the X-ray photoelectron spectrum on single crystals of α-BiB3O6. We also present first principles calculations of the band structure and density of states using the full potential augmented plane wave method. In this paper we make a detailed comparison of the density of states deduced from the X-ray photoelectron spectra with our calculations. We find that the valence band maximum (VB) is located at M symmetry point, while and the conduction band minimum is around half way between the symmetry points Z and Γ resulting in an indirect energy gap of 4.1 eV compared to our measured experimental value of 4.55 eV. The theoretical results of the density of states are in reasonable agreement with the X-ray photoelectron spectroscopy (VB-XPS) measurements with respect to peak positions. We have analyzed the calculated density of states and find a strong/weak hybridization between the B, O, and Bi states in the valence and conduction bands.

Optical second harmonic generation in Yttrium Aluminum Borate single crystals (theoretical simulation and experiment)

Experimental measurements of the second order susceptibilities for the second harmonic generation are reported for YAl3(BO3)4 (YAB) single crystals for the two principal tensor components xyz and yyy. First principles calculation of the linear and nonlinear optical susceptibilities for Yttrium Aluminum Borate YAl3(BO3)4 (YAB) crystal have been carried out within a framework of the full-potential linear augmented plane wave (FP-LAPW) method. Our calculations show a large anisotropy of the linear and nonlinear optical susceptibilities. The observed dependences of the second order susceptibilities for the static frequency limit and for the frequency may be a consequence of different contribution of electron-phonon interactions. The imaginary parts of the second order SHG susceptibility χ123(2)(ω)MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8bkY=wiFfYlOipiY=Hhbbf9v8qqaqFr0xc9vqpe0di9q8qqpG0dHiVcFbIOFHK8Feei0lXdar=Jb9qqFfeaYRXxe9vr0=vr0=LqpWqaaeaabiGaciaacaqabeaabeqacmaaaOqaaiabeE8aJnaaDaaaleaacqaIXaqmcqaIYaGmcqaIZaWmaeaacqGGOaakcqaIYaGmcqGGPaqkaaGcdaqadaqaaiabeM8a3bGaayjkaiaawMcaaaaa@35B5@, χ112(2)(ω)MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8bkY=wiFfYlOipiY=Hhbbf9v8qqaqFr0xc9vqpe0di9q8qqpG0dHiVcFbIOFHK8Feei0lXdar=Jb9qqFfeaYRXxe9vr0=vr0=LqpWqaaeaabiGaciaacaqabeaabeqacmaaaOqaaiabeE8aJnaaDaaaleaacqaIXaqmcqaIXaqmcqaIYaGmaeaacqGGOaakcqaIYaGmcqGGPaqkaaGcdaqadaqaaiabeM8a3bGaayjkaiaawMcaaaaa@35B1@, χ222(2)(ω)MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8bkY=wiFfYlOipiY=Hhbbf9v8qqaqFr0xc9vqpe0di9q8qqpG0dHiVcFbIOFHK8Feei0lXdar=Jb9qqFfeaYRXxe9vr0=vr0=LqpWqaaeaabiGaciaacaqabeaabeqacmaaaOqaaiabeE8aJnaaDaaaleaacqaIYaGmcqaIYaGmcqaIYaGmaeaacqGGOaakcqaIYaGmcqGGPaqkaaGcdaqadaqaaiabeM8a3bGaayjkaiaawMcaaaaa@35B5@, and χ213(2)(ω)MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8bkY=wiFfYlOipiY=Hhbbf9v8qqaqFr0xc9vqpe0di9q8qqpG0dHiVcFbIOFHK8Feei0lXdar=Jb9qqFfeaYRXxe9vr0=vr0=LqpWqaaeaabiGaciaacaqabeaabeqacmaaaOqaaiabeE8aJnaaDaaaleaacqaIYaGmcqaIXaqmcqaIZaWmaeaacqGGOaakcqaIYaGmcqGGPaqkaaGcdaqadaqaaiabeM8a3bGaayjkaiaawMcaaaaa@35B5@ are evaluated. We find that the 2ω inter-band and intra-band contributions to the real and imaginary parts of χijk(2)(ω)MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbwvMCKfMBHbqedmvETj2BSbqee0evGueE0jxyaibaieYdOi=BI8qipeYdI8qiW7rqqrFfpeea0xe9LqFf0xc9q8qqaqFn0dXdHiVcFbIOFHK8Feei0lXdar=Jb9qqFfeaYRXxe9vr0=vr0=LqpWqaaeaabiGaciaacaqabeaabeqacmaaaOqaaiabeE8aJnaaDaaaleaacaWGPbGaamOAaiaadUgaaeaacaGGOaGaaGOmaiaacMcaaaGcdaqadaqaaiabeM8a3bGaayjkaiaawMcaaaaa@3752@ show opposite signs. The calculated second order susceptibilities are in reasonable good agreement with the experimental measurements.PACS Codes: 71.15. Mb; 71.15.-m