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Bi12SiO20 single crystals have attracted interest due to their remarkable photorefractive characteristics. Since bandgap and refractive index are related theoretically to each other, it takes much attention to investigate temperature dependency of bandgap energy to understand the behavior of photorefractive crystals. The present study aims at investigating structural and optical characteristics of photorefractive Bi12SiO20 single crystals grown by the Czochralski method. The structural characterization methods indicated that atomic composition ratios of constituent elements were well-matched with the chemical compound Bi12SiO20, and grown crystals have a cubic crystalline structure. Optical properties of crystals were investigated by room temperature Raman spectroscopy and temperature-dependent transmission measurements between 10 and 300 K. The analyses of transmittance spectra by absorption coefficient and derivative spectrophotometry techniques resulted in energy bandgaps decreasing from 2.61 to 2.48 eV and 2.64 to 2.53 eV as temperature was increased from 10 to 300 K. The Varshni model was applied to analyze temperature-bandgap energy dependency. [ABSTRACT FROM AUTHOR]

Spectroscopic ellipsometry studies of AgSbSe2 are conducted, and the spectra of the permittivity and optical constants in the energy range 0.07–6.5 eV are determined. To describe the experimental spectra, the Tauc–Lorentz, modified Forouhi–Bloomer, and Cody–Lorentz models are used. It is found that the Cody–Lorentz model more adequately describes the near-edge region of the spectra of optical constants. It is shown that the optical properties, the shape of the absorption edge, and the structure of the band gap are substantially influenced by the spatial structural disorder of AgSbSe2 crystals. From analysis of the experimental spectra by different methods, the band gap of AgSbSe2, Eg, is determined: Eg = 0.32 eV. [ABSTRACT FROM AUTHOR]

Spectroscopic ellipsometry studies of AgSbSe2 are conducted, and the spectra of the permittivity and optical constants in the energy range 0.07–6.5 eV are determined. To describe the experimental spectra, the Tauc–Lorentz, modified Forouhi–Bloomer, and Cody–Lorentz models are used. It is found that the Cody–Lorentz model more adequately describes the near-edge region of the spectra of optical constants. It is shown that the optical properties, the shape of the absorption edge, and the structure of the band gap are substantially influenced by the spatial structural disorder of AgSbSe2 crystals. From analysis of the experimental spectra by different methods, the band gap of AgSbSe2, Eg, is determined: Eg = 0.32 eV. [ABSTRACT FROM AUTHOR]

The photoluminescence excitation and emission spectra of n-type stain etched porous silicon layers were investigated. From these spectra the average values of optical bandgap and photoluminescence peak position were determined. Based on these experimental data, the photoluminescence emission spectra of porous silicon were analyzed by the phenomenological theory and the fitting parameters of the theory were defined. The size and bandgap distributions of silicon nanoparticles were determined and their mean values were calculated. It was found that the investigated PS samples are the ensemble of nanoparticles with size between 1.5 nm and 2.8 nm and a bandgap from 2 eV to 3.2 eV distributed with different probabilities depending on the formation time of porous silicon. It is shown that with increasing formation time, the average size of nanocrystals is slightly increasing, while the average bandgap is slightly narrowing. [ABSTRACT FROM AUTHOR]