Browsing by Author "Yükselici, M. H."

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An Urbach study of the degree of structural disorder in CdTe nanocrystals in glass matrix
(Видавництво Львівської політехніки, 2012) Ince, A. T.; Torun, M. K.; Yükselici, M. H.
CdTe nanocrystals embedded in matrixes such as, glass, plastic and, aqueous solution have been investigated extensively due to their potential applications in nonlinear optical devices, biotechnology and medicine. When the size of bulk semiconductor is reduced to nanometer scales, the crystal gains new optical and electronic properties. Energy levels are quantized as in atoms and the energy difference between levels widens with the inverse of the size squared. CdTe nanocrystals were grown in glass by solid-state phase precipitation at the above glass transition temperature. A size dependent blue shift in the asymptotic absorption edge was observed in optical absorption spectra. The crystalline composition was studied by Resonant Raman spectroscopy. The width of the optical absorption tail at long wavelengths depends on the spread of electron energy levels within the structure, called the Urbach energy, which was calculated depending on size. We observe that the Urbach tail narrows as the surface to volume ratio of the nanocrystals decreases.
CdTe nanocrystals studied through in-situ electro-modulation spectroscopy
(Видавництво Львівської політехніки, 2012) Ince, R.; Patan Alper, F. M.; Yükselici, M. H.; Asıkoğlu, A.; Allahverdi, Ç.
Non-linear optical properties of weakly confined CdTe nanocrystals in a glass matrix were studied by electro-modulation spectroscopy. Copper electrodes of about 10 nm thick were deposited on both sides of glass samples of thickness 0.8 mm by physical vapor deposition. Optical transmission spectra of the samples were recorded under dc high voltage applied to the electrodes. The absorption band is observed to broaden. This is most likely caused by state filling.
The dependence of optical properties of LiNbO3 crystal on the impurity content studied toward the advancement of volume holographic data storage technology
(Видавництво Львівської політехніки, 2012) Yükselici, M. H.; Asıkoğlu, A.; Bulut, D.; Sugak, D.; Solskii, I.; Syvorotka, I.; Zhydachevskii, Ya.; Ubizskii, S.; Buryy, O.
Research on holographic data storage has been carried out by using continuous wave laser at 632.8. The erasure time constants for continuous readout have been determined. Defect structures of congruent lithium niobate crystal heat-treated at high temperature were identified by optical absorption spectroscopy and the effect of defect bands modified by high temperature heat treatment on the continuous illumination life time of holograms stored in the crystal were studied.
The effect of high temperature heat treatment on the directional homogeneity of LiNbO3 crystal studied through transmission ellipsometry
(Видавництво Львівської політехніки, 2012) Asıkoğlu, A.; Yükselici, M. H.; Bulut, D.; Sugak, D.; Solskii, I.; Syvorotka, I.; Zhydachevskii, Ya.; Ubizskii, S.; Buryy, O.
Pure and doped lithium niobate (LiNbO3) crystals heat treated at temperatures up to 1000oC under reduced/oxidized atmospheres were studied through normal incidence transmission ellipsometry in which a laser with a wavelength of 632.8 nm was employed. The differences in refractive indices between two orthogonal directions were calculated. Results show that the birefringence varies depending on thermal history of the samples.