Researcher:
Erdamar, Ahmet Koray

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Master Student

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Ahmet Koray

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Erdamar

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Erdamar, Ahmet Koray

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2007 - 20082

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Researcher Of Publications: search.filters.isAuthorOfPublication.191848c2-cb9f-42cf-b106-194072a9ccc0

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    Synthesis and characterization of poly(acrylic acid) stabilized cadmium sulfide quantum dots
    (Amer Chemical Soc, 2007) N/A; N/A; Department of Physics; Department of Physics; Department of Chemistry; Çelebi, Serdar; Erdamar, Ahmet Koray; Sennaroğlu, Alphan; Kurt, Adnan; Acar, Havva Funda Yağcı; Master Student; Master Student; Faculty Member; Teaching Faculty; Faculty Member; Department of Physics; Department of Chemistry; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; College of Sciences; N/A; N/A; 23851; 194455; 178902
    Cadmium sulfide (CdS) nanoparticles (NPs) capped with poly(acrylic acid) (PAA) were prepared in aqueous solutions from Cd(NO3)(2) and NaS. Influence of the COOH/Cd ratio (0.8-12.5), reaction pH (5.5 and 7.5), and PAA molecular weight (2100 and 5100 g/mol) on the particle size, colloidal stability, and photoluminescence were investigated. A Cd/S ratio of < 1 causes ineffective passivization of the surface with the carboxylate and therefore results in a red shift of the absorption band and a significant drop in photoluminescence. Therefore, the Cd/S ratio was fixed at 1.1 for all experiments studying the mentioned variables. PAA coating provided excellent colloidal stability at a COOH/Cd ratio above 1. Absorption edges of PAA-coated CdS NPs are in the range of 460-508 nm. The size of the NPs increases slightly with increasing PAA molecular weight and COOH/Cd ratio at pH 7.5. It is demonstrated that there is a critical COOH/Cd ratio (1.5-2) that maximizes the photoluminescence intensity and quantum yield (QY, 17%). Above this critical ratio, which corresponds to smaller crystal sizes (3.7-4.1 nm) for each reaction set, the quantum yield decreases and the crystal size increases. Moreover, US NPs prepared at pH 7.5 have significantly higher QY and absorb at lower wavelengths in comparison with those prepared at pH 5.5. Luminescence quenching has not been observed over 8 months.
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    Absorption saturation analysis of Cr2+: ZnSe and Fe2+: ZnSe
    (Optical Soc Amer, 2008) N/A; N/A; N/A; Department of Physics; Çankaya, Hüseyin; Demirbaş, Ümit; Erdamar, Ahmet Koray; Sennaroğlu, Alphan; Researcher; Master Student; Master Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; 20328; N/A; 23851
    We propose several methods for the accurate determination of the cross sections of solid-state saturable absorbers and apply them to the analysis of polycrystalline Cr2+ :ZnSe and Fe2+ :ZnSe. In the case of Cr2+ :ZnSe, both z-scan and power-dependent transmission measurements were made by using a continuous-wave fiber laser at 1800 nm and a pulsed optical parametric oscillator at 1570 nm. The average ground-state absorption cross sections at the wavelengths of 1800 and 1570 nm were determined to be 6.17 x 10(-19) cm(2) and 2.24 x 10(-19) cm(2), respectively. Furthermore, the ratio of the cross sections at these wavelengths (2.75) was close to the value of 2.55 obtained from absorption spectrum measurements. Excited-state absorption was found to be negligible at both wavelengths. In the case of Fe2+ : ZnSe, a tunable, pulsed Cr2+ :ZnSe laser was used to obtain saturation data (z-scan and power-dependent saturation) at the wavelengths of 2645 and 2730 nm. Average ground-state absorption cross sections at 2645 and 2730 nm were determined to be 1.73 x 10(-19) cm(2) and 2.47 x 10(-19) cm(2), respectively, again in very good agreement with those obtained from absorption spectrum measurements. (c) 2008 Optical Society of America.