Third-order optical nonlinearity of CdS nanocrystals embedded in sodium borosilicate glass studied by the Z-scan techniq
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Xi-yan Zhang College of Materials Science and Engineering, Changchun University of Science and Technology, Changchun 130022, China
Xiao-juan Liang and Hai-tao Liu College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou 325035, China
Shi-xun Dai and Fei-fei Chen College of Information Science and Engineering, Ningbo University, Ningbo 315211, China (Received 22 August 2009; accepted 14 December 2009)
CdS nanocrystals embedded in sodium borosilicate glass were synthesized through sol-gel process. The CdS nanocrystals were usually 10 to 20 nm in size. The microstructure of CdS nanocrystals was determined to be of the hexagonal phase. The morphology and microstructure of the glass were examined using diverse techniques including scanningprobe microscopy (SPM), x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), energy dispersion x-ray spectra (EDAX), and high-resolution TEM (HRTEM). The linear optical absorption spectrum of the glass showed a blue shift as a result of quantum-size effect. Furthermore, the third-order optical nonlinearities of the glass were studied by Z-scan technique at a wavelength of 770 nm. The results showed that the third-order optical nonlinear refractive index g, absorption coefficient b, and susceptibility w(3) were determined to be 2.16 1016 m2/W, 6.32 1011 m/W, and 1.20 1010 esu, respectively, which were greater than those reported previously for CdS nanocrystals embedded in different matrices.
I. INTRODUCTION
Semiconductor nanocrystals embedded in various matrices have recently attracted considerable attention because of their promising applications in fields of nonlinear optics, optical telecommunication, signal processing, optical switching, and so forth. In particular, research efforts have been focused on the third-order optical nonlinearity of semiconductor nanocrystals because of their tunable optical properties arising from the quantum-size effect,1 which may lead to potential applications in ultrafast all-optical switching.2–6 Those nanometer-sized crystals, which are comparable with the bulk exciton Bohr radius, exhibit intermediate behavior between a bulk crystal and an isolated molecule,7 such as a large optical nonlinearity. However, these nanometer-sized crystals have a large percentage of sura)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0063 J. Mater. Res., Vol. 25, No. 3, Mar 2010
face atoms; they are active under ambient conditions. To avoid the degradation of these active nanocrystals, they are usually embedded into a host matrix to form composites. In recent years, a lot of studies reported the nonlinear optical effects in these nanocomposites.8–10 CdS, as an important II-VI semiconductor compound, has attracted considerable attention because of their potential applications in nonlinear optical devices, flat panel displays, light-emitting diodes, laser, logic gates, transistors, and so forth.11–13 It is a
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