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Study on Preparation and Second-order Nonlinear Optical Properties in CdS Microcrystalline Doped Glasses

Author: LiuHao
Tutor: ZhaoXiuJian;LiuQiMing
School: Wuhan University of Technology
Course: Building materials and engineering
Keywords: CdS Nanocrystals Glass Electrical poling Second harmonic generation (SHG) Second order nonlinear optical coefficient
CLC: TQ171.1
Type: PhD thesis
Year: 2007
Downloads: 269
Quote: 1
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Abstract

With the development of optical communications and the coming of photon times,practical demands from all optical switch and space modulators have been presentedfor optical properties of materials, and the key for optical technology is thedevelopment of nonlinear optical materials. Although the nonlinear effects of glassare not the best in all kinds of nonlinear optical materials, it has special structure,properties, good chemic and thermal stability, and so on. Thus glass may be. one ofthe materials for nonlinear optical apparatus. Glasses contain heavy metal ions ornanocrystals generally have larger nonlinear optical coefficient than other systems.Therefore, doped with nanocrystals, the research and application of glasses containingheavy metal ions possess large significance.Contained with heavy metal ions, glasses have large nonlinear optical effects. Theanalysis of nonlinear optical mechanism will be more complicated with the doping ofnanocrystals. Na₂O-Cs₂O-B₂O₃-SiO₂ system, which can not generate second ordernonlinearity after poling treatment, was chosen to dope CdS nanocrystal andinvestigate the structure and nonlinear optical properties. Based on that, correlativeproperties of CdS doped lead silicate glasses were researched, and the nonlinearoptical coefficients of the two systems were both presented. Glasses were prepared bymelt-quenching method. Utilizing Maker fringe method, second-harmonic generation（SHG） has been investigated on the glasses systems throughheat-auxiliary-electric-field polarizing technique.In the alkali borosilicate glass system, CdS crystals could precipitate with thedopant at 3～5at% for CdS and the ratio of 5～7 for ZnO/CdS; And they were 3at%,6～8 for the lead silicate glass system.The states and types of CdS crystals precipitated were affected greatly by the kindsof base glasses. In alkali borosilicate system, hexagonal CdS was the main crystalphase, co-precipitated with a little cubic CdS. Nanocrystals grew gradually withenhancing the heat-treatment conditions, and the shift to long wave direction forcharacteristic peaks of optical transmission spectra and fluorescent spectra means theexistence of distinct quantum size effects. In lead silicate system, the displace of Pbfor Cd in CdS resulted in the precipitation of orthogonal CdS for samples with theration of PbO/（PbO+SiO₂） at 0.30. The state of CdS crystals for this system is not asgood as the alkali system, emitting strong fluorescence of surface and disfigurementin the nanocrystals.As for the CdS doped alkali borosilicate glasses, distinct SHG can not be observedin the base glass; Without any poling procedure, evident SHG can be observed in CdSdoped glasses, resulted from the polarization of Cd and S atoms on the surface of crystals by the application of laser light; After poling treatment, the SH intensityenhanced greatly, mainly from the directional array of dipoles and the increasingprecipitation of hexagonal CdS. Increasing the poling temperatures and voltages werein favor of the enhancement of SH intensity. In the 10μm nonlinear layer, thehexagonal CdS whose precipitation had been enhanced during the poling process isthe centre to generate the nonlinear optical effects. The second order nonlinear opticalcoefficient X^（2） for the sample with the largest SH intensity was calculated at 1.75pm/V,the coherent length was 4.07μm. Accordingly, they were 2.09pm/V and 4.231μm forthe nonlinear optical layer.As for CdS doped lead silicate glass system, SHG can all be observed for sampleswithout any poling treatment; The SH intensity increased with increasing the polingtemperature and voltage; The great enhancement of SH intensity happened at theinitial tens of minutes of the poling procedure, and it can be attributed to the inducedstructural distortion, which is the reason of the large enhancement for SH intensity;The x^（2） for this system was calculated at 3.49pm/V for sample with the largest SHintensity, which is larger than the alkali borosilicate glass system. The results meanthat in order to prepare glass materials with large x^（2）, it is logical to select leadsilicate glass system as the base glass to dope CdS nanocrystals.

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