CdBr 2 nanocrystalline layers as nonlinear optical materials
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CdBr2 nanocrystalline layers as nonlinear optical materials K. J. Plucinski • G. Lakshminarayana
Received: 2 September 2013 / Accepted: 8 October 2013 / Published online: 19 October 2013 Ó Springer Science+Business Media New York 2013
Abstract A new type of nanomaterial for optoelectronic is proposed. As such a material cleaved nanolayers of layered CdBr2 single crystals is chosen. A principal possibility to prepare thin hexagonal single crystalline layers of CdBr2 nanocrystals (possessing 6H polytype) with thickness up to several nanometers was shown. The studies of the optical absorption clearly show an occurrence of the blue spectral shift for the absorption edge up to 30 nm. During illumination by the 5 ns nitrogen laser at the wavelength at about 337 nm below the energy band gap it was established a substantial increase of the photoinduced absorption coefficient up to 25 cm-1 at pump power density equal to about 1 GW cm-2. The maximal photoinduced effect was observed for the thinnest film possessing thickness about 4 nm. The linear electrooptical effect was maximal at ambient temperature.
1 Introduction The layered halogenide single crystals (first of all CdI2 and its derivatives) possess a lot of polytypes [1–3] which are both centrosymmetric as well as non-centrosymmetric. Despite most of them are centro symmetrical, particular interest for the optics and nonlinear optoelecronic present the acentric polytypes, like hexagonal polytypes (6H) [4, 5] possessing C46v space group. These crystals show a second K. J. Plucinski (&) Electronic Department, Military University Technology, Kaliskiego 2, 00-908 Warsaw, Poland e-mail: [email protected]; [email protected] G. Lakshminarayana Materials Science and Technology Division (MST-7), Los Alamos National Laboratory, Los Alamos, NM 87545, USA
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harmonic generation and the linear electrooptical effect (Pockels effect) [6–8]. They are described by third rank polar tensors. It is crucial that degree of their non-centrosymmetry may be varied by changing the number of the particular layers and introducing some impurities between the layers. Additionally principal role may play interlayer acoustic vibrations [9–11] superposition of which may lead to changes of degree of non-centrosymmetry. More important is a fact that these crystals allow to achieve very thin thickness with high quality mirror-like optical layers with almost 100 % light reflectance [12]. The latter one allows to use the such natural surfaces for the creation of the chip nano-layered structure. Most of the such layers were obtained using the adhesive tape allowing to achieve the thin cleaved layers without any additional chemical treatment which allow to use them in the studies of high quality optical spectra [13]. The cleaving was performed by a shift of the attached adhesive tape to the upper level and quick shifting of this layer. As a consequence very thin layers were obtained. However, the study of the effect with respect to the nano-confined optical effects [14] was limited. Additionally during the cl
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