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Study of structural and optical properties of AuCl semiconductor nanocrystals embedded in KCl single crystals grown by Czochralski method

 

F. Zehani* and H. Zaioune

 

Laboratoire d’Étude des Matériaux (LEM), Université de Jijel, Jijel, Algérie

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Semiconductor nanocrystals embedded in wide gap matrices, such as alkali halides [1, 2] have received in recent years a great interest for both fundamental research and technical application. The nanocrystals are characterized by a dominant surface effect and they have a considerable surface/volume [3]. In that respect, the optical properties of semiconductors change considerably when their sizes become comparable to the bulk Bohr radius of an exciton [4]. This change permits to get the quantum confinement of the electronic excitations

[5]. The confinement in three dimensions of the exciton could be at the origin of strong nonlinear properties, which make them suitable materials for use in laser devices.

During the past decade, a considerable effort has been spent in the preparation and investigation of the I-VII family of semiconductor nanocrystals. Among all the I-VII compounds, gold monochloride or AuCl is one of the most interesting materials because it is characterized by its interesting optical absorption and emission in the visible region [6].

The samples of KCl single crystals doped with AuCl nanocrystals are elaborated using the Czochralski method, which consists of melting the gold thin films deposited on pure KCl pastilles. The single crystals are cleaved perpendicularly to the crystallographic direction [100]. The cleavage permits to obtain samples with 1 mm thickness. The thermal treatment of samples is performed at 650°C during 3 hours. After the annealing, the samples are cooled slowly at room temperature.

The X-ray diffraction of KCl doped AuCl nanocrystals after annealing at 650°C for 3 h shows

 

the  intense  peaks  of  KCl  single  crystals  situated  at


2θ = 28,37°


and


2θ = 58,68° ,

 

corresponding to (200) plane and its harmonic (400) of KCl single crystals, as identified by using  JCPDS  file  41-1476,  and  two  diffraction  peaks  with  a  weak  intensity, situated  at

 

2θ = 31,74° and


2θ = 65,83° . These peaks are attributed respectively to (211) and (422) planes

 

of AuCl tetragonal structure with a space group


I 41 / amd , comparing with the literature data

 

of JCPDS file 30-0603. The average radius of the AuCl nanocrystals is estimated using the Scherrer formula, it has been found in the range 3,4-18,7 nm. The photoluminescence spectra presented  a  band  emission  situated  at  580 nm  leading  to  the  formation  of  the  AuCl nanocrystals within KCl, with a shift from the bulk emission of 52 nm.

 

Keywords: AuCl, semiconductor nanocrystals, X-ray diffraction, photoluminescence

 

[1] T. Itoh, Y. Iwabuch and M. Kotaoka, Phy. Stat. Sol (b), 145, 567-577 (1988). [2] T. Itoh, Y. Iwabuch and T. Kirihara, Phy. Stat. Sol (b), 146,  531-543 (1988). [3] A. Ekimov, J. Lumin., 70, 1-20 (1996).

[4] A.I. Ekimov, Phys. Scr., T39, 217-222 (1991).

[5] A.I. Ekimov, Al.L. Efros, M.G. Ivanov, A.A. Onushchenko and S.K. Shumilov, Sol. Stat.

Commun., 69, 565-568 (1989).

[6] Claude Schwab, Jean Martin, Manuel Sieskind and Serge Nikitine, C. R. Acad. SC. Paris, t. 264, Série B, 1739-1742 (1967).