Effect of iodine content on optical properties of chalcohalide glasses Ix(As20Se80)100-x
Introduction
There is an increasing interest of combining chalcogenide and halide glasses in order to use their individual characteristics and overcome their shortcomings [1], [2], [3], [4], [5], [6]. From one side, chalcogenide glasses (ChGs) have good transparency in the mid - near infrared region and good chemical stability making them essential materials for infrared devices [7]. From other side, halide glasses (HGs) are also good infrared optical materials [8] and are known for their low optical loss but have less chemical stability, low glass transition temperature and high crystallizing ability compared to their ChG counterpart. Consequently, chalcohalides should have both good IR transmissions extended to the mid-infrared range as well as good chemical stability and enhanced glass forming ability. In general, chalcohalide shows enhanced infrared optical properties and good chemical stability. Furthermore, the structure becomes less cross-linked and shows a better capability of dissolving rare-earth ions which makes these glasses good candidate for active devices as fiber amplifiers or micro lasers [6,9,10].
The binary chalcogenide system AsxSe1-x is known for its wide applications and large photosensitivity resulting in the ability of photo-induced surface gratings or structural changes [11], [12], [13]. Hence many investigations aimed to correlate its structural and physical properties [14], [15], [16]. Particularly, the composition dependence of AsxSe1-x shows a clear maximum [14] at the coordination 2.4 as proposed by the rigidity model based on percolation proposed by Philipps and Thorpe [17].
Iodine (I) has a low melting temperature (113.7°C) and large atomic radius (133 pm), hence its addition to chalcogenides has interested many authors [2,3,18] and was found to enhance the packing density and improves the glass formation ability by preventing crystallization. Furthermore, iodine could broaden the transmission window by shifting upward the mid-infrared cutoff. Consequently, the introduction of iodine is expected to lower the absorption in the atmospheric IR windows making these compounds interesting for solar cells. The increasing optical application of chalcohalide is urging scientists to study the effect of incorporating halide within chalcogenide glasses on the optical properties mainly the index of refraction n and the extinction coefficient k. In order to study thermally evaporated thin glassy films, the commonly used experimental methods to deduce n and k of a glassy thin film is by analyzing either the single transmission spectrum [19], or both transmission and reflection spectra [20]. In addition to these methods, we could also use a single reflection spectrum to deduce optical constants as in this work and which was introduced by Minkov [21].
In this article, we start by calculating for Ix (As20Se80)100-x (where x=0, 4, 8, 12, 16 at. %) the mean coordination number (NC), the constraints number (Ns), the cohesion energy CE, the heat of atomization Hs, the mean overall bonding energy and then propose theoretical estimations of the band gap based on Manca's relation. The experimental evaluation of different linear and nonlinear optical features is then deduced from single reflection spectrum.
Section snippets
Theoretical estimation of different properties
Taking into account the element's bonding manner in their neighborhood as well as their coordination number which could be deduced from the 8-N rule, one could calculate an important structural parameter, the so called mean coordination number Nc for our ternary glasses Ix(As20Se80)100-x (0 ≤ x ≤ 16 at. %) using the following relation:
The needed coordination numbers of the involved elements As, Se, and I as well as their different physical properties used in this
Experimental details
The common melt quenching method was used to prepare different compositions of bulk glassy chalcogenides Ix(As20Se80)100-x where (0 ≤ x ≤ 16 at. %). High purity (5N) elements from Sigma–Aldrich were introduced into pre-cleaned silica tubes in proper amounts. A high precision balance was used for this purpose. The sample's tubes were continously evacuated down to 5 × 10−5 Torr, then sealed off also under vacuum. The ampoules were introduced in a programmable oven, where the rate of heating 20
Results and discussion
The measured reflectance spectra for the deposited thin films of Ix(As20Se80)100-x, R(λ), and the glass substrate, Rs(λ) are represented both in Fig. 1 simultaneously with the created envelopes RM and Rm as supported by the study of Manifacier et al. [39]. Minkov [21] gave an analyzing method to evaluate from the maxima and minima of the interference fringes the film thickness and the index of refraction (n) of the deposited thin films. This method was widely applied in other chalcogenide
Conclusions
Incorporation of iodine at different contents in As20Se80 was achieved by the melt quenching technique and different thins films of Ix (As20Se80)100-x (x=0, 4, 8, 12, 16 at. %) were thermally evaporated. After estimating theoretically different structural, energetic and optical features, one deduced the linear and nonlinear optical properties using single reflection method. It was found that different relations deduced from Manca's relation give good estimations of the decreasing experimental
CRediT authorship contribution statement
R. Neffati: Writing - original draft, Writing - review & editing. Imed Boukhris: Visualization. Imen Kebaili: Validation. K.A. Aly: Methodology. Y.B. Saddeek: Conceptualization. A. Dahshan: Supervision.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
The authors extend their appreciation to the Deanship of Scientific Research at King Khalid University for financial support through research groups program under grant number (R.G. P2/81/41).
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Chalcohalide glasses
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