Thin films containing Mn-doped ZnS nanocrystals synthesised by chemical method and study of some of their optical properties

Abstract

In this article, we present the optical properties of thin films containing Mn-doped ZnS nanocrystals synthesised by the chemical method. The ZnS nanoparticles within the polymer matrix (polyvinyl alcohol) were investigated by SEM and TEM images and analysed by X-ray diffraction. The effect of polymer concentration on the direct band gap of Mn-doped ZnS thin films was calculated from the data for absorption measurements. The values of the band gap are in the range of 3.73-3.90 eV. In addition, we discuss the photoluminescence of these films. IntroductionZnS nanomaterials are semiconductor materials with direct band gap larger than that of ZnO. The direct band gap of ZnS is 3.6 eV for a bulk ZnS material, and this can reach 3.98 eV for a ZnS nanomaterial at 300 K [1], or 4.4 eV [2] in a Wurzite structure. Moreover, the melting temperatures of A II B VI materials are very high. ZnS is therefore considered one of the most promising materials which find applications in optoelectronic devices, blue emitting diodes, electroluminescent devices and others [3,4].ZnS nanoparticles radiate luminescence with a wavelength of 420-480 nm. In order to receive radiation in the visible region, ZnS used to be doped by transition metals, such as Mn 2þ , Cu 2þ and Ni 2þ [5][6][7][8]. It is known that the optical properties of nanomaterials show they are highly sensitive to synthesis conditions [9][10][11] and are dependent on the type on precursor used, pH level, doping concentration and temperature regime. It is also known that the direct band gap of nanomaterials can be controlled by doping, using polymer coating [12] and manipulating synthesis conditions. As certain polymers (polyvinyl alcohol (PVA), polyacrylic, polystyrene) are transparent to visible light, they will not have any effect on the emission wavelengths of ZnS nanoparticles when they are being diffused into the polymer matrix. On the contrary, these polymers can prevent nanoparticles from aggregating, in the mechanism of steric and electrostatic stabilisation. Thus, polymer coating plays a role in providing a protective environment for ZnS nanoparticles [1,2].Previous results on the optical properties of ZnS:Mn showed that the luminescence intensity increased considerably with an optimal nominal Mn concentration of about 9-10% [13].

Characterization of Sn Doped ZnS Thin Films Synthesized by CBD

“…While cubic ZnS has been reported to have a wide direct bandgap of ~3.6 eV at 300K, hexagonal ZnS has been reported to have a bandgap of ~ 3.91 eV 3 . The material has huge potential application in both bulk and thin film form in various photovoltaic and optoelectronic devices 4 .It is used as key material for solar control coating, optoelectronic devices, electroluminescence devices, sensors and others 5 . ZnS is a prospective material to be used in solar cell as passivation layer for better photovoltaic properties 6 .…”

Effect of Annealing Temperature and Spin Coating Speed on Mn-Doped ZnS Nanocrystals Thin Film by Spin Coating

“…It is relatively easy to fabricate the nanomaterial with the intended optical and electrical properties through controlling the shape of its nanostructure [1,2]. It has a wide energy band gap with a value of 3.68 eV for cubic phase and 3.77 eV for hexagonal phase [3][4][5][6][7][8][9][10]. There are several physical methods (ion sputtering, laser ablation, gas condensation, pyrolysis, etc.)…”

Effect of bath temperature on morphological and optical properties of ZnS films prepared by electrochemical deposition technique

“…While cubic structure of ZnS has been reported to have a wide direct band gap of ∼ 3.6 eV at optimum temperature, hexagonal structure of ZnS has been reported to have a bandgap of ∼ 3.91 eV [3]. The material has been huge potential application in both thick and thin film form in various photovoltaic and optoelectronic devices [4] This optical transparency combined with chemical and thermal stability makes zinc sulfide used as key material for solar control coating, window layer solar cell, electroluminescence devices, optoelectronic devices, sensors and others [5]. Zinc sulfide is a promising material to be used in solar cell as passivation layer for better photovoltaic properties [6].…”

“…Thus they have become more popular in recent times. ZnS thin film has been grown by using electrodepositon and various chemical techniques [10] such as Sol-gel [1], Spin coating [5], Spray Pyrolysis [11], chemical vapor deposition and chemical bath deposition [12] etc. The technique of electrodepositon is simple, inexpensive and can be adaptable to large area processing with low fabrication cost.…”