Kiran John U, Siby Mathew
Department of Physics, Sacred Heart College, Thevara, Kochi 682013, India
## Abstract
Hybrid freestanding films of polyvinyl alcohol incorporated with silver and CdZnTe quantum dots were synthesized. The effect of varying silver concentration on optical and dielectric properties were studied. Structural and morphological analysis of hybrid films were done using X-ray diffraction and transmission electron microscopy. Optical parameters like absorption coefficient, extinction coefficient, refractive index, optical bandgap, urbach energy and optical conductivity were studied for the polymer nanocomposite for 0 to 0.3 wt percentage of silver content. With increasing silver content, a decrease in bandgap energy and an increase in urbach energy was observed. Dielectric constants, loss tangent and AC conductivity values of hybrid films were found to improve, with silver addition and highest values were obtained for 0.2 wt percentage. Complex impedance plots provided semicircles and Cole-Cole parameters were calculated. The nature of impedance plot revels single relaxation process and this was effectively modelled through an equivalent RC parallel circuit.
## Introduction
Polymer nanocomposites are new class of emerging hybrid materials in polymer science. The ordinary polymer matrix has the advantages of flexibility, stability and processibility. But the polymer matrices can not be extended to advanced applications due to the lack of improved structural, spectroscopic and dielectric properties. In order to make them compatible for suitable applications, the polymer matrix is dispersed with certain nano sized materials, especially nano semiconductor materials [1], [2], [3]. The nano semiconductor/ quantum dots exhibit tuneable optical, morphological and electronic properties. The high surface to volume ratio, quantum confinement effect and size tuneable physiochemical properties made quantum dot semiconductors highly recommended as dopants for polymers [4], [5], [6]. The polymer matrix can also fill with multiple nano systems like metal-metal, metal-semiconductor or semiconductor-semiconductor nanoparticles for achieving better physical and chemical characteristics [7], [8], [9], [10]. Depending on the nature, composition, size and concentration of the dopants the polymer nanocomposites can be considered for tailored applications [6,[11], [12], [13]]. The hybrid polymer films were widely promoted in the fields of integrated circuits, organic gadgets, flexible appliances, dielectric applications and micro/ nano sensors for various sensing applications [8,14,15]. A nano semiconductor - metal composites in polymers is highly encouraged for applications like memory devices, solar cells, light emitting diodes, photodiodes, organic light emitters, biolabeling, photovoltaics and many optoelectronics fields [16], [17], [18].
II–VI binary quantum dots like CdSe, CdS, CdTe, ZnS, ZnSe and metal oxides like ZnO, SiO2, TiO2 are potential dopants for the polymer matrices due to their excellent physiochemical characteristic like high quantum yield, photoluminescence stability, narrow emission lines, size tunable bandgap and quantum confinement effect [18], [19], [20], [21], [22], [23], [24], [25]. Zein K. Heiba et al. synthesized quantum composites of CdSe quantum dots decorated polyvinyl alcohol matrices using solution casting process to investigate the variations in optical and electrical properties. The optical and electrical properties of PVA were greatly enhanced with CdSe introduction into PVA matrix [26]. Free radical polymerization method was adopted by Debashish Nayak et al. to synthesize PMMA- ZnS nanocomposites for OLED applications. They obtained agglomerated pebble like morphology for the nanocomposite and observed enhancements in dielectric and conductivity values [15]. Prathibha Vasudevan et al. reports the synthesis and dielectric studies of PVP-TiO2 composites using sol-gel method and attained the conductivity values in the range 10−7–10−8 S/cm [27]. Ramneek Kaur et al. investigated the effect of Ag in CdSe-PVP nanocomposite synthesized through chemical route. They explored the memory and switching performance based on the I-V and C-V measurements of Ag-CdSe-PVP nanocomposites [28]. Vineeshkumar et al. synthesized alloyed Zn1-x-yCdxCuyS quantum dots dispersed in PVA matrix through in-situ preparation method. The structural, spectroscopic and nonlinear studies confirmed that the materials are well suited for optical switching and limiting applications [29].
The alloyed semiconductor quantum dots give an additional advantages of composition tuneability other than the size depended properties. Ternary alloyed CdZnTe quantum dots gaining great interest among the alloyed quantum dots due to high quantum yield, bandgap tuning, excellent photoluminescence properties etc. [30,31]. In addition, the reduced toxicity in CdZnTe compared to the parental binary CdTe encouraged their applicability in many fields like biolabeling, solar cells, fluorescent probes, display and LED applications [30], [31], [32], [33]. Now a days metal nanoparticles like Ag, Au, Co, Mn and Cu co-doped with quantum dots to get Metal- semiconductor nano systems [34,35]. This metal-semiconductor nano systems can disperse in polymer matrix like PVA to achieve hybrid polymer nanocomposites [7]. Among the various polymers available, PVA can act as good eco-friendly dispersion medium for multi-phase systems. Also, PVA have lot of advantages like high water solubility, durability, flexibility and biocompatibility [6,26,36]. But PVA carries disadvantages like poor optical, dielectric and conductivity properties [1,26,37]. So, to overcome these hurdles, metal-semiconductor nano systems doped in PVA are designed to form hybrid films and have been highly promoted for attaining enhanced optical, electronic and dielectric properties.
In this report, we followed in-situ chemical procedure to synthesize Ag: CdZnTe-PVA freestanding hybrid films in open atmosphere conditions. The variations in bandgap, Urbach energy and optical constants were investigated for the CdZnTe doped and Ag co-doped films. The dielectric and conductivity behavior for the hybrid films also explored. The power law parameters, complex impedance plots and Cole-Cole
CdZnTe Association (CdZnTe.com)
https://www.cdznte.com/thesis/optical-and-dielectric-investigations-on-ag-cdznte-hybrid-polyvinyl-alcohol-freestanding-films.html