Journal of the Korean Physical Society, Vol. 64, No. 4, February 2014, pp. 561∼566 Electrical and Optical Properties of Air-stable, Iodine-doped Natural Cotton Fibers A. S. Zakirov, Sh. U. Yuldashev, H. D. Cho, H. C. Jeon and T. W. Kang ∗ Quantum-Functional Semiconductor Research Center, Dongguk University, Seoul 100-715, Korea A. T. Mamadalimov Department of Physics, National University of Uzbekistan, Tashkent 100175, Uzbekistan (Received 10 June 2013, in final form 1 October 2013) The influence of sodium-hydroxide treatment and iodine doping on the optical and the electrical properties of cotton fibers is investigated by using photoluminescence (PL), as well as photoconduc- tivity, measurements. The iodine doping results in a quenching of the PL and an enhancement of the photoconductivity due to the photo-induced charge transfer between the dopants and the cotton fibers. The conductivity of the iodine-doped cellulose fibers shows a significant enhancement by more than five orders of magnitude as compared to that of the undoped samples. A good correlation is found between the changes in the fiber’s morphology and the electrical and optical properties of the fiber, which opens interesting perspectives for molecular donor-acceptor device applications. PACS numbers: 72.80.Le, 72.20.-I, 73.50.Pz Keywords: Cellulose fibers, Iodine doping, Charge transport, Photoluminescence, Photoconductivity DOI: 10.3938/jkps.64.561 I. INTRODUCTION Recent progress in the processing of conducting poly- mers has significantly improved the quality of the mate- rials with corresponding improvements in their electrical conductivity [1]. Of particular and increasing interest are those polymers with active optical, photosensitive, and electron transfer properties. Their prospective appli- cations in modern technologies are data storage, holog- raphy, imaging, and recording materials; resist technol- ogy, rechargeable batteries, photovoltaic devices, sensors, biotechnology devices, and medicinal chemistry devices. Recent efforts have focused on searching for inexpensive renewable conducting polymers combined with the cor- responding effective stable dopants [2]. As one of the most common low-cost and renewable natural polymers, cotton cellulose fibers (CFs) with chemical doping have tremendous potential commercial uses as an alternative to synthetic conducting polymers. Cellulose embodies multiple functionalities, optical transparencies and processabilities. The mechanism of a NaOH interaction with cellulose is of interest to re- searchers because cellulose treatment with NaOH solu- tion has numerous applications in fiber modification, dis- solution, and regeneration [3]. The detailed structure modification and the physicochemical and mechanical * E-mail: twkang@dongguk.edu; Fax: +82-2-2278-4519 properties of the cotton cellulose have been quite well studied [4–6]. The unique atomic and electronic struc- tures of CFs consisting of variable carboxyl/carbonyl fractions open up possibilities for new functionalities. For optoelectronic applications, cellulose, of course, has to be chemically modified by appending functional groups in order to provide the desired optical and electri- cal properties. Many research groups have been studying these modifications by using different approaches that include a variety of chemical treatments, grafting, cou- plings between the fiber and the matrix, and physical coverage of the fibers by using a polymer sleeve [7]. Coat- ing the surfaces of fibers with nano-TiO 2 /-ZnO particles and conductive polymers is one approach to the produc- tion of highly-active surfaces for UV-blocking, antimicro- bial properties and for enhancing the conductive prop- erties for emission layers and photovoltaic cells [8–10]. Previous studies have shown that individual natural or- ganic polymer fibers, cellulose- based fabrics and papers, may be successfully coated with conducting polymers by using several coating techniques [11, 12]. However, some of these techniques consume more material by fill- ing fiber interstices, need excess solvent (water), energy, etc., and affect surface properties, gloss and brightness [13]. Thus, improved techniques compatible with coat- ing on a nanoscale and consuming less material are re- quired. Directly doping with appropriate dopants is gen- erally preferred as it would cause web breaks and streak defects, and would have certain advantages in terms of -561-