Novel, Flexible and Low-power Driven AC Electroluminescent Lamp from Carbon Nanotube Embedded Phosphor Material D. Haranath , Deepika Yadav, Sonal Sahai and Virendra Shanker CSIR-National Physical Laboratory, Dr K S Krishnan Road, New Delhi 110 012, India E-mail: haranath@nplindia.org , Tel: +91-11-4560 9385, FAX: +91-11-4560 9310 ABSTRACT We present a novel methodology to design a hybrid electroluminescent (EL) lamp by embedding carbon nanotubes (CNTs) inside the ZnS:Mn phosphor particles. By doing so, the phosphor particles exhibited increase in EL brightness and efficiency at low operating voltages (<100 V AC ). Interestingly shorter the length of CNTs used, greater was the field enhancement effect observed in the EL lamps. The role of CNTs have been identified to form conductive paths inside the ZnS particle thereby triggering EL due to electron injection to active centres at nominal voltges. In addition, a detailed electrical characterization of the novel EL lamp along with its spectral energy distribution studies are presented. Keywords: electroluminescence, phosphor, carbon nanotube, hybrid material, electro-optical studies 1 INTRODUCTION There are innumerable potential applications of carbon nanotubes (CNTs) in electronics, composites, energy and life sciences. Due to their high electrical conductivity and the unbeatable sharpness of their tip they are the best field emitters of any known material and similarly due to the high current density, low turn-on and operating voltage, steady and long-lived behaviour make CNTs ideal field emitters for illumination and display applications [1–3]. Thare are few reports on enhanced electroluminescence (EL) at reduced threshold and operating voltages when CNTs are used as a field enhancer before the phosphor layer [4, 5]. The electroluminescence (EL) phenomenon has been strong potential for display applications due to many advantages such as non-thermal light source, high energy conversion efficiency, better brightness and contrast, wide viewing angle and ease of fabrication without vacuum requirement [6]. Alternating current driven EL lamps already occupy a segment of the high-resolution, flat pa nel display market. AC-EL displays in thin-film form are robust, possess long lifetimes, and offer high luminance with relatively low power consumption [7-9]. However, some constraints originating from the use of high driving voltages (>1000 V AC ) and/or short life times (few hundred hours) limit its commercial use [10-12]. Hence, in this paper a novel, cost-effective and facile technique is suggested, in which CNTs are deliberately embedded into a ZnS:Mn phosphor material forming a hybrid system which exhibits efficient EL at low voltages (<100 V AC ). 2 EXPERIMENTAL 2.1 Preparation of the Sample Orange emitting ZnS:Mn phosphor has been synthesized by sol- gel method and was used as a starting material. The multi-walled carbon nanotubes (CNTs) were grown by chemical vapor deposition technique and procured from M/s J. K. Impex, India. Since, the weighing of lower amounts of CNTs with precision is a tedious job, we have dispersed a known weight of CNT in ethyl alcohol and ultra-sonicated rigorously for 2 h to make a suspension. This was further added to ZnS:Mn phosphor and allowed to dry at room temperature (25˚C). After complete drying the mixture was blended mechanically and annealed at 450˚C under an inert N 2 atmosphere. The amount of CNT addition is found to be highly critical in our experiments. An admissible range to exhibit EL was only 0.005–0.03 wt%. However, ~0:01 wt% of CNT was found to be optimum and showed stable and bright EL from the ZnS/CNT hybrid system. 2.2 EL Lamp Fabrication Figure 1: Schematic diagram of inorganic ZnS:Mn phosphor powder EL lamp. The bar indicates a scale of 10 μm NSTI-Nanotech 2013, www.nsti.org, ISBN 978-1-4822-0581-7 Vol. 1, 2013 721