Journal of Luminescence 122–123 (2007) 646–648 Electroluminescence of cadmium selenium nanocrystals synthesized in aqueous solution Yinhao Gao, Chunjun Liang à , Aiwei Tang, Feng Teng, Dan Li, Zhenbo Deng, Shihua Huang Key Laboratory of Luminescence and Optical Information, Ministry of Education, Institute of Optoelectronic Technology, Beijing Jiaotong University, Beijing 100044, China Available online 15 March 2006 Abstract Cadmium selenium (CdSe) nanocrystals in aqueous system upon addition of mercaptoacetic acid as a stabilizer were synthesized. These were observed in a transmission electron microscope (TEM) and photoluminescence (PL) in aqueous solution were further measured to confirm its nanometer scale size. A surfactant was used to transfer the nanocrystals from the aqueous solution to organic solvent so that both CdSe and poly(N-vinylcarbazole) (PVK) were able to mix sufficiently in organic solvent. A multi-layer structured electroluminescence device was fabricated using a CdSe:PVK thin film as the emitting layer. PL and electroluminescence (EL) properties of the CdSe:PVK film were studied. It was found that CdSe dominated the emission in EL spectra and PVK served primarily as a hole injection and transport media. r 2006 Elsevier B.V. All rights reserved. Keywords: CdSe; Aqueous solution; Photoluminescence; Electroluminescence 1. Introduction Hybrid light-emitting diodes that incorporate cadmium selenium (CdSe) quantum dots (QDs) in the organic layers have been investigated recently [1–5]. These devices combine the diversity of organic materials with the high performance electronic and optical properties of inorganic nanocrystals. Generally, the structure of these devices is either multi-layers or blends of CdSe QDs and organic materials. The electroluminescence (EL) emission peak of the devices using different size of CdSe QDs as emitting layer can be tuned from 530 to 650 nm. In these devices, CdSe QDs were often prepared using Tri-n-octylphosphine (TOP) and Tri-n-octylphosphine oxide (TOPO) as the organic solvents that are expensive and poisonous. More- over the synthesis method was relatively complicated. Thus searching for an alternative and environmentally green synthesis methods is necessary. Synthesis of CdSe QDs in aqueous solution has been carried [6,7]. The advantages of this synthesis method are easy control and low cost. In this paper, the CdSe QDs were prepared in aqueous system upon addition of mercaptoacetic acid as a stabilizer. QD- LEDs were fabricated and the CdSe QDs emission in EL spectra was eventually obtained. 2. Experimental 2.1. Synthesis of CdSe An aqueous solution of Cd(CH 3 OO) 2  2H 2 O and mercaptoacetic acid was adjusted to pH ¼ 10 followed by addition of an aqueous solution of Na 2 SeSO 3 under vigorous stirring in N 2 atmosphere. Then the solution was heated to 80 1C and refluxed for 2 h. It precipitated when adding the acetone to the solution. The resulting CdSe powders were obtained by size-selective precipitation and heating to 60 1C for 12 h. Then the powders were redispersed in the aqueous solution and a surfactant was used to transfer them from the aqueous solution to organic solvent. 2.2. Device fabrication A polymer material poly(N-vinylcarbazole) (PVK) was introduced as matrix that might improve carrier injection ARTICLE IN PRESS www.elsevier.com/locate/jlumin 0022-2313/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jlumin.2006.01.249 à Corresponding author. Tel.: +86 10 51683414; fax: +86 10 51683933. E-mail address: chunjunliang@163.com (C. Liang).