Manifested luminescence and magnetic responses of stoichiometry dependent Cd 1  x Mn x Se quantum dots Runjun Sarma, Geetamoni Deka, Dambarudhar Mohanta * Nanoscience and Soft Matter Laboratory, Department of Physics, Tezpur University, Napaam, Assam 784028, India A R T I C L E I N F O Article history: Received 5 June 2014 Received in revised form 2 November 2014 Accepted 3 November 2014 Available online 6 November 2014 Pacs No.: 78.67.Bf 61.82.Fk 81.05.Dz 63.20.-e 75.50. Pp Keywords: A. Chalcogenides A. Nanostructures A. Semiconductors B. Chemical synthesis C. Raman spectroscopy C. X-ray diffraction D. Crystal structure D. Luminescence D. Magnetic properties A B S T R A C T We report on stoichiometry dependent manifested physical properties of thioglycolic acid (TGA) coated Cd 1  x Mn x Se QDs. While possessing a wurtzite phase, with increasing x, the QDs exhibited a notable blue- shifting of the onset of absorption. Attributed to V Cd –V Se di-vacancies, the QDs describe an intense deep- defect related emission response at smaller values of x (=0 to 0.3). Due to the facilitation of magnetic Mn 2+ ion migration from the core to the QD surfaces, 4 T 1 – 6 A 1 transition based Mn 2+ orange emission get suppressed at a higher x (=0.6 to 1). While the FT-IR spectra of the alloyed QDs display characteristic Mn– OH stretching mode at 644 cm 1 , the peak located at 703 cm 1 is assigned to Cd-Se bending. Furthermore, the QDs with a low x (=0.3), exhibit paramagnetic characteristics owing to the presence of uncorrelated, isolated Mn 2+ spins. The collective luminescence and magnetic features would find immense scope in bio-labeling and imaging applications, apart from solid state luminescent components. ã 2014 Elsevier Ltd. All rights reserved. 1. Introduction Semiconductor nanocrystals are known for their bright emission response with size dependent color tunability between the ultra violet (UV) and near infra-red (NIR) region of the electromagnetic spectrum. Of particular interest, the magnetic impurity doped systems (magnetic semiconductor nanocrystals/ quantum dots, ms-NCs/QDs), such as, nanoscale Cd 1  x Mn x Se systems, have received growing interest owing to their immense potential in magneto-optics, nonlinear optics, nano-photonics and nano-biotechnology. This is because, these QDs exhibit special properties, like localization of magnetic ions that result in free electron and hole carriers [1,2], size-dependent sp-d exchange interaction [3,4] along with introduction of new energy levels within the forbidden gap. The strong sp-d exchange interaction may result in enhanced spin relaxation [5], giant Zeeman splitting of the electron and hole states when subjected to a magnetic field [6], along with the formation of excitonic magnetic polarons [3,7]. These interesting characteristics occurring in ms-NCs ensure their potential applicability in various fields including spintronics [8], tunable lasers [9], solar cells [10], magneto-optic elements [11], quantum computing etc. Over the years, magnetic semiconductor systems of the form A II 1  x M x B VI , (with cations A II = Cd 2+ , M = Mn 2+ , anion B VI = Se 2 ) have drawn significant research interest owing to the strong dependence of sp–d exchange interaction on the amount of doping (mole fraction, x). Moreover, highly fluorescent II–VI semiconduc- tor systems, mostly Cd-based ones (e.g., CdSe, CdTe, CdS, CdSe/ZnS core shell QDs etc.), have been investigated in great detail including their extensive deployment in biolabeling and bioimag- ing studies [12]. In this work, we demonstrate a simple, user- friendly approach for synthesizing Cd 1  x Mn x Se QDs, using thioglycolic acid (TGA) as the capping agent. Although TGA in excess amount is somewhat toxic, but due to its ability to provide effective surface functionalization and extra-photostability to the fluorescent QDs, the TGA capped QDs are found to be extremely * Corresponding author. Tel.: +91 3712 275558; fax: +91 3712 267005. E-mail addresses: best@tezu.ernet.in, dmohanta1973@gmail.com (D. Mohanta). http://dx.doi.org/10.1016/j.materresbull.2014.11.011 0025-5408/ ã 2014 Elsevier Ltd. All rights reserved. Materials Research Bulletin 62 (2015) 71–79 Contents lists available at ScienceDirect Materials Research Bulletin journal homepage: www.else vie r.com/locat e/mat resbu