Cadmium Free Quantum Dots: Principal Attractions, Properties, and Applications
For the past thirty years, interest on semiconductor nanocrystals from versatile systems of II–VI Quantum Dots (QDs) has been actively grown depending upon their application to light-emitting diodes (Gaponik in Mater Chem 10:2163–2166, 2000 [1 ]), lasers
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Cadmium Free Quantum Dots: Principal Attractions, Properties, and Applications Anush Mnoyan, Yonghee Lee, Hankyeol Jung, Somang Kim and Duk Young Jeon
Abstract For the past thirty years, interest on semiconductor nanocrystals from versatile systems of II–VI Quantum Dots (QDs) has been actively grown depending upon their application to light-emitting diodes (Gaponik in Mater Chem 10: 2163–2166, 2000 [1]), lasers (Artemyev et al. in Nano Lett 1:309–314, 2001 [2]), and biomedical research (Bruchez et al. in Science 281:2013–2016, 1998 [3]; Chan and Nie in Science 281:2016–2018, 1998 [4]; Michalet et al. in Science 307:538– 544, 2005 [5]). However, the presence of highly toxic cadmium limits the application range particularly in the lighting and biological fields. To lessen the toxicity issue, various approaches were developed, such as overcoating the toxic core by non-toxic ZnS shell preventing the leakage of cadmium ions (Chou and Chan in Nat Nanotechnol 7(7):416–417, 2012 [6]; Ghaderi et al. in J Drug Targeting 19:475– 486, 2011 [7]; Winnik and Maysinger in Acc Chem Res 46:672–680, 2012 [8]). Despite this action, II–VI QDs still remain unsafe due to initiated response to UV irradiation- or oxidation-resulted cadmium release through oxidized surface sites (Derfus et al. in Nano Lett 4:11–18, 2004 [9]). Therefore, the research focus was shifted to so-called cadmium free QDs, such as ZnSe, InP, and CuInS2.
15.1
II–VI Compounds: ZnSe-Based Semiconductor Nanocrystals
15.1.1 Introduction Among non-cadmium-based II-VI groups, zinc chalcogenides have been attracting much scientific interest due to the demand for replacing heavy metal-based toxic semiconductor materials including Cd, Pb, and Hg [10].
A. Mnoyan Y. Lee H. Jung S. Kim D.Y. Jeon (&) Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291, Daehak-ro, Yuseong-gu, Daejeon 305-338, South Korea e-mail: [email protected] © Springer Science+Business Media Singapore 2016 R.S. Liu (ed.), Phosphors, Up Conversion Nano Particles, Quantum Dots and Their Applications, DOI 10.1007/978-981-10-1590-8_15
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The most developed zinc chalcogenides nanocrystals (NCs) via solution-based synthetic approach are zinc selenide (ZnSe) and zinc sulfide (ZnS) NCs which have remarkable versatility and long been subjects of study in science and engineering. Since photoluminescence (PL) of ZnS under irradiation was first discovered in 1930, [11] ZnS has been utilized to the diverse applications including light-emitting diodes (LEDs), electroluminescence (EL) devices, sensors, and solar cells. Due to its intrinsic low PL quantum yield (less than 5 %) and largest bandgap 3.72 eV (for cubic zinc-blende) among semiconductor materials, ZnS NC has been explored as a transition metal-doped NC, or shell material passivating core resulting in the type-I core/shell structured nanocrystals [12]. More recently, colloidal ZnSe-based nanocrystals have been spotlighted by many researchers as promising alternatives to C
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