Doubly Doped Nanocrystals DOI: 10.1002/anie.201100464 Bright White-Light Emitting Manganese and Copper Co-Doped ZnSe Quantum Dots** Subhendu K. Panda, Stephen G. Hickey,* Hilmi Volkan Demir, and Alexander Eychmüller White-light emission (WLE) from semiconductor nanostruc- tures is presently a research area of intense interest, especially where the primary objective is to replace conventional light sources in order to minimize energy costs and therefore global energy consumption for lighting. [1–8] Presently the general methods to achieve white-light emission are either by coating a yellow phosphor or by combining green and red phosphors on a background consisting of a blue-light emitting diode (LED) or by employing nanocrystals (NCs) of the three primary colors (red, green, blue) using multilayer structures in LEDs. However, when one simply mixes these nanocrystal quantum dots (QDs) of different colors together to generate white light, the efficiencies are often observed to decrease due to the re-absorption of light and subsequent undesired energy transfer (ET). This may lead to undesirable changes in the chromaticity coordinates and photometric performance due to the different relative temporal stabilities of the compo- nents. Hence the use of a single-emitting component offers many advantages over multiple component systems for white- light emitting sources such as LEDs, amongst which are: greater reproducibility, low cost preparation, ease of modifi- cation, and simpler fabrication processes. Therefore, it is of great importance for many applications to find high-quality single source white-light emitters through low-cost chemical synthesis approaches that will allow the production of white light while meeting the needs of industry, such as satisfactory Commission International dEclairage (CIE) coordinates. One route that offers the possibility by which such materials may be accessed is that of the colloidal synthesis of doped semiconductor nanocrystals, which has already proven itself to be an interesting field for future nano- technologies as it can presently provide highly efficient emission sources for various applications. [9–12] Although various attempts have been made towards the growth of doped QDs in solution, it still remains a challenge to dope all of the nanocrystals present in the reaction mixture simulta- neously with the different dopants, as the host matrix tends to expel the dopant ions from the internal crystal lattice to the surface, in a sort of “self-purification” process. [13] Therefore, even in the most favorable cases of the dopant ions having the same valence state and similar ionic radius as those of the corresponding host, successful doping remains difficult to achieve by the simple addition of a small amount of dopant precursors during the synthesis of the host NCs. To overcome this, a number of doping strategies, such as nucleation–doping and growth–doping, where the doping is decoupled from the nucleation and/or growth, provide ample possibilities to selectively introduce dopants at desired positions within the host materials to generate different emission centers inside of a single quantum dot. [14] Usually, in a Mn 2+ -doped ZnSe system there is a dominant yellow/orange emission present at 585 nm which results from the 4 T 1 – 6 A 1 transition of the Mn 2+ impurity excited by energy transfer from the host lattice. [15, 16] Therefore, if one can supply a source of blue and/or green emission within such a system, then white-light emission is likely to result. In fact, Mn 2+ -doped CdS [17] and ZnS [18, 19] NCs with white-light emission have been successfully prepared by the combination of the orange emission of the Mn 2+ impurity and the blue and/or green emission of the surface defect states of the NCs. There are also a number of reports which describe the synthesis of semiconductor NCs with white-light emission such as “magic-sized” CdSe NCs, [1] trap-rich CdS-QDs and onion-like CdSe/ZnS/CdSe/ZnS-QDs, [2] alloyed Zn x Cd 1Àx Se quantum dots, [3] ZnS:Pb, [4] ZnS incorporated into porous Silicon, [5] and ZnSe. [6] However, all the above-mentioned systems rely on the manipulation of surface-state emission from the NCs, which is notoriously difficult to control and/or reproduce and, in addition, the temporal stability of these states varies with the environmental conditions in a manner which is presently still not fully understood. Also the intrinsic toxicity of cadmium and lead sheds a doubt on the future applicability of these NCs, particularly in view of recent environmental regulations. Herein we report a method which overcomes these difficulties through the successful synthesis of doubly doped QDs using a versatile hot-injection colloidal synthesis to produce Mn and Cu co-doped ZnSe QDs (Cu:Mn-ZnSe), where white-light emission can be readily realized and its characteristics tuned. The two dopants have been introduced into the host material in a two-step process such that the dopants retain their individual emission properties which cover most of the visible spectral range. Also we demonstrate versatility of the tuning of the white-light generation with [*] Dr. S. K. Panda, Dr. S. G. Hickey, Prof. A. Eychmüller Physical Chemistry/Electrochemistry, TU Dresden Bergstrasse 66b, 01062 Dresden (Germany) Fax: (+ 49) 351-463-37164 E-mail: s.hickey@chemie.tu-dresden.de Prof. H. V. Demir Department of Electrical and Electronics Engineering, Department of Physics, UNAM—National Nanotechnology Research Center and Institute of Materials Science and Nanotechnology, Bilkent Uni- versity, Ankara 06800 (Turkey) [**] S.K.P. is grateful for a research fellowship provided by the Alexander von Humboldt Foundation. S.G.H. and H.V.D. acknowledge financial support through the FP7 Network of Excellence “Nano- photonics4Energy” and BMBF/TUBITAK joint project No. TUR09/ 001 and TUBITAK EEEAG No. 109E002. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/anie.201100464. Communications 4432  2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. Int. Ed. 2011, 50, 4432 –4436