The Big Red Shift of Photoluminescence of Mn Dopants in Strained CdS: A Case Study of Mn-Doped MnS-CdS Heteronanostructures Taisen Zuo, †,§ Zhipeng Sun, †,§ Yuliang Zhao, † Xiaoming Jiang, ‡ and Xueyun Gao* ,† Lab for Biomedical Effects of Nanomaterials and Nanosafety and Beijing Synchrotron Radiation Laboratory, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, P. R. China Received January 8, 2010; E-mail: gaoxy@ihep.ac.cn Transition-metal-doped nanosemiconductors have attracted more attention in the past few years because of their interesting optical properties. 1-5 For example, the d electronic states of Mn ions act as luminescent centers while interacting strongly with the s and p electronic states of the host nanocrystal into which external electronic excitation is directed, and an orange photoluminescence is produced therein. 3-5 However, when Mn-doped nanocrystals are utilized in bioimaging, longer-wavelength emissions are more desirable. 6 To date, no approaches for achieving the red emission of Mn dopants in situ have been reported, although their emission could shift to lower energies when gigapascal-level hydrostatic pressure is applied to them in a diamond anvil cell because the external high pressure makes the crystal-field splitting of the Mn d orbitals become narrower. 7 To overcome the disadvantage of hydrostatic pressure via a diamond anvil cell, we explored a new way to introduce lattice strain to Mn dopants in host nanocrystal via heteronanostructure growth, where Mn-doped CdS nanocrystals crystallize onto the surface of MnS nanoparticles. Because of the difference between the lattices of MnS and CdS, in situ lattice compression of CdS occurs. Such compressions result in lattice strain in CdS, as would occur with external hydrostatic pressure, and further change the emission of Mn dopants to a longer wavelength. In our studies, such an approach was able to change the emission of Mn dopants from orange to red, meaning that gigapascal-level stress occurred in Mn dopants in MnS-CdS heteronanostructures in situ. 7 The Mn-doped MnS-CdS heteronanostructures, pristine MnS and CdS nanoparticles, and Mn-doped CdS were synthesized via facile metal-organic reactions (see section S1 in the Supporting Information). In order to observe the lattice compression of CdS in MnS-CdS heteronanostructures, high-resolution transmission electron microscopy (HRTEM) was used to study the lattice fringes of MnS-CdS, MnS, and CdS nanoparticles (see section S2). Figure 1a shows the pristine MnS nanoparticles; the upper-left inset shows nanoparticles with diameters of 2-3 nm. Fast Fourier transform (FFT) analysis was conducted on a selected area of a single nanoparticle in Figure 1a, and the results are displayed in the upper- right inset. The FFT clearly showed that the d spacings of (110) and (002) are 0.200 and 0.323 nm, respectively, which are in good agreement with those of hexagonal MnS with the wurtzite structure (see JCPDS card no. 41-1049). HRTEM images and FFT data of single Mn-doped MnS-CdS heteronanostructures are displayed in Figure 1b. FFTs of selected areas located in the lower and upper parts of the MnS-CdS image are displayed in upper-left and upper- right insets, respectively. In the lower part of the MnS-CdS image, the d spacings of (100) and (002) are 0.352 and 0.325 nm, respectively, which match those of hexagonal MnS with the wurtzite structure (see JCPDS card no. 41-1049). Notably, the d spacing of 0.325 nm for this (002) is similar to the value of 0.323 nm for pristine MnS in Figure 1a. In the upper part of the MnS-CdS image, the d spacings of (100) and (002) are 0.357 and 0.335 nm, respectively, which match those of hexagonal CdS with the wurtzite structure (see JCPDS card no. 65-3413), and the (100) d spacing of 0.357 nm is the same as that of pristine CdS displayed in Figure 1c. HRTEM observations of single MnS-CdS nanocrystals showed no defects in the lattice fringes in MnS-CdS heteronanostructures although there is a lattice mismatch between bulk CdS and MnS, implying that the larger d spacing of CdS was compressed to match † Lab for Biomedical Effects of Nanomaterials and Nanosafety. ‡ Beijing Synchrotron Radiation Laboratory. § These authors contributed equally. Figure 1. (a-c) HRTEM images and (insets) FFT patterns of (a) pristine MnS, (b) Mn-doped MnS-CdS, and (c) pristine CdS. (d) EDS data for Mn-doped MnS-CdS. Figure 2. (a) XRD patterns of Mn-doped MnS-CdS. (b) Illustrations of the compression of the d spacing of CdS at the MnS-CdS interface. Published on Web 04/28/2010 10.1021/ja100136a  2010 American Chemical Society 6618 9 J. AM. CHEM. SOC. 2010, 132, 6618–6619