Ultranarrow and Widely Tunable Mn 2þ -Induced Photoluminescence from Single Mn-Doped Nanocrystals of ZnS-CdS Alloys Abhijit Hazarika, 1 Arunasish Layek, 2 Suman De, 2 Angshuman Nag, 1 Saikat Debnath, 3 Priya Mahadevan, 3 Arindam Chowdhury, 2 and D. D. Sarma 1,4,5, * 1 Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012, India 2 Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India 3 Department of Condensed Matter Physics and Material Science, S. N. Bose National Centre for Basic Sciences, Kolkata 700098, India 4 Council of Scientific and Industrial Research-Network of Institutes for Solar Energy (CSIR-NISE), Anusandhan Bhawan, New Delhi 110001, India 5 Department of Physics and Astronomy, Uppsala University, Box-516, SE-75120 Uppsala, Sweden (Received 2 August 2012; revised manuscript received 22 February 2013; published 28 June 2013) Extensively studied Mn-doped semiconductor nanocrystals have invariably exhibited photolumines- cence over a narrow energy window of width 150 meV in the orange-red region and a surprisingly large spectral width ( 180 meV), contrary to its presumed atomic-like origin. Carrying out emission mea- surements on individual single nanocrystals and supported by ab initio calculations, we show that Mn PL emission, in fact, can (i) vary over a much wider range ( 370 meV) covering the deep green—deep red region and (ii) exhibit widths substantially lower ( 60–75 meV) than reported so far, opening newer application possibilities and requiring a fundamental shift in our perception of the emission from Mn-doped semiconductor nanocrystals. DOI: 10.1103/PhysRevLett.110.267401 PACS numbers: 78.67.Hc, 61.72.uj, 71.55.Gs, 73.22.f Doping of semiconductor nanocrystal hosts with a localized, often magnetic and essentially atomic-like im- purity constitutes one of the most active research fields, yielding a wide range of interesting properties [1–12]. One of the most intensely pursued properties from such systems is the extraordinarily bright photoluminescence (PL) of a variety of Mn-doped semiconductor nanocrystals (NCs) [13–23]. There are two distinct classes of semiconductor NCs with contrasting PL properties, namely doped and undoped ones. The undoped ones possess size-dependent tunable excitonic emission, which, however, has draw- backs due to self-absorption of emission by other NCs in the ensemble [24] and its long-term stability [25]. Both these problems are avoided in the alternate route of dopant emission, where the energy following the electron-hole excitation in the host is transferred to a dopant ion and the deexcitation involves only dopant states [13,14]. However, the involvement of the atomic-like Mn d states implies that the emission wavelength of Mn is relatively unaffected by the size of the semiconductor host and, therefore, missing the important functionality of tunability available from excitonic emission. Experimentally, it has indeed been seen that Mn emission has very limited tuna- bility, typically <150 meV, around 585 nm independent of the size and, to a large extent, even the chemical nature of the host NC [18,26–28]. Another intriguing aspect is that Mn d emission has been invariably found to have a large spectral width ( 200–250 meV), incompatible with an atomic-like 4 T 1  6 A 1 Mn emission. This large width has been explained in terms of coupling of Mn d levels to the vibrational structure of the host [29], though this spectral width is considerably larger than even that ( 120–140 meV) found in Mn-doped bulk semiconduc- tors, like ZnS [1,5]. It should be noted that these two well- accepted beliefs, namely the lack of substantial tunability of Mn emission wavelength and the inevitable presence of a large spectral width due to a fundamental quantum mechanical process, place serious limits on the general usefulness of Mn dopant emissions from nanostructured host materials. The importance of the present work based on spatially resolved experiments dispels both these long- standing myths, providing direct evidence of wide ranging colors from Mn emission in a semiconductor NC host and of spectral linewidths that are ultranarrow (60–75 meV), lower by a factor of about three from the narrowest width obtained in ensemble measurements. We discuss the origin and implications of these findings with the help of exten- sive ab initio calculations. Among the most studied Mn-doped chalcogenide NCs, CdS is not suitable for the present investigation, since surface emissions from CdS host NCs often overlap the Mn emission [24], causing avoidable complications. Additionally, the band gap of ZnS NCs, being in the UV region, is not compatible with our excitation source. In order to avoid these difficulties, we doped 0.9% Mn in Zn 0:25 Cd 0:75 S alloyed NC hosts having wurtzite structure and an average diameter of 5.5 nm with large enough band gap of 465 nm (see Figs. S1, S2, and S3 in the Supplemental Material (SM) [30] for standard character- izations of the sample), compatible with our experimental PRL 110, 267401 (2013) PHYSICAL REVIEW LETTERS week ending 28 JUNE 2013 0031-9007= 13=110(26)=267401(5) 267401-1 Ó 2013 American Physical Society