Optically Bi-functional Hetero-Structured Nanocrystals. Supporting Information

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1 Optically Bi-functional Hetero-Structured Nanocrystals Angshuman Nag, Akshay Kumar, P. Prem Kiran, Ұ S. Chakraborty, G. Ravindra Kumar and D.D. Sarma,,* Supporting Information Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 5600, India. Ұ Advanced Centre of Research in High Energy Materials, University of Hyderabad, Hyderabad , India. Centre for Advanced Materials, Indian Association for the Cultivation of Science, Kolkata-70003, India. Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai , India.

2 Synthesis: A mixture of CdO (0.386 mmol), ZnO (0.609 mmol), oleic acid (OA, mmol) and technology grade octadecene (ODE, 0 ml) was heated in a 5 ml three-necked round-bottom flask and maintained at 300 O C. A solution with various compositions of Se (0.0, 0.08 and 0.3 mmol) and S (.9 mmol) in trioctylphosphine (TOP,.0 ml) was injected in the CdO/ZnO/OA/ODE solution with vigorous stirring. Color of the reaction mixture changes immediately and the reaction was stopped after minute. Inert atmosphere has been maintained throughout the whole process until the final reaction mixture is cooled to room temperature. The resulting nanocrystals were tracted and washed by adding butanol and methanol followed by centrifugation and drying under vacuum. The obtained powder can be re-dissolved in non-polar solvents like n-heptane, toluene etc. Fitting of Photoelectron Spectra: Photoelectron spectroscopy was performed on sample-i with 365.8, 60., 73. and ev photon energies using synchrotron radiation source as well as Al Ka photon source. We have studied the S p and Se 3p core levels that fall on the same binding energy range. S p show a spin-orbit split doublet with separation of. ev and with a constant intensity ratio of : between p 3/ and p / ; similarly, Se 3p also show a spin-orbit splitting with a separation of 5.8 ev and with a constant intensity ratio of : between 3p 3/ and 3p /. Lorentzian functions were used for lifetime broadening of each component of the spectra, which are then convoluted with a Gaussian function to account for the instrumental resolution. We varied the wihs of the two functions as well as peak positions of the component spectra constraining the intensity ratio of the spin-orbit split doublet to get the best fit to the perimental spectra using least-squared-error analysis. Lorentzian function is kept same for the same spectral component at all the four photon energies. On the other hand instrumental broadening is same for all the components for a given photon energy, so the Gaussian function was kept same for all components during the fitting of spectra recorded at fixed photon energy.

3 Fig. S: Powder x-ray diffraction (XRD) patterns for sample-i, II and III. Intensity (a. u.) Sample-I Sample-II Sample-III CdS bulk CdSe bulk θ o 3

4 Fitting of open aperture Z-scan data: E (a) p e (b) n LUMO 0 E g Se HOMO (S,D)3/ (S,D)3/ (P,F)3/ 3(S,D) 3/ (P,F) 3/ S/ Fig. S: Schematic representation of (a) possible optical transitions in the nanocrystallline system (b) simplified model to quantify the processes. We used a spectroscopic model that takes into account both intraband cited state absorption (ESA) and interband two photon absorption (TPA). Under the resonant condition, Fig. S (a) shows the possible optical transitions in the nanocrystalline system considering the mixing of valence bands and Fig. S (b) shows the simplified quantitative model, where all the possible single-photon interband citon transitions including HOMO ( ) LUMO ( ) contribution with a cross-section of ; contributions from all the intraband LUMO ( ) higher electron states ( n ) transitions leading to ESA with a cross-section and two TPA contribution involving n transition with a cumulative TPA co-efficient b were included. Rate equations were obtained after denoting the population in level i by n i and is written below. 4

5 dn dn dn n I n = - I n - + I n I n n = - - I n I nn = + - () nn + (3) () The intensity transmitted through the sample is given by di dz = - I n - I n - I (4) where,, is the energy of the citation photon and is the cumulative TPA co-efficient from P e (S,D) 3/ and S e (P,F) 3/ transitions. I is the intensity as a function of r, t, and z of the Gaussian beam. These differential equations were solved numerically followed by a least square fit of the perimental data to obtain, and.,3 The TPA cross-section, PA = ( n) ; where n is the number density of the dots in the solution. 4 References:. Savitski, V. G.; Malyarevich, A. M.; Demchuk, M. I.; Yumashev, K. V.; Raaben, H.; Zhilin, A. A. J. Opt. Soc. Am. B. 005,, Kiran, P. P.; Reddy, D. R.; Maiya, B. G.; Dharmadhikari, A. K.; Kumar, G. R.; Rao, D. N. Opt. Commun., 005, 5, Srinivas, N. K. M. N.; Rao, S.V.; Rao, D.N. J. Opt. Soc. Am. B., 003, 0, He, G. S.; Bhawalkar, J. D.; Zhao, C. F.; Prasad, P. N. Appl. Phys. Lett., 995, 67,