SUPPORTING INFORMATION

Transcription

1 SUPPORTING INFORMATION Type-II Core/Crown CdSe/CdTe Semiconductor Nanoplatelets Silvia Pedetti 1,2, Sandrine Ithurria 2, Hadrien Heuclin 1, Gilles Patriarche 3, Benoit Dubertret 2 1 Nexdot, 10 rue Vauquelin Paris, France. 2 Laboratoire de Physique et d Etude des Matériaux, ESPCI-ParisTech, PSL Research University, Sorbonne Université UPMC Univ Paris 06, CNRS, 10 rue Vauquelin Paris, France. 3 Laboratoire Photonique et Nanostructures, CNRS, Marcoussis, France. Fluorescence excitation spectra at different wavelength: λ max, λ max +1/2, λ max -1/2. 1,2 1,0 SP195CdSeCdTe PLE630 PLE 656 PLE 680 PL/PLE (a.u.) 0,8 0,6 0,4 0, Figure S1 Excitation spectra of 4 MLs thick CdSe/CdTe core/crown NPLs recorded fixing the emission wavelength at 630 nm, 656 nm and 680 nm. The three spectra reveal the same features and the overlap of the curve indicates a size monodispersion of the NPLs present in solution. S1

2 Core/crown structure confirmed by high resolution TEM and intensity profile CdTe core CdSe core 5.4 nm CdTe core 4.5 nm 5.2 nm 15.1 nm Figure S2 a) HR HAADF image of CdSe/CdTe core/crown NPLs with 4 MLs thickness. In the bottom profile intensity of the area delimited by the blue rectangle is reported, showing an higher intensity for the external region of the NPL. S2

3 Optical features of 4 MLs CdSe/CdTe core/crown NPLs abs/pl/ple (a.u.) 2 1 PL CdSe/CdTe NPLs 4 MLs ple at667 ple at634 ple 700 Abs CdSe/CdTe NPLs 4 MLs Figure S3 Absorption, emission and excitation spectra corresponding to the final CdSe/CdTe core/crown NPLs of 4 MLs product, after 15 min of reaction, reported on figure 3a in the main text. Absorption, emission and excitation spectra of CdSe/CdTe core/crown NPLs corresponding to figure 3a in the main text Optical Density (a. u.) a) 4 MLs CdSe/CdTe core/crownpls * * * at 235 C t=70 min at 235 C t=40min at 235 C t=20 min at 235 C t=5 min Intensity (a.u.) SP 235 C At 5 min at 20 min at 40 min at 70 min at 235 C t= Figure S4 Absorption (a) and emission ( spectra recorded during the synthesis of 4 MLs CdSe/CdTe core/crown NPLs. The synthesis was performed mixing in the reaction flask, CdSe core NPLs [0.4] µm, acid oleic (0.75 mmol), Cd(Prop) 2 (0.5 mmol) in ODE and adding mmol of Te and mmol of TOP at different reaction time at T=235 C. In the graphic on the left side the stars indicate spectra recorded after each addition. S3

4 Crown extension a) Figure S5 TEM images of 4 MLs CdSe/CdTe core/crown NPLs with different lateral extension. Respectively a) and correspond to the blue and red spectra in Figure 3b (left side) in the main text. The averaged lateral size increases from 22 nm x 10 nm in a) to 26 nm x 12 nm in. Lateral extension on 3 MLs CdSe/CdTe core/corwn NPLs a) CdSe CdTe PL PLE at 567 abs at 6' at 3' abs/pl/ple (a.u.) Optical Density (a;u.) at 15' at 2' at 1' Figure S6 a) Absorption spectra recorded during the CdTe lateral extension on CdSe core NPLs of 3 MLs thickness. The first excitonic peak corresponding to the CdSe core NPLs and the CdTe crown are marked. Pholotuminescence, PL excition and absorption spectra relative to the final product CdSe/CdTe core/crown NPLs 3 MLs thick. The PLE shows that the emission is not due to other species. S4

5 CdTe NPLs secondary nucleation and purification of CdSe/CdTe core/crown NPLs Figure S7 TEM images of CdSe/CdTe core/crown NPLs of 4 MLs thickness and the CdTe NPLs of 3 MLs thickness. The ratio CdTe/CdSeCdTe is 500 nm/20 nm= 25. This difference in the lateral size allows a complete separation of the secondary nucleation from the core/crown product. EDX probe resolution a) Figure S8 a) HAADF STEM image of a single NPL after EDX analysis. The contamination trace is visible and the intensity profile ( shows a resolution of ca 1 nm for the EDX probe. S5

6 Stability of NPLs in presence of TOP without or with cadmium salts Absoprtion Intensity (a.u.) 0,8 0,6 0,4 0,2 a) CdSe NPLs, t=0 CdSe NPLs after 5' heating at T=235 C in presence of TOP, t=5' Absorption Intensity (a.u.) 1,0 0,8 0,6 0,4 0,2 CdSe NPLs, t=0 CdSe NPLs after 5 min heating at 235 C in presence of carboxylates, t=5' Fluorescence Intensity (a.u.) CdSe NPLs t=0 CdSe NPLs t=5' Figure S9 a) Absorption spectra recorded on CdSe NPLs 4 MLs before and after heating at 235 C in presence of TOP. Absorption and fluorescence spectra of CdSe NPLs before and after heating at 235 C in presence of TOP, Cd(myr) 2 and Cd(OAc) 2. S6

7 Spectral features and TEM images of 4 MLs CdSe/CdTeSe core/alloyed-crown NPLs 1,5 a) CdSe/CdTeSe PL CdSe/CdTeSe PLE CdSe/CdTeSe abs Abs/PL/PLE (a.u.) 1,0 0,5 1, prod ple prod prec Abs/PL/PLE (a.u.) 0,5 c) PL PLE Abs Abs/PL/PLE (a.u.) 1,0 0, Figure S10 a) UV-Vis, PL and PLE spectra of CdSe/CdTeSe core/alloyed-crown NPLs correspondent to the diffractogram c) of Figure 5 of the main text. On the right TEM image. UV-Vis, PL and PLE spectra of CdSe/CdTeSe core/alloyed-crown NPLs. Related photoluminescence lifetime is reported in Figure 6 in the main text (decay c). On the right TEM image c) UV-Vis, PL and PLE spectra of CdSe/CdTeSe core/alloyed-crown NPLs with gradient interface. Related photoluminescence lifetime is reported in Figure 6 in the main text (decay d). On the right TEM image. S7

8 a) Fluorescence decay for thick CdSe/CdTe core crown NPLs MLs CdSe/CdTe core/crown NPLs Intensity (counts) Residual Time (ns) Intensity (counts) SP MLs CdSe/CdTe core/crown NPLs a) ns, 21.76% ns, 57.83% c) 1058 ns, 20.42% t avr= ns 10 Residual Time (ns) Figure S11 a) PL decay curve with three-exponential fit of 5 MLs CdSe/CdTe core/crown NPLs, emitting at 730 nm. It corresponds to the decay a) in figure 6 of the main text. At the bottom of the figure the residuals are reported. The decay constants are: 265 ns (41.21% of amplitude), 659 ns (42.94% of amplitude) and µs (15.84% of amplitude). PL decay curve with three-exponential fit of 4 MLs CdSe/CdTe core/crown NPLs, emitting at 656 nm. At the bottom of the figure the residuals are reported. The decay constants are: ns (21.76 % of amplitude), ns (57.83 % of amplitude) and µs (20.42 % of amplitude). S8

9 Method and material Syntheses Preparation of 3 MLs CdSe NPLs In a 100 ml three neck flask 480 mg of Cd(OAc) 2 (1.8 mmol) and 900 µl of oleic acid (2.70 mmol) are mixed in 30 ml of ODE. The mixture is degassed under vaccum at 80 C for 1 hour and then, under Ar flow, the temperature is set at 170 C. When the temperature reaches 170 C, 300 µl of TOPSe 1 M are swiftly introduced into the flask. After 15 minutes the reaction is quenched by addition of 2 ml of OA and the mixture is rapidly cooled down at room temperature. The NPLs are purified by selective precipitation adding 30 ml of hexane and 30 ml of ethanol and performing a centrifugation at 6000 rpm for 10 minutes. Then the surnatant is discarded and the precipitate is redissolved in 10 ml of hexane. Preparation of 5 MLs CdSe NPLs In a 100 ml three neck flask 340 mg of Cd(myr) 2 (0.6 mmol) is mixed in 28 ml of ODE. The mixture is degassed under vaccum at room temperature for 20 minutes and then, under Ar flow, the temperature is set at 250 C. When the temperature reaches 250 C, 24 g of Se powder (0.3 mmol) in 2 ml of ODE are swiftly introduced into the flask. After 30 seconds 300 mg of Cd(OAc) 2 are added to the mixture. The reaction is quenched after 7 minutes with addition of 2 ml of OA and the mixture is rapidly cooled down at room temperature. The NPLs are purified by selective precipitation adding 30 ml of hexane and 40 ml of ethanol and performing a centrifugation at 6000 rpm for 10 minutes. Then the surnatant is discarded and the precipitate is re-dissolved in 10 ml of hexane. Preparation of 3 MLs CdSe/CdTe core/shell NPLs 3 MLs CdSe NPLs (2.5 ml) are precipitated with ethanol, re-dispersed in 10 ml of ODE and transferred into a threeneck flask. Te powder (0.07 mmol) is added and the mixture is degassed under vacuum at room temperature for 30 minutes. Then, under Ar flow, the temperature is risen and at 200 C and 130 mg of Cadmium propionate (0.5 mmol) are swiftly added. 30 seconds after the addition, a mixture of OA (1.12 mmol, 355 µl), TOP (0.1 ml, 0.22 mmol) in 3 ml of ODE, is continuously injected with an injection rate of 36 ml/h. At t = 15 min, 1.5 ml of OA is added and the mixture is rapidly cooled down at room temperature. The core/crown NPLs are purified by selective precipitation with hexane (10 ml) and ethanol (5 ml) and centrifugation at 5000 rpm for 10 minutes. The precipitated is finally dispersed in toluene. Preparation of 4 MLs CdSe/CdTe core/shell NPLs Into a three-neck flask behenic acid (255 mg, 0.75 mmol) and cadmium propionate (130 mg, 0.5 mmol) were added to 5 ml of ODE. The mixture is degassed under vacuum at 60 C for 1 hour. Meanwhile 4 ml of 5 MLs CdSe NPLs previously synthesized were precipitated in ethanol and re-dispersed in 4 ml of ODE. Then, under Ar flow, the temperature of the reaction mixture was risen at 200 C and 5 MLs CdSe NPLs in ODE were swiftly injected. Successively, at T=240 C, Te powder (9 mg) was added followed by continuous injection of TOP (80 µl, 0.18 mmol) in 1 ml of ODE with injection rate of 40 ml/h. At t = 15 min, 1 ml of OA is added and the mixture is rapidly cooled down at room temperature. The core/crown NPLs are purified by selective precipitation with hexane (10 ml) and ethanol (5 ml) and centrifugation at 5000 rpm for 10 minutes. The precipitated is finally dispersed in toluene. S9

10 Quantum Yield measurement The quantum yield was measured by comparative method using Rhodamine 6G as reference fluorophore, with a tabulated QY of in ethanol when excited at 480 nm. For each measurement, the sample absorption was measured at several concentrations and the emission intensity was recorded using the same excitation wavelength for the samples and the fluorophore. The absorption was always taken < 0.1 at the excitation wavelength. We then used the formula: 2 Where: And n = solvent refractive index ɸ = ɸ = To verify the validity of the results, the QY of a demonstrative sample (4 MLs CdSe/CdTe core/crown) was doublechecked using Rhodamine B as reference (QY is 0.70 in ethanol when excited at 510 nm). 3 The QY measured with Rhodamine 6G is 0.62 while the QY measured with Rhodamine B is (1) Kubin, R. F.; Fletcher, A. N. J. Luminesc. 1982, 27, 455. (2) Lakowicz, J. R.; Second Edition ed.; Press, K. A. P., Ed.; : New York, (3) F. López Arbeloa; Ojeda, P. R.; Arbeloa, I. L. J. Luminesc. 1989, 44. S10