Supporting Information

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1 Supporting Information High Quality Ultrathin Lanthanide Selenide Nanostructures with Dual Modal Functionalities Na Li, Lei Qin, Hongyang Zhao, Zhengqing Liu, Xinyu Zhang, Yanzhen Zheng and Yaping Du* Experimental Section Chemicals. oleylamine (OM, 70 %), oleic acid (OA, 90 %) and octylamine (OTA, 99 %) were obtained from Aldrich and used without further purification. The selenium power (Se, >99.5 %), selenium dioxide (SeO 2, 99.8%), europium(iii) acetate (Eu(CH 3 COO) 3, 99.9 %), gadolinium (III) acetate hydrate (Gd(CH 3 COO) 3 6H 2 O, 99.9 %), yttrium (III) chloride hexahydrate (YCl 3 6H 2 O, 99.9 %),ytterbium (III) acetate hydrate (Yb(CH 3 COO) 3 6H 2 O, 99.9 %), europium (III) nitrate hexahydrate (Eu(NO 3 ) 3 6H 2 O, 99.9 %) were purchased from Alfa Aesar and used as received. Absolute ethanol, methanol, N, N-dimethyl formamide and cyclohexane were of analytical reagent grade. Instrumentation TEM images were acquired by a Hitachi HT-7700 transmission electron microscope (TEM, Japan) operating at 100 kv. High-resolution TEM (HRTEM) micrographs were obtained with a Philips Tecnai F20 FEG-TEM (The USA) operated at 200 kv. Samples for TEM analysis were prepared by drying a drop of cyclohexane solution containing the nanocrystals on the surface of a carbon-coated copper grid. The X-ray diffraction XRD patterns were obtained using a Rigaku D/MAX-RB with monochromatized Cu Kα radiation (λ= Å) in the 2 ranging from 20 to 80. Infrared spectra were recorded on a Nicolet 6700 FT-IR spectrometer. UV-vis absorption spectra were measured on a Perkin-Elmer Lambda 35UV-vis spectrophotometer. Photoluminescence (PL) spectra were recorded on a Hitachi F-4600 spectrofluorophotometer at room temperature. Magnetic susceptibility measurements were performed with a Quantum Design MPMS-XL7 SQUID. The photoluminescent quantum yields (QYs) of ultrathin EuSe NWs were determined by comparing the integral emission intensity of the dilutions of the concentrated nanocrystals dispersion in cyclohexane with that of quinine sulfate in sulfuric acid solution at an excitation of 350 nm with collection between 360 and 600 nm at room temperature. Experimental Section Synthesis of lanthanide selenides (LnSe) (Ln = Eu, Gd) nanowires. For the synthesis of LnSe (Ln = Eu, Gd) sample, lanthanide (Ln(CH 3 COO) 3 xh 2 O, 0.5 mmol) and selenium (Se, g, 1 mmol) were dispersed in a mixture of 9 ml of absolute ethanol in a 20 ml Teflon-lined autoclave, into which oleylamine (OM, 4.5 ml) and oleic acid (OA, 4.5 ml) mixtures were added, the whole system was stirred for 30 min, affording a homogeneous solution. The autoclave was sealed and heated at 180 C for 72 h in an oven, and then cooled down to room temperature. After being cooled naturally, the nanocrystals were precipitated by adding an excess amount of absolute ethanol and separated from the solution by centrifugation (9000 rpm, 10 min), followed by drying in an oven at 60 C. The as-prepared dried nanocrystals could be easily dispersed in various 1

2 nonpolar organic solvents such as cyclohexane and toluene. The yields of all the obtained nanocrystals were about 90 %. Synthesis of EuSe nanorods-short. The synthetic procedure was similar to that of EuSe nanowires, except that europium(iii) acetate hydrate (Eu(CH 3 COO) 3, g, 0.5 mmol) and selenium (Se, g, 1 mmol) were dissolved in a mixture of 12 ml of octylamine and 6 ml of oleic acid with vigorous stirring, affording a homogeneous solution. It was sealed in a 20 ml capacity Teflon-lined autoclave and heated at 180 C for 72 h. Synthesis of EuSe nanorods-long. The synthetic procedure was similar to that of EuSe NWs, except that 0.5 mmol of Eu(CH 3 COO) 3 and 1 mmol of selenium were dispersed in a mixture of 14 ml of octylamine and 4 ml of oleic acid with vigorous stirring. After the slurry was further stirred for 30 min, it was sealed in a 20 ml capacity Teflon-lined autoclave and heated at 180 C for 72 h. Synthesis of ultrathin YSe nanowires. The synthetic procedure was similar to that of EuSe NWs, except that 0.5 mmol of YCl 3 6H 2 O and 1 mmol of selenium were dispersed in a mixture of 14 ml of octylamine and 4 ml of oleic acid with vigorous stirring. After the slurry was further stirred for 30 min, it was sealed in a 20 ml capacity Teflon-lined autoclave and heated at 180 C for 72 h. Synthesis of ultrathin YbSe nanowires. The synthetic procedure was similar to that of EuSe NWs, except that 0.5 mmol of Yb(CH 3 COO) 3 6H 2 O and 1 mmol of selenium were dispersed in a mixture of 12 ml of octylamine and 6 ml of oleic acid with vigorous stirring. After the slurry was further stirred for 30 min, it was sealed in a 20 ml capacity Teflon-lined autoclave and heated at 180 C for 72 h. Figure S1. Powder XRD pattern of the as-prepared EuSe nanocrystals (cubic, space group: Fm3m, JCPDS: , a = b = c = Å). Namely, EuSe NPs with ~5 nm, ultrathin EuSe NWs with diameter of ~2.5 nm, EuSe NRs-short with diameter of ~5 nm and length of ~50 nm, and EuSe NRs-long with diameter of ~20 nm and length of ~500 nm. 2

3 Figure S2. The energy dispersive X-ray analysis (EDAX) spectra of ultrathin EuSe NWs. As demonstrated from EDAX analysis, the atomic ratio of Eu:Se was calculated to be 1:0.7, which was in agreement with the stoichiometric ratio of EuSe compounds. 3

4 Figure S3. The unit cell and modeling structure of the ultrathin EuSe NWs in different viewing direction. (a) The ultrathin EuSe NWs unit cell, with its atom layer is Eu-[Se-Eu-Se]-Eu and the calculated lattice constants of a = b = c = Å. (b) A cross section of ultrathin EuSe NWs and the modeling structure viewed from the 111 direction. (c) The modeling structure of ultrathin EuSe NWs viewed from the 110 direction. The diameter of a single ultrathin EuSe NWs is ~2.5 nm and the diameter of the unit cell is 0.62 nm, in addition to this, and the existence of OM and OA result in the surface atom layer of Eu 2+ cations, so the atom layer of a modeling single NC from 110 direction is Eu-Se-Eu-Se-Eu, and the thickness of the modeling structure is ~2.5 nm, which is match well with the real measured diameter from HRTEM image. 4

5 Figure S4. (a) (c) Different magnification TEM images of ultrathin EuSe NWs. (d) TEM image showing that the ultrathin EuSe NWs were broke under electron beam. 5

6 Figure S5. Fourier transform infrared (FTIR) spectra (Nicolet 6700) of oleylamine, oleic acid, and as-prepared ultrathin EuSe NWs dispersed in cyclohexane. The presence of acyclic C H stretching at 2919 and 2849 cm 1 indicate the co-existence of oleic acid and oleylamine. The peaks at 1527 and 1450 cm 1 are assigned to C=O stretch and carboxylate (COO ) stretch, implying the COO ligand exists on the NWs surface, and the three sharp peaks at 719 and 967 cm 1 are indexed to C N stretch of oleylamine. Based on the FTIR analysis of ultrathin EuSe NWs, it is confirmed that ultrathin NWs are possibly coated by two kinds of organic molecules, oleylamine and oleic acid [1,2]. 6

7 Figure S6. The X-ray photoelectron spectroscopy (XPS) of (a) Eu3d, (b) Se3d, (c) O1s for the ultrathin EuSe NWs. Ultrathin EuSe NWs put in air for one month. Figure S6 showed the XPS signals taken from the Eu 3d, Se 3d, and O 1s regions of ultrathin EuSe NWs. The peaks at and ev in Figure S6a were assigned to the Eu 3d 3/2 and Eu 3d 5/2 of Eu 3+ ions, while the peaks at and ev were assigned to the Eu 3d 3/2 and Eu 3d 5/2 of Eu 2+ ions, suggesting that the Eu 2+ ions on the surface was partly oxidized to Eu 3+ ions while exposing in air, which was consistent with the reported results. [3] As seen from Figure S6b, the peaks at 55.4 ev could be assigned to the binding energies of ionic metal selenide 3d. The peak shown in Figure S6c located at ev could be assigned to the O 1s. 7

8 Figure S7. TEM images of the ultrathin EuSe NWs synthesized from the solvothermal of 0.5 mmol Eu(CH 3 COO) 3 and 1 mmol Se in absolute ethanol/oa/om (9.0 ml : 4.5 ml : 4.5 ml) at 180 C for different reaction time: (a) 12 h, (b) 24 h, (c) 48 h, and (d) 72 h. Figure S8. TEM image of the EuSe nanostructures synthesized from the solvothermal of 0.5 mmol Eu(CH 3 COO) 3 and 1.0 mmol Se in absolute ethanol/oa/om (9.0 ml: 4.5 ml : 4.5 ml = 2:1:1, the volume ratio) at 180 C for 120 h. 8

9 Note that we have conducted a series of experiments to optimize the reaction conditions for preparation of ultrathin EuSe NWs with high quality. In current synthesis, the solvents, compositions of surfactants, as well as the reaction temperature and the selenium source (such as: Se, SeO 2 ) were found to play crucial roles in the formation of high quality ultrathin EuSe NWs. For example, under the fixed experimental conditions, i.e. the precursors consisted of Eu(CH 3 COO) 3 (0.5 mmol) and Se (1.0 mmol), the reaction was fixed at 180 C for 72 h, replacing absolute ethanol with absolute methanol, only monodisperse EuSe NPs were found in the final products (Figure S9a). However, both EuSe NWs with low yields along with unshapely EuSe nanorods were obtained in the absence of absolute ethanol (Figure S9b). The ultrathin EuSe NWs with high yields were only harvested at an optimized absolute ethanol/om/oa volume ratio of 2 : 1 : 1 (9 ml : 4.5 ml : 4.5 ml) (Figure 1d and S9c). Besides the solvents, the compositions of surfactants were essential for the preparation of high quality ultrathin EuSe NWs. For instance, keeping other reaction conditions unchanged, when pure OM (9 ml) was used as the surfactant, only severely aggregated nanoplates with poor dispersibility were harvested (Figure S10a), and no discernable products were obtained when the surfactant was pure OA (9 ml) (Figure S10b). This phenomenon was due to the OA molecules could partially transformed into carboxylate anions, as shown in Equation (1). [4,5] The carboxylate anions have a higher electron-donating ability, and the formed carboxylate anions (OM : OA=1 : 1) preferential bind with the EuSe NCs than the sole OM or OA molecules. Thus, the poor electron-donating ability of pure OM led to irregular EuSe morphologies (Figure S10a). At the same time, in the pure OA, the acidity of reaction mixture was increased and inhibited the formation of EuSe NCs. [6] RCOOH + R'NH 2 RCOO - + R'NH 3 + (R = CH 3 (CH 2 ) 7 CH=CH(CH 2 ) 7, R' = CH 3 (CH 2 ) 7 CH=CH(CH 2 ) 8 ) (1) In addition, we found that both the reaction temperature and the selenium source (Se powder, SeO 2 ) remarkably affected the quality of the products. For example, we investigated the influence of temperature on the formation of EuSe NCs. The XRD pattern of the obtained EuSe NCs (Figure S11) at different temperature for 72 h showed as the reaction temperature were 100 C and 120 C, there were only the peaks of Se power, no EuSe NCs formation. As the temperature increased to 150 C, the peaks of Se totally disappeared and hardly any solid matter appeared after the precipitation treatment (Figure S12). Obviously, with the reaction temperature increased to 180 C, there were only peaks of EuSe and Eu 2 O 3, indicating the deficient energy for the formation of EuSe NCs at a relative low temperature. [7] Moreover, at the fixed reaction temperature of 180 C, replacing Se with SeO 2, only nanoparticles were obtained after final reaction (Figure S13). 9

10 Figure S9. TEM images of the obtained ultrathin EuSe NWs via solvothermal of 0.5 mmol Eu(CH 3 COO) 3 and 1.0 mmol Se in different solvents mixture at 180 C for 72 h: (a) absolute methanol/oa/om (9.0 ml: 4.5 ml : 4.5 ml) = 2:1:1, (b) OA/OM (9.0 ml : 9.0 ml) = 1:1, and (c) absolute ethanol/oa/om (9.0 ml: 4.5 ml : 4.5 ml) = 2:1:1. 10

11 Figure S10. TEM images of the obtained ultrathin EuSe NWs via solvothermal of 0.5 mmol Eu(CH 3 COO) 3 and 1.0 mmol Se in absolute ethanol solvent of different surfactants at 180 C for 72 h: (a) absolute ethanol /OM (9.0 ml: 9.0 ml) = 1:1, (b) absolute ethanol/oa (9.0 ml: 9.0 ml) = 1:1. Figure S11 Powder XRD pattern of the obtained EuSe NCs at different temperature for 72 h. 11

12 Figure S12. TEM image of the ultrathin EuSe NWs synthesized from the solvothermal of 0.5 mmol Eu(CH 3 COO) 3 and 1 mmol Se in absolute ethanol/oa/om (9.0 ml: 4.5 ml : 4.5 ml = 2:1:1, the volume ratio) at 150 C for 72 h. Figure S13. TEM image of the ultrathin EuSe NWs synthesized from the solvothermal of 0.5 mmol Eu(CH 3 COO) 3 and 1 mmol SeO 2 in absolute ethanol/oa/om (9.0 ml: 4.5 ml : 4.5 ml = 2:1:1, the volume ratio) at 180 C for 72 h. 12

13 Particularly, our method allows us to modulate the morphologies of EuSe nanostructures in a controlled manner. For example, when substituting octylamine (OTA) for OM, uniform EuSe nanorods (NRs) with different sizes were produced (Figure S14). In our synthesis, we fixed the molar ratios of Eu(CH 3 COO) 3 (0.5 mmol)/se (1.0 mmol) = 1 : 2, reaction time and temperature (180 C, 72 h), and altered the volume ratios of OTA and OA from pure OA (18.0 ml), 1:1 (9.0 ml: 9.0 ml), 2:1 (12.0 ml: 6.0 ml), 7:2 (14.0 ml: 4.0 ml), 8:1 (16.0 ml: 2.0 ml), and pure OTA (18.0 ml). Monodisperse EuSe nanorods with diameter of ~5 nm and length of ~50 nm (EuSe NRs-short, Figure S14a) were prepared with 12 ml OTA and 6 ml OA, when the volume of OTA was increased to 14 ml and OA to 4 ml, the EuSe nanorods with diameter of ~20 nm and length of ~500 nm were harvested (EuSe NRs-long, Figure S14b). Furthermore, when increasing the volume of OTA to 16 ml and OA was reduced to 2 ml, only nanorods coexisted with irregular nanoplates (Figure S15a). While increasing the volume of OTA to 18 ml, the EuSe nanorods disappeared and a great amount of non-uniform nanoparticles and nanosheets were produced (Figure S15b). Decreasing the volume of OTA to 9 ml and OA to 9 ml resulted in severely aggregated nanoplates with poor dispersibility coexisted with quite a few nanorods and nanowires (Figure S15c). Pure OA (18 ml) resulted in some unshapely nanoparticles with low yields (Figure S15d). In addition, the solvents, the reaction temperature and Eu source (Eu(CH 3 COO) 3, Eu(NO 3 ) 3 6H 2 O) were found to play important roles in the formation of uniform EuSe nanostructures as well (Figure S16, 17, 18). Figure S14. TEM images of the EuSe nanostructures prepared with the feed molar ratios of Eu(CH 3 COO) 3 (0.5 mmol) : Se (1.0 mmol) = 1 : 2 at different surfactant compositions: (a) OTA (12.0 ml) : OA (6.0 ml) = 2 : 1, 180 C/72 h, (b) OTA (14.0 ml) : OA (4.0 ml) = 7 : 2, 180 C/72 h. The insets are the HRTEM images of EuSe nanostructures. 13

14 Figure S15. TEM images of the obtained EuSe nanostructures via solvothermal of 0.5 mmol Eu(CH 3 COO) 3 and 1.0 mmol Se in different ratio (OTA/OA) of surfactant mixture at 180 C for 72 h: (a) OTA/OA (16.0 ml: 2.0 ml) = 8:1, (b) OTA = 18.0 ml, (c) OTA/OA (9.0 ml: 9.0 ml) = 1:1, and (d) OA = 18 ml. 14

15 Figure S16. TEM images of the EuSe nanostructures via solvothermal of 0.5 mmol Eu(CH 3 COO) 3 and 1.0 mmol Se in different solvents and surfactants at 180 C for 72 h: (a) absolute ethanol/ota/oa (9.0 ml: 4.5 ml : 4.5 ml) = 2:1:1, (b) absolute ethanol/ota (9.0 ml: 9.0 ml) = 1:1, (c) absolute methanol/ota/oa (9.0 ml: 4.5 ml : 4.5 ml) = 2:1:1, and (c) N, N-dimethyl formamide/ota/oa (9.0 ml: 4.5 ml : 4.5 ml) = 2:1:1. 15

16 Figure S17. TEM image of the EuSe nanostructures synthesized from the solvothermal of 0.5 mmol Eu(NO 3 ) 3 6H 2 O and 1.0 mmol Se in OTA (18.0 ml) at 180 C for 72 h. Figure S18. TEM image of the EuSe nanostructures synthesized from the solvothermal of 0.5 mmol Eu(CH 3 COO) 3 and 1.0 mmol Se in OTA (18.0 ml) at 150 C for 72 h. Figure S19. The fluorescence micrograph of ultrathin EuSe NWs solid film evaporated in air from colloidal solution. 16

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