FUNCTIONALIZED SEMICONDUCTOR NANOPARTICLES AND METHOD FOR THE MANUFACTURE THEREOF

Abstract

Method for manufacturing fluoro(hydro)carbon-substituted silicon or germanium quantum dots which comprises the steps of:—reacting a Zintl salt or intermetallic compound of post-transition metals or metalloids of silicon or germanium with a halogen-containing oxidizing agent to form halide-terminated silicon or germanium quantum dots,—reacting the halide-terminated silicon or germanium quantum dots with a fluoro(hydro)carbon agent selected from the group of metal-fluoro (hydro)carbon compounds of the formula MRq, wherein M is a metal selected from Group 1, 2, 4, 11, 12, 13, or 14 of the periodic table of elements, q is an integer which corresponds to the valence of the metal, and R is CFnHm-fluoro/hydro-carbon, wherein n is 1 or 2, m is 0 or 1, and the total of n and m is 2, wherein each R may be the same or different, metal-fluoro (hydro)carbon halide compounds of the formula NQaRp wherein N is a metal selected from Group 1, 2, 4, 11, 12, 13, or 14 of the periodic table of elements, Q is a halogen selected from F, Cl, Br, or I, wherein each Q may be the same or different, a and p are integers in the range of 1-3, and the total of a and p corresponds to the valence of the metal, and R is as defined above, and metal-fluoro (hydro)carbon compounds of the formula CuR2Li, wherein R is as defined above, to form fluoro(hydro)carbon-substituted silicon or germanium quantum dots. The method makes it possible to obtain quantum dots with a tailored emission spectrum with high quality in a stable process. The particles obtained by this process are also claimed.

Claims

1. A method for manufacturing fluoro(hydro)carbon-substituted silicon or germanium quantum dots which comprises the steps of: reacting a Zintl salt or intermetallic compound of post-transition metals or metalloids of silicon or germanium with a halogen-containing oxidizing agent to form halide-terminated silicon or germanium quantum dots, reacting the halide-terminated silicon or germanium quantum dots with a fluoro(hydro)carbon agent selected from the group consisting of: metal-fluoro(hydro)carbon compounds of the formula MR.sub.q, wherein M is a metal selected from Group 1, 2, 4, 11, 12, 13, or 14 of the periodic table of elements, q is an integer which corresponds to the valence of the metal, and R is CFnHM-gluoro/hydrocarbon, wherein n is 1 or 2, m is 0 or 1, and the total of n and m is 2, and wherein each R may be the same or different, metal-fluoro(hydro)carbon halide compounds of the formula NQ.sub.aR.sub.p wherein N is a metal selected from Group 1, 2, 4, 11, 12, 13, or 14 of the periodic table of elements, Q is a halogen selected from F, Cl, Br, or I, wherein each Q may be the same or different, a and p are integers in a range of 1-3, a total of a and p corresponds to the valence of the metal, and R is as defined above, and metal-fluoro(hydro)carbon compounds of the formula CuR.sub.2Li, wherein R is as defined above, to form fluoro(hydro)carbon-substituted silicon or germanium quantum dots.

2. The method according to claim 1, wherein the Zintl salt or intermetallic compound of post-transition metals or metalloids of silicon or germanium is selected from the group consisting of Mg.sub.2Si, NaSi, KSi, Ca2Si, Mg.sub.2Ge, NaGe, KGe, and Ca.sub.2Ge.

3. The method according to claim 1, wherein the Zintl salt is a silicon Zintl salt.

4. The method according to claim 1, wherein the halogen-containing oxidizing agent is selected from the group consisting of Cl.sub.2, Br.sub.2, F.sub.2, I.sub.2, and mixtures thereof.

5. The method according to claim 1, wherein R has at least 3 carbon atoms and/or at most 16 carbon atoms.

6. The method according to claim 1, wherein R is an alkyl group.

7. The method according to claim 1, wherein the fluoro(hydro)carbon agent is selected from the group consisting of n-perfluoroalkyl lithium of the formula LiC.sub.nF.sub.2n+1, wherein n is 1-20, and n-perfluoroalkyl magnesium bromide of the formula BrMgC.sub.nF.sub.2n+1 wherein n is 1-20.

8. Silicon or germanium quantum dots derived from a Zintl salt or intermetallic compound of post-transition metals or metalloids of silicon or germanium comprising CFnHm-fluoro/hydrocarbon groups bonded directly to the silicon or germanium of the particle.

9. The quantum dots according to claim 8, having a number average particle size of 0.5-5 nm, as determined by transmission electron microscopy.

10. The quantum dots according to claim 9, having a number average particle size of 2.2+/−0.5 nm, as determined by transmission electron microscopy.

11. The quantum dots according to claim 8, having a quantum yield of at least 1%.

12. The quantum dots according to claim 8, having an emission spectrum which shows a red-shift of 20-100 nm, as compared to the same particles substituted with perhydroalkyl ligands.

13. The quantum dots according to claim 8, having an emission spectrum with a peak in a range of 495-570 nm.

14. The method according to claim 3, wherein the Zintl salt is a silicon Zintl salt selected from the group consisting of Mg.sub.2Si, NaSi, KSi and Ca.sub.2Si.

15. The method according to claim 4, wherein the halogen-containing oxidizing agent is Br.sub.2.

16. The method according to claim 5, wherein R has at least 5 carbon atoms, and/or at most 11 carbon atoms.

17. The method according to claim 6, wherein R is a straight-chain alkyl group.

18. The method according to claim 7, wherein the fluoro(hydro)carbon agent is selected from the group consisting of n-perfluoroalkyl lithium of the formula LiC.sub.nF.sub.2n+1, wherein n is 4-12, and n-perfluoroalkyl magnesium bromide of the formula BrMgC.sub.nF.sub.2+1 wherein n is 4-12.

19. The quantum dots according to claim 8, having a quantum yield of at least 5%.

20. The quantum dots according to claim 8, having a quantum yield of at least 11%.

Description

EXAMPLE 1: PREPARATION OF SUBSTITUTED SILICON QUANTUM DOTS

[0074] First, Mg.sub.2Si (0.5 g, 6.5 mmol) was added into n-octane (500 mL). Vacuum degassing under nitrogen filling cycles were performed three times to remove any oxygen from the reaction system. Then Br.sub.2 (2.7 mL, 52 mmol) was added under N.sub.2 atmosphere under continuous stirring. The suspension was stirred at 130° C. for 3 days. When the reaction was completed, the suspension was kept under N.sub.2, while solvents were removed by distillation. To the flask fresh N.sub.2-bubbled n-octane (500 mL) was added, and the obtained halide terminated Si QD suspension was cooled on ice. Then perfluorohexylmagnesium bromide was added to the above suspension. The reaction mixture was stirred overnight, and MeOH was added dropwise to quench any excess Grignard reagents. The mixture was stirred for 1 h. The mixture was filtered and the filtrate was subsequently extracted with aqueous HCl (1M) (1×) and distilled water (3×), and finally the organic fractions were dried over Na2SO4. Solvent was removed under reduced pressure, yielding ˜134 mg Si quantum dots as a dark red solid. The quantum yields of crude products are approximately 1%. Subsequent purification via column chromatography typically yields products with increased quantum yields of 5-6%.

[0075] The particles had a particle size of 2.2 nm+/−0.5 nm, as determined via TEM.

[0076] They showed absorption ranging from UV (<200 nm) to (infra)red (>800 nm), though most strongly in the range from UV to 400 nm). The emission maximum was at 525-530 nm.

[0077] 19F NMR spectroscopy displayed relatively broad signals corresponding to silicon bound perfluoroalkyl chains at chemical shifts in the −65 to −70 ppm range, −80 to −90 ppm range and −115 to −130 ppm range.

EXAMPLE 2: COMPARISON OF EMISSION OF ALKYL-SUBSTITUTED SILICON QUANTUM DOTS AND PERFLUOROALKYL SUBSTITUTED QUANTUM DOTS

[0078] Particles substituted with per-hydroalkyl groups were prepared as described in Dohnalová, K.; Poddubny, A. N.; Prokofiev, A. A.; de Boer, W. D.; Umesh, C. P.; Paulusse, J. M. J.; Zuilhof, H.; Gregorkiewicz, T. Light Sci. Appl. 2013, 2 (1), e47.

[0079] FIG. 1 provides the emission spectra of the per-fluoro-alkyl substituted particles of example 1 and of the per-hydro-alkyl substituted particles of Dohnalova et al. As can be seen from the FIGURE, the perfluoro-alkyl substituted quantum dots show a peak in the emission spectrum in the range of 495-570 nm, while the alkyl-substituted quantum dots show a peak at lower wavelengths in the range of 410-460 nm. Expressed otherwise, the emission of the per-fluoro-alkyl substituted particles shows a red-shift of about 20-80 nm.