DOPED SEMICONDUCTOR NANOCRYSTALS, METHOD FOR PREPARING SAME AND USES THEREOF

Abstract

A set of nanocrystals comprising a semiconductor comprising A representing a metal or metalloid in the +III oxidation state and B representing an element in the −III oxidation state, the nanocrystals being doped, on average per nanocrystal, by an atom of C chosen from the transition metals in the +I or +II oxidation state and various uses thereof.

Claims

1. Set of nanocrystals comprising a semiconductor comprising A representing a metal or metalloid in the +III oxidation state and B representing an element in the −III oxidation state, said nanocrystals being doped, on average per nanocrystal, by an atom of C which is selected from the transition metals in the +I or +II oxidation state.

2. Set of nanocrystals according to claim 1, wherein A, said metal or metalloid in the +III oxidation state, forming with B the semiconductor comprised in the nanocrystals according to the invention is selected from gallium (Ga), indium (In), aluminium (Al) and mixtures thereof.

3. Set of nanocrystals according to claim 1, wherein B, said element in the −III oxidation state, forming with A the semiconductor comprised in the nanocrystals according to the invention, is selected from antimony (Sb), arsenic (As), phosphorus (P), nitrogen (N) and mixtures thereof.

4. Set of nanocrystals according to claim 1, wherein said nanocrystals comprise, in addition to a semiconductor of formula AB and one C atom per nanocrystal, at least one other element D in the form of a metal or metalloid in the +II or +III oxidation state.

5. Set of nanocrystals according to claim 1, wherein C, said transition metal in the +I or +II oxidation state, doping the nanocrystals is selected from copper (Cu), silver (Ag), mercury (Hg), gold (Au) and mixtures thereof.

6. Set of nanocrystals according to claim 1, wherein said nanocrystals correspond to any of the following formulae: Ag:InP, Au:InP, Cu:InP, Ag:In(Zn)P, Au:In(Zn)P and Cu:In(Zn)P.

7. Set of nanocrystals according to claim 1, wherein said nanocrystals have a shell arranged on or covering all or part of their surface.

8. Set of nanocrystals according to claim 1, wherein said nanocrystals have a core comprising a semiconductor material corresponding to any of the following formulae: Ag:InP, Au:InP, Cu:InP, Ag:In(Zn)P, Au:In(Zn)P and Cu:In(Zn)P and a shell comprising or consisting of a semiconductor material of formula ZnS.sub.1-xE.sub.x, with E and x with E representing an element in the −II oxidation state and x being a decimal number such that 0≤x<1.

9. Method for the preparation of a set of nanocrystals as defined in claim 1, said method comprising steps of: a) preparing nanocrystals comprising a semiconductor comprising A representing a metal or metalloid in the +III oxidation state and B representing an element in the −III oxidation state and optionally D representing a metal or metalloid in the +II or +III oxidation state; b) contacting the nanocrystals prepared in step (a) with a precursor of C, C being selected from the transition metals in the +I or +II oxidation state, at a temperature T.sub.b and for a period D.sub.b making it possible to obtain nanocrystals comprising a semiconductor comprising A representing a metal or metalloid in the +III oxidation state and B representing an element in the −III oxidation state and optionally D representing a metal or metalloid in the +II oxidation state, doped, on average per nanocrystal, by a C atom selected from the transition metals in the +I or +II oxidation state; c) optionally coating all or part of the surface of nanocrystals comprising a semiconductor comprising A representing a metal or metalloid in the +III oxidation state and B representing an element in the −III oxidation state, doped, on average per nanocrystal, by a C atom obtained in step (b), with a shell the outer part of which comprises or consists of an oxide or a semiconductor material.

10. Method according to claim 9, wherein said step (a) of the method according to the invention comprises substeps of: a.sub.1) preparing a solution comprising at least a precursor of A and optionally at least a precursor of D at a temperature T.sub.a1; a.sub.2) bringing the mixture obtained in substep (a.sub.1) from temperature T.sub.a1 to temperature T.sub.a2 higher than temperature T.sub.a1; a.sub.3) introducing, into the mixture obtained in substep (a.sub.2) and maintained at temperature T.sub.a2, at least a precursor of B; and a.sub.4) optionally purifying nanocrystals comprising a semiconductor comprising A representing a metal or metalloid in the +III oxidation state and B representing an element in the −III oxidation state and optionally D representing a metal or metalloid in the +II or +III oxidation state.

11. Method according to claim 10, wherein said precursor of A is selected from the salts of A, the halides of A, the oxides of A and the organometallic compounds of A.

12. Method according to claim 10, wherein said precursor of D is selected from the group consisting of the salts of D, the halides of D, the oxides of D and the organometallic compounds of D.

13. Method according to claim 10, wherein said solution prepared in said substep (a.sub.1) comprises a solvent and an element selected from the group consisting of a stabiliser for the surface of the nanocrystals, a primary amine and a mixture thereof.

14. Method according to claim 10, wherein said temperature T.sub.a2 is lower than 300° C., notably between 100° C. and 300° C., in particular, between 150° C. and 280° C.

15. Method according to claim 10, wherein said precursor of B is a compound of formula B(F(R.sub.11).sub.3).sub.3, of formula B(R.sub.12).sub.3 or of formula B(N(H)R.sub.13).sub.3, wherein: each F is selected from the group consisting of silica (Si), germanium (Ge) and tin (Sn); each R.sub.11, identical or different, is a linear, branched or cyclic alkyl group, optionally substituted, of 1 to 10 carbon atoms, notably of 1 to 6 carbon atoms and, in particular of 1 to 3 carbon atoms; each R.sub.12, identical or different, is a hydrogen atom, a halogen such a chlorine (Cl), bromine (Br), iodine (I) or fluorine (F) or a linear, branched or cyclic alkyl group, optionally substituted, of 1 to 10 carbon atoms, notably of 1 to 6 carbon atoms and, in particular of 1 to 3 carbon atoms; and each R.sub.13, identical or different, is a hydrogen atom, a linear, branched or cyclic alkyl group, optionally substituted, of 1 to 10 carbon atoms, notably of 1 to 6 carbon atoms and, in particular of 1 to 3 carbon atoms or a linear, branched or cyclic alkenyl group, optionally substituted, of 2 to 30 carbon atoms, notably of 2 to 25 carbon atoms and, in particular, of 2 to 20 carbon atoms.

16. Method according to claim 10, wherein said precursor of C is selected from the group consisting of the salts of C, the halides of C, the oxides of C and the organometallic compounds of C.

17. Method according to claim 9, wherein said temperature T.sub.b is between 100° C. and 200° C.

18. Use of a set of nanocrystals as defined in claim 1 or capable of being prepared according to a method as defined in any one of claims 9 to 17, in a light-emitting diode, in a photovoltaic cell, in a luminescent concentrator for a solar cell and for the fluorescent labelling of chemical or biological molecules.

19. Set of nanocrystals according to claim 8, wherein said nanocrystals have a core consisting of a semiconductor material corresponding to any of the following formulae: Ag:InP, Au:InP, Cu:InP, Ag:In(Zn)P, Au:In(Zn)P and Cu:In(Zn)P and a shell comprising or consisting of a semiconductor material of formula ZnS.sub.1-xE.sub.x, with E and x with E representing an element in the −II oxidation state and x being a decimal number such that 0≤x<1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0137] FIG. 1 shows the UV-visible and photoluminescence adsorption spectra of InP nanocrystals with statistically one dopant (Ag) per nanocrystal. Line width at mid-height: 70 nm.

[0138] FIG. 2 shows the photoluminescence spectra of undoped InP nanocrystals (“core”), or doped with silver after 15 min of doping (“Ag-15”) or after 30 min of doping (“Ag-30”), or doped again with silver after 30 min of doping then covered with a ZnS shell (“AgCS”). Line width at mid-height: 72 nm for AgCS.

[0139] FIG. 3 shows the evolution of photoluminescence spectra (excitation wavelength: 400 nm) as a function of the amount of dopant used (ratio Ag:In:Ag125=0.0125; Ag250=0.025; Ag500=0.05; Ag1000=0.1; Ag2000=0.2).

[0140] FIG. 4 shows X-ray diffractograms of undoped InP nanocrystals (“no dopant”) or prepared with silver in a ratio Ag:In=1:40 i.e. 2.5% (“Ag250”) or in a ratio Ag:In=1:20 i.e. 5% (“Ag500”).

[0141] FIG. 5 shows a transmission electron microscopy image of weakly doped core/shell nanocrystals Ag:In(Zn)P/ZnS with an average of one atom of dopant per na nocrystal.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0142] I. Material and Methods

[0143] I.A. Preliminary Remarks

[0144] All the syntheses are carried out in an inert atmosphere using argon gas.

[0145] For the characterisations, the UV-visible absorption spectra were measured on a HP8420A spectrometer (spectral range in wavelength: 190 nm to 820 nm, resolution 2 nm), the photoluminescence spectra were acquired with a HORIBA Fluorolog iHR320 spectrometer. For these spectroscopic measurements, the colloidal solutions of nanocrystals diluted in hexane were placed in small quartz cells with an optical path of 1 cm. The fluorescence quantum yields at ambient temperature were obtained by comparing the emission intensity—spectrally integrated—of the dispersion of nanocrystals in the hexane with that of a solution of rhodamine 6 G in ethanol, the two solutions having the same optical density (<0.03) at the excitation wavelength (490 nm). The X-ray diffractograms were obtained on a Philips Panalytical device, using a source of copper, at 40 kV and 40 mA. Transmission electron microscopy images were obtained with a FEI Polara microscope.

[0146] All products apart from the zinc distearate (Riedel de Haën) were purchased from Sigma-Aldrich and used as such: indium chloride (InCl.sub.3, purity 99.999%), zinc distearate (purity 90%), dodecanethiol (purity 98%), 1-octadecene (purity 90%). Tris(dimethylamino)phosphine (PNMe.sub.2).sub.3 (97%), oleylamine (OLA, 98%). NaOH, stearic acid and AgNO.sub.3.

[0147] I.B. Preparation of the Precursor of Phosphorus (Trioleylamine Phosphine, P(OLA).sub.3)

[0148] For the preparation of the solution of P(OLA).sub.3, tris(dimethylamino)phosphine (PNMe.sub.2).sub.3 (1.3 mL, 7.2 mmol) is added to oleylamine (OLA, 7.1 mL, 21.6 mmol) and heated at 70° C. for 10 h under primary vacuum (10.sup.−2−10.sup.−1 mbar) and agitation. The solution obtained has to be stored and used in an inert atmosphere (for example of argon or nitrogen).

[0149] I.C. Preparation of Silver Stearate (AgSt):

[0150] 1 mL of an aqueous solution of NaOH (1 M) is added to 100 mL of an aqueous solution of stearic acid (0.15 M), heated to 80° C. While stirring 17 mL of an aqueous solution of AgNO.sub.3 (1 M) is added. The white precipitate which forms is filtered and washed three times with 50 mL distilled water, then dried in an oven at 50° C.

[0151] I.D. Synthesis of Ag:In(Zn)P Nanocrystals (Ag500)

[0152] Indium chloride (InCl.sub.3, 0.3 mmol), zinc distearate (ZnSt.sub.2, 0.3 mmol), oleylamine (OLA, 1 mmol), 1-dodecanethiol (1-DDT, 0.3 mmol) and 1-octadecene (ODE, 25 mmol, 8 mL) were mixed in a three-neck flask and purged under vacuum for 30 min.

[0153] Then the flask was filled with argon and the reaction solution was heated to 220° C., with a rapid injection of trioleylamine phosphine (P(OLA).sub.3, 1.2 mmol). The reaction solution was cooled at the end of 3 min.

[0154] Silver stearate (AgSt, 15 μmol) in a mixture of octadecene and oleylamine (2 mL ODE/OLA mixture (1:1 vol:vol)) was added, dropwise, to the reaction solution containing the In(Zn)P nanocrystals at 130° C., for 30 min.

[0155] I.E. Synthesis of Core/Shell Ag:In(Zn)P/ZnS Nanocrystals

[0156] After 30 min of doping, the reaction solution was heated again to 220° C. to allow the shell to grow for 1 hour.

[0157] I.F. Other Syntheses for Comparison

[0158] Synthesis Corresponding to Ag250 in FIGS. 3 and 4:

[0159] The procedure is the same as the one described for weakly doped Ag:In(Zn)P nanocrystals (Ag500), but using a quantity of 7.5 μmol silver stearate in a mixture of ODE and OLA (2 mL, 1:1 vol:vol).

[0160] Syntheses Corresponding to Ag125/Ag1000/Ag2000 in FIG. 3:

[0161] The procedure is same as the one described for the weakly doped Ag:In(Zn)P nanocrystals (Ag500) but using a quantity of 3.75/30/60 μmol silver stearate in a mixture of ODE and OLA (2 mL, 1:1 vol:vol).

[0162] II. Results

[0163] II.A. Optical Properties

[0164] The UV-vis absorption and photoluminescence spectra of the samples obtained after the method as described in points I.C and I.D are shown in FIGS. 1 and 2. FIG. 1 shows the absorption and photoluminescence spectra (excitation wavelength: 400 nm) of Ag:In(Zn)P/ZnS core/shell nanocrystals weakly doped with on average one atom of dopant per nanocrystal. The excitonic peak in the region of 550 nm is visible in the UV-vis absorption spectrum, and the photoluminescence spectrum shows a narrow emission line centred at around 700 nm.

[0165] FIG. 2 shows the evolution of the photoluminescence spectra (excitation wavelength: 400 nm) before doping (“core”) and during the contact period between the dopant and the core nanocrystals (15:15 min, 30:30 min) as well as after the growth of the ZnS shell (“AgCS”).

[0166] FIG. 3 shows the evolution of the photoluminescence spectra (excitation wavelength: 400 nm) as a function of the quantity of the dopant used (ratio Ag:In:Ag125=0.0125; Ag250=0.025; Ag500=0.05; Ag1000=0.1; Ag2000=0.2). The contact time between the dopant and the In(Zn)P nanocrystals was 30 min for all the samples except for (90 min), referred to as “Ag500 90 min”. It can be seen that i) for a used Ag:In ratio of 0.05 (Ag500) the photoluminescence intensity is at a maximum; ii) a prolongation of the contact time from 30 to 90 min leads to a decrease in the photoluminescence intensity.

[0167] II.B. Physicochemical Analysis by X-Ray Diffractometry

[0168] The X-ray diffractogram of powder for a control sample. i.e. undoped sample and for samples prepared according to the methods described in I.D and I.F are provided in FIG. 4.

[0169] For nanocrystals doped statistically with 1 dopant per nanocrystal (Ag250, Ag500), the X-ray diffractogram corresponds to that of the control sample without dopant.

[0170] The transmission electron microscopy image shown in FIG. 5 shows weakly doped Ag:In(Zn)P/ZnS core/shell nanocrystals with on average one atom of dopant per nanocrystal. The average size is 4.3±0.4 nm.

REFERENCES

[0171] [1] U.S. Pat. No. 9,260,652 published on 16 Feb. 2016. [0172] [2] Thuy et al, 2013, Dalton Trans., vol. 42, page 12606-12610. [0173] [3] U.S. Pat. No. 9,543,385 published on 10 Jan. 2017. [0174] [4] Sahu et al, 2012, Nano Lett., vol. 12, pages 2587-2594. [0175] [5] International application WO 2010/052221, published on 14 May 2010.