WO2013058900A1 - Nanocristaux semi-conducteurs hautement confinés - Google Patents

Nanocristaux semi-conducteurs hautement confinés Download PDF

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WO2013058900A1
WO2013058900A1 PCT/US2012/055008 US2012055008W WO2013058900A1 WO 2013058900 A1 WO2013058900 A1 WO 2013058900A1 US 2012055008 W US2012055008 W US 2012055008W WO 2013058900 A1 WO2013058900 A1 WO 2013058900A1
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semiconductor
nanocrystals
nanocrystal
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solution
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Keith Brian Kahen
Matthew Holland
Sudeep PALLIKKARA KUTTIATOOR
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Eastman Kodak Company
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Priority claimed from US13/275,595 external-priority patent/US8784703B2/en
Priority claimed from US13/275,424 external-priority patent/US20130092883A1/en
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Publication of WO2013058900A1 publication Critical patent/WO2013058900A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/70—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing phosphorus
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/02—Use of particular materials as binders, particle coatings or suspension media therefor
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/88—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing selenium, tellurium or unspecified chalcogen elements
    • C09K11/881—Chalcogenides
    • C09K11/883—Chalcogenides with zinc or cadmium

Definitions

  • the present invention relates to nanocrystals, wherein the inner homogenous region of the core is highly confined.
  • CCT color rendering index
  • colloidal quantum dot phosphors A way to overcome the backscattering loss issue is to form colloidal quantum dot phosphors.
  • the crystallinity of colloidal quantum dots can be made to be very high which results in solution quantum yields being 80-90%>, and sometimes nearly 100% (J. McBride, et al, Nano Lett. 6 (7), 1496 (2006)).
  • colloidal quantum dot phosphors also enjoy the advantages of ease of color tuning, improved CRI, a lower cost deposition process, and a broader wavelength spectrum for optical pumping.
  • colloidal quantum dot phosphors have not been introduced into the marketplace due to two major shortcomings; namely, poor temperature stability (thermal quenching of quantum efficiency) (N.
  • the disadvantages of this approach are that the peak emission wavelengths of the nanocrystals are limited by the particular choice of dopant materials, the spectral widths of the photoluminescence are typically larger for impurity emission, and the quantum efficiency of these types of nanocrystals is below that of undoped nanocrystals.
  • One way for reducing the thickness of the shell, while increasing the quality of the shell growth is to use outer shells of the widest bandgap, such as, ZnS for CdSe, while employing a graded shell interface region to enable a smooth transition from the core to the shell regions, for example, varying from the CdSe-like core to the ZnS- like outer shell region (K. Char et al., U.S. Patent Application Publication
  • the engineered nanocrystals had other problems, such as, reduced quantum efficiencies at room temperature. As such, there is a need for a new class of colloidal nanocrystals, which have very good quantum efficiencies at room temperature, and maintain these efficiencies at elevated temperatures.
  • This invention relates to high confinement semiconductor nanocrystals, that have high quantum efficiencies at room temperature and maintain that efficiency to temperatures up to 175 °C.
  • a high confinement semiconductor nanocrystal comprises:
  • a gradient alloy region comprised of a second varying alloy composition which extends from the surface of the compact homogenous semiconductor region to the surface of the nanocrystal.
  • the high confinement semiconductor nanocrystals formed in accordance with the present invention exhibit the desirable properties of good quantum efficiencies (>70%) at room temperature and maintain these good quantum efficiencies at elevated temperatures (up to temperatures of -175 °C). It is also an advantage that the electron-phonon interaction is reduced in these nanocrystals. Another benefit of the present invention is that high confinement semiconductor nanocrystals exhibiting these properties can be used to create advantaged quantum dot phosphors, high intensity LEDs, and both optically and electrically pumped lasers.
  • FIG. 1 shows a schematic of a high confinement semiconductor nanocrystal
  • FIG. 2 is a plot showing data for the absorbance and photoluminescence response of the invented core-shell high confinement semiconductor nanocrystals
  • FIG. 3 is a plot showing data for the absorbance of nanocrystals comprised of the invented compact homogenous semiconductor region.
  • FIG. 4 includes four plots showing the temperature dependent photo luminescent response of: A) the inventive nanocrystals with three shell layers; B) the inventive nanocrystals with two shell layers; C) the prior art nanocrystals; and D) all three nanocrystal types.
  • the keys properties to focus on are: 1) Maintaining stable excitons, 2) Preventing the electrons and holes from sampling the surface states, and 3) Minimizing the electron-phonon interaction. All three properties are more problematic at elevated temperatures. The first two properties are well-known effects, the third one requires additional explanation.
  • the inventive nanocrystals have the attributes of significantly reducing the polarization charge of the combined electron and hole distributions, while simultaneously preventing, to a large extent, either charge distribution from sampling the surface states of the nanocrystals.
  • the third property of stable excitons is a natural consequence of minimizing the polarization charge.
  • the issues associated with trapped charge can be generalized to include any internal defects in the nanocrystals that also need to be minimized in order to improve the thermal stability of the nanocrystals.
  • having a high, room-temperature quantum efficiency is indicative of a minimum of internal defects and successful passivation of the surface states.
  • the Bohr radius can be quite large (34 nm in InAs, 46 nm in PbSe, and 54 nm in InSb).
  • the Bohr radii are 6 and 11 nm, respectively. Focusing on these cases for now, the highly confined center region should have a diameter less than 2.0 nm, preferably in the range of 1.0 to 2.0 nm.
  • Forming typical core-shell nanocrystals occurs by the process of growing the cores in the 260-310 °C range, lowering the temperature to typical shelling values of -190 °C (adding some additional ligands if necessary) and then dripping in the shell precursors.
  • the problem with this generic procedure especially when the core diameter is less than 2.0 nm, is that the small core nanocrystals are dominated by surface states, which makes it problematic to shell them properly.
  • the crystalline quality of II -VI and many III-V nanocrystals is the highest when the nanocrystals are grown in the 270-310 °C range, preparing small-diameter nanocrystals is difficult to control, especially without some growth occurring at lower temperatures.
  • the inventive high confinement semiconductor nanocrystal 100 is schematically illustrated in FIG. 1.
  • the nanocrystal includes two sections, a compact homogenous semiconductor region 105, in the center area of the high confinement semiconductor nanocrystal 100, and a gradient alloy region 110, which extends from the surface of the compact homogenous semiconductor region 105 to the surface of the high confinement semiconductor nanocrystal 100.
  • the diameter of the compact homogenous semiconductor region 105 is less than 2.0 nm, with a preferred range of 1.0 to 2.0 nm.
  • the compact homogenous semiconductor region 105 is confined by a gradient alloy region since it enables the confinement layer to be grown simultaneously with the highly confined core area (and at the same temperatures), while reducing the defects associated with the shelling of the very small cores by employing a gradient alloy composition instead of an abrupt change in
  • the semiconductor region 105 is composed of InP
  • the gradient alloy region 110 is composed of InGaP, in which the Ga content increases from the surface of the compact homogenous semiconductor region 105 to the surface of the gradient alloy region 110. This results in the electrons and holes of the compact homogenous semiconductor region 105 being confined by the potential energy barriers of the gradient alloy region 110.
  • the thickness of the gradient alloy region 110 needs to be sufficient to enable proper confinement, with a desired range of 2 to 20 monolayers.
  • the only constraint on the varying alloy composition is that the confinement of the layers increases as the position of the materials proceeds away from the center of the nanocrystal.
  • the Ga content can increase linearly, quadratically, or exponentially (or combinations thereof) away from the surface of the compact homogenous semiconductor region 105.
  • Other functional dependencies for the Ga content variation are possible.
  • the compact homogenous semiconductor region 105 is composed of homogenous binary or ternary semiconductor material.
  • semiconducting materials are II -VI, III-V, or IV-VI compounds.
  • Representative binary materials are CdSe, CdS, CdTe, ZnTe, InP, InSb, InAs, GaAs, GaSb, PbSe, PbS, and PbTe
  • representative ternary materials are CdSeS, InAsP, InSbP, and PbSeS.
  • Other binary or ternary combinations are possible.
  • the gradient alloy region 110 again illustrative semiconducting materials are II-VI, III-V, or IV-VI compounds.
  • the compact homogenous semiconductor region 105 is composed of homogenous binary semiconductor material
  • the gradient alloy region 110 is composed of ternary or quaternary semiconductor material.
  • the compact homogenous semiconductor region 105 is composed of homogenous binary semiconductor material
  • the gradient alloy region 110 is composed of ternary or quaternary semiconductor material.
  • the compact homogenous semiconductor region 105 is composed of homogenous
  • the semiconductor region 105 is composed of homogenous ternary semiconductor material
  • the gradient alloy region 110 is composed of quaternary semiconductor material.
  • Representative quaternary materials are ZnMgSeSe, CdZnSeS, and InAlAsP. Other quaternary combinations are possible.
  • the high confinement semiconductor nanocrystal 100 is composed of semiconductors from the same family (III-V, II-VI, or IV-VI) in order to reduce defect formation.
  • both the compact homogenous semiconductor region 105 and the gradient alloy region 110 are composed of III-V material.
  • the quantum efficiency and environmental stability of nanocrystals can be increased by shelling them with wider bandgap semiconductor materials. Additionally, as discussed above, good temperature stability is aided by preventing the electron and hole wavefunctions from sampling the surface of the overall nanocrystals. Appropriate shelling is easiest to illustrate by two examples. In the first one the compact homogenous semiconductor region 105 is composed of CdSe, while the gradient alloy region 110 is composed of CdZnSe, with the Zn content of the alloy region being highest at the surface of the high confinement semiconductor nanocrystal 100.
  • Some appropriate wider bandgap semiconductor materials for shelling the Cd-based high confinement semiconductor nanocrystal 100 are ZnSe, ZnS, ZnSeS, ZnMgSe, ZnMgS, and ZnMgSeS.
  • the shelling materials should be chosen to reduce the lattice constant variation, while improving the electron and hole confinement.
  • one particular shell combination is ZnSe, followed by ZnSeS and then ZnS.
  • the thickness and type of each shell layer is also varied in order to enhance the quantum efficiency and temperature stability of the overall nanocrystals.
  • Each shell layer can have a thickness from 1 to 20 monolayers, with the number of possible different shell materials being unlimited (since the shell layers can be composed of either binary, ternary, or quaternary semiconductor material, or combinations thereof).
  • this structure can be shelled with either wide bandgap III-V or II-VI materials, with the latter being the more common choice, as is well known in the art. Going this route, one particular shell combination is again ZnSe, followed by ZnSeS and then ZnS.
  • the shells can be composed of II-VI, III-V, or IV-VI semiconductor materials, or combinations thereof.
  • a number of procedures can be applied for creating the high confinement semiconductor nanocrystal 100.
  • One particular approach will be related in detail. Shelling of the nanocrystals follows standard processes in the art; however, some representative shelling procedures will also be discussed.
  • the compact homogenous semiconductor region 105 composed of binary or ternary semiconductor material needs to be synthesized by well-known procedures in the art.
  • a typical synthetic route is decomposition of molecular precursors at high temperatures in coordinating solvents (C. B. Murray et al., Annu. Rev. Mater. Sci. 30, 545 (2000)).
  • the binary or ternary compact homogenous semiconductor region 105 is preferably composed of II-VI, III-V, or IV -VI semiconducting material. Other processes have been employed to form core nanocrystals, such as, solvothermal methods, however, they do not lend themselves to creating the gradient alloy region 110.
  • the growth rate of the nanocrystals be constrained in order to enable nanocrystals of these sizes.
  • the growth rate for typical CdSe nanocrystals is very high, however, adding tetradecylphosphonic acid (TDPA) to the growth ligands is known to significantly reduce the CdSe growth rate, while enabling the formation of high quality nanocrystals.
  • TDPA tetradecylphosphonic acid
  • another scheme for reducing the growth rate is to reduce the initial precursor concentrations.
  • a typical growth process for forming the compact homogenous semiconductor region 105 will involve: 1) Adding into a flask a first solution comprised of a solvent (either coordinating or non-coordinating), some growth ligands, and at most one nanocrystal precursors (sometimes the precursors are only added in step 3); 2) Heating the flask to the nanocrystal nucleation temperature, while vigorously stirring its contents; 3) Adding to a first syringe, a second solution containing a solvent, at least one additional and different precursor than that in the first solution, and some growth ligands; and 4) Swiftly injecting the contents of the syringe into the heated flask to form a crude solution composed of nanocrystals having a compact homogenous semiconductor region.
  • the growth rate of the compact homogenous semiconductor region 105 determines the time delay between the step 4 injection and the injection of the additional precursors that enable the formation of the gradient alloy region 110.
  • This time delay can typically vary from 0.5 s to 20 s.
  • the growth temperatures for the nanocrystals composed of column II-VI and III-V materials are typically between 250 and 320 °C, in order to obtain materials of the highest quality.
  • the cation used for synthesizing the high confinement semiconductor nanocrystal 100 is a group lib, Ilia, or IVa material.
  • group lib cation precursors are Cd(Me) 2 , CdO, CdC0 3 , Cd(Ac) 2 , CdCl 2 , Cd(N0 3 ) 2 , CdS0 4 , ZnO, ZnC0 3 , Zn(Ac) 2 , Zn(Et) 2 , Hg 2 0, HgC0 3 and Hg(Ac) 2 .
  • group Ilia cation precursors are In(Ac) 3 , InCl 3 , In(acac) 3 , In(Me) 3 , ln 2 0 3 , Ga(acac) 3 , GaCl 3 , Ga(Et) 3 , and Ga(Me) 3 .
  • Other appropriate cation precursors can also be used as is well known in the art.
  • the anion precursor used for the synthesis of the high confinement semiconductor nanocrystal 100 is a material selected from a group consisting of S, Se, Te, N, P, As, and Sb.
  • corresponding anion precursors are bis(trimethylsilyl)sulfide, tri-n-alkylphosphine sulfide, hydrogen sulfide, tri-n- alkenylphosphine sulfide, alkylamino sulfide, alkenylamino sulfide, tri-n- alkylphosphine selenide, alkenylamino selenide, tri-n-alkylamino selenide, tri-n- alkenylphosphine selenide, tri-n-alkylphosphine telluride, alkenylamino telluride, tri-n-alkylamino telluride, tri-n-alkenylphosphine telluride,
  • tris(trimethylsilyl)phosphine triethylphosphite, sodium phosphide, potassium phosphide, trimethylphosphine, tris(dimethylamino)phosphine,
  • tricyclopentylphosphine tricyclohexylphosphine, triallylphosphine, di-2- norbornylphosphine, dicyclopentylphosphine, dicyclohexylphosphine,
  • dibutylphosphine tris(trimethylsilyl)arsenide, bis(trimethylsilyl)arsenide, sodium arsenide, and potassium arsenide.
  • Other appropriate anion precursors can also be used as is well known in the art.
  • coordination ligands that can be used are alkyl phosphine, alkyl phosphine oxide, alkyl phosphate, alkyl amine, alkyl phosphonic acid, and fatty acids.
  • the alkyl chain of the coordination ligand is preferably a hydrocarbon chain of length greater than 4 carbon atoms and less than 30 carbon atoms, which can be saturated, unsaturated, or oligomeric in nature. It can also have aromatic groups in its structure.
  • Suitable coordination (growth) ligands and ligand mixtures include, but are not limited to, trioctylphosphine,
  • tributylphosphine tri(dodecyl)phosphine, trioctylphosphine oxide
  • tris(tridecyl)phosphate triisodecyl phosphate, bis(2-ethylhexyl)phosphate, tris(tridecyl)phosphate, hexadecylamine, oleylamine, octadecylamine, bis(2- ethylhexyl)amine, octylamine, dioctylamine, cyclododecylamine, n,n- dimethyltetradecylamine, ⁇ , ⁇ -dimethyldodecylamine, phenylphosphonic acid, hexyl phosphonic acid, tetradecyl phosphonic acid, octylphosphonic acid, octadecyl phosphonic acid, propylphosphonic acid, aminohexyl phosphonic acid, oleic acid, stearic acid, myristic acid, palmitic acid, lauric acid, and decanoic acid.
  • the coordinating ligand can be used by diluting the coordinating ligand with at least one solvent selected from a group consisting of 1-nonadecene, 1-octadecene, cis-2- methyl-7-octadecene, 1-heptadecene, 1-pentadecene, 1-tetradecenedioctylether, dodecyl ether, and hexadecyl ether, or the like.
  • at least one solvent selected from a group consisting of 1-nonadecene, 1-octadecene, cis-2- methyl-7-octadecene, 1-heptadecene, 1-pentadecene, 1-tetradecenedioctylether, dodecyl ether, and hexadecyl ether, or the like.
  • the growth ligands include column II metals, including Zn, Cd or Mg.
  • the zinc compound is zinc carboxylate having the formula:
  • R is a hydrocarbon chain of length equal to or greater than 1 carbon atom and less than 30 carbon atoms, which are saturated, unsaturated, or oligomeric in nature. It can also have aromatic groups in its structure.
  • suitable zinc compounds include, but are not limited to, zinc acetate, zinc undecylenate, zinc stearate, zinc myristate, zinc laurate, zinc oleate, or zinc palmitate, or combinations thereof.
  • non-coordinating or weakly coordinating solvents include higher homologues of both saturated and unsaturated hydrocarbons.
  • the solvent is selected from unsaturated high boiling point hydrocarbons,
  • the solvents used in the first syringe can be coordinating or non- coordinating, a list of possible candidates being given above. It is preferred that the solvent have a boiling point above that of the growth temperature; as such, prototypical coordinating and non-coordinating solvents are trioctylphosphine and octadecene, respectively.
  • the compact homogenous semiconductor region 105 is permitted to grow for the appropriate time (to get to a diameter of less than 2.0 nm), before beginning the formation of the gradient alloy region 110 that surrounds it. Its formation requires filling a second syringe with a third solution containing a solvent, appropriate growth ligands, and additional precursor(s) that result in the formation of a ternary or quaternary gradient alloy region 110.
  • the time delay between injecting the first and second syringes is typically 0.5 to 20 s.
  • the second syringe is injected rapidly. Following its injection, the growth temperature is lowered (typically 10 to 50 °C below that of the nucleation growth temperature) and the gradient alloy region 110 is permitted to grow for the appropriate time (varying from 1 to 60 minutes).
  • additional precursor(s) can either be cations or anions.
  • the additional precursors In order to properly grow the gradient alloy region 110 it is important that the additional precursors have matched reactivities to those of the initial ones. More particularly, taking the example of an InP -based compact homogenous semiconductor region 105 formed from trimethylindium and
  • the chosen Ga precursor should have matched reactivities to that of trimethylindium. Otherwise, the tris(trimethylsilyl)phosphine will react preferentially with the trimethylindium to form InP, and not InGaP.
  • An example of a precursor with matched reactivities to that of trimethylindium is
  • single or multiple shelling layers can be added onto the high confinement semiconductor nanocrystal 100 by well-known procedures in the art.
  • the shelling is typically accomplished via the decomposition of molecular precursors at high temperatures in coordinating solvents (M. A. Hines et al, J. Phys. Chem. 100, 468 (1996)). Additional discussions of forming semiconducting shells on nanocrystal cores can be found in Masala (O. Masala and R. Seshadri, Annu. Rev. Mater. Res. 34, 41 (2004)) and U.S. Patent No. 6,322,901.
  • the shell(s) can be composed of II-VI, III-V, or IV- VI semiconducting materials.
  • the shelling temperatures are typically from 170 to 230 °C.
  • the shell precursors are either slowly drip together or the shell precursors are added one-half monolayer at a time (again typically at a slow rate).
  • II-VI materials it is also preferred that the surface of the nanocrystals be etched in weak acids (E. Ryu et al, Chem.
  • a useful weak acid is acetic acid.
  • ligands are primary amines, such as, hexadecylamine, or acid-based amines, such as, oleylamine.
  • a useful shell would be a multiple one comprising shell layers of ZnSe, ZnSeS, and ZnS.
  • the shell thicknesses and S content of the middle shell are determined by optimizing the nanocrystals for quantum efficiency and temperature stability. It is also beneficial to anneal the nanocrystals near the shelling temperatures following each shelling step for times ranging from 10 to 30 minutes.
  • 0.12 g (0.52mmol) myristic acid, 0.045 g (O. lmmol) Zn undecylenate and 7 ml 1-octadecene (ODE) were loaded into a three neck flask. The mixture was degassed at 100 °C for 1 hour. After switching to N 2 overpressure, the flask contents were heated to 300 °C, while vigorously stirring its contents. Two precursor solutions were prepared and loaded into corresponding syringes.
  • the first precursor solution contained 0.013 g (0.08 mmol) trimethylindium (In(Me) 3 ), 0.012 g (0.048 mmol) tris(trimethylsilyl)phosphine (P(TMS) 3 ), 0.08 mmol oleylamine and 2 ml ODE;
  • the second precursor solution contained 0.013 g (0.08mmol) triethylgallium (Ga(Et) 3 ), 0.08 mmol oleylamine and 1.5 ml ODE.
  • the second syringe was rapidly injected into the hot flask to form the gradient alloy region of InGaP. After the second injection, the flask temperature was lowered to 270 °C and the nanocrystals were grown for 36 minutes in total. The reaction was stopped by removing the heating source.
  • the above III-V based nanocrystals were shelled with wide bandgap II- VI materials.
  • the shelling begins with the weak acid etch of the nanocrystals.
  • 150 ul (2.6 mmol) degassed acetic acid was loaded into a syringe and then injected into the flask. This was followed by annealing the contents of the flask for 60 minutes at 240 °C. Since the nanocrystals aggregated following this step, the reaction flask was cooled to 190 °C, 0.5ml (1.5 mmol) oleylamine was injected into the flask, and its contents were annealed at 190 °C for 10 minutes.
  • the second shell of ZnSeo.25So.75 (by material content) was then grown by dripping in a solution of 0.61 mmol DEZ, 200ul tri-n- butylphosphine, 0.01 g (0.13 mmol) selenium, 0.012 g (0.037 mmol) sulfur, and 2.5 ml ODE under vigorous stirring. The flask contents were then annealed at 190 °C for 10 minutes.
  • the data shows that the nanocrystals had an emission peak at 563 nm and a spectral full width at half maximum (FWHM) of 72 nm.
  • 0.12 g (0.52mmol) myristic acid, 0.045 g (O. lmmol) Zn undecylenate and 7 ml ODE were loaded into a three neck flask. The mixture was degassed at 100 °C for 1 hour. After switching to N 2 overpressure, the flask contents were heated to 300 °C, while vigorously stirring its contents. Two precursor solutions were prepared and loaded into corresponding syringes.
  • the first precursor solution contained 0.013 g (0.08 mmol) trimethylindium, 0.012 g (0.048 mmol) tris(trimethylsilyl)phosphine, 0.08 mmol oleylamine and 2 ml ODE;
  • the second precursor solution contained 0.013 g (0.08mmol) triethylgallium, 0.08 mmol oleylamine and 1.5 ml ODE.
  • the above III-V based nanocrystals were shelled with wide bandgap II- VI materials.
  • 150 ul (2.6 mmol) degassed acetic acid was loaded into a syringe and then injected into the flask. This was followed by annealing the contents of the flask for 60 minutes at 240 °C.
  • the reaction flask was then cooled to 190 °C, 0.5ml (1.5 mmol) oleylamine was injected into the flask, and its contents were annealed at 190 °C for 10 minutes.
  • Two ZnSeS-based shells were grown on the etched nanocrystals by the following procedure.
  • the first solution of 0.315 mmol DEZ and 1 ml ODE was added dropwise to the reaction mixture under vigorous stirring; the flask contents were then annealed at 190 °C for 10 minutes to form a one-half monolayer of Zn.
  • a second solution of 0.028 g (0.35 mmol) selenium, 200 ul tri-n-butylphosphine, and 1.5 ml ODE was added dropwise to the reaction mixture under vigorous stirring; the flask contents were then annealed at 190 °C for 10 minutes to form a one-half monolayer of Se.
  • ZnSeo.25So.75 (by material content) was grown by dripping in a solution of 0.61 mmol DEZ, 200ul tri-n-butylphosphine, 0.01 g (0.13 mmol) selenium, 0.012 g (0.037 mmol) sulfur, and 2.5 ml ODE under vigorous stirring. The flask contents were then annealed at 190 °C for 10 minutes.
  • the resulting nanocrystals had a relative quantum efficiency of
  • the InP cores were formed by the following process. 0.12 g (0.52mmol) myristic acid, 0.045 g (O.lmmol) Zn undecylenate and 7 ml ODE were loaded into a three neck flask. The mixture was degassed at 100 °C for 1 hour. After switching to N 2 overpressure, the flask contents were heated to 300 °C, while vigorously stirring its contents. Two precursor solutions were prepared and loaded into corresponding syringes. The first precursor solution contained 0.013 g (0.08 mmol) trimethylindium, 0.012 g (0.048 mmol)
  • the reaction flask reached 300 °C, the first syringe was quickly injected into the hot flask. After a time delay of 0.5 to 1.0 s, the second syringe was rapidly injected into the hot flask. After the second injection, the flask temperature was lowered to 270 °C and the nanocrystals were grown for 36 minutes in total. The reaction was stopped by removing the heating source.
  • the above III-V based nanocrystals were shelled with wide bandgap II- VI materials.
  • 150 ul (2.6 mmol) degassed acetic acid was loaded into a syringe and then injected into the flask. This was followed by annealing the contents of the flask for 60 minutes at 240 °C.
  • the reaction flask was then cooled to 190 °C, 0.5ml (1.5 mmol) oleylamine was injected into the flask, and its contents were annealed at 190 °C for 10 minutes.
  • Two ZnSeS-based shells were grown on the etched nanocrystals by the following procedure.
  • the first solution of 0.315 mmol DEZ and 1 ml ODE was added dropwise to the reaction mixture under vigorous stirring; the flask contents were then annealed at 190 °C for 10 minutes to form a one-half monolayer of Zn.
  • a second solution of 0.028 g (0.35 mmol) selenium, 200 ul tri-n-butylphosphine, and 1.5 ml ODE was added dropwise to the reaction mixture under vigorous stirring; the flask contents were then annealed at 190 °C for 10 minutes to form a one-half monolayer of Se.
  • the second shell of ZnSeo.25So.75 (by material content) was grown by dripping in a solution of 0.61 mmol DEZ, 200ul tri-n-butylphosphine, 0.01 g (0.13 mmol) selenium, 0.012 g (0.037 mmol) sulfur, and 2.5 ml ODE under vigorous stirring. The flask contents were then annealed at 190 °C for 10 minutes.
  • the resulting nanocrystals had a relative quantum efficiency of 78% (room temperature) at an excitation wavelength of 472 nm.
  • photoluminescence data shows that the nanocrystals had an emission peak at 554 nm and a spectral FWHM of 53 nm.
  • Compact homogenous semiconductor regions 105 composed of InP, were formed by the following procedure. 0.12 g (0.52mmol) myristic acid, 0.045 g (0.1 mmol) Zn undecylenate and 7 ml ODE were loaded into a three neck flask. The mixture was degassed at 100 °C for 1 hour. After switching to N 2 overpressure, the flask contents were heated to 300 °C, while vigorously stirring its contents. Two precursor solutions were prepared and loaded into
  • the first precursor solution contained 0.013 g (0.08 mmol) trimethylindium, 0.012 g (0.048 mmol) tris(trimethylsilyl)phosphine, 0.08 mmol oleylamine and 2 ml ODE; the second precursor solution contained 10.0 ml ODE.
  • the reaction flask reached 300 °C, the first syringe was quickly injected into the hot flask to form InP. After a time delay of 0.5 to 1.0 s, the second syringe was rapidly injected into the hot flask, resulting in an immediate and large drop in the flask temperature. Simultaneously, the hot flask was removed from its heat source.
  • FIG. 3 shows the absorbance of the crude solution.
  • the data from Talapin (D. Talapin et al, J. Phys. Chem B 106, 12659 (2002)) can be used to gauge the size of the compact homogenous semiconductor regions 105 composed of InP.
  • data of theirs shows that for 1.7 nm diameter InP nanocrystals, the absorbance curve begins to increase at -540 nm.
  • FIG. 3 shows that the absorbance curve begins to rise at ⁇ 510 nm. Consequently, the InP -based compact homogenous semiconductor regions 105 likely have a size of -1.6 nm.
  • the compact homogenous semiconductor regions 105 (see Example 1-1) that resulted in high quantum efficiencies at high temperatures have sizes near the middle of the desired 1.0 to 2.0 nm size range.
  • the temperature dependences of the photoluminescent (PL) response of the nanocrystals were measured from room temperature up to 150 °C.
  • the measurements were performed using cuvettes filled with 1 ml of the corresponding nanocrystal crude solution and 2 ml of ODE.
  • the excitation wavelength was 450 nm and the PL was measured using a monochrometer. Measurements were taken both upon heating the solutions up to 150 °C and back down to room temperature. At all temperature points, the same PL was obtained for both the heating and cooling phases.
  • the results of the measurements are shown in FIGS. 4A-D.
  • FIGS. 4A-D The results of the measurements are shown in FIGS. 4A-D.
  • FIG. 4A-4C correspond to the temperature-dependent photoluminescent response of the inventive nanocrystals with three shell layers, the inventive nanocrystals with two shell layers, and the prior art nanocrystals with two shell layers, respectively.
  • FIG. 4D plots the integrated PL response of each nanocrystal type as a function of temperature, with the circles, triangles, and squares corresponding to the data from FIGS 4A-4C, respectively.
  • FIG. 4 shows that the inventive nanocrystals with three shell layers had the best temperature response, losing only 17% in photoluminescence intensity at 150° C. This compares with a drop of 33% in photoluminescence intensity (at 150° C) for the prior art nanocrystals, a factor of two poorer temperature stability.
  • nanocrystals with the inventive enhanced confinement had superior temperature stability compared with prior art nanocrystals comprised of typical cores.
  • the temperature-dependent absorbance of the nanocrystals from Example 1-1 was measured, which showed that the absorbance at 450 nm decreased from room temperature to 150 °C; more specifically, it dropped by 9.2%.
  • Combining this absorbance data with the temperature-dependent PL data results in the quantum efficiency only falling by 10% at 150 °C relative to its efficiency value at room temperature (84%).
  • the quantum efficiency of the invented nanocrystals from Example 1-1 at 150 °C is 76%.
  • the significance of this temperature-stable efficiency is best seen when compared to that of typical CdSe nanocrystals. In that case the PL intensity falls off significantly below 100 °C, more specifically it drops by -62% at 90 °C (N. Pradhan et al, J. Amer. Chem. Soc. 129, 3339 (2007))..
  • the core/shell high confinement nanocrystals of examples 1-1 and 1-2 exhibit high quantum efficiency at both room temperature and at elevated temperatures (150 °C). As such, they would be effective materials to be used in high temperature applications, such as, lasers and high power LEDs.

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  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Luminescent Compositions (AREA)

Abstract

La présente invention porte sur un nanocristal semi-conducteur à confinement élevé et un procédé de réalisation d'un tel nanocristal. Le nanocristal comprend une région de semi-conducteur homogène compact ayant une première composition dans la zone centrale du nanocristal, avec son diamètre qui est inférieur à 2,0 nm; et une région d'alliage à gradient comprenant une seconde composition d'alliage variable qui s'étend de la surface de la région de semi-conducteur homogène compact à la surface du nanocristal.
PCT/US2012/055008 2011-10-18 2012-09-13 Nanocristaux semi-conducteurs hautement confinés WO2013058900A1 (fr)

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CN109312228A (zh) * 2016-05-19 2019-02-05 纳米系统公司 改善高度发光的纳米结构的核/壳量子点形态的方法
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AU2017267735B2 (en) * 2016-05-19 2021-11-04 Shoei Chemical Inc. Method to improve the morphology of core/shell quantum dots for highly luminescent nanostructures
CN109312228B (zh) * 2016-05-19 2022-02-25 纳米系统公司 改善高度发光的纳米结构的核/壳量子点形态的方法
WO2018114982A1 (fr) 2016-12-23 2018-06-28 Universiteit Gent Points quantiques ayant un noyau iii-v et une enveloppe externe ii-vi alliée
CN110088227A (zh) * 2016-12-23 2019-08-02 根特大学 具有iii-v族核心和合金化ii-vi族外壳的量子点
EP3865554A1 (fr) 2016-12-23 2021-08-18 QustomDot B.V. Points quantiques ayant un noyau iii-v et une coque externe i-vi en alliage
CN110088227B (zh) * 2016-12-23 2023-01-10 库斯图姆多特公司 具有iii-v族核心和合金化ii-vi族外壳的量子点
CN115893474A (zh) * 2022-09-05 2023-04-04 浙江大学 弱限域半导体纳米晶、其制备方法以及应用

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