Synthesis of indium pnictide nanocrystals

Abstract

The present invention provides the use of trialkoxy pnictide compounds in the preparation of indium pnictide nanocrystals. Additionally, the present invention provides a method for producing an indium pnictide nanocrystal composition, the method comprising a contacting step comprising contacting a precursor composition comprising an indium-containing compound with reagents comprising a trialkoxy pnictide compound.

Description

[0001] SYNTHESIS OF INDIUM PNICTIDE NANOCRYSTALS

[0002] FIELD OF THE INVENTION

[0003] The present invention relates in general to nanocrystals. In particular, the present invention relates to the use of trialkoxy pnictide compounds in the preparation of indium pnictide nanocrystals. Additionally, the present invention relates to a method for producing an indium pnictide nanocrystal composition, the method comprising a contacting step comprising contacting a precursor composition comprising an indium-containing compound with reagents comprising a trialkoxy pnictide compound.

[0004] BACKGROUND

[0005] Indium pnictide (InPn) quantum dots (QDs) are known materials, having first been synthesised over a decade ago. First generation InPn photodiodes were fabricated based on materials with an absorption at 940 nm and managed to achieve external quantum efficiencies (EQE) in the region of 40% with subnanosecond response times.

[0006] Recent research has sought to grow the size of these QDs in order to push their absorption further into the SWIR region. By doing so, the materials move out of direct competition with silicon and instead enter into the relatively uncrowded SWIR absorption window. An absorption peak beyond the ‘eye-safe threshold’ of 1350 nm is of particular interest for photosensing applications.

[0007] Since the first functioning ln(As,P) QD photodiode was reported in 2022 by Hens et al.1, the performance of InPn QD based photodiodes has been iteratively improved. The EQE for lead-free devices can now exceed 25% (-1V, 1400nm, InSb), whilst the dark current densities have been reduced to below 9.6 pA crrT2(-1V, InSb). Hitherto, the synthetic routes to InPn QDs have proceeded via one of three ways:

[0008] (a) The in-situ formation of indium-oleate and its reaction with tris(trimethylsilyl)pnictide in a continuous growth method. (b) The transamination of indium(lll) and pnictogen(lll) salts with a long chain amine and their subsequent reduction using a strong reducing agent.

[0009] (c) The transamination of indium(l) and tris(dimethylamino)pnictide with a long chain amine and their subsequent reduction at elevated temperature.

[0010] The synthetic routes to InAs QDs detailed under (a) and (b) utilize difficult to procure and dangerous chemicals ( / .e. tris(trimethylsilyl)arsine and reducing agents). These chemicals are pyrophoric and accordingly strict protocols must be followed when handling and manipulating them, giving a barrier to process scaling.

[0011] Meanwhile, using synthetic route (c) leads to InAs QDs showing absorbance features below 1200 nm only, with poor size control as evidenced by poor peak to valley (PA / ) ratios and broad exciton full-width-at-half-maximum (FWHM) values. Whilst this can partially be explained by the morphology-dependent absorbance of InPn QDs, which can vary according to QD size and precursor, generally a loss of synthetic control leads to non-specific absorbance profiles.

[0012] Better electronic properties of InAs QD-based SWIR photodiodes are needed if lead-free technologies are to compete with lead-based QDs in the future. There is therefore an unmet need in the art for InPn QDs which have an absorbance in the SWIR region, particularly above the eye-safe threshold, which maintain excellent optical properties.

[0013] SUMMARY OF INVENTION

[0014] It is an object of the present invention to provide a method for producing InPn nanocrystals having an absorbance in the SWIR region which maintain excellent optical properties. In this respect, the inventors have found that the use of trialkoxy pnictide compounds as starting materials in the preparation of indium pnictide nanocrystals leads to improved optical properties whilst also allowing the production of indium pnictide nanocrystals in the SWIR.

[0015] According to a first aspect, the present invention provides a method for producing an indium pnictide nanocrystal composition, the method comprising: a contacting step comprising contacting a precursor composition comprising an indium-containing compound with reagents comprising a trialkoxy pnictide compound.

[0016] According to a second aspect, the present invention provides the use of a trialkoxy pnictide compound in the preparation of an indium pnictide nanocrystal.

[0017] By using a trialkoxy pnictide compounds, the use of hazardous reducing agents and As(-3) precursors may be avoided, such that pyrophoric agents are eliminated from the synthesis. The liquid state of trialkoxy pnictides (compared to group V halides, for example) provides the ancillary benefit of ease of manipulation and combination with a variety of reaction and ligand media.

[0018] Furthermore, we show that even greater synthetic control can be achieved when using triethoxyarsine over, for example, tris(dimethylamino)arsine.

[0019] The inventors have also discovered a remarkable effect when a fluoride- containing compound is introduced into the synthesis. In particular, the inventors have found that, when fluoride is introduced, the resultant nanocrystals exhibit an absorption peak in the far SWIR range.

[0020] According to a third aspect, the present invention provides a indium pnictide nanocrystal exhibiting an absorption peak in the range of 2500 nm to 3500 nm.

[0021] BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 shows the UV-vis spectrum of InAs seeds after being produced according to Example 1 .

[0023] Figure 2 shows the UV-vis spectra of the In-As complex formed after the addition of the a trialkoxy pnictide, and the transition from the complex to form InAs clusters over time. Figure 3 shows the colour change of the purple In-As complex formed after the addition of the a trialkoxy pnictide, and the transition from the complex to form InAs clusters over time. The cluster composition appears a deep red.

[0024] Figure 4 shows UV-vis spectra of InAs nanocrystals that have been prepared using different zinc salts, and shows the effect of each salt on the absorbance of the resultant nanocrystals.

[0025] Figure 5 shows TEM images of InAs nanocrystals that have been prepared using different zinc salts - (a) ZnBr2, and (b) ZnF2- and shows the effect of each salt on the shape of the resultant nanocrystals.

[0026] Figure 6 shows the UV-vis spectra of InAs nanocrystals prepared using different solvents, and shows the effect that the solvent can have on the absorbance of the resultant nanocrystals.

[0027] Figure 7 shows the UV-vis spectra of InAs nanocrystals prepared using different indium (III) containing compounds, and shows the effect of each compound on the absorbance on the resultant nanocrystals.

[0028] Figure 8 shows the UV-vis spectra of InAs seeds prepared using different metal (III) containing compounds, and shows the effect of each compound on the absorbance on the resultant seeds.

[0029] Figure 9 shows the UV-vis spectrum of InAs nanocrystals exhibiting an absorbance above 1250 nm.

[0030] Figure 10 shows (a) the schematic of the interband, (b) intraband transitions with an example of InAs QDs, and (c) the UV-vis spectrum and overlapping FTIR spectrum of InAs QDs showing an absorbance corresponding to an intraband transition at around 3000 nm.

[0031] Figure 11 shows the UV-vis spectra of InAs nanocrystals when (a) no zinc (II) containing compound is used, (b) a zinc-containing compound other than ZnF2is used, and (c) ZnF2is used. Figure 12 shows the (a) UV-vis and (b) FTIR spectra of n-doped InAs nanocrystals over time, demonstrating their superior aerobic stability.

[0032] Figure 13 shows the UV-vis spectrum of InAs quantum dots exhibiting an absorbance maximum at 1400 nm.

[0033] Figure 14 shows the UV-vis spectra of InAs quantum dots at different stages over the course of their synthesis, as described in example 1a.

[0034] Figure 15 shows the normalized UV-vis spectra of InSb quantum dots QD1 , QD2 and QD3, synthesised at three different temperatures of 210 °C, 260 °C and 300 °C respectively.

[0035] DETAILED DESCRIPTION

[0036] When describing the aspects of the invention, the terms used are to be construed in accordance with the following definitions, unless a context dictates otherwise.

[0037] As used in the specification and the appended claims, the singular forms "a", "an," and "the" include both singular and plural referents unless the context clearly dictates otherwise. By way of example, "a nanocrystal" means one nanocrystal or more than one nanocrystal. By way of example, “an indium-containing compound” means one indium-containing compound or more than one indium- containing compound. References to a number when used in conjunction with comprising language include compositions comprising said number or more than said number.

[0038] The terms "comprising", "comprises" and "comprised of’ as used herein are synonymous with "including", "includes" or "containing", "contains", and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. The terms "comprising", "comprises" and "comprised of’ also include the term "consisting of”.

[0039] As used herein, the term "and / or," when used in a list of two or more items, means that any one of the listed items can be employed by itself or any combination of two or more of the listed items can be employed. For example, if a list is described as comprising group A, B, and / or C, the list can comprise A alone; B alone; C alone; A and B in combination; A and C in combination, B and C in combination; or A, B, and C in combination.

[0040] As used herein, unless otherwise expressly specified, all numbers such as those expressing values, ranges, amounts of percentages may be read as if prefaced by the word “about”, even if the term does not expressly appear.

[0041] The term "about" as used herein when referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, indicates that a value includes the standard deviation of error for the device or method being employed to determine the value. The term "about" is meant to encompass variations of + / - 10% or less, + / -5% or less, or + / -0.1 % or less of and from the specified value, insofar such variations are appropriate to perform in the disclosure. It is to be understood that the value to which the modifier "about" refers is itself also specifically disclosed.

[0042] The recitation of numerical ranges by endpoints includes all integer numbers and, where appropriate, fractions subsumed within that range (e.g. 1 to 5 can include 1 , 2, 3, 4 when referring to, for example, a number of elements, and can also include 1 .5, 2, 2.75 and 3.80, when referring to, for example, measurements). The recitation of end points also includes the end point values themselves (e.g. from 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges subsumed therein.

[0043] Unless otherwise defined, all terms used in the disclosure, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. By means of further guidance, definitions for the terms used in the description are included to better appreciate the teaching of the present disclosure. All publications referenced herein are incorporated by reference thereto. As used herein, unless otherwise defined, the term "composition" may be open ended or closed. For example, “composition” comprises the specified material, i.e., the nanocrystals, and further unspecified material, or may consist of the specified material, i.e., to the substantial exclusion of non-specified materials.

[0044] Trialkoxy pnictides for preparing nanocrystals

[0045] According to a first aspect, the present invention provides a method for producing an indium pnictide nanocrystal composition, the method comprising: a contacting step comprising contacting a precursor composition comprising an indium-containing compound with reagents comprising a trialkoxy pnictide compound.

[0046] Any suitable indium-containing compound may be used. The trialkoxy pnictide precursor may be used stepwise, in a ‘cluster’ or ‘seed’ phase as well as in a continuous injection phase. The synthetic method may include heat-up, continuous, or hot-addition stages. To the best of our knowledge, this precursor has hitherto not been used in the formation of colloidal indium pnictide semiconductors.

[0047] Advantageously, the inventors avoid using reducing agents and As(-3) precursors, thereby eliminating pyrophoric materials from the synthesis. Furthermore, the trialkoxy pnictides are in a liquid state, whereas previously used group V halides are generally not liquid. Trialkoxy pnictides therefore provide an additional bonus effect in that they are easy to handle and combine with a variety of reaction and ligand media.

[0048] As used herein, the term “trialkoxy pnictide” is used to refer to a compound represented by the formula Pn(OR)s, wherein Pn is a pnictogen, and R is an alkyl group.

[0049] As used herein, the term “nanocrystal” is used to refer to a crystalline particle with at least one dimension measuring less than 100 nanometres (nm). The nanocrystals described herein are generally colloidal quantum dots, and can be made from typical solution processing. The nanocrystals of the present invention are soluble in a variety of non-polar solvents as-synthesised and are generally capped by ligands coordinated to the surface of the crystalline core of the nanocrystals. As used herein, the term “semiconductor nanocrystal” is used interchangeably with the term “quantum dot”, and is used to refer to a semiconductor crystalline material exhibiting quantum confinement effects that allow it to mimic the properties of an atom. Quantum dots may also be known as zero-dimensional nanocrystals.

[0050] Indium pnictide nanocrystals provide a promising alternative to heavy metal-based materials, but are not yet fully utilised as their performance and optical properties do not yet match those of lead-based nanocrystals. As used herein, the term “indium pnictide nanocrystal” is used to refer to a nanocrystal comprising indium and a group V element. As used herein, the term “group V element”, “pnictogen” or “pnictide” is used to refer to an element in group 15 of the periodic table of elements. For example, a group V element may be nitrogen, phosphorus, arsenic, antimony or bismuth. Preferably, the group V element is antimony, i.e. the preferred indium pnictide nanocrystal is an InSb nanocrystal.

[0051] In a preferred embodiment, the indium-containing compound is an indium halide, preferably wherein the indium-containing compound is an indium (I) halide, an indium (II) halide, or an indium (III) halide, or a mixture thereof. More preferably the indium-containing compound is an indium chloride, wherein the indium chloride is InCi, lnCl2, InCh or a mixture thereof. More preferably, the indium- containing compound is InCi or I nCl2.

[0052] InCi and I nCl2 are both capable of undergoing disproportionation. These species are particularly preferred, as it is believed that indium in its +1 or +2 oxidation state can behave as a redox reagent and act as an electron source for the reduction of Sb(lll) and As(lll) into their (-3) states necessary for bonding to In(lll). This means that InCi and / or I nCl2 can be used without the deployment of a reducing agent in combination with As(lll) to successfully form InAs nanocrystals. Reducing agents are typically air and moisture sensitive and may give off flammable gases when handled in air, and so it is advantageous to avoid their use in the production of InAs nanocrystals. In a preferred embodiment, the precursor composition further comprises a solvent. Preferably the solvent is a polar solvent or a non-polar solvent, preferably wherein the solvent is a non-polar solvent. More preferably the solvent is selected from the group consisting of octadecene, oleylamine, octylamine, butylamine, dioctylamine, heptadecane, hexadecane, oleic acid, tertiary phosphines (such as trialkylphosphines, for example trioctylphosphine and triphenylphosphine) and secondary phosphines.

[0053] Preferably, the mixture further comprises a ligand. Preferably, the ligand is a C2- C24 organic compound comprising a functional group selected from the group consisting of amino, thiol, hydroxyl and carboxylic acid. The ligand is capable of forming a complex with a nanocrystal by coordinating to a surface of the nanocrystal. A nanocrystal generally comprises a crystalline core with dimensions in the order of tens of nanometres. They are typically stabilised as a colloidal solution by surface capping ligands, which may coordinate to the crystalline core as Lewis acidic (Z-type), Lewis basic (L-type) or anionic (X-type) species.

[0054] As used herein, the term “organic compound” is used to refer to a compound comprising carbon atoms covalently bound to other atoms. As used herein, the term “Cx-Cy” organic compound, wherein x and y are integers, is used to refer to an organic compound containing at least x and no more than y carbon atoms.

[0055] More preferably, the ligand is an aromatic or aliphatic compound comprising a functional group selected from the group consisting of amino, thiol, hydroxyl and carboxylic acid. Preferably, the ligand is a C2-C24 aromatic or aliphatic organic compound comprising a functional group selected from the group consisting of amino, thiol, hydroxyl and carboxylic acid. More preferably, the ligand is a compound selected from the group consisting of trialkylphosphines, aminobenzoic acids, dicarboxylic acids, aminoalkylcarboxylic acids, mercaptopropionic acid, mercaptobenzoic acid, thioalkanes, dithioalkanes, thiocarboxylic acids, thioglycolic acid, polyethylene glycol), polyethylene glycol) bis(3-aminopropyl) terminated, didodecyldimethylammonium bromide, n-dodecylammonium bromide, dodecyltrimethylammonium bromide, dimercaptosuccinic acid, oleic acid, oleylamine, bis(diphenylphosphino)methane, alkylamines, and mixtures thereof. Oleylamine and trialkylphosphines such as trioctylphosphine and triphenylphosphine are particularly preferred.

[0056] Preferably, the ligand is a compound selected from the group consisting of mercaptopropionic acid, mercaptobenzoic acid, thioglycolic acid, polyethylene glycol), polyethylene glycol) bis(3-aminopropyl) terminated, didodecyldimethylammonium bromide, n-dodecylammonium bromide, dodecyltrimethylammonium bromide, dimercaptosuccinic acid, oleic acid, oleylamine, bis iphenylphosphino)methane, trioctylphosphine, triphenylphosphine and mixtures thereof.

[0057] The contacting step may be carried out in a number of different ways, as described below. The methods are all used to produce indium arsenide semiconductor nanocrystals. In one embodiment, the semiconductor nanocrystals are produced via a heat-up method, optionally in combination with a continuous addition. In an alternative embodiment, the semiconductor nanocrystals are produced via a hot addition method, optionally in combination with a continuous addition. In an alternative embodiment, the semiconductor nanocrystals are produced via a continuous addition. In an alternative embodiment, the semiconductor nanocrystals are produced via a combination of the abovementioned methods. The use of a continuous growth method is preferred as it is believed to be excellent at maintaining colloidal stability and monodispersity within our QDs.

[0058] Various aspects of the methods of the invention, such as the particular reagents and / or reaction conditions, may be varied so as to provide nanocrystals of a desired size so as to achieve desired optical properties, such as desired absorption and emission (for example for a particular use of the nanocrystals).

[0059] For example, the reagents used (particularly the indium-containing compound and arsenic-containing compound) in the methods may be varied to provide nanocrystals of a desired size so as to achieve desired optical properties, such as desired absorption and emission (for example for a particular use of the nanocrystals). For example, the reaction conditions of the methods may be varied to provide nanocrystals of a desired size so as to achieve desired optical properties, such as desired absorption and emission (for example for a particular use of the nanocrystals).

[0060] In other words, the uses and methods of the invention may be used to prepare nanocrystals having size-tuneable optical properties. Examples of the reagents and / or reaction conditions that may be varied are discussed herein.

[0061] Hot addition

[0062] As described in the review by Tamang et al. (Chem. Rev. 2016, 116, 10731-10819), in the case of the hot addition method, the separation of nucleation and growth can be achieved by the rapid injection of the reagents into the hot solvent, which raises the concentration in the reaction flask above the nucleation threshold. The hot injection leads to a nucleation burst, which is quickly quenched by two factors: (i) the fast cooling of the reaction mixture, enhanced by the fact that the solution to be injected is at room temperature; (ii) the decreased supersaturation due to precursor / monomer consumption during nucleation.

[0063] In a certain embodiment, the contacting step comprises: a) heating the mixture to a first temperature, wherein the mixture comprises the precursor composition, b) adding the reagents to the mixture, c) maintaining the mixture at the first temperature for a first predetermined length of time to form a plurality of indium pnictide seed particles.

[0064] Preferably, the first temperature is in the range of 200 °C to 320 °C, preferably in the range of 220 °C to 300 °C, preferably in the range of 240 °C to 280 °C.

[0065] Preferably, prior to addition to the mixture in step b), the plurality of reagents have a temperature in the range of 5 °C to 50 °C, preferably in the range of 10 °C to 35 °C, preferably in the range of 15 °C to 25 °C, preferably about room temperature. Preferably, the first predetermined length of time is in the range of 10 minutes to 60 minutes, preferably in the range of 15 minutes to 50 minutes, preferably in the range of 20 minutes to 40 minutes, preferably in the range of 25 minutes to 35 minutes.

[0066] Preferably, the contacting step further comprises: d) reducing the temperature of the mixture to a second temperature, e) continuously adding the reagents to the mixture for a second predetermined length of time to produce an indium pnictide semiconductor nanocrystal.

[0067] Preferably, the second temperature is lower than the first temperature and is in the range of 150 °C to 275 °C, preferably in the range of 175 °C to 275 °C, preferably in the range of 200 °C to 260 °C.

[0068] Preferably, the second predetermined length of time is in the range of 60 minutes to 180 minutes, preferably in the range of 90 minutes to 150 minutes, preferably in the range of 100 minutes to 140 minutes, preferably in the range of 110 minutes to 130 minutes.

[0069] Continuous addition

[0070] In an alternative embodiment, the contacting step comprises: a) heating the mixture to a third temperature, wherein the mixture comprises the precursor composition, b) continuously adding the plurality of reagents to the mixture for a third predetermined length of time to produce an indium pnictide semiconductor nanocrystal.

[0071] Preferably, the third temperature is in the range of 150 °C to 275 °C, preferably in the range of 175 °C to 275 °C, preferably in the range of 200 °C to 260 °C.

[0072] Preferably, the third predetermined length of time is in the range of 60 minutes to 180 minutes, preferably in the range of 90 minutes to 150 minutes, preferably in the range of 100 minutes to 140 minutes, preferably in the range of 110 minutes to 130 minutes.

[0073] Heat up method

[0074] As outlined in Tamang et al., the heat up method relies on attaining the degree of supersaturation necessary for homogeneous nucleation via the in situ formation of reactive species upon supply of thermal energy.

[0075] In an alternative embodiment, the contacting step comprises: a) adding the plurality of reagents to the mixture, wherein the mixture comprises the precursor composition, and b) heating the mixture to a fourth temperature.

[0076] Preferably, the fourth temperature is in the range of 150 °C to 275 °C, preferably in the range of 175 °C to 275 °C, preferably in the range of 200 °C to 260 °C.

[0077] Preferably, the contacting step further comprises: c) maintaining the mixture at the fourth temperature for a fourth predetermined length of time.

[0078] Preferably, the fourth predetermined length of time is in the range of 60 minutes to 180 minutes, preferably in the range of 90 minutes to 150 minutes, preferably in the range of 100 minutes to 140 minutes, preferably in the range of 110 minutes to 130 minutes.

[0079] Preferably, the contacting step further comprises: d) continuously adding the plurality of reagents to the mixture for a fifth predetermined length of time to produce an indium pnictide semiconductor nanocrystal.

[0080] Preferably, the fifth predetermined length of time is in the range of 60 minutes to 180 minutes, preferably in the range of 90 minutes to 150 minutes, preferably in the range of 100 minutes to 140 minutes, preferably in the range of 110 minutes to 130 minutes. Introduction of fluoride

[0081] In a particularly preferred embodiment, the method comprising introducing a fluoride-containing compound. Preferably, the fluoride-containing compound is selected from ZnF2, I nF3, NaF and mixtures thereof.

[0082] Without wishing to be bound by theory, the inventors believe that group lll-V QDs (e.g. indium pnictide nanocrystals) synthesised in the presence of zinc halides exhibit significantly improved aerobic stability. This is an indication that surface passivation is occurring. Furthermore, and as explained in more detail in Example 7, it has been found by the inventors that fluoride introduction (via gr. I, gr. II, transition metal or main group salts) leads to hitherto unreported and unprecedented n-doping of InAs QDs, resulting in intraband absorbance in the far SWIR region (>2000nm).

[0083] Cluster and seed method

[0084] In a further particularly preferred embodiment, the method comprises:

[0085] (a) forming an indium pnictide cluster composition by:

[0086] (i) contacting a first indium-containing compound and a first organic solvent to form a solution;

[0087] (ii) adding a first trialkoxy pnictide compound to the solution to form the indium pnictide cluster composition;

[0088] (b) forming an indium pnictide seed composition by:

[0089] (i) contacting an indium (I) containing compound and a metal (III) containing compound to form a mixture;

[0090] (ii) adding a second organic solvent to the mixture;

[0091] (iii) adding a solution comprising a second trialkoxy pnictide compound to the mixture to form an indium pnictide seed composition;

[0092] (c) adding the indium pnictide cluster composition to the indium pnictide seed composition to form an indium pnictide nanocrystal composition.

[0093] Once the indium pnictide cluster composition is formed, it may then be centrifuged to remove insoluble by-products. The indium pnictide clusters typically constitute fewer than 100 core InPn atoms. They are atomically precise and can be resolved using single crystal diffraction. They are molecular in nature and show absorbance features in the visible or UV region, owing to HOMO-LUMO transitions. Clusters represent the molecular limit of single crystal NCs (<2nm in size). They nucleate and then partially or fully redissolve before QD growth proceeds.

[0094] In contrast, QD seeds are ensembles of many thousands of atoms that cannot be resolved using single crystal diffraction. They are atomically precise, but no two QDs are the same as they will contain a range of total atom numbers. QDs can be considered as excitonic, where you have a continuum of energy levels which become known as the valence and conductance bands.

[0095] The first organic solvent and the second organic solvent may be degassed prior to being used. Steps (a) and (b) may each be carried out in a flask. In step (b), the solution may be heated to a temperature in the range of 50 °C to 150 °C, preferably around 80 °C, after the organic solvent is added. Further, the flask may be held under vacuum for a period of time after the organic solvent is introduced, preferably around 15 minutes to 1 hour, more preferably 30 minutes, before then placing it under nitrogen.

[0096] Once the indium pnictide seed composition is formed, it may be purified before step (c) is carried out. For example, the mother solution may be centrifuged to remove insoluble by-products, and the supernatant combined with, for example, acetone (e.g. at a 1 :4 ratio with respect to QD containing solution). The suspension may then again be centrifuged (for example, at 6000 rpm for 3mins) and the supernatant discarded. The remaining solid pellet may then be dissolved in toluene (for example, 5 mL) with sonication and centrifuged to remove insoluble impurities. The supernatant may then be syringe-driven to yield the final QD solution (for example, through 0.22 pm PTFE).

[0097] Preferably, step (a) further comprises:

[0098] (iii) removing any insoluble by-products from the solution. Preferably, step (a) further comprises:

[0099] (iv) leaving the solution to age for at least 1 day, preferably at least 3 days, more preferably at least 5 days, more preferably 7 days.

[0100] During the aging of the solution, the colour changes from purple to a deep red. This indicates the change in the structure of the In-Pn product in the solution, starting off as an In-Pn complexwith discrete absorption peaks as shown in Figure 2 and ending up as InPn clusters ready to be added to the InPn seed composition. Once the solution has turned a deep red, it may be centrifuged again to remove insoluble impurities.

[0101] Preferably, the first indium-containing compound is an indium halide, preferably wherein the indium halide is selected from the group consisting of an indium (I) halide, an indium (II) halide, and an indium (III) halide.

[0102] Preferably, the first indium-containing compound is an indium chloride, preferably wherein the indium chloride is indium (I) chloride.

[0103] Preferably, the first organic solvent and the second organic solvent are each independently selected from the group consisting of octadecene, oleylamine, octylamine, butylamine, dioctylamine, heptadecane, cetane, oleic acid, tertiary phosphines, and secondary phosphines.

[0104] Preferably, the first trialkoxy pnictide and the second trialkoxy pnictide compound are each independently selected from the group consisting of a trialkoxy arsine compound, trialkoxy antimony compound, a trialkoxy phosphine compound, and mixtures thereof. Preferably, the first trialkoxy pnictide and the second trialkoxy pnictide compound are each independently a trialkoxy arsine compound.

[0105] Preferably, the first trialkoxy pnictide and the second trialkoxy pnictide compound are each independently selected from the group consisting of triethoxy arsine, tributoxy antimony, triethoxy antimony, and mixtures thereof. Preferably, the first trialkoxy pnictide and the second trialkoxy pnictide compound are each independently triethoxy arsine. Preferably, the indium (I) containing compound is an indium (I) halide, preferably wherein the indium (I) halide is indium (I) chloride.

[0106] Preferably, the metal (III) containing compound is an indium (III) containing compound or an antimony (III) containing compound. Preferably, the indium (III) containing compound is an indium (III) halide, preferably wherein the indium (III) halide is indium (III) chloride. In an alternative preferred embodiment, the antimony (III) containing compound is an antimony (III) halide, preferably wherein the antimony (III) halide is antimony (III) chloride.

[0107] Preferably, step (b)(i) comprises: contacting the indium (I) containing compound and the metal (III) containing compound with a zinc (II) containing compound to form the mixture.

[0108] Preferably, the zinc (II) containing compound is a zinc (II) halide, preferably wherein the zinc (II) halide is selected from the group consisting of zinc (II) fluoride, zinc (II) chloride, zinc (II) bromide, zinc (II) iodide and mixtures thereof. Preferably, the zinc (II) halide is zinc (II) fluoride.

[0109] Preferably, the method is carried out in an inert atmosphere.

[0110] In this method, the synthesis parameters may be adapted to in order to tune the bandgap of the resultant nanocrystals. This method advantageously provides several ways of achieving this band gap tuning, in particular by varying the sysnthesis solvents, the precursors for the seeds, clusters and QDs, and also the additives which may be included in the synthesis if desired. The synthesis solvents, precursors and additives include but are not limited to: triethoxy arsine, tributoxy antimony, triethoxy antimony, octadecene, oleylamine, octylamine, butylamine, dioctylamine, heptadecane, cetane, oleic acid, tertiary phosphines, secondary phosphines, indium(l) halides, indium(ll) halides, indium(lll) halides, antimony(lll) halides, hydrobromic acid, hydrochloric acid, hydroiodic acid, ammonium halides, sodium halides, zinc halides, zinc acetate, zinc esters, alkyl thiols, trialkylphosphine chalcogenides, group 1 halides, group 2 halides, benzoic acid (and its derivatives), C1 -C5 carboxylic acids, C3- C10 alcohols, trimethylsilyl halides.

[0111] Each of these components may be added (or left out) to affect the band gap of the nanocrystals, , passivate surface defects, and / or improve colloidal stability. This is demonstrated by the examples contained in this application. Figure 4, Figure 5 and Table 1 provide an illustration of the sort of QD band gap and morphology tunability that is possible by varying the zinc halides salt, for example. The inventors have furthermore shown that judicious solvent choice (Figure 6) and M (111) salt selection (Figure 7, Figure 8) can similarly influence the reaction kinetics to allow access to QDs of varying sizes. By varying the synthetic parameters the inventors have evidence to show that InAs QDs showing absorbance maxima beyond 1250 nm (Figure 9) can be achieved.

[0112] Preferably, step (b)(iii) is carried out by:

[0113] (A) heating the mixture to a first temperature in the range of 200 °C to 350 °C;

[0114] (B) adding the solution comprising the second trialkoxy pnictide compound to the mixture;

[0115] (C) cooling the solution to a temperature in the range of 0 °C to 100 °C, preferably room temperature.

[0116] Preferably, the first temperature is in the range of 240 °C to 300 °C, preferably in the range of 250 °C to 290 °C, more preferably 270 °C.

[0117] Preferably, step (B) comprises adding the solution comprising the second trialkoxy pnictide compound to the mixture via injection, wherein the injection is complete within 30 seconds, preferably within 20 seconds, more preferably within 10 seconds, more preferably within 5 seconds, more preferably within 2 seconds.

[0118] Preferably, this solution comprises a further organic solvent, preferably selected from the group consisting of octadecene, oleylamine, octylamine, butylamine, dioctylamine, heptadecane, cetane, oleic acid, tertiary phosphines, and secondary phosphines. This solution may be formed separately before being added to the mixture, for example by combining the two components and stirring for approximately one hour. This is preferably carried out at room temperature.

[0119] Preferably, step (C) comprises:

[0120] (C-1 ) maintaining the solution at a temperature in the range of 200 to

[0121] 350 °C for a predetermined length of time prior to cooling the solution.

[0122] Preferably, the predetermined length of time is at least 1 minute, preferably at least 2 minutes, more preferably at least 5 minutes, more preferably at least 10 minutes, more preferably 15 minutes.

[0123] Preferably, the method further comprises purifying the mixture.

[0124] Preferably, step (c) comprises:

[0125] (i) heating the indium pnictide seed composition to a growth temperature in the range of 200 °C to 350 °C;

[0126] (ii) continuously adding the indium pnictide cluster composition to the indium pnictide seed composition over a predetermined length of time.

[0127] Preferably, the predetermined length of time is at least 1 minute, preferably at least 10 minutes, more preferably at least 30 minutes, more preferably at least 1 hour, more preferably at least 2 hours, more preferably at least 3 hours, more preferably at least 4 hours. Preferably, the predetermined length of time is in the range of 4 hours to 8 hours.

[0128] Further cluster and seed method

[0129] In a further particularly preferred embodiment, the method comprises:

[0130] (a) forming an indium pnictide cluster composition by:

[0131] (i) contacting a first indium-containing compound and a first organic solvent to form a solution;

[0132] (ii) adding a first trialkoxy pnictide compound to the solution to form the indium pnictide cluster composition;

[0133] (b) forming an indium pnictide seed composition by: (i) contacting an indium (I) containing compound and a metal (III) containing compound to form a mixture;

[0134] (ii) adding a second organic solvent to the mixture;

[0135] (iii) adding a solution comprising a second trialkoxy pnictide compound to the mixture to form an indium pnictide seed composition;

[0136] (c) adding part of the indium pnictide cluster composition to the indium pnictide seed composition to form an intermediate indium pnictide nanocrystal composition; and

[0137] (d) adding the remaining indium pnictide cluster composition to the intermediate indium pnictide nanocrystal composition to form an indium pnictide nanocrystal composition.

[0138] Once the indium pnictide cluster composition is formed, it may then be centrifuged to remove insoluble by-products.

[0139] The indium pnictide clusters typically constitute fewer than 100 core InPn atoms. They are atomically precise and can be resolved using single crystal diffraction. They are molecular in nature and show absorbance features in the visible or UV region, owing to HOMO-LUMO transitions. Clusters represent the molecular limit of single crystal NCs (<2nm in size). They nucleate and then partially or fully redissolve before QD growth proceeds.

[0140] In contrast, QD seeds are ensembles of many thousands of atoms that cannot be resolved using single crystal diffraction. They are atomically precise, but no two QDs are the same as they will contain a range of total atom numbers. QDs can be considered as excitonic, where you have a continuum of energy levels which become known as the valence and conductance bands.

[0141] The first organic solvent and the second organic solvent may be degassed prior to being used. Steps (a) and (b) may each be carried out in a flask. In step (b), the solution may be heated to a temperature in the range of 50 °C to 150 °C, preferably around 80 °C, after the organic solvent is added. Further, the flask may be held under vacuum for a period of time after the organic solvent is introduced, preferably around 15 minutes to 1 hour, more preferably 30 minutes, before then placing it under nitrogen.

[0142] Once the indium pnictide seed composition is formed, it may be purified before step (c) is carried out. For example, the mother solution may be centrifuged to remove insoluble by-products, and the supernatant combined with, for example, acetone (e.g. at a 4:1 ratio with respect to mother solution). The suspension may then again be centrifuged (for example, at 6000 rpm for 3mins) and the supernatant discarded. The remaining solid pellet may then be dissolved in toluene (for example, 5-10 mL) with sonication and centrifuged to remove insoluble impurities. The supernatant may then be syringe-driven to yield the final seed containing solution (for example, through 0.22 pm PTFE).

[0143] Preferably, step (a) further comprises:

[0144] (iii) removing any insoluble by-products from the solution.

[0145] Preferably, step (a) further comprises:

[0146] (iv) leaving the solution to age for at least 1 day, preferably at least 3 days, more preferably at least 5 days, more preferably 7 days.

[0147] During the aging of the solution, the colour changes from purple to a deep red. This indicates the change in the structure of the In-Pn product in the solution, starting off as an In-Pn complexwith discrete absorption peaks as shown in Figure 2 and ending up as InPn clusters ready to be added to the InPn seed composition. Once the solution has turned a deep red, it may be centrifuged again to remove insoluble impurities.

[0148] Preferably, the first indium-containing compound is an indium halide, preferably wherein the indium halide is selected from the group consisting of an indium (I) halide, an indium (II) halide, and an indium (III) halide.

[0149] Preferably, the first indium-containing compound is an indium chloride, preferably wherein the indium chloride is indium (I) chloride. Preferably, the first organic solvent and the second organic solvent are each independently selected from the group consisting of octadecene, oleylamine, octylamine, butylamine, dioctylamine, heptadecane, cetane, oleic acid, tertiary phosphines, and secondary phosphines.

[0150] Preferably, the first trialkoxy pnictide and the second trialkoxy pnictide compound are each independently selected from the group consisting of a trialkoxy arsine compound, trialkoxy antimony compound, a trialkoxy phosphine compound, and mixtures thereof. Preferably, the first trialkoxy pnictide and the second trialkoxy pnictide compound are each independently a trialkoxy arsine compound.

[0151] Preferably, the first trialkoxy pnictide and the second trialkoxy pnictide compound are each independently selected from the group consisting of triethoxy arsine, tributoxy antimony, triethoxy antimony, and mixtures thereof. Preferably, the first trialkoxy pnictide and the second trialkoxy pnictide compound are each independently triethoxy arsine.

[0152] Preferably, the indium (I) containing compound is an indium (I) halide, preferably wherein the indium (I) halide is indium (I) chloride.

[0153] Preferably, the metal (III) containing compound is an indium (III) containing compound or an antimony (III) containing compound. Preferably, the indium (III) containing compound is an indium (III) halide, preferably wherein the indium (III) halide is indium (III) chloride. In an alternative preferred embodiment, the antimony (III) containing compound is an antimony (III) halide, preferably wherein the antimony (III) halide is antimony (III) chloride.

[0154] Preferably, step (b)(i) comprises: contacting the indium (I) containing compound and the metal (III) containing compound with a zinc (II) containing compound to form the mixture.

[0155] Preferably, the zinc (II) containing compound is a zinc (II) halide, preferably wherein the zinc (II) halide is selected from the group consisting of zinc (II) fluoride, zinc (II) chloride, zinc (II) bromide, zinc (II) iodide and mixtures thereof. Preferably, the zinc (II) halide is zinc (II) fluoride. Preferably, the method is carried out in an inert atmosphere.

[0156] In this method, the synthesis parameters may be adapted to in order to tune the bandgap of the resultant nanocrystals. This method advantageously provides several ways of achieving this band gap tuning, in particular by varying the sysnthesis solvents, the precursors for the seeds, clusters and QDs, and also the additives which may be included in the synthesis if desired. The synthesis solvents, precursors and additives include but are not limited to: triethoxy arsine, tributoxy antimony, triethoxy antimony, octadecene, oleylamine, octylamine, butylamine, dioctylamine, heptadecane, cetane, oleic acid, tertiary phosphines, secondary phosphines, indium(l) halides, indium(ll) halides, indium(lll) halides, antimony(lll) halides, hydrobromic acid, hydrochloric acid, hydroiodic acid, ammonium halides, sodium halides, zinc halides, zinc acetate, zinc esters, alkyl thiols, trialkylphosphine chalcogenides, group 1 halides, group 2 halides, benzoic acid (and its derivatives), C1 -C5 carboxylic acids, C3- C10 alcohols, trimethylsilyl halides.

[0157] Each of these components may be added (or left out) to affect the band gap of the nanocrystals, passivate surface defects, and / or improve colloidal stability. This is demonstrated by the examples contained in this application. Figure 4, Figure 5 and Table 1 provide an illustration of the sort of QD band gap and morphology tunability that is possible by varying the zinc halides salt, for example. The inventors have furthermore shown that judicious solvent choice (Figure 6) and M (111) salt selection (Figure 7, Figure 8) can similarly influence the reaction kinetics to allow access to QDs of varying sizes. By varying the synthetic parameters the inventors have evidence to show that InAs QDs showing absorbance maxima beyond 1250 nm (Figure 9) can be achieved.

[0158] Preferably, step (b)(iii) is carried out by:

[0159] (A) heating the mixture to a first temperature in the range of 200 °C to 350 °C;

[0160] (B) adding the solution comprising the second trialkoxy pnictide compound to the mixture; (C) cooling the solution to a temperature in the range of 0 °C to 100 °C, preferably room temperature.

[0161] Preferably, the first temperature is in the range of 240 °C to 300 °C, preferably in the range of 250 °C to 290 °C, more preferably 270 °C.

[0162] Preferably, step (B) comprises adding the solution comprising the second trialkoxy pnictide compound to the mixture via injection, wherein the injection is complete within 30 seconds, preferably within 20 seconds, more preferably within 10 seconds, more preferably within 5 seconds, more preferably within 2 seconds.

[0163] Preferably, this solution comprises a further organic solvent, preferably selected from the group consisting of octadecene, oleylamine, octylamine, butylamine, dioctylamine, heptadecane, cetane, oleic acid, tertiary phosphines, and secondary phosphines. This solution may be formed separately before being added to the mixture, for example by combining the two components and stirring for approximately one hour. This is preferably carried out at room temperature.

[0164] Preferably, step (C) comprises:

[0165] (C-1 ) maintaining the solution at a temperature in the range of 200 to

[0166] 350 °C for a predetermined length of time prior to cooling the solution.

[0167] Preferably, the predetermined length of time is at least 1 minute, preferably at least 2 minutes, more preferably at least 5 minutes, more preferably at least 10 minutes, more preferably 15 minutes.

[0168] Preferably, the method further comprises purifying the mixture.

[0169] Preferably, step (c) comprises:

[0170] (i) heating the indium pnictide seed composition to a growth temperature in the range of 200 °C to 350 °C;

[0171] (ii) continuously adding the indium pnictide cluster composition to the indium pnictide seed composition over a predetermined length of time. Preferably, the predetermined length of time is at least 1 minute, preferably at least 10 minutes, more preferably at least 30 minutes, more preferably at least 1 hour, more preferably at least 2 hours, more preferably at least 3 hours, more preferably at least 4 hours. Preferably, the predetermined length of time is in the range of 4 hours to 8 hours.

[0172] Once the intermediate indium pnictide nanocrystal composition is formed, it may be purified before step (d) is carried out. For example, the crude reaction mixture may be centrifuged (for example, at 6000 rpm for 1 minute) to remove insoluble impurities and then may be combined with for example, acetone (e.g. at a 4: 1 ratio with respect to the crude reaction mixture). The suspension may then again be centrifuged (for example, at 6000 rpm for 3mins) and the supernatant discarded. The remaining solid may be collected in a volume of toluene (for example, 10 mL) and centrifuged to remove insoluble impurities. The supernatant may then be syringe-driven to yield the intermediate indium pnictide nanocrystal composition (for example, through a 0.22 pm PTFE filter).

[0173] Preferably, step (d) comprises:

[0174] (i) heating the intermediate indium pnictide nanocrystal composition to a growth temperature in the range of 200 °C to 350 °C;

[0175] (ii) continuously adding the remaining indium pnictide cluster composition to the intermediate indium pnictide nanocrystal composition over a predetermined length of time.

[0176] Preferably, the predetermined length of time is at least 1 minute, preferably at least 10 minutes, more preferably at least 30 minutes, more preferably at least 1 hour, more preferably at least 2 hours, more preferably at least 3 hours, more preferably at least 4 hours. Preferably, the predetermined length of time is in the range of 4 hours to 8 hours.

[0177] Once the indium pnictide nanocrystal composition is formed, it may be purified. For example, the crude reaction mixture may be centrifuged (for example, at 6000 rpm for 1 minute) to remove insoluble impurities and then may be combined with for example, acetone (e.g. at a 4: 1 ratio with respect to the crude reaction mixture). The suspension may then again be centrifuged (for example, at 6000 rpm for 3mins) and the supernatant discarded. The remaining solid may be collected in a volume of toluene (for example, 10 mL) and centrifuged to remove insoluble impurities. The supernatant may then be syringe-driven to yield the intermediate indium pnictide nanocrystal composition (for example, through a 0.22 pm PTFE filter).

[0178] Use of trialkoxy pnictides

[0179] According to a second aspect, the present invention provides the use of a trialkoxy pnictide compound in the preparation of an indium pnictide nanocrystal.

[0180] Nanocrystal with intraband absorption

[0181] According to a third aspect, the present invention provides an indium pnictide nanocrystal composition comprising indium pnictide nanocrystals, wherein the nanocrystals exhibit an absorption peak in the range of 2500 nm to 3500 nm.

[0182] As used herein, the term “absorption peak” takes its standard meaning in the art. It is used to refer to a wavelength at which the composition of nanocrystals exhibits a local maximum absorbance (or optical density) in the ultraviolet-visible region of the electromagnetic spectrum. This may be measured by UV-vis spectroscopy, or UV-vis-NIR spectroscopy may be required to capture SWIR / MWIR absorbance features. In a typical UV-vis(-NIR) spectrum, an absorption peak is identified as a maximum point on the absorption vs wavelength curve, where the gradient of the absorbance curve is equal to 0.

[0183] Preferably, the absorption peak corresponds to an intraband transition. More preferably, the intraband transition is a 1Se-1 Pe intraband transition.

[0184] The inventors have discovered that fluoride introduction, as discussed above, (via gr. I, gr. II, transition metal or main group salts) leads to hitherto unreported and unprecedented n-doping of InPn (e.g. InAs) QDs, resulting in intraband absorbance in the far SWIR region (>2000nm). Figure 10 shows the schematic of the bleach of the 1Sh-1Se interband transition and the opening up of an intense strong 1Se-1 Pe intraband transition transitions with an example of InAs QDs showing the intraband transition around 3000 nm in MWIR range.

[0185] There is a fundamental limitation in bandgap engineering of most QDs, in that you are restricted by the band gap of the bulk material. This restricts the number of potential applications for many QD materials to vis, NIR, SWIR regions. Only materials with very small band gaps can extend into the MWIR / LWIR region. However, these materials are generally toxic (eg HgCdTe) and high cost. However, this bandgap limitation can instead be bypassed by exploiting intraband transitions, and the inventors have hereby discovered a new way of achieving this. MWIR photodiodes are of particular interest for a variety of applications as there is less interference of MWIR radiation within the Earth’s atmosphere than there is SWIR radiation. There are also anticipated applications in the telecoms and mid- IR bioimaging industries. This invention therefore potentially allows the InPn QDs to be used for a new range of applications.

[0186] In a preferred embodiment, the absorption peak is in the range of 2600 nm to 3400 nm, preferably 2700 nm to 3300 nm, more preferably 2800 nm to 3200 nm.

[0187] Preferably, the nanocrystals are selected from the group consisting of InAs nanocrystals, InSb nanocrystals, InAs / Sb nanocrystals, and mixtures thereof. Most preferably, the nanocrystals are InAs nanocrystals.

[0188] The nanocrystals are preferably quantum dots, more preferably colloidal quantum dots.

[0189] Preferably, the nanocrystals have a median particle diameter in the range of 2 nm to 20 nm, preferably 2.5 nm to 15 nm, preferably 3 nm to 12 nm, preferably 4 nm to 10 nm.

[0190] Preferably, the nanocrystal composition exhibits absorption full width at half maximum (FWHM) values of less than 250 nm, preferably less than 225 nm, preferably less than 200 nm, preferably less than 175 nm. Preferably, the nanocrystal composition exhibits emission full width at half maximum (FWHM) values of less than 250 nm, preferably less than 225 nm, preferably less than 200 nm, preferably less than 175 nm.

[0191] Preferably, the nanocrystals exhibit a relative size dispersion of less than 25%, preferably less than 15%, preferably less than 10%, preferably in the range of 1 % to 25%, preferably in the range of 2% to 20%, preferably in the range of 3% to 15%, preferably in the range of 4% to 10%.

[0192] According to a fourth aspect, the present invention provides a device selected from the group consisting of IR sensor, photodetector, sensor, solar cell, a bioimaging or bio-sensing composition, photovoltaic system, display, battery, laser, photocatalyst, spectrometer, injectable composition, field-effect transistor, lightemitting diode, photonic or optical switching device or metamaterial, fiber amplifier, optical gain media, optical fiber, infrared LEDs, lasers, and electroluminescent device, comprising an indium pnictide semiconductor nanocrystal composition of the present invention. Preferably, the IR sensor or photodetector are modified for application as 3D cameras and 3D Time of flight cameras in mobile and consumer, automotive, medical, industrial, defence or aerospace applications. Preferably, the bio-imaging or bio-sensing compositions are modified for use as bio-labels or bio-tags in in vitro or ex vivo applications. Preferably, the infrared LEDs and electroluminescent devices are modified for use in telecommunication devices, night vision devices, solar energy conversion, surveillance devices, thermoelectric or energy generation applications.

[0193] According to a fifth aspect, the present invention provides a film comprising the indium pnictide nanocrystal composition of the present invention.

[0194] EXAMPLES

[0195] Examples are described hereunder illustrating the methods according to the present disclosure.

[0196] Whereas particular examples of this invention have been described below for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.

[0197] Unless other indicated, all parts and all percentages in the following examples, as well as throughout the specification, are parts by weight or percentages by weight respectively.

[0198] Absorption spectra of colloidal quantum dots or quantum dots films were obtained on a JASCO V-770 UV-visible / NIR spectrometer which can provide measurements in the 400 to 3200nm wavelength.

[0199] TEM images and high-resolution transmission electron microscope (HRTEM) images were obtained with an FEI Talos F200X microscope equipped with an X- FEG electron source. The experiment was performed using an acceleration voltage of 200kV and a beam current of approximately 5 nA. Images were recorded with an FEI CETA 4k x 4k CMOS camera. In each case a few drops of the dispersed quantum dots in solvent were placed on a carbon coated copper grid and allow to evaporate. Samples were used as such or treated with acetone then methanol to clean unwanted organic materials before imaging.

[0200] FTIR spectra of the nanocrystals / quantum dots were obtained using a PerkinElmer Spectrum Two FT-IR spectrometer (LiTaO3 detector), with a default scan range of 4000-450 cm-1. Measurements were acquired by dropping the colloidal solution on top of the sample holder.

[0201] Example 1 - Preparation of InAs nanocrystals (CQDs) with trialkoxy pnictide

[0202] In this example, it is demonstrated that trialkoxy pnictide can successfully be used to prepare InPn nanocrystals.

[0203] Preparation of InAs seeds

[0204] InCi (225 mg), InCh (23 mg), ZnF2(26 mg) and a magnetic stirring bead are loaded into a 3-necked 100 ml_ round-bottomed flask and sealed in a water free and nitrogen filled glovebox with rubber septa and a Young’s tap. The flask is cycled onto a Schlenk manifold and equipped with a thermocouple. Degassed oleylamine (OLA) (20 mL) is introduced and the temperature is increased to 80 °C. The flask is then held under vacuum for 30 minutes before placing under nitrogen and increasing the temperature to 270 °C. Separately, and in a nitrogen filled glovebox, As(OEt)3(200 pL) is combined with OLA (258 pL) and stirred at room temperature for 1 hour. 180 pL of this solution is injected at once into the round bottomed flask and the temperature maintained for 15 minutes before cooling to room temperature using a compressed airstream. Purification is performed in a nitrogen filled glovebox. The mother sol is centrifuged to remove insoluble by-products, and the supernatant combined with acetone (1 :4 with respect to QD containing solution). The suspension is centrifuged (6000 rpm, 3mins) and the supernatant discarded. The solid pellet is dissolved in toluene (5 mL) with sonication and centrifuged to remove insoluble impurities. The supernatant is syringe-driven through 0.22 pm PTFE to yield the final QD solution (Figure 1).

[0205] Preparation of amorphous InAs clusters

[0206] InCi (7.4 g) was complexed with HOAm (oleylamine) (50 mL) under sonication, followed by the addition of As(OEt)3(2.8 mL) and stirring overnight. At this point a purple solution is formed, taken to be the formation of an aerobically unstable InAs complex with discrete absorbance features at 542 and 408 nm (Figure 2). The solution is centrifuged to remove insoluble by-products and the supernatant left to age for 7 days until the solution has turned a deep red colour, and the complex is taken to have been converted to clusters (Figure 3). The cluster solution is centrifuged once more to remove insoluble impurities and is ready for use in the continuous growth of InAs seeds.

[0207] Figure 2 in particular shows that when theAs(OEt)3, initially an In-As complex may be formed, as shown by the two discrete absorbances in the UV-vis spectra at day 0. Very quickly these absorbances disappear, indicating the transition to InAs clusters. Figure 3 also demonstrates this transition by showing the colour change of the solution from purple to a deep red. Preparation of InAs nanocrystals

[0208] The cluster growth phase then involves the addition of the InPn clusters to the composition of InPn QD seeds, resulting in the growth of the seeds. This pushes the absorbance of the InPn QDs further into the SWIR spectrum. This may preferably be carried out by any one of the hot addition, continuous addition, or heat-up methods as described above to produce InPn quantum dots exhibiting an absorption maximum in the SWIR spectrum, above 1400 nm, with excellent optical properties.

[0209] Example 1a - Preparation of InAs nanocrystals (CQDs) with trialkoxy pnictide

[0210] In this example, it is demonstrated that trialkoxy pnictide can successfully be used to prepare InPn quantum dots with an absorbance maximum of around 1400 nm.

[0211] Preparation of InAs seeds (absorption maxima -930-960 nm)

[0212] All reagents are dried and degassed, where appropriate, before use. In a N2-filled glovebox, charge a 3-necked 100 mL flask with InCi (225 mg), InCh (23 mg), ZnCI2(822 mg) and a magnetic stirring bar. Fit a closed Young’s adapter to the central neck and seal the remaining side-necks with rubber septa. (NB. glass stoppers should be avoided as they tend to get stuck under vacuum application and become difficult to remove. Neck adapters can be used if required). Cycle the flask onto a Schlenk line via the Young’s adapter three times, maintaining a vacuum until a pressure of less than 0.1 mbar is achieved before cycling to nitrogen. Add 20 mL of oleylamine (OLA) and insert a temperature probe before placing the flask under vacuum and holding at 80 °C for 30 minutes. After this time, place the flask under N2and increase the temperature to 280 °C.

[0213] Separately and in the glovebox, As(OEt)3(200 uL) is combined with OLA (0.258 mL) and stirred in a sealed vial at room temperature for 1 hour. 0.18 mL of this solution is injected at once to the reaction flask and allowed to react for 15 mins. The flask is then cooled to room temperature and placed under vacuum for transfer into the glovebox for purification. The reaction mixture is centrifuged to remove insoluble impurities, and the supernatant combined with acetone (4:1 ratio with respect to the mother sol). The solution is centrifuged and the precipitate combined in a total of 10 mL toluene. The solution is sonicated to dissolve, centrifuged, and the supernatant filtered through 0.22 pm PTFE (polytetrafluoroethylene) to yield the final solution. UV-vis absorption of the product is run at 10x dilution to provide the optical density of the dots for further manipulation.

[0214] The absorption spectrum of these InAs seeds is shown as “Starting QDs” in Figure 14. It can be seen from Figure 14 that these InAs seeds have absorbance maxima in the region of approximately 1000 nm.

[0215] Preparation of InAs clusters

[0216] All reagents are dried and degassed, where appropriate, before use. In a N2-filled glovebox, charge a 100 mL Schott bottle with with InCi (3.7 g), OLA (25 mL) and a magnetic stirring bar. Under vigorous stirring 0.7 mL As(OEt)3is introduced and the bottle capped. The solution is left stirring overnight at room temperature, yielding a deep purple solution. The solution is centrifuged to remove unreacted solid precursors and I n(0), and the supernatant stored in a sealed vial for aging. After 7 days, the solution will have become a deep red colour, indicating a transition from the molecular (amorphous) complex to magic-sized clusters.

[0217] The solution is again centrifuged to remove any insoluble impurities, and the supernatant combined with I PA (isopropyl alcohol) (6:1 ratio with respect to cluster solution). The destabilized solution is centrifuged, and the precipitate is collected in a total of 50 mL TOP (trioctylphosphine) with sonication, or the precipitate is dispersed in a combination of oleyl amine and TOP. UV-vis absorption of the product is run at 20x dilution to provide the optical density of the clusters, taken at A = 400 nm.

[0218] 1stGrowth of InAs seeds using InAs clusters (producing quantum dots with absorption maxima -1200 nm)

[0219] A solution of InAs seeds dispersed in TOP with optical density of 0.4 is prepared in the glovebox. This is done by introducing the corresponding amount of InAs in toluene to 5 mL TOP in a 3-necked 100 mL RBF before removing the toluene in vacuo at 40 °C on a Schlenk line. The vacuum is maintained for 30 minutes or until a pressure of less than 0.05 mbar is achieved, whichever comes last. The flask is then placed under N2and the temperature increased to 290 °C and allowed to stabilize for 1 hour.

[0220] 5 mL InAs clusters in TOP and oleyl amine with an optical density of 11 at 400 nm is loaded into a syringe and mounted into a syringe pump. 4 mL of this solution is injected continuously over 4 hours before cooling the flask to room temperature with a compressed air stream and placing the flask under vacuum for transfer into the glovebox.

[0221] The crude reaction mixture is combined with acetone (4:1 with respect to the mother sol) and centrifuged to precipitate. The solid is collected in a combined volume of 10 mL toluene, centrifuged, and the supernatant driven through a 0.22 pm PTFE filter. The purified quantum dots are then used as seeds to grow quantum dots with absorption maxima around 1400 nm as is demonstrated below.

[0222] The absorption spectrum of these purified quantum dots of this step is shown as “Intermediate QDs” in Figure 14. It can be seen that these intermediate QDs have higher absorption maxima than the starting QDs, in the region of 1200 nm.

[0223] Growth of InAs intermediate quantum dots using InAs clusters (producing quantum dots with absorption maxima -1400 nm)

[0224] A solution of InAs intermediate quantum dots dispersed in TOP with optical density of 0.4 is prepared in the glovebox. This is done by introducing the corresponding amount of InAs intermediate quantum dots in toluene to 5 mL TOP in a 3-necked 100 mL RBF before removing the toluene in vacuo at 40 °C on a Schlenk line. The vacuum is maintained for 30 minutes or until a pressure of less than 0.05 mbar is achieved, whichever comes last. The flask is then placed under N2and the temperature increased to 290 °C and allowed to stabilize for 1 hour.

[0225] 5 mL InAs clusters in TOP and oleyl amine with an optical density of 11 at 400 nm is loaded into a syringe and mounted into a syringe pump. 4 m L of this solution is injected continuously over 4 hours before cooling the flask to room temperature with a compressed air stream and placing the flask under vacuum for transfer into the glovebox.

[0226] The crude reaction mixture is combined with acetone (4:1 with respect to the mother sol) and centrifuged to precipitate. The solid is collected in a combined volume of 10 mL toluene, centrifuged, and the supernatant driven through a 0.22 pm PTFE filter, which produces the final purified quantum dots.

[0227] The absorption spectrum of the quantum dots produced in this final step is shown as “Final QDs” in Figure 14. The absorption spectrum of these quantum dots is also shown in Figure 13. It can be seen that the growth method disclosed above is able to produce quantum dots with absorbance maxima at 1400 nm.

[0228] This method shows the successful use of trialkoxy pnictides to produce InPn quantum dots exhibiting an absorption maximum in the SWIR spectrum, around 1400 nm, with excellent optical properties.

[0229] Example 2 - Effects of different zinc-containing compounds

[0230] The method of the present invention may include the use of different zinc- containing compounds, and these lead to significant effects on the absorbance and shape of the resultant nanocrystals.

[0231] The method of example was followed which uses ZnF2. For the other zinc- containing compounds, the same method was followed, but ZnF2was substituted for the other zinc-containing compounds, whilst keeping the moles of zinc the same.

[0232] Table 1 : The influence of the zinc halides on the optical properties of the resulting InAs QDs. zinc-containing compound used during the synthesis. Furthermore, Figure 5 demonstrates that different zinc-containing compounds also lead to different morphologies. For example, the use of ZnBr2leads to the formation of tetrahedral quantum dots, where the use of ZnF2leads to the formation of tetrapods. The morphologies can therefore be tuned by choice of zinc-containing compound.

[0233] Without wishing to be bound by theory, it is believed that the aerobic stability of lll-V QDs is improved when synthesised in the presence of zinc halide. This is in itself an indication that surface passivation is occurring.

[0234] Example 3 - Effects of different solvents

[0235] This example demonstrates that different solvents, used in different ratios, can also influence the optical properties of the resultant nanocrystal seeds. This is referring to the solvent which is introduced prior to the temperature increase to 80 °C during the preparation of the InAs seeds. In Example 1 , this is oleylamine (OLA) (20 mL).

[0236] In this example, the method of forming the InAs seeds of Example 1 is repeated, and the ratio of oleylamine and heptadecane was varied, while keeping the overall volume of solvent used the same. As seen in Figure 6, the different ratios of solvents lead to different absorbance peaks observed in the UV-vis spectra, indicating that the solvent can be used to tune the band gap of the resultant nanocrystals. Example 4 - Effects of different indium (III) containing compounds

[0237] This example demonstrates that different metal (III) containing compounds, in particular different indium (III) containing compounds, can also influence the optical properties of the resultant nanocrystal seeds This is referring to the indium (III) containing compound used in the preparation of the InAs seeds. In Example 1 , this is InCh.

[0238] In this example, the method of forming the InAs seeds of Example 1 is repeated, and the indium (III) containing compound was varied. As seen in Figure 7, the different indium (III) containing compounds lead to very different absorption peaks, confirming that the indium (III) containing compound can be used to tune the band gap of the resultant nanocrystals.

[0239] Example 5 - Effects of different metal (III) containing compounds

[0240] This example demonstrates that different metal (III) containing compounds, in particular different metals in the metal (III) containing compounds, can also influence the optical properties of the resultant nanocrystal seeds. This is referring to the metal (III) containing compound used in the preparation of the InAs seeds. In Example 1 , this is InCh.

[0241] In this example, the method of forming the InAs seeds of Example 1 is repeated, and the metal (III) containing compound was varied. The other metal (III) containing compound used in the example is SbCh. As seen in Figure 8, the different metal (III) containing compounds lead to different absorption peaks, confirming that the metal in the metal (III) containing compound can be used to tune the band gap of the resultant nanocrystals.

[0242] Example 6 - Achieving an absorption maximum beyond 1250 nm

[0243] This example demonstrates that, by varying the synthetic parameters, it is possible to produce InAs QD seeds showing absorbance maxima beyond 1250 nm. In this example, the nanocrystals were produced according to the following: InCi (300 mg), triphenylphosphine (300 mg) and a magnetic stirring bead are loaded into a 3-necked 100 mL round-bottomed flask and sealed in a water free and nitrogen filled glovebox with rubber septa and a Young’s tap. The flask is cycled onto a Schlenk manifold and equipped with a thermocouple. Degassed oleylamine (OLA) (15 mL) is introduced and the temperature is increased to 80 °C. The flask is then held under vacuum for 30 minutes before placing under nitrogen and increasing the temperature to 280 °C. Separately, and in a nitrogen filled glovebox, As(OEt)3(168 pL) is combined with OLA (600 pL) and stirred at room temperature for 1 hour. 100 pL of this solution is injected at once into the round bottomed flask and the temperature maintained allowed to reduce to 250 °C. 300 pL of the As(OEt)3 / OLA solution is then continuously injected over 3 hours and left a further two hours before cooling to room temperature using a compressed air stream. Purification is performed in a nitrogen filled glovebox. The mother sol is centrifuged to remove insoluble by-products, and the supernatant combined with acetone (1 :4 with respect to QD containing solution). The suspension is centrifuged (6000 rpm, 3mins) and the supernatant discarded. The solid pellet is dissolved in toluene (5 mL) with sonication and centrifuged to remove insoluble impurities. The supernatant is syringe-driven through 0.22 pm PTFE to yield the final QD solution (Figure 1).

[0244] As seen in Figure 9, the absorbance of these nanocrystal seeds has been pushed beyond 1250 nm ready for further growth into the SWIR region.

[0245] Example 7 - Bonus effects of fluoride-containing compounds

[0246] This example demonstrates that the introduction of fluoride into the synthesis of the InAs seeds and nanocrystals leads to n-doping, and results in an absorbance in the far SWIR region.

[0247] In particular, it was found that fluoride introduction via any or all of group I, group II, transition metal or main group salts leads to hitherto unreported and unprecedented n-doping of InAs QDs, resulting in intraband absorbance in the far SWIR region (>2000nm). n-doping results in bleach of 1Sh-1Se interband transition and opens up an intense strong 1Se-1 Pe intraband transition. Figure 10 shows the schematic of these transitions with an example of InAs QDs showing intraband transition around 3000nm. These n-doped InAs QDs show remarkable air stability both in solution and film even after storing the QDs for several weeks in air under ambient conditions (see Figure 12). We can control the doping by synthesis design.

[0248] There were three sets of samples in this experiment:

[0249] A. Synthesis of Example 1 with no zinc halides

[0250] B. Synthesis of Example 1 with ZnBr2

[0251] C. Synthesis of Example 1 with ZnF2

[0252] To prepare each of these samples, the method of Example 1 was repeated once exactly (except the change in zinc-containing compound). For samples A and B, the method of Example 1 was repeated once again with the further exception that the time at which the mixture was maintained at 270 °C after the addition of the trialkoxy pnictide was 5 mins, rather than 15mins, before cooling to room temperature. The UV-vis spectra for these InAs nanocrystal compositions is shown in Figure 11.

[0253] As shown in Figure 11 , the n-doping and the far infrared peak are only exhibited by the ZnF2sample.

[0254] In the absence of Zn-halides and in the presence of ZnBr2, InAs QDs do not exhibit any n-doping (see Figure 11). However, when we introduce fluoride source (ZnF2, lnF3, NaF) in the synthesis, n-doping is observed (see Figure 11). This phenomenon therefore appears uniquely beneficial to fluoride. We can control the onset and extent of doping by tuning the synthesis parameters. It is believed that further synthetic tuning can lead to MWIR absorbance (>2000-6000nm).

[0255] Figure 12 shows the absorbance of the n-doped QDs over time. As shown in Figure 12, the absorbance of the n-doped QDs shows minimal change over time in both the interband and intraband transitions. This indicates that the QDs have excellent aerobic stability in solution. Example 8 - Production of Indium Antimony (InSb) Quantum Dots using trialkoxy antimony precursors

[0256] Some examples above focus on the synthesis of indium arsenic quantum dots using trialkoxy arsenic compounds. However, the methods of this disclosure may be used to produce a variety of indium pnictide quantum dots from various trialkoxy pnictide precursors. This includes the production of indium antimony quantum dots through the use of trialkoxy antimony compounds, as is demonstrated in this example.

[0257] This example also demonstrates how fine tuning of reaction conditions, such as temperature, can produce quantum dots with improved optical and electronic properties. The use of trialkoxy antimony compounds enables the synthesis of InSb quantum dots which have absorption wavelengths in the SWIR (short-wave infrared) to MWIR (mid-wave infrared) regions and even to the LWIR (long-wave infrared) region. The quantum dots produced in this example may be used as seeds, in combination with appropriate clusters, for further growth of larger InSb quantum dots with extended absorption wavelengths.

[0258] Preparation of InSb QDs lnCI3(332 mg, 1.5mmol), ZnBr2(1013 mg, 4.5mmol) and a magnetic stirring bead are loaded into a 3-necked 100 ml_ round-bottomed flask and sealed in a water free and nitrogen filled glovebox with rubber septa and a Young’s tap. The flask is cycled onto a Schlenk manifold and equipped with a thermocouple. Degassed oleylamine (OLA) (10 mL) and degassed heptadecane (10 mL) is introduced and the temperature is increased to 80 °C. The flask is then held under vacuum for 60 minutes before placing under nitrogen and decreasing the temperature to 50 °C. Separately, and in a nitrogen filled glovebox, Sb(OEt)3(127 pL, 0.75mmol) is combined with OLA (373 pL) and stirred at room temperature for 1 hour. 500 pL of this solution is injected at once into the round bottomed flask and the temperature maintained for 15 minutes before heating up to desired temperature. Additionally, in a nitrogen filled glovebox, a reducing agent, NaBH3CN (425.5mg, 6.7mmol) is combined with 5mL diglyme or bis(2-methoxyethyl) ether and stirred at room temperature for an hour. The entire solution is simultaneously added along with Sb-oleyl amine solution. The temperature of the reaction may be varied from 50 °C-330 °C. The reaction time may be varied from 1 to 30 minutes.

[0259] The reaction temperature may be varied and, in this example, the reaction detailed above was carried out three times at different temperatures to produce three different sets of quantum dots. The first quantum dots, QD1 , were synthesised at 210 °C. The second quantum dots, QD2, were synthesised at 260 °C. The third quantum dots, QD3, were synthesised at 300 °C.

[0260] Purification is performed in a nitrogen filled glovebox. The mother sol is centrifuged to remove insoluble by-products, and the supernatant combined with acetone (1 :4 with respect to QD containing solution). The suspension is centrifuged (6000 rpm, 3mins) and the supernatant discarded. The solid pellet is dissolved in toluene (5 mL) with sonication and centrifuged to remove insoluble impurities. The supernatant is syringe-driven through 0.22 pm PTFE to yield the final quantum dot solution (InSb QDs).

[0261] The normalised UV-Vis spectra of QD1 , QD2 and QD3 are shown in Figure 15. This figure demonstrates the ability of the present inventors to tune the UV-Vis spectra of InSb quantum dots into different wavelength regions through variations in reaction temperature. The variation in reaction temperature between each different synthesis leads to variations in the size of the resulting quantum dots, which ultimately leads to the variation in optical and electronic properties seen on the UV-Vis spectra. Larger quantum dots exhibit absorbance peaks at higher wavelengths in comparison to smaller quantum dots. QD1 has an absorption peak at around 800 nm, QD2 has an absorption peak at around 1000 nm and QD3 has an absorption peak at around 1200 nm. Therefore, by increasing the temperature from 210 °C, to 260 °C to 300 °C, the present inventors have managed to push the absorbance peak of these InSb quantum dots towards a higher wavelength and into the SWIR region. REFERENCES

[0262] 1 . Leemans et al., Adv. Sci. 2022, 2200844.

[0263] 2. Tamang et al., Chem. Rev. 2016, 116, 10731-10819.

Claims

CLAIMS1 . A method for producing an indium pnictide nanocrystal composition, the method comprising: a contacting step comprising contacting a precursor composition comprising an indium-containing compound with reagents comprising a trialkoxy pnictide compound.

2. The method of claim 1 , wherein the indium-containing compound is an indium halide, preferably wherein the indium-containing compound is an indium (I) halide, an indium (II) halide, or an indium (III) halide, or a mixture thereof, more preferably wherein the indium-containing compound is an indium chloride, wherein the indium chloride is InCi, lnCl2, InCh or a mixture thereof, more preferably wherein the indium-containing compound is InCi or lnCl2, more preferably wherein the indium-containing compound is lnCl2.

3. The method of any one of the preceding claims, wherein the precursor composition further comprises a solvent, preferably wherein the solvent is a polar solvent or a non-polar solvent, preferably wherein the solvent is a non-polar solvent, more preferably wherein the solvent is selected from the group consisting of octadecene, oleylamine, octylamine, butylamine, dioctylamine, heptadecane, hexadecane, oleic acid, tertiary phosphines and secondary phosphines.

4. The method of any one of the preceding claims, wherein the contacting step comprises: a) heating a mixture to a first temperature, wherein the mixture comprises the precursor composition, b) adding the reagents to the mixture, c) maintaining the mixture at the first temperature for a first predetermined length of time to form a plurality of indium pnictide seed particles,preferably wherein the first temperature is in the range of 275 °C to 350 °C, preferably in the range of 275 °C to 325 °C, preferably in the range of 290 °C to 310 °C, preferably wherein prior to addition to the mixture in step b), the reagents have a temperature in the range of 5 °C to 50 °C, preferably in the range of 10 °C to 35 °C, preferably in the range of 15 °C to 25 °C, preferably about room temperature, and preferably wherein the first predetermined length of time is in the range of 10 minutes to 60 minutes, preferably in the range of 15 minutes to 50 minutes, preferably in the range of 20 minutes to 40 minutes, preferably in the range of 25 minutes to 35 minutes.

5. The method of claim 4, wherein the contacting step further comprises: d) reducing the temperature of the mixture to a second temperature, e) continuously adding the reagents to the mixture for a second predetermined length of time to produce an indium pnictide semiconductor nanocrystal, preferably wherein the second temperature is lower than the first temperature and is in the range of 150 °C to 275 °C, preferably in the range of 175 °C to 275 °C, preferably in the range of 200 °C to 260 °C, preferably wherein the second predetermined length of time is in the range of 60 minutes to 180 minutes, preferably in the range of 90 minutes to 150 minutes, preferably in the range of 100 minutes to 140 minutes, preferably in the range of 110 minutes to 130 minutes.

6. The method of any one of claims 1 to 3, wherein the contacting step comprises: a) heating a mixture to a third temperature, wherein the mixture comprises the precursor composition, b) continuously adding the plurality of reagents to the mixture for a third predetermined length of time to produce an indium pnictide semiconductor nanocrystal,preferably wherein the third temperature is in the range of 150 °C to 275 °C, preferably in the range of 175 °C to 275 °C, preferably in the range of 200 °C to 260 °C, preferably wherein the third predetermined length of time is in the range of 60 minutes to 180 minutes, preferably in the range of 90 minutes to 150 minutes, preferably in the range of 100 minutes to 140 minutes, preferably in the range of 110 minutes to 130 minutes.

7. The method of any one of claims 1 to 3, wherein the contacting step comprises: a) adding the plurality of reagents to the mixture, wherein the mixture comprises the precursor composition, and b) heating the mixture to a fourth temperature, preferably wherein the fourth temperature is in the range of 150 °C to 275 °C, preferably in the range of 175 °C to 275 °C, preferably in the range of 200 °C to 260 °C.

8. The method of claim 7, wherein the contacting step further comprises: c) maintaining the mixture at the fourth temperature for a fourth predetermined length of time, preferably wherein the fourth predetermined length of time is in the range of 60 minutes to 180 minutes, preferably in the range of 90 minutes to 150 minutes, preferably in the range of 100 minutes to 140 minutes, preferably in the range of 110 minutes to 130 minutes.

9. The method of claim 7 or claim 8, wherein the contacting step further comprises: d) continuously adding the plurality of reagents to the mixture for a fifth predetermined length of time to produce an indium pnictide semiconductor nanocrystal, preferably wherein the fifth predetermined length of time is in the range of 60 minutes to 180 minutes, preferably in the range of 90 minutes to 150 minutes, preferably in the range of 100 minutes to 140 minutes, preferably in the range of 110 minutes to 130 minutes.

10. The method of any one of the preceding claims, wherein the method comprising introducing a fluoride-containing compound.

11. The method of claim 10, wherein the fluoride-containing compound is selected from ZnF2, I nF3, NaF and mixtures thereof.

12. The method of any one of the preceding claims, comprising:(a) forming an indium pnictide cluster composition by:(i) contacting a first indium-containing compound and a first organic solvent to form a solution;(ii) adding a first trialkoxy pnictide compound to the solution to form the indium pnictide cluster composition;(b) forming an indium pnictide seed composition by:(i) contacting an indium (I) containing compound and a metal (III) containing compound to form a mixture;(ii) adding a second organic solvent to the mixture;(iii) adding a solution comprising a second trialkoxy pnictide compound to the mixture to form an indium pnictide seed composition;(c) adding the indium pnictide cluster composition to the indium pnictide seed composition to form an indium pnictide nanocrystal composition.

13. The method of claim 12, wherein step (a) further comprises:(iii) removing any insoluble by-products from the solution.

14. The method of claim 12 or claim 13, wherein step (a) further comprises:(iv) leaving the solution to age for at least 1 day, preferably at least 3 days, more preferably at least 5 days, more preferably 7 days.

15. The method of any one of claims 12 to 14, wherein the first indium- containing compound is an indium halide, preferably wherein the indium halide is selected from the group consisting of an indium (I) halide, an indium (II) halide, and an indium (III) halide.

16. The method of any one of claims 12 to 15, wherein the first indium- containing compound is an indium chloride, preferably wherein the indium chloride is indium (I) chloride.

17. The method of any one of claims 12 to 16, wherein the first organic solvent and the second organic solvent are each independently selected from the group consisting of octadecene, oleylamine, octylamine, butylamine, dioctylamine, heptadecane, cetane, oleic acid, tertiary phosphines, and secondary phosphines.

18. The method of any one of claims 12 to 17, wherein the first trialkoxy pnictide and the second trialkoxy pnictide compound are each independently selected from the group consisting of a trialkoxy arsine compound, trialkoxy antimony compound, a trialkoxy phosphine compound, and mixtures thereof.

19. The method of any one of claims 12 to 18, wherein the first trialkoxy pnictide and the second trialkoxy pnictide compound are each independently selected from the group consisting of triethoxy arsine, tributoxy antimony, triethoxy antimony, and mixtures thereof.

20. The method of any one of claims 12 to 19, wherein indium (I) containing compound is an indium (I) halide, preferably wherein the indium (I) halide is indium (I) chloride.21 . The method of any one of claims 12 to 20, wherein metal (III) containing compound is an indium (III) containing compound or an antimony (III) containing compound.

22. The method of claim 21 , wherein the indium (III) containing compound is an indium (III) halide, preferably wherein the indium (III) halide is indium (III) chloride.

23. The method of claim 21 , wherein the antimony (III) containing compound is an antimony (III) halide, preferably wherein the antimony (III) halide is antimony (III) chloride.

24. The method of any one of claims 12 to 23, wherein step (b)(i) comprises:contacting the indium (I) containing compound and the metal (III) containing compound with a zinc (II) containing compound to form the mixture.

25. The method of claim 24, wherein the zinc (II) containing compound is a zinc (II) halide, preferably wherein the zinc (II) halide is selected from the group consisting of zinc (II) fluoride, zinc (II) chloride, zinc (II) bromide, zinc (II) iodide and mixtures thereof.

26. The method of any one of claims 12 to 25, wherein the method is carried out in an inert atmosphere.

27. The method of any one of claims 12 to 26, wherein step (b)(iii) is carried out by:(A) heating the mixture to a first temperature in the range of 200 °C to 350 °C;(B) adding the solution comprising the second trialkoxy pnictide compound to the mixture;(C) cooling the solution to a temperature in the range of 0 °C to 100 °C, preferably room temperature.

28. The method of claim 27, wherein the first temperature is in the range of 220 °C to 300 °C, preferably in the range of 250 °C to 290 °C, more preferably 270 °C.

29. The method of claim 27 or claim 28, wherein step (B) comprises adding the solution comprising the second trialkoxy pnictide compound to the mixture via injection, wherein the injection is complete within 30 seconds, preferably within 20 seconds, more preferably within 10 seconds, more preferably within 5 seconds, more preferably within 2 seconds.

30. The method of any one of claims 27 to 29, wherein step (C) comprises: (C-1 ) maintaining the solution at a temperature in the range of 200 °C to 350 °C for a predetermined length of time prior to cooling the solution.

31. The method of claim 30, wherein the predetermined length of time is at least 1 minute, preferably at least 2 minutes, more preferably at least 5 minutes, more preferably at least 10 minutes, more preferably 15 minutes.

32. The method of any one of claims 12 to 31 , wherein the method further comprises purifying the mixture.

33. The method of any one of claims 12 to 32, wherein step (c) comprises:(i) heating the indium pnictide seed composition to a growth temperature in the range of 200 °C to 350 °C;(ii) continuously adding the indium pnictide cluster composition to the indium pnictide seed composition over a predetermined length of time.

34. The method of claim 33, wherein the predetermined length of time is at least 1 minute, preferably at least 10 minutes, more preferably at least 30 minutes, more preferably at least 1 hour, more preferably at least 2 hours, more preferably at least 3 hours, more preferably at least 4 hours.

35. The method of claim 33 or claim 34, wherein the predetermined length of time is in the range of 4 hours to 8 hours.

36. The method of any one claims 1 to 11 , comprising:(a) forming an indium pnictide cluster composition by:(i) contacting a first indium-containing compound and a first organic solvent to form a solution;(ii) adding a first trialkoxy pnictide compound to the solution to form the indium pnictide cluster composition;(b) forming an indium pnictide seed composition by:(i) contacting an indium (I) containing compound and a metal (III) containing compound to form a mixture;(ii) adding a second organic solvent to the mixture;(iii) adding a solution comprising a second trialkoxy pnictide compound to the mixture to form an indium pnictide seed composition;(c) adding part of the indium pnictide cluster composition to the indium pnictide seed composition to form an intermediate indium pnictide nanocrystal composition; and(d) adding the remaining indium pnictide cluster composition to the intermediate indium pnictide nanocrystal composition to form an indium pnictide nanocrystal composition.

37. The method of claim 36, wherein step (a) further comprises:(iii) removing any insoluble by-products from the solution.

38. The method of claim 36 or claim 37, wherein step (a) further comprises:(iv) leaving the solution to age for at least 1 day, preferably at least 3 days, more preferably at least 5 days, more preferably 7 days.

39. The method of any one of claims 36 to 38, wherein the first indium- containing compound is an indium halide, preferably wherein the indium halide is selected from the group consisting of an indium (I) halide, an indium (II) halide, and an indium (III) halide.

40. The method of any one of claims 36 to 39, wherein the first indium- containing compound is an indium chloride, preferably wherein the indium chloride is indium (I) chloride.41 . The method of any one of claims 36 to 40, wherein the first organic solvent and the second organic solvent are each independently selected from the group consisting of octadecene, oleylamine, octylamine, butylamine, dioctylamine, heptadecane, cetane, oleic acid, tertiary phosphines, and secondary phosphines.

42. The method of any one of claims 36 to 41 , wherein the first trialkoxy pnictide and the second trialkoxy pnictide compound are each independently selected from the group consisting of a trialkoxy arsine compound, trialkoxy antimony compound, a trialkoxy phosphine compound, and mixtures thereof.

43. The method of any one of claims 36 to 42, wherein the first trialkoxy pnictide and the second trialkoxy pnictide compound are each independentlyselected from the group consisting of triethoxy arsine, tributoxy antimony, triethoxy antimony, and mixtures thereof.

44. The method of any one of claims 36 to 43, wherein indium (I) containing compound is an indium (I) halide, preferably wherein the indium (I) halide is indium (I) chloride.

45. The method of any one of claims 36 to 44, wherein metal (III) containing compound is an indium (III) containing compound or an antimony (III) containing compound.

46. The method of claim 45, wherein the indium (III) containing compound is an indium (III) halide, preferably wherein the indium (III) halide is indium (III) chloride.

47. The method of claim 45, wherein the antimony (III) containing compound is an antimony (III) halide, preferably wherein the antimony (III) halide is antimony (III) chloride.

48. The method of any one of claims 36 to 47, wherein step (b)(i) comprises: contacting the indium (I) containing compound and the metal (III) containing compound with a zinc (II) containing compound to form the mixture.

49. The method of claim 48, wherein the zinc (II) containing compound is a zinc (II) halide, preferably wherein the zinc (II) halide is selected from the group consisting of zinc (II) fluoride, zinc (II) chloride, zinc (II) bromide, zinc (II) iodide and mixtures thereof.

50. The method of any one of claims 36 to 49, wherein the method is carried out in an inert atmosphere.51 . The method of any one of claims 36 to 50, wherein step (b)(iii) is carried out by:(A) heating the mixture to a first temperature in the range of 200 °C to 350 °C;(B) adding the solution comprising the second trialkoxy pnictide compound to the mixture;(C) cooling the solution to a temperature in the range of 0 °C to 100 °C, preferably room temperature.

52. The method of claim 51 , wherein the first temperature is in the range of 220 °C to 300 °C, preferably in the range of 250 °C to 290 °C, more preferably 270 °C.

53. The method of claim 51 or claim 52, wherein step (B) comprises adding the solution comprising the second trialkoxy pnictide compound to the mixture via injection, wherein the injection is complete within 30 seconds, preferably within 20 seconds, more preferably within 10 seconds, more preferably within 5 seconds, more preferably within 2 seconds.

54. The method of any one of claims 51 to 53, wherein step (C) comprises: (C-1 ) maintaining the solution at a temperature in the range of 200 °C to 350 °C for a predetermined length of time prior to cooling the solution.

55. The method of claim 54, wherein the predetermined length of time is at least 1 minute, preferably at least 2 minutes, more preferably at least 5 minutes, more preferably at least 10 minutes, more preferably 15 minutes.

56. The method of any one of claims 36 to 55, wherein the method further comprises purifying the mixture.

57. The method of any one of claims 36 to 56, wherein step (c) comprises:(i) heating the indium pnictide seed composition to a growth temperature in the range of 200 °C to 350 °C;(ii) continuously adding the indium pnictide cluster composition to the indium pnictide seed composition over a predetermined length of time.

58. The method of claim 57, wherein the predetermined length of time is at least 1 minute, preferably at least 10 minutes, more preferably at least 30 minutes, more preferably at least 1 hour, more preferably at least 2 hours, more preferably at least 3 hours, more preferably at least 4 hours.

59. The method of claim 57 or claim 58, wherein the predetermined length of time is in the range of 4 hours to 8 hours.

60. The method of any one of claims 57 to 59, wherein step (c) further comprises purifying the intermediate indium pnictide nanocrystal composition.61 . The method of any one of claims 36 to 60, wherein step (d) comprises:(i) heating the intermediate indium pnictide nanocrystal composition to a growth temperature in the range of 200 °C to 350 °C;(ii) continuously adding the indium pnictide cluster composition to the intermediate indium pnictide nanocrystal composition over a predetermined length of time.

62. The method of claim 61 , wherein the predetermined length of time is at least 1 minute, preferably at least 10 minutes, more preferably at least 30 minutes, more preferably at least 1 hour, more preferably at least 2 hours, more preferably at least 3 hours, more preferably at least 4 hours.

63. The method of claim 61 or claim 62, wherein the predetermined length of time is in the range of 4 hours to 8 hours.

64. Use of a trialkoxy pnictide compound in the preparation of an indium pnictide nanocrystal.

65. Indium pnictide nanocrystal composition comprising indium pnictide nanocrystals, wherein the nanocrystals exhibit an absorption peak in the range of 2500 nm to 12000 nm, preferably wherein the range is 2500 nm to 3500 nm.

66. Indium pnictide nanocrystal composition of claim 65, wherein the absorption peak is in the range of 2600 nm to 3400 nm, preferably 2700 nm to 3300 nm, more preferably 2800 nm to 3200 nm.

67. Indium pnictide nanocrystal composition of claim 65, wherein the absorption peak is in the range of 3000 nm to 5000 nm.

68. Indium pnictide nanocrystal composition of claim 65, wherein the absorption peak is in the range of 8000 nm to 12000 nm.

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