Development of Indium Antimonide Colloidal Quantum Dots from Novel Precursors

Abstract

A method for the production of InSb colloidal quantum dots comprises the steps of: a) providing a reaction solution comprising a solvent and a single-source precursor; and b) heating the reaction solu

Description

FIELD OF THE INVENTION The present invention relates to Indium Antimonide colloidal quantum dots, precursors thereof, and methods for their production. BACKGROUND Infrared (IR) imaging allows the visualisation of features that are undetectable to the human eye and has wide-ranging applications, including consumer, industrial, and health. Colloidal quantum dots (QDs) have the potential for improvements over current silicon-based photodetectors and InGaAs photodetectors in terms of efficiency and spectral tunability in the short-wavelength infrared (SWIR), as well as the potential for reduced costs and scalable fabrication allowing high volume applications in automotive sensing, machine vision, and consumer electronics. Current developments in quantum dots for infrared applications are focussed on materials such as PbS, PbSe, and HgTe, due to their wide range of absorption and well-established synthetic protocols. However, these materials are inherently problematic due to their inclusion of heavy metals and the associated regulatory, health, and environmental concerns, with Group Ill-V semiconductor quantum dots are being explored as alternatives. The properties of certain of these materials are summarised in Table 1. Material Group Bandgap (eV) Absorption Electron mobility (cm2 / Vs) NIR SWIR MWIR PbS IV-VI 0.37 X 600 PbSe IV-VI 0.26 z 1000 InP lll-V 1.34 • / X X <400 In As lll-V 0.35 • / • / X <40000 InSb lll-V 0.17 • / • / <77000 Table 1: Summary of IR absorption and other properties of various semiconductor materials InAs colloidal quantum dots have been extensively explored as a suitable material due to their similar optical properties to PbS and established routes of synthesis, however, the inclusion of As is undesirable. InSb is a promising material for quantum dots for IR applications due to its wide range of accessible wavelengths (from NIR to MWIR), superior electron mobility, and lower toxicity. However, the colloidal synthesis of InSb is a heretofore-unsolved challenge. Where syntheses based on trimethylsilyl- (TMS-) organometallic precursors, such as P(TMS)3 and As(TMS)3, have been successful for other Group lll-V colloidal quantum dots, such as InP and InAs, these have been ineffective for InSb colloidal quantum dots, with the analogous Sb(TMS)3 yielding materials with poor size distributions. A number of other approaches have been taken for the synthesis of InSb colloidal quantum dots, each of which exhibits flaws in the process scalability and / or the resulting InSb colloidal quantum dots. Liu et al (J. Am. Chern. Soc., 2012, 134, 20258) describe the hot-injection synthesis of InSb colloidal quantum dots via co-reduction of InCh and Sb[N(SiMe3)2]3 using superhydride at temperatures in excess of 200°C, with the resulting quantum dots having a broad size distribution. This process was modified by Krylsky &Zhukov (Tech. Phys. Lett., 2019, 45, 801) by mixing InCh with ln(ac)3 in a 4:1 ratio, which reduced aggregation. Bussato etal (ACS Nano, 2020, 14, 13146) describe the hot-injection synthesis of InSb colloidal quantum dots via coreduction of an In-Sb acid-base adduct using superhydride, with the resulting quantum dots having a broad size distribution. Crisp et al (Nanoscale, 2019, 10, 11110) describe the formation of SbHs by in situ reduction with n-BuLi, which is then reacted with In-oleate to produce small InSb colloidal quantum dots with absorption in the visible range (i.e. 400 to 600 nm). Maurice et al (Part. Part. Syst. Charact., 2013, 30, 828) describe a similar approach, forming gaseous SbHs, which is bubbled through a solution of In precursor, with the resulting quantum dots having a broad size distribution. Seo et al (Adv. Sci., 2024, 11, 2306439) describe the synthesis of InSb colloidal quantum dots via heat-up of mixed indium sources (ln(PA)3) and (InCh) in the presence of Sb(TMS)3, producing quantum dots with photoabsorption in the range of 1000 to 1700 nm. Yarema &Kovachenko (Chem. Mater., 2013, 25, 1788) describe the synthesis of InSb colloidal quantum dots from In and Sb amines (e.g. ln[N(SiMe3)2]3 and Sb[NMez]3) with size tuneable absorption and broad size distribution. It is an object of the present invention to address the foregoing challenges with the provision of colloidal quantum dots for IR absorption, particularly MWIR absorption. SUMMARY OF THE INVENTION A first aspect of the present invention relates to a method for the production of InSb colloidal quantum dots comprising the steps of: a) providing a reaction solution comprising a solvent and a single-source precursor; and b) heating the reaction solution to a reaction temperature for a reaction period such that the single-source precursor thermally decomposes to form InSb quantum dots, wherein the single-source precursor is selected from InSb adducts, InSb oligomers, and combinations thereof. Heating the reaction solution to the reaction temperature may comprise increasing the temperature of the reaction solution. That is to say, heating the reaction solution so as to gradually increase the temperature of the single-source precursor therein over time. Optionally, the method may further comprise heating the reaction solution to a second reaction temperature for a second reaction period, wherein the second reaction temperature is greater than the first reaction temperature. Further optionally, the method may comprise heating the reaction solution to a third reaction temperature for a third reaction period, wherein the third reaction temperature is greater than the second reaction temperature. Heating the reaction solution to the reaction temperature comprises adding the reaction solution to a hot solvent that is at the reaction temperature. That is to say, rapidly heating the single-source precursor within the reaction solution. In embodiments, the method may further comprise the addition of an additional solution, the additional solution comprising single-source precursor and a solvent. The solvent may be a non-coordinating organic solvent, optionally the solvent is selected from squalane, squalene, 1-octadecene, and combinations thereof. The single-source precursor may be an InSb oligomer having the formula [R22lnSb(SiR33)2]x or [R22lnSb(GeR33)2]x, wherein: each of R2 and R3 is an alkyl group; and x is from 2 to 3. The InSb oligomer may be a heterocycle, by which it is meant the indium and antimony atoms alternate in a ring. The InSb oligomer may be a mixture of dimer and trimer when in the reaction solution. The InSb oligomer may have the formula [Et2lnSb(SiMe3)2]x or ['Pr2lnSb(SiMe3)2]x. The InSb may be the product of the reaction of an In organoindium halide having the formula lnXR22 with an Sb trialkylsilyl having the formula Sb(SiR33)3, wherein: each of R2 and R3 is an alkyl group; and X is selected from I, Br, and Cl. The single-source precursor may be an In-Sb adduct having the formula R3ln«— Sb(SiR13)3 or R3ln<-Sb(GeR13)3, wherein each of R and R1 is an alkyl group. The In-Sb adduct may have the formula Et3ln<—Sb(SiMe3)3 or iPr3ln<— Sb(SiMe3)3. At least one of the reaction solution, the hot solvent, and the additional solution may further comprise additional sources of In, additional sources of Sb, and / or additives, such as ligands. The additives may be selected from zinc salts, such as zinc chloride, zinc oleate, zinc halides, zinc carboxylates (e.g. zinc isostearate or zinc acetate), amines such as oleylamine, hexadecylamine, and dodecylamine, PR43 compounds where R4 is selected from alkyl or aryl groups (such as trioctylphosphine or triphenylphosphine), acids (such as oleic acid) and combinations thereof. A second aspect of the present invention relates to the use of an InSb oligomer in the synthesis of InSb colloidal quantum dots. The InSb oligomer may be as described herein. A third aspect of the present invention relates to a plurality of InSb colloidal quantum dots. The plurality of InSb colloidal quantum dots may formed by the method of the first aspect of the present invention. The plurality of InSb colloidal quantum dots may have an average particle size of from 1.5 to 12 nm, preferably from 2 to 10 nm, more preferably from 4 to 9 nm, further preferably from 5 to 8 nm, yet further preferably from 5.5 to 7.5 nm, most preferably from 6 to 7 nm, such as about 6.5 nm. The average particle size of the plurality of InSb colloidal quantum dots dot may have a standard deviation of from 1 to 20%, optionally from 5 to 15%, optionally from 8 to 12%, such as about 10%. The plurality of InSb colloidal quantum dots may have a peak absorption centred on from 700 to 3000 nm, preferably from 800 to 1800 nm, more preferably from 900 to 1600 nm, further preferably from 1000 to 1500, nm, yet further preferably from 1100 to 1400 nm, most preferably from 1200 to 1300 nm. The plurality of InSb colloidal quantum dots may have a peak-to-valley ratio of from 1.1 to 3, preferably from 1.2 to 2, more preferably from 1.3 to 1.8, further preferably from 1.4 to 1.6, most preferably about 1.5. The plurality of InSb colloidal quantum dots may have a % Trough of from 9 to 67, preferably from 16 to 50, more preferably from 23 to 44, further preferably 28 to 38, most preferably about 33. The plurality of InSb colloidal quantum dots may have a HWHM of from 10 to 200 meV, preferably from 20 to 160 meV, more preferably from 30 to 120 meV, further preferably from 40 to 100 meV, most preferably from 50 to 80 meV, such as about 60 meV. DESCRIPTION OF THE DRAWINGS Fig. 1 is a depiction of a typical photoabsorbance plot annotated to show how Peak:Valley ratio (PA / ), % Trough, and HWHM are derived. Fig. 2 is a plot of the % Trough achieved for InSb colloidal quantum dots with absorbance at various wavelengths, the InSb colloidal quantum dots synthesised using oligomers wherein R2 is iPr (circles) or Et (triangles). It can be seen that InSb oligomers where R2 is iPr have slower growth and produce quantum dots with better optical properties (i.e. a higher % Trough at a given absorbance wavelength). Fig. 3A is a series of absorbance spectra at different time points tracking an InSb colloidal quantum dots synthesis where the PR43 compound (TOP) has been added prior to addition of the single-source precursor (an oligomer). Fig. 3B is a series of absorbance spectra at different time points tracking an InSb colloidal quantum dots synthesis where the PR43 compound (TOP) has been added after addition of the single-source precursor (an oligomer). Fig. 3C is a plot of the % Trough achieved by the InSb colloidal quantum dots in Fig. 3A (circles, addition of the PR43 compound before the oligomer) and Fig. 3B (triangles, addition of the PR43 compound after the oligomer). It can be seen that addition of the PR43 compound after addition of the oligomer results in quantum dots with better optical properties (i.e. a higher % Trough at a given absorbance wavelength). Fig. 4 is the absorbance spectrum for Comparative Example 1, showing no defined features. Fig. 5A is the absorbance spectrum for Example 1, showing an absorbance peak centred on 1250 nm, and Fig. 5B is the XRD spectrum for the same, showing that phase pure InSb has been formed. Fig. 6 is the absorbance spectrum for Example 2, showing an absorbance peak centred on 980 nm and having HWHM of 126.6 meV. Fig. 7 is the absorbance spectrum for Example 3, showing an absorbance peak centred on 860 nm. Fig. 8 is the absorbance spectrum for Example 4, showing an absorbance peak centred on 875 nm. Fig. 9 is the absorbance spectrum for Example 5, showing an absorbance peak centred on 1120 nm. Fig. 10 is the absorbance spectrum for Example 6, showing an absorbance peak centred on 1050 nm. Fig. 11 is the absorbance spectrum for Example 7, showing an absorbance peak centred on 1400 nm. Fig. 12A is the absorbance spectrum for Example 8, showing an absorbance peak centred on 1460 nm with a HWHM of 113.4 meV, and Fig. 12B is the XRD spectrum for the same, showing that phase pure InSb has been formed. Fig. 13 is the absorbance spectrum for Example 9, showing an absorbance peak centred on 1100 nm. The dashed trace is an absorbance spectrum for an aliquot withdrawn during the course of the reaction, showing smaller InSb colloidal quantum dots. The presence of a trough in the first excitonic peak in the dashed trace indicates a narrower size distribution at this stage. Fig. 14 is the absorbance spectrum for Example 10, showing an absorbance peak centred on 1700 nm and having HWHM of 79.9 meV. Fig. 15 is the absorbance spectrum for Example 11, showing an absorbance peak centred on 820 nm with a P / V ratio of 1.11, a % Trough of 9.6, and a HWHM of 154.7 meV. Fig. 16 is the absorbance spectrum for Example 12, showing an absorbance peak centred on 1084 nm, with a P / V ratio of 1.33, a % Trough of 24.7, and a HWHM of 103.5 meV. Fig. 17A is the absorbance spectrum for Example 13, showing an absorption peak centred on 1457 nm with a P / V ratio of 1.64, a % Trough of 38.9, and a HWHM of 60.4 meV, and Fig. 17B is a STEM image for the same, showing an average particle size of 5.98 nm with a standard deviation of 10.78 %. Fig. 18A is the absorbance spectrum for Example 14, showing an absorption peak centred on 1288 nm with a P / V ratio of 1.56, a % Trough of 36.0, and a HWHM of 69.6 meV, and Fig. 18B is a STEM image for the same, showing an average particle size of 5.22 nm with a standard deviation of 9.74 %. Fig. 19A is the absorbance spectrum for Example 15, showing an absorption peak centred on 1723 nm with a P / V ratio of 1.22, a % Trough of 18.0, and HWHM of 41.8 meV, and Fig. 19B is a STEM image for the same, showing an average particle size of 7.29 nm with a standard deviation of 15.95 %. DEFINITIONS By “colloidal InSb quantum dots” it is meant InSb quantum dots that are formed in solution using a ‘bottom up’ approach and typically having surface ligands. The InSb quantum dots may comprise indium and antimony, but may include further elements as dopants. Alternatively, the InSb quantum dots may consist essentially of, or consist of, indium and antimony. It will be understood that the ratio of indium to antimony will be present in approximately equimolar amounts, but that the ratio may be varied. For example, the quantum dots may contain a molar ratio of ln:Sb of from 2:1 to 1:2, preferably from 1.5:1 to 1:1.5, more preferably from 1.3:1 to 1:1.3, most preferably from 1.1:1 to 1:1.1, such as about 1:1. NIR - near infrared describes light with a wavelength below 1 pm (e.g. from 0.7 to 1 pm). SWIR - short wavelength infrared describes light with a wavelength of 1 to 3 pm. MWIR - medium wavelength infrared describes light with a wavelength of 3 to 8 pm. TMS is trimethylsilyl, [-Si(CH3)3]. Due to the wavelengths at which the quantum dots of the present invention absorb light, it is often not possible to accurately define their full-width-at-half-maximum. Accordingly, a number of other measures are used as indicators of the polydispersity of these quantum dots. In general, a narrow particle size distribution is indicated by a high peak-to-valley ratio, a high % trough, and a narrow half-width-at-half-maximum. These measures are defined below, with reference to Fig. 1. Peak-to-valley ratio (Peak:Valley ratio or P / V) refers to the ratio of the peak to valley of the first excitonic absorption peak. Peak-to-valley ratio is a measure of how disperse the plurality of quantum dots is, with a larger ratio indicating a narrower size dispersion. % Trough is a measure of the depth of the valley behind the first excitonic absorption peak. A higher % Trough indicates a narrower size dispersion and can be calculated as follows: %Trough = (1-(V / P)) x 100 Half-width-at-half-maximum (HWHM) is a measure of the width of the first excitonic absorption peak at half its maximum, taken towards longer wavelengths. A lower HWHM indicates a narrower size dispersion. Particle sizes were determined using scanning transmission electron microscopy (STEM). Determining the particle sizes comprised selecting a representative sample of quantum dots, measuring the major (largest) and minor (smallest) dimension for each quantum dot, and taking the mean to be the average size of each individual quantum dot. The average sizes of each individual quantum dot were then averaged to provide a mean particle size and standard deviation for the plurality of quantum dots. The aspect ratio may also determined by dividing the major dimension by the minor dimension. DETAILED DESCRIPTION In-Sb Adducts as Single-Source Precursors Indium readily forms compounds that are classified as Lewis acids, while Sb readily forms compounds that are classified as Lewis bases. Mixing In-Lewis acids with Sb-Lewis bases produces In-Sb adducts that may be thermally decomposed to produce InSb colloidal quantum dots. Use of the In-Sb adducts pre-forms a bond between the In and Sb components, ensures a 1:1 molar ratio between the In and Sb atoms, and additionally stabilises the reactive Sb components that are otherwise prone to premature decomposition. In-Sb adducts suitable for single-source precursors may have the formula Rsln*—Sb(SiR13)s or Rain*—Sb(GeR13)3, where R and R1 are as described subsequently herein in relation to the In-Lewis acids and Sb-Lewis bases that may be used to form the In-Sb adducts. The In-Sb adduct may have the formula Et3ln^Sb(SiMe3)3 or iPr3ln«-Sb(SiMe3)3. Suitable In-Lewis acids include In trialkyls having the formula InRs. R may be any suitable alkyl group, for example -Ci-ealkyl or -Cs-ecycloalkyl, optionally with substitutions. In embodiments, R may be selected from methyl, ethyl, n-propyl, / so-propyl, n-butyl, / so-butyl, sec-butyl, tert-butyl, and combinations thereof. Preferably, R is -Ci-3alkyl. Most preferably, R is an ethyl group. Suitable Sb-Lewis bases include Sb trialkylsilyls having the formula Sb(SiR13)3 and Sb trialkylgermanium compounds having the formula Sb(GeR13)3. R1 may be any suitable alkyl group, for example -Ci-ealkyl or -Cs-ecycloalkyl, optionally with substitutions. In embodiments, R1 may be selected from methyl, ethyl, n-propyl, / so-propyl, n-butyl, / so-butyl, sec-butyl, tert-butyl, and combinations thereof. Preferably, R1 is -Ci-3alkyl. Most preferably, R1 is a methyl group. To produce the In-Sb adduct, the In-Lewis acid and the Sb-Lewis base are mixed in a solvent. Mixing in a solvent may comprise dissolving the In-Lewis acid and the Sb-Lewis base in the same volume of solvent, either sequentially or simultaneously. Alternatively, mixing in a solvent may comprising dissolving the In-Lewis acid and the Sb-Lewis base in separate volumes of solvent and then combining the resulting solutions. The mixing may be performed at a temperature between 5 and 50°C, preferably between 10 and 30°C, more preferably between 15 and 25°C. The mixing may be performed for any suitable time period including up to 24 hours, such as between 10 and 300 minutes, preferably between 20 and 150 minutes, more preferably between 30 and 60 minutes. The mixing may be performed in an atmosphere that is inert, such as N2 or argon, and is preferably performed in anhydrous conditions. The In-Lewis acid and the Sb-Lewis base may be mixed in equimolar quantities. The solvent may be any solvent, or mixture of solvents, able to dissolve both the InLewis acid and the Sb-Lewis base. The solvent is preferably non-polar (i.e. has a dielectric constant of 5 or lower), for example being a hydrocarbon solvent, optionally being drawn from alkanes, alkenes, and aromatics. Suitable solvents include pentane, hexane, heptane, octane, cyclohexane, benzene, toluene, xylene, chloroform, dioxane, diethyl ether, squalane, squalene, 1-octadecene, and mixtures thereof. Preferably, the solvent is, or the mixture of solvents includes, a solvent with a boiling point suitable for thermal decomposition of the In-Sb adduct, for example from 120°C to 350°C, from 150°C to 350°C, or from 180°C to 350°C, or from 200°C to 350°C. Preferred solvents include high boiling alkanes (such as nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, nonadecane, and icosane) and high boiling alkenes (such as 1-octadecene). InSb Oligomers as Single-Source Precursors Sb trialkylsilyls, such as Sb(TMS)3, and Sb trialkylgermanium compounds, such as Sb(GeR33)3, will react with organoindium halides via dehalosilylation to form fourmembered heterocycles (dimers) or six-membered heterocycles (trimers) that include o-bonds between alternating In and Sb atoms around the heterocycle (see S. Schulz, Coord. Chem. Rev., 2001, 215, 1-37). These InSb oligomers may be thermally decomposed to produce InSb colloidal quantum dots. Use of InSb oligomers pre-forms a bond between the In and Sb components, ensures a 1:1 molar ratio between the In and Sb atoms, and additionally stabilises the reactive Sb components that are otherwise prone to premature decomposition. The InSb oligomer may have the formula [R22lnSb(SiR33)2]x or [R22lnSb(GeR33)2]x, where R2 and R3 are as described subsequently herein. The oligomer may be a heterocycle, by which it is meant that the indium and antimony atoms alternate around a closed ring. Although having a single form in the solid state, it is known that species of this nature are in dynamic equilibrium between the dimeric and trimeric forms when in solution. This behaviour is known for [Et2GaSb(SiMe3)2]2 (being the dimer in the solid state) and for [Et2lnSb(SiMe3)2]3 (being a trimer in the solid state), each described in Foos et al (Journal of Organometallic Chemistry, 598, 2000, p182-186). The position of this equilibrium varies between each species and also varies with temperatures for each species. As such, when expressing the formula of the oligomer in solution, x takes an average value reflective of the position of the equilibrium. When the oligomer is in solution, x may take values from 2 to 3, with x = 2 being pure dimer and x = 3 being pure trimer. Particular examples of the InSb oligomer suitable for producing InSb colloidal quantum dots are of the formula [Et2lnSb(SiMe3)2]x and ['Pr2lnSb(SiMe3)2]x when in solution, with x being from 2 to 3. For the avoidance of doubt, the oligomer [Et2lnSb(SiMe3)2]x is a mixture of the dimeric ([Et2lnSb(SiMe3)2]2) and trimeric ([Et2lnSb(SiMe3)2]3) forms in solution and the oligomer ['Pr2lnSb(SiMe3)2]x is a mixture of the dimeric (['Pr2lnSb(SiMe3)2]2) and trimeric (['Pr2lnSb(SiMe3)2]3) forms in solution. Suitable In organoindium halides have the formula lnXR22. R2 may be any suitable alkyl group, for example -Ci-ealkyl or -Cs-ecycloalkyl, optionally with substitutions. X may be any suitable halide. Preferably, R2 is-Ci-3alkyl. In embodiments, R2 may be selected from methyl, ethyl, n-propyl, / so-propyl, n-butyl, / so-butyl, sec-butyl, tert-butyl, and combinations thereof, and X is selected from I, Br, and Cl. Preferably, R2 is an ethyl or / so-propyl group, and X is Cl. The identity of R2 has been found to have an effect on the rates of nucleation and growth of InSb colloidal quantum dots. As shown in Fig. 2, compared to InSb oligomers where R2 is Et, InSb oligomers where R2 is iPr have slower growth and produce quantum dots with better optical properties. Without wishing to be bound by theory, it is thought that this can be attributed to steric effects. Sb trialkylsilyls have the formula Sb(SiR33)3. R3 may be any suitable alkyl group, for example -Ci-6alkyl or -Cs-ecycloalkyl, optionally with substitutions. Preferably, R3 is -Cisalkyl. In embodiments, R3 may be selected from methyl, ethyl, n-propyl, / so-propyl, n-butyl, / so-butyl, sec-butyl, tert-butyl, and combinations thereof. Preferably, R3 is a methyl group. Sb trialkylgermanium compounds have the formula Sb(GeR33)3. R3 may be any suitable alkyl group, for example -Ci-salkyl or -Cs-ecycloalkyl, optionally with substitutions. Preferably, R3 is -Ci-3alkyl. In embodiments, R3 may be selected from methyl, ethyl, n-propyl, / so-propyl, n-butyl, / so-butyl, sec-butyl, tert-butyl, and combinations thereof. Preferably, R3 is a methyl group. To produce the InSb oligomer, the In organoindium halide and the Sb trialkylsilyl or trialkylgermanium compound are mixed in a solvent. The mixing may be performed at a temperature between 5 and 50°C, preferably between 10 and 30°C, more preferably between 15 and 25°C. The mixing may be performed for any suitable time period, such as between 3 and 24 hours, preferably between 6 and 18 hours, more preferably between 10 and 14 hours. The mixing may be performed in an atmosphere that is inert, such as N2 or argon. Preferably mixing is performed in anhydrous conditions. Preferably, light is excluded from the reaction. The In organoindium halide and the Sb trialkylsilyl or trialkylgermanium compound may be mixed in equimolar quantities. The solvent may be any solvent, or mixture of solvents, able to dissolve both the In organoindium halide and the Sb trialkylsilyl or trialkylgermanium compound. Suitable solvents include hexane. Preferably the In organoindium halide is produced in situ by the comproportionation of an In trialkyl and an In trihalide. Suitable In trialkyls having the formula lnR23. R2 may be any suitable alkyl group, for example -Ci-ealkyl or -Cs-ecycloalkyl, optionally with substitutions. Preferably, R2 is -Ci-3alkyl. In embodiments, R2 may be selected from methyl, ethyl, n-propyl, / so-propyl, n-butyl, / so-butyl, sec-butyl, tert-butyl, and combinations thereof. Preferably, R2 is an ethyl or / so-propyl group. Suitable In trihalides have InXa. X may be selected from I, Br, and Cl. Preferably X is Cl. The comproportionation typically involves mixing the In trialkyl and the In trihalide in a 2:1 molar ratio in a solvent, such as hexane. The mixing may be performed at a temperature between 5 and 50°C, preferably between 10 and 30°C, more preferably between 15 and 25°C. The mixing may be performed for any suitable time period, such as between 3 and 21 hours, preferably between 6 and 18 hours, more preferably between 10 and 14 hours. The mixing may be performed in an atmosphere that is inert, such as N2 or argon, and is preferably performed in anhydrous conditions. Preferably, light is excluded from the reaction. Conversion of Single-Source Precursors to InSb Colloidal Quantum Dots The single-source precursors heretofore described may be converted to InSb colloidal quantum dots by thermal decomposition. Typically, the single-source precursor is dissolved in a solvent to form a reaction solution and then heated to a reaction temperature to effect decomposition of the single-source precursor. The reaction may be performed in the presence of additional sources of In, additional sources of Sb, and / or additives, such as ligands. The single-source precursor may be selected from In-Sb adducts as described herein, InSb oligomers as described herein, and combinations thereof. Any suitable high-boiling solvent that is able to dissolve the single-source precursor may be used. Typical solvents include Lewis base type coordinating solvents, such as a phosphine (e.g. TOP), a phosphine oxide (e.g. TOPO), an amine (e.g. oleylamine, hexadecylamine, and dodecylamine), non-coordinating organic solvents (e.g. alkanes and alkenes, such as squalane, squalene, and 1-octadecene), or heat transfer fluids (such as hydrogenated terphenyl (e.g. Therminol® 66), mixtures of biphenyl and diphenyl oxide (e.g. Dowtherm™), ethers, and xylenes). The solvent is preferably anhydrous and degassed prior to heating to the reaction temperature. Degassing may be performed to remove volatiles (such as low boiling solvents or dissolved gases) before or after addition of the single-source precursor and / or other components (such as additional sources of In, additional sources of Sb, and / or additives as described herein) by heating the solvent to an intermediate temperature, such as 120°C, under a reduced pressure. The heating may be achieved through hot-injection or heat-up methodologies. The heat-up methodology gradually increases the temperature of the reaction solution, which is a more scalable method, but risks broader particle size distribution for poorly selected metal precursors (i.e. those that are not single-source precursors as described herein). The reaction temperature may be at least 150°C, preferably at least 180°C, more preferably at least 200°C, further preferably at least 220°C, yet further preferably at least 250°C, or most preferably at least 275°C. The reaction temperature may be at most 300°C, preferably at most 275°C, more preferably at most 250°C, further preferably at most 220°C, yet further preferably at most 200°C, most preferably at most 180°C. In embodiments, the reaction temperature is between 150 and 300°C, preferably between 220 and 275°C, more preferably between 240 and 260°C. The reaction temperature is maintained for a reaction period, which may be any length of time suitable to effect conversion of the single-source precursor to InSb colloidal quantum dots. In embodiments, the reaction temperature is maintained for a period between 5 and 240 minutes, preferably between 10 and 120 minutes, more preferably between 20 and 90 minutes. In embodiments, the reaction solution is heated to subsequent, higher reaction temperatures for further periods. For example, the reaction may be heated to a second reaction temperature for a second period, the second reaction temperature being greater than the first reaction temperature. The reaction solution may then by heated to a third reaction temperature for a third period, the third reaction temperature being greater than the second reaction temperature. The hot-injection methodology adds a volume of the reaction solution to a hot solvent that has been preheated to the reaction temperature. The hot solvent typically has a larger volume than the reaction solution. The hot solvent may contain an In precursor or an Sb precursor. The hot-injection technique is characterized by a rapid injection of a cooler precursor into a reaction at markedly higher temperatures. Upon injection, the concentration of reactive monomers increases rapidly (via reaction of two species or breakdown of a single-source precursor) and a nucleation threshold concentration is breached, beginning nucleation. At the same time as the temperature falling, the concentration of monomers rapidly falls below the nucleation threshold concentration, halting nucleation and allowing the remaining monomers to only grow on to existing nuclei, thereby focusing the size distribution. The method may further comprise the step of adding an additional solution comprising In precursor and Sb precursor and a solvent while the reaction temperature is maintained. Preferably, the In precursor and Sb precursor are the same compound (i.e. are in the form of a single-source precursor). This step occurs after the reaction solution has been heated at the reaction temperature for the period and enables further growth of the InSb colloidal quantum dots formed during the heating step by providing further In and Sb. The additional solution may be added at a rate of 0.5 to 25 mL / hour, preferably at a rate of 5 to 20 mL / hour, more preferably at a rate of 10 to 15 mL / hour. The rate at which the additional solution is added may be varied depending on the concentration of the precursor (e.g. single-source precursor) within the additional solution, the reaction temperature, and the quantity of quantum dots formed in the initial nucleation event. The reaction solution may further comprise additional sources of In, additional sources of Sb, and / or additives, such as ligands. The hot solvent may further comprise additional sources of In, additional sources of Sb, and / or additives, such as ligands. The additional solution may further comprise additives, such as ligands. Additional sources of In may comprise In carboxylates, wherein the carboxylate may be selected from fatty acids, such as caprylate, caprate, laurate, myristate (Ma or MA), palmitate (Pa or PA), stearate, arachidate, behenate, lignocerate, and cerotate, and Ci-7 carboxylates, such as acetate (Ac), propionate, butanoate, pentanoate, hexanoate, and heptanoate, and combinations thereof. In embodiments, the In carboxylate may comprise ln(Ma)3-x(Ac)x, wherein 0 <x <3, such as x being about 1.5. In embodiments using the hot-injection methodology, the additional sources of In may be present in the hot solvent prior to addition of the reaction solution. In embodiments using the heat-up methodology, the additional sources of In may be added to the reaction solution prior to addition of the single-source precursor. The molar ratio of In to Sb in the reaction solution may be from 1:1 to 8:1, optionally from 2:1 to 6:1, such as about 4:1. Suitable additives may be selected from zinc salts, such as zinc isostearate, zinc chloride, zinc oleate, zinc halides, zinc carboxylates (e.g. zinc acetate), amines, such as olelyamine, hexadecylamine, and dodecylamine, PR43 compounds where R4 is selected from alkyl or aryl groups (such as trioctylphosphine (TOP) or triphenylphosphine), acids, such as oleic acid and combinations thereof. PR43 compounds are particularly preferred additives as they have been found to improve consistency in particle shape and to narrow size distribution. Without wishing to be bound by theory, it is believed that PR43 compounds slow the growth of the nanoparticles, stabilising intermediate clusters that can then be decomposed in a more controlled manner. Where zinc salts, such as zinc carboxylate, are present, the molar ratio of Zn to Sb may be from 1:1 to 10:1, optionally from 2:1 to 8:1, optionally from 3:1 to 7:1, such as about 5:1. In embodiments using the hot-injection methodology, the zinc salts may be present in the hot solvent prior to addition of the reaction solution. In embodiments using the heat-up methodology, the zinc salts may be added to the reaction solution prior to addition of the single-source precursor. Where amines, such as oleylamine, are present, the molar ratio of amine to Sb may be from 0.5:1 to 4:1, preferably from 1:1 to 2:1, such as about 1.8:1. The amine may be added to the reaction solution following addition of the single-source precursor. Where PR43 compounds, such as TOP, are present, the ratio of PR43 compounds to Sb may be from 1:1 to 20:1, optionally from 5:1 to 15:1, such as around 12:1. In embodiments using the hot-injection methodology, the PR43 compounds may be present in the hot solvent prior to addition of the reaction solution. In embodiments using the heat-up methodology, the PR43 compounds may be added to the reaction solution following addition of the single-source precursor. Figs. 3A and 3B are absorbance spectra at different time points following the progress of quantum dot syntheses where the PR43 compound (TOP) has been added prior to (Fig. 3A), or after (Fig. 3B) the single-source precursor (in this case, an oligomer). As shown in Fig 3C, addition of the PR43 compound following addition of the single-source precursor improves the quality of the resulting InSb colloidal quantum dots. Without wishing to be bound by theory, it is believed that the addition of PR43 compounds following addition of the single-source precursor slows the growth rate of the quantum dots. Where acids, such as oleic acid, are present, the molar ratio of acid to Sb may be from 1:1 to 6:1, preferably from 2:1 to 5:1, more preferably from 3:1 to 4:1, such as about 3.8:1. The acid may be added to the reaction solution prior to addition of the singlesource precursor. In one embodiment, wherein the single-source precursor is an In-Sb adduct, the method of producing InSb colloidal quantum dots comprises: a) Combining a solvent, a zinc salt, and an additional In source; b) Adding the In-Sb adduct to form the reaction solution; c) Adding an amine to the reaction solution; d) Heating to a first temperature for a first period, such as 220°C for 50 mins; e) Optionally, heating to a second temperature for a second period, such as 280°C for 45 mins. The zinc salt may be a zinc carboxylate, such as zinc iso-stearate. The additional In source may be an In carboxylate, such as ln(Ma)3-x(Ac)x, wherein 0 <x <3, such as x being about 1.5. The In-Sb adduct may be Etsln*— Sb(SiMe3)3. The amine may be oleylamine. The first temperature may be from 150°C to 300°C, optionally from 180°C to 280°C, optionally from 200°C to 250°C, such as about 220°C. The first period may be from 10 to 240 minutes, optionally from 30 to 120 minutes, optionally from 40 to 60 minutes, such as about 50 minutes. The second temperature may be higher than the first temperature, such as from 200°C to 300°C, optionally from 250°C to 280°C. The second period may be from 10 to 240 minutes, optionally from 30 to 120 minutes, optionally from 40 to 60 minutes, such as about 45 minutes. In a particular embodiment, the zinc salt is a zinc carboxylate, the additional In source is an In carboxylate, the In-Sb adduct is Etsln-*—Sb(SiMe3)3, and the amine is oleylamine. In another preferred embodiment, wherein the single-source precursor is an InSb oligomer, the method of producing InSb colloidal quantum dots comprises: a) Combining a solvent, an additional In source, an InSb oligomer and an acid to form a reaction solution; b) Adding a PR43 compound; and c) Heating to a first temperature, such as 230°C for a first period, and, while at the first temperature, adding an additional solution comprising oligomer. In embodiments, the method further comprises heating to a second temperature, such as about 250°C, and, optionally, to a third temperature, such as about 280°C. Preferably, the PR43 compound, such as TOP, is added following addition of the InSb oligomer. The additional In source may be an In carboxylate, such as ln(Ma)3-x(Ac)x, wherein 0 <x <3, such as x being about 1.5. The InSb oligomer may be ['Pr2lnSb(SiMe3)2]3 or ['Pr2lnSb(SiMe3)2]2. The acid may be oleic acid. The additional solution may further comprise an additional In source, an InSb oligomer, and an acid. Optionally, the additional solution is the same as the reaction solution, for example being obtained by dividing the reaction solution prior to heating to the first temperature. The additional solution may be added at a rate of 7.5 mL / h. Preferably, the additional In source is an In carboxylate, the InSb oligomer is [iPr2lnSb(SiMe3)2]3 or [iPr2lnSb(SiMe3)2]2, and the PR43 compound is TOP. Pluralities of InSb Colloidal Quantum Dots A further aspect of the present invention relates to pluralities of InSb colloidal quantum dots, preferably formed from a single-source precursor as described herein. The plurality of InSb colloidal quantum dots may have an average particle size of from 1.5 to 12 nm, preferably from 2 to 10 nm, more preferably from 4 to 9 nm, further preferably from 5 to 8 nm, yet further preferably from 5.5 to 7.5 nm, most preferably from 6 to 7 nm, such as about 6.5 nm. The plurality of InSb colloidal quantum dots may have an average particle size of at least 1.5 nm, at least 2 nm, at least 4 nm, at least 5 nm, at least 5.5 nm, at least 6 nm, at least 6.5 nm, at least 7 nm, at least 7.5 nm, at least 8 nm, at least 9 nm, or at least 10 nm. The plurality of InSb colloidal quantum dots may have an average particle size of less than 12 nm, less than 10 nm, less than 9 nm, less than 8 nm, less than 7 nm, less than 6.5 nm, less than 6 nm, less than 5.5 nm, less than 5 nm, less than 4 nm, or less than 2 nm. The plurality of InSb colloidal quantum dots are preferably of substantially the same size (i.e. are monodisperse). The average particle size of the plurality of quantum dots may have a standard deviation of from 1 to 20%, optionally from 5 to 15%, optionally from 8 to 12 %, such as about 10%. The average particle size of the plurality of quantum dots may have a standard deviation of less than 20%, less than 15%, less than 12%, less than 10%, less than 8%, less than 5%, less than 4%, less than 3%, or less than 2%. The plurality of InSb colloidal quantum dots may have a consistent morphology, preferably being substantially spherical. The aspect ratio of the quantum dots may be from 1 to 2, preferably from 1 to 1.5, more preferably from 1 to 1.3, further preferably from 1 to 1.2, most preferably from 1 to 1.1, such as about 1. The aspect ratio of the quantum dots may be less than 2, less than 1.5, less than 1.3, less than 1.2, or less than 1.1, such as about 1. The plurality of InSb colloidal quantum dots may have a peak absorption in the infrared region of the light spectrum (i.e. in the NIR, SWIR, or MWIR), preferably in the NIR or SWIR. The peak absorption may be centred on from 700 to 3000 nm, preferably from 800 to 1800 nm, more preferably from 900 to 1600 nm, further preferably from 1000 to 1500 nm, yet further preferably from 1100 to 1400 nm, most preferably from 1200 to 1300 nm. The peak absorption may be centred on a wavelength of at least 700 nm, at least 800 nm, at least 900 nm, at least 1000 nm, at least 1100 nm, at least 1200 nm, at least 1300 nm, at least 1400 nm, at least 1500 nm, or at least 1600 nm. The peak absorption may be centred on a wavelength of less than 3000 nm, less than 1800 nm, less than 1600 nm, less than 1500 nm, less than 1400 nm, less than 1300 nm, less than 1200 nm, less than 1100 nm, less than 1000 nm, or less than 900 nm. The plurality of InSb colloidal quantum dots may have a peak-to-valley ratio of greater than 1, optionally from 1.1 to 3, further optionally from 1.2 to 2, further optionally from 1.3 to 1.8, further optionally from 1.4 to 1.6, such as about 1.5. The plurality of InSb colloidal quantum dots may have a peak-to-valley ratio of at least 1.1, at least 1.2, at least 1.3, at least 1.4, at least 1.5, at least 1.6, at least 1.8, or at least 2. The plurality of InSb colloidal quantum dots may have a peak-to-valley ratio of less than 3, less than 2, less than 1.8, less than 1.6, less than 1.5, less than 1.4, less than 1.3, or less than 1.2. The plurality of InSb colloidal quantum dots may have a % Trough of from 9 to 67, optionally from 16 to 50, further optionally from 23 to 44, further optionally 28 to 38, such as about 33. The plurality of InSb colloidal quantum dots may have a % Trough of at least 9, at least 16, at least 23, at least 28, at least 33, at least 38, at least 44, or at least 50. The plurality of InSb colloidal quantum dots may have a % Trough of less than 67, less than 50, less than 44, less than 38, less than 33, less than 28, less than 23, or less than 16. The plurality of InSb colloidal quantum dots may have a HWHM of from 10 to 200 meV, optionally from 20 to 160 meV, further optionally from 30 to 120 meV, further optionally from 40 to 100 meV, further optionally from 50 to 80 meV, such as about 60 meV. The plurality of InSb quantum dots may have a HWHM of less than 200 meV, less than 160 meV, less than 120 meV, less than 100 meV, less than 80 meV, less than 60 meV, less than 50 meV, less than 40 meV, less than 30 meV, or less than 20 meV. The plurality of InSb quantum dots may have a HWHM of at least 10 meV, at least 20 meV, at least 30 meV, at least 40 meV, at least 50 meV, at least 60 meV, at least 80 meV, at least 100 meV, at least 100 meV, at least 120 meV, or at least 160 meV. EXAMPLES Absorption spectra were obtained using a Cary 5000 UV-vis-NIR spectrophotometer. Samples were measured in quartz cuvettes, in tetrachloroethylene solvent, using a 1 cm path length. Scans were typically run from 400 - 2,400 nm. Preparation of Indium Carboxylate A mixed indium carboxylate is used in the following syntheses of InSb colloidal quantum dots. The mixed indium carboxylate comprising mixed indium acetates and myristates, with a molecular weight of 541.1 g / mol and an empirical stoichiometry of ln(Ma)i.48(Ac)i,52 (i.e. comprising 21% indium by mass). The mixed indium carboxylate is converted to indium myristate in situ during the degassing step at elevated temperature. Degassed Therminol 66 (7.594 kg) was charged to a 20 L reactor and heated to 35 °C, followed by addition of myristic acid (4.050 kg). Indium acetate (2.352 kg) was added and the mixture degassed at 200 rpm for 2 hours. The agitation was increased to 250 rpm and the temperature increased to 140 °C for 2 hours under vacuum, with acetic acid being collected in a distillation head. The reaction temperature was maintained for a further 4 hours under vacuum, after which the reaction mixture being golden-coloured and turbid. The reaction mixture was allowed to settle before half of the mixture was transferred to a 30L filter and stirred with acetone (14.004 kg) to induce precipitation. A further charge of acetone (14.004 kg) is added before the second half of the reaction mixture is transferred to the filter. The precipitates were collected and washed with acetone (6 by 4.86 kg), with resuspension between filtrations. The precipitate is dried to constant mass via nitrogen purge (at 0.5 bar for 1 hour), under vacuum for 8 hours, and finally in a vacuum oven at 50 °C and 10 mbar. Comparative Example 1 - Synthesis of InSb Quantum Dots via Heat-Up Methodology using SbfTMSh Indium carboxylate (0.99 g), zinc isostearate (2.5 g) and 1-octadecene (10 mL) were degassed at 110°C for 1 h and then cooled to room temperature under N2. Sb(TMS)3 in sgualane (0.5 M; 1 mL) was added over 5 minutes. The reaction solution turned dark brown in colour. This was degassed for 30 minutes at room temperature, before heating under N2 to 220°C for 1 hour and then to 280°C for 1 hour. The final product was colloidally stable, but had no defined features in its absorption spectrum, indicating a broad particle size distribution (see Fig. 4). Example 1 - Adduct-based Synthesis of InSb Colloidal Quantum Dots from Sb(TMS)3 and Etsln, via Hot-Injection Flask A Squalane (10 mL), indium carboxylate (0.54 g) and zinc stearate (1.28 g) were degassed under vacuum at 120°C. After backfilling with N2, octadecylamine was added, followed by degassing for 30 minutes at 120°C. After backfilling with N2, Flask A was heated to 250°C. Flask B In a separate flask, degassed squalane (5 mL) was added to a mixture of Sb(TMS)s (0.5 M solution in hexane, 2 mL) and Etsln (0.5 M solution in hexane, 2 mL), then degassed to remove the hexane. 1 mL of the contents of Flask B was injected into Flask A via syringe, with the temperature of Flask A maintained at 250°C. The remaining 4 mL of the contents of Flask B were added at a rate of 10 mL / h. The flask was cooled to 80°C and octane (10 mL) was added, before transferring the contents to a Schlenk tube and glovebox. To isolate the quantum dots, the solution was centrifuged at 6,000 rpm for 10 minutes. The supernatant was extracted, mixed with acetone (25 mL) and centrifuged at 6,000 rpm for 10 minutes, resulting in a small amount of precipitation. The clear layer was discarded and the oily layer was divided into two centrifuge tubes. To the two tubes, acetone (40 mL total; 20 mL to each tube) was added, followed by centrifugation at 6,000 rpm for 10 minutes. The clear top layer was discarded. To the bottom oily layer, isopropanol (40 mL) was added, followed by centrifugation at 6,000 rpm for 10 minutes. The contents of the two tubes were combined with octane (4 mL) and precipitated with acetone (15 mL). The oily precipitate was washed twice with acetone, redispersed in octane (<2 mL), and precipitated with acetone and centrifuged at 6,000 rpm for 4 minutes. The solid was redispersed in octane (1 mL). The absorption spectrum of the solid shows an absorption peak centred around 1250 nm (see Fig. 5A) and the XRD pattern matched that of phase pure InSb (see Fig. 5B). Example 2 - Adduct-based Synthesis of InSb Colloidal Quantum Dots from Sb(TMS)3 and Etaln, via Heat-up Method Indium carboxylate (0.72 g), zinc isostearate (2.5 g) and 1-octadecene (10 mL) were degassed at 110°C for 2 hours, then cooled to room temperature under N2. In a separate flask, Etsln in squalane (0.5 M; 1 mL) and Sb(TMS)s in squalane (0.5 M; 1 mL) were premixed in a glovebox for 1 hour at room temperature. This was then added to the degassed indium carboxylate / zinc isostearate mixture at room temperature, over 5 minutes. The colour slowly changed from yellow, to orange, to dark brown. After the addition, the flask was degassed for 30 minutes and then backfilled with N2. Degassed oleylamine (0.3 mL) was added before heating to 220°C and annealing for 50 minutes, heating to 280°C and annealing for 45 minutes, before cooling to room temperature. Octane (10 mL) and acetone (30 mL) were added to precipitate some solid (Fraction 1) and an oily supernatant. The supernatant was precipitated with isopropanol (20 mL), leaving an oily residue that was precipitated with further isopropanol (20 mL). This was dispersed in octane (5 mL), then precipitated with isopropanol (20 mL). The slightly oily residue was dispersed in octane (2 mL) and centrifuged at 6,000 rpm for 10 minutes. Some solids settled and the supernatant was collected as Fraction 2. The isolated quantum dots from Fraction 2 had an absorption feature around 980 nm with a HWHM of 136.6 meV (see Fig. 6). Example 3 - Adduct-based Synthesis of InSb Colloidal Quantum Dots from Sb(TMS)3 and Etsln, via Heat-up Method In an N2-filled glovebox, Sb(TMS)3 in squalane (0.5 M; 0.5 mL) and Etsln (0.5 M; 0.5 mL) were mixed in a glass vial in a 1:1 ratio to prepare the In-Sb adduct. The contents of the vial were vortexed and transferred out of the glovebox in a syringe. Indium carboxylate (0.54 g), oleic acid (0.3 mL) and 1-octadecene (8 mL) were degassed at 110°C for 90 minutes in a 3-necked round-bottom flask, before cooling to 40°C under N2. Trioctylphosphine (1.33 mL) was added via a single injection. Under N2, the In-Sb adduct was added to the flask using a syringe pump, over 5 minutes, at 40°C. The flask was then degassed at 40°C for 30 minutes, before heating under N2 to 90'C and annealing for 5 minutes. The temperature was increased to 130°C and the reaction was annealed for 5 minutes. The temperature was increased to 150°C and the reaction was annealed for 7 minutes, followed by heating to 180°C and annealing for 200 minutes. After annealing at 180°C for 200 minutes, the absorption spectrum shows an absorption feature centred around 860 nm (see Fig. 7). Example 4 - Adduct-based Synthesis of InSb Colloidal Quantum Dots from Sb(TMS)3 and Etsln, via Heat-up Method In an N2-filled glovebox, Sb(TMS)3 in squalane (0.5 M; 0.5 mL) and Etsln (0.5 M; 0.5 mL) were mixed in a glass vial in a 1:1 ratio to prepare the In-Sb adduct. The contents of the vial were vortexed and transferred out of the glovebox in a syringe. Indium carboxylate (0.54 g), oleic acid (0.3 mL) and 1-octadecene (5 mL) were degassed at 110°C for 90 minutes in a 3-necked round-bottom flask, before cooling to 40°C under N2. Trioctylphosphine (1.33 mL) was added via a single injection, followed by the addition of the In-Sb adduct over 5 minutes using a syringe pump. The reaction was degassed at 40°C for 30 minutes while stirring. The reaction was then heated under N2 to 90°C and annealed for 5 minutes, followed by heating to 120°C and annealing for 5 minutes, then heating to 150°C and annealing for 7 minutes, then heating to 180°C and annealing for 60 minutes. Oleylamine (150 pL) was injected in through a single injection, followed by annealing at 180°C for a further 12 minutes. The reaction was then heated to 220°C and annealed for 70 minutes. The temperature was lowered to 180°C and oleylamine (150 pL) was added. The reaction was heated to 230°C and annealed for 30 minutes. After annealing at 230°C for 30 minutes, the absorption spectrum shows an absorption feature centred around 875 nm (see Fig. 8). Example 5: Synthesis of InSb Colloidal Quantum Dots from InSb Oligomer Preparation of InSb Oligomer ([Et2lnSb(SiMe3)Jx) in Hexane InCh (0.11 g) was stirred in hexane (18 mL) at room temperature. Etsln in hexane (0.5 M; 2 mL). EtzInCI was formed as a white solid. After stirring overnight, Sb(TMS)3 in hexane (0.5 M; 3 mL) was added slowly. The vessel was covered in aluminium foil and then stirred overnight at room temperature, forming a light yellow or colourless solution. Preparation of InSb Colloidal Quantum Dots Indium carboxylate (0.54 g), oleic acid (0.3 mL) and 1-octadecene (10 mL) were degassed for 90 minutes at 110°C and then cooled to 35°C. InSb oligomer in hexane (3.8 mL) was added, after which the colour of the solution slowly turned from colourless to yellow, orange, red, and then brown. After stirring for 2 minutes, the solution was degassed to remove the hexane, followed by heating to 220°C and annealing for 24 minutes. To isolate the quantum dots, octane (6 mL) was added at 50°C, before transferring to a glovebox. Insoluble material was removed via centrifugation. The supernatant was precipitated with acetone (30 mL). The solid was dispersed in octane (3 mL) and then precipitated with acetone (8 mL). The final solid was dispersed in octane (3 mL). The absorption spectrum shows an absorption peak centred around 1120 nm (see Fig. 9)- Example 6: Synthesis of InSb Colloidal Quantum Dots using InSb Oligomer, via Heatup Method Preparation of [EtJnSb(SiMe3) Jx Oligomer in Squalane InCh (111 mg) and Etsln in squalane (0.5 M, 2 mL) were added to squalane (18 mL). Et2lnCI was formed as a white solid. After stirring overnight, Sb(TMS)3 solution in squalane (0.5 M; 3 mL) was added dropwise. The solids dissolved, resulting in a very pale straw-coloured solution. Preparation of InSb Colloidal Quantum Dots Indium carboxylate (0.72 g), zinc isostearate (2.56 g) and 1-octadecene (10 mL) were degassed at 120°C for 1 h. The flask was cooled to room temperature, then [Et2lnSb(SiMe3)2]x oligomer in squalane (7.6 mL) was added over 10 minutes, resulting in a colour change to red-brown. The solution was degassed for 30 minutes, then the temperature was increased, under N2, first to 180°C, then to 220°C. After holding at 220°C for 60 minutes, an absorption feature was observed. The reaction was then cooled to room temperature. To isolate the quantum dots, dry octane (10 mL) was added, before transferring to a dry Schlenk tube, which was taken into a glovebox and centrifuged at 6,000 rpm for 5 minutes. A small amount of grey precipitate was discarded. To the brown solution, acetone (40 mL) was added, followed by centrifugation at 6,000 rpm for 15 minutes. The clear supernatant was discarded, then the oily residue was washed twice with isopropanol (80 mL each time). After each wash, the pale yellow-brown supernatant was discarded. The residual material was dissolved in octane (20 mL). The absorption spectrum shows an absorption peak centred around 1050 nm (see Fig. 10). Example 7: Synthesis of InSb Colloidal Quantum Dots using InSb Oligomer, via Heatup Method Preparation of [EtJnSbfSiMeaJJx Oligomer in Squalane In a glovebox, InCL (0.11 g) was added to anhydrous hexane (5 mL), followed by Etsln in squalane (0.5 M; 2 mL). This was left to stir overnight, forming a white turbid solution. Sb(TMS)3 in squalane (0.5 M; 3 mL) was added slowly. The solids dissolved, forming a colourless to yellowish solution in an hour. The following day, the solution had turned dark brown. This was filtered using a 0.43 pm syringe filter. Preparation of InSb Colloidal Quantum Dots Indium carboxylate (1.44 g), zinc isostearate (5 g) and 1-octadecene (20 mL) were degassed at 120°C for 1 h. After cooling to 40°C, InSb oligomer in squalane (6 mL) was added over 5 minutes at a rate of 72 mL / h. The solution was then degassed for 30 minutes, before backfilling with N2 and adding oleylamine (0.6 mL). The total volume was 28 mL, of which 21 mL was taken into a syringe. The remaining 7 mL was heated to 220°C, then to 280°C. At 280°C, 4 mL from the syringe containing 21 mL was fed in at a rate of 14 mL / h, before cooling to room temperature. To isolate the quantum dots, octane (10 mL) was added to the mixture at 70°C, then cooled to room temperature and transferred to a glovebox. Two equivalents of a 1:1 mixture of isopropanol and acetone were added, followed by centrifugation at 6,000 rpm for 10 minutes. The solids were redispersed in octane (4 mL), then precipitated with two equivalents of a 1:1 mixture of isopropanol and acetone. This step was repeated once, then the final solids were redispersed in octane (3 mL). The absorption spectrum shows an absorption peak centred around 1400 nm (see Fig. 11). Example 8: Synthesis of InSb Colloidal Quantum Dots using InSb Oligomer, via Heatup Method Preparation of [(‘PfylnSbfSiMesjJx Oligomer in Squalane A 30 mL glass vial was dried in an oven and taken into a glovebox. InCh (0.111 g) was weighed into the vial and suspended in degassed squalane (18 mL). 'Prsln solution in squalane (0.5 M; 2 mL) was added via a syringe and the mixture was stirred overnight, forming a white solid ('Pr2lnCI). Sb(TMS)3 in squalane (0.5 M; 3 mL) was then added dropwise via a syringe. The white solid rapidly dissolved to form a pale straw coloured solution. The vial was wrapped in foil and stored in the glovebox prior to use. Preparation of InSb Colloidal Quantum Dots 1-octadecene (5 mL), zinc isostearate (2.5 g) and indium carboxylate (0.72 g) were degassed at 110°C for 1 hour, before cooling to room temperature under N2. [('Pr)2lnSb(SiMe3)2]x oligomer in squalane (7.6 mL) was added over 5 minutes, then degassed at room temperature for 30 minutes. After backfilling with N2, oleylamine (0.3 mL) was added. The total volume was 14 mL. 7 mL was transferred to a flask and the remaining 7 mL into a syringe. The contents of the flask was heated to 280 C and annealed for 4 minutes, after which the contents of the syringe was added at 14 mUh while maintaining the flask temperature at 280°C. At the end of the addition, the flask was cooled to 60°C and octane (10 mL) was added, before transferring to a glovebox. To isolate the nanoparticles, the contents of the flask was precipitate with 1 equivalent of acetone and 1 equivalent of isopropanol, followed by centrifugation at 6,000 rpm for 10 minutes. The solids were dispersed in acetone (4 mL), then precipitated with two equivalents of a 1:1 mixture of acetone:isopropanol, followed by centrifugation at 6,000 rpm for 10 minutes. This step was repeated. The final solids were redispersed in octane (4.5 mL). After centrifugation at 6,000 rpm for 10 minutes, some grey solids remained. The product was filtered through a 0.1 pm syringe filter. The absorption spectrum shows an absorption peak centred around 1460 nm with a HWHM of 113.4 meV (see Fig. 12A) and the XRD spectrum is consistent with phase pure InSb (see Fig. 12B). Example 9: Synthesis of InSb Colloidal Quantum Dots using InSb Oligomer, via Heatup Method [('Pr)2lnSb(SiMe3)2]3 oligomer in squalane was prepared according to Example 8. Preparation of InSb Colloidal Quantum Dots 1-octadecene (5 mL), zinc isostearate (2.56 g) and indium carboxylate (0.81 g) were degassed at 110°C for 1 hour, before cooling to 35°C under N2. [fPr^lnS^SiMesHx oligomer in squalane (7.6 mL) was added over 5 minutes, then degassed at 35 C for 30 minutes. After backfilling with N2, trioctylphosphine (0.45 mL) was added. The total volume was 14 mL. 7 mL was transferred to a flask and the remaining 7 mL into a syringe. The contents of the flask was heated to 280°C and annealed for four minutes, at which point an aliquot was taken from the reaction solution, which showed an absorption feature at 850 nm. After 4 minutes the contents of the syringe was added at 14 mL / h while maintaining the flask temperature at 280°C. At the end of the addition, the flask was cooled to room temperature. To isolate the nanoparticles, the flask was heated to 60°C and octane (10 mL) was added. The contents of the flask were transferred to a Schlenk tube and centrifuged at 6,000 rpm for 10 minutes. The liquid fractions were precipitated with 2 volume equivalents of 50:50 acetone:isopropanol, followed by centrifugation at 6,000 rpm for 5 minutes. The oily residue was diluted in octane (10 mL) and precipitated with 2 volume equivalents of 50:50 acetone:isopropanol followed by centrifugation at 6,000 rpm for 10 minutes. The final solids were redispersed in octane (4 mL). After centrifugation at 6,000 rpm for 10 minutes the product was filtered through a 0.1 pm syringe filter. The absorption spectrum shows an absorption peak centred around 1100 nm (see Fig. 13). It is noted that the dashed line (the absorbance spectrum for the aliquot withdrawn after 4 minutes) has a trough in the first excitonic absorption peak, indicative of an improvement in the particle size distribution at that stage of the reaction. Example 10: Synthesis of InSb Colloidal Quantum Dots using InSb Oligomer, via Heatup Method [('Pr)2lnSb(SiMe3)2]x oligomer in squalane was prepared according to Example 8. Preparation of InSb Colloidal Quantum Dots 1-octadecene (50 mL), zinc isostearate (5 g) and indium carboxylate (1.44 g) were degassed at 110°C for 1 hour, before cooling to 35°C under N2. [('Pr)2lnSb(SiMe3)2]x oligomer in squalane (15.4 mL) was added over 15 minutes, then degassed at 35°C for 30 minutes. After backfilling with N2, oleylamine (0.6 mL) was added. The total volume was 28 mL. 7 mL was transferred to a flask and the remaining 21 mL into a syringe. The contents of the flask was heated to 280°C the contents of the syringe was added at 14 mUh while maintaining the flask temperature at 280°C. After 7 mL had been added from the syringe the additional rate was increased to 17 mL / h. After a further 7 mL had been added addition was ceased and the flask cooled to room temperature. To isolate the nanoparticles, the flask was heated to 60°C and octane (10 mL) was added. The contents of the flask were transferred to a Schlenk tube and centrifuged at 6,000 rpm for 10 minutes. The liquid fractions were precipitated with 30 mL of 50:50 acetone:isopropanol, followed by centrifugation at 6,000 rpm for 5 minutes. The oily residue was diluted in octane (8 mL) and precipitated with 16 mL of 50:50 acetone:isopropanol followed by centrifugation at 6,000 rpm for 10 minutes. The final solids were redispersed in octane (6 mL). After centrifugation at 6,000 rpm for 10 minutes the product was filtered through a 0.1 pm syringe filter. The absorption spectrum shows an absorption peak centred around 1700 nm with a HWHM of 79.9 meV (see Fig. 14). Example 11: Synthesis of InSb Colloidal Quantum Dots using InSb Oligomer, via Heatup Method Preparation of [Et2lnSb(SiMe3)Jx Oligomer in Squalane A 30 mL glass vial was dried in an oven and taken into a glovebox. InCh (0.111 g) was weighed into the vial and suspended in degassed squalane (18 mL). Etaln solution in squalane (0.5 M; 2 mL) was added via a syringe and the mixture was stirred overnight, forming a white solid (Et2lnCI). Sb(TMS)3 in squalane (0.5 M; 3 mL) was then added dropwise via a syringe. The white solid rapidly dissolved to form a pale straw coloured solution. The vial was wrapped in foil and stored in the glovebox and filtered using 1 pm syringe filter prior to use. Preparation of InSb Colloidal Quantum Dots 1-octadecene (5 mL), indium carboxylate (0.54 g), and oleic acid (0.3 mL) were degassed at 110°C for 90 minutes, before cooling to 40°C under N2. 1.33 mL trioctylphosphine was added to the mixture. Then [(Et)2lnSb(SiMe3)2]x oligomer in squalane (3.8 mL) was added over 5 minutes, then degassed at room temperature for 30 minutes and backfilled with N2. The contents of the flask was heated to 150°C and annealed for 5 minutes, followed by annealing at 180°C for 3 h before cooling to room temperature. The absorption spectrum shows an absorption peak centred on 820 nm with a P / V ratio of 1.11, a % Trough of 9.6, and a HWHM of 154.7 meV (see Fig. 15) Example 12: Synthesis of InSb Colloidal Quantum Dots using InSb Oligomer, via Heatup Method [(Et)2lnSb(SiMe3)2]x oligomer in squalane was prepared according to Example 11. Preparation of InSb Colloidal Quantum Dots 1-octadecene (15 mL), indium carboxylate (1.62 g), and oleic acid (0.9 mL) were degassed at 110°C for 90 minutes, before cooling to 40°C under N2. 4 mL trioctylphosphine was added to the mixture. Then [(Et)2lnSb(SiMe3)2]x oligomer in squalane (11.4 mL) was added over 5 minutes, then degassed at room temperature for 30 minutes and backfilled with N2. The total volume was 31 mL. 10 mL was transferred to a flask and the remaining 21 mL into a syringe. The contents of the flask was heated to 150°C and annealed for 5 minutes, followed by annealing at 180°C for 1h. 0.15 mL of degassed oleylamine was injected and the contents were heated to 230°C. At this temperature, the contents of the syringe was added at 10.5 mL / h, and after 3 mL the addition rate was increased to 15.5 mUh. A total of 21 mL from was added and the flask was cooled to 60°C and octane (20 mL) was added, before transferring to a glovebox. To isolate the nanoparticles, the contents of the flask was precipitate with 1 equivalent of acetone and 1 equivalent of isopropanol, followed by centrifugation at 6,000 rpm for 10 minutes. The solids were discarded and the strongly coloured supernatant was precipitated by adding 1 equivalent of isopropanol, followed by centrifugation at 6,000 rpm for 10 minutes. The solids were dispersed in octane (5 mL) and precipitated with two equivalents isopropanol, followed by centrifugation at 6,000 rpm for 10 minutes. The final solids were redispersed in octane (6 mL). After centrifugation at 6,000 rpm for 10 minutes the product was filtered through a 0.1 pm syringe filter. The absorption spectrum shows an absorption peak centred on 1084 nm, with a P / V ratio of 1.33, a % Trough of 24.7, and a HWHM of 103.5 meV (see Fig. 16). Example 13: Synthesis of InSb Colloidal Quantum Dots using InSb Oligomer, via Heatup Method Preparation of [(’Pr^lnSbfSiMesJzJx Oligomer in Squalane A 100 mL amber Schott bottle was dried in an oven and taken into a glovebox. InCh (0.222 g) was weighed into the vial and suspended in degassed squalane (36 mL). 'Praln solution in squalane (0.5 M; 4 mL) was added via a syringe and the mixture was stirred overnight, forming a white solid. Sb(SiMe3)3 in squalane (0.5 M; 6 mL) was then added dropwise via a syringe. The white solid rapidly dissolved to form a pale straw coloured solution which was stirred overnight at room temperature inside glovebox. The final solution was filtered using 1 pm syringe filter prior to use. Synthesis of InSb Colloidal QDs 1-octadecene (50 mL), indium carboxylate (5.4 g), and oleic acid (3 mL) were degassed at 110°C for 90 minutes, before cooling to 40'C under N2. Then the above prepared [('Pr)2lnSb(SiMe3)2]x oligomer in squalane (39 mL) was added over 15 minutes, then the mixture was degassed at room temperature for 30 minutes and backfilled with N2. 13.2 mL of trioctylphosphine was then added to the mixture. The total volume at this stage was 100 mL. 95 mL of the mixture was transferred into syringes and the remaining 5 mL was heated to 230°C. When the temperature was reached, the contents from the syringe were added to the flask at 7.5 mL / h. After the addition of 95 mL the reaction was cooled to room temperature for isolation. To isolate the QDs, 20 mL of the reaction mixture was added to 10 mL of octane and transferred to the glovebox and precipitated with 3 equivalents of isopropanol, followed by centrifugation at 6,000 rpm for 10 minutes. The clear supernatant was discarded and the solids were dispersed in octane (5 mL) and precipitated with three equivalents isopropanol, followed by centrifugation at 6,000 rpm for 10 minutes. The final solids were washed twice with acetone and dried before re-dispersing in octane (5 mL). After centrifugation at 6,000 rpm for 10 minutes the product was filtered through a 0.1 pm syringe filter. The absorption spectrum (Fig. 17A) shows an absorption peak centred on 1457 nm with a PA / ratio of 1.64, a % Trough of 38.9, and a HWHM of 60.4 meV. STEM imaging (Fig. 17B) shows an average particle size of 5.98 nm with a standard deviation of 10.78%. Example 14: Synthesis of InSb Colloidal Quantum Dots using InSb Oligomer, via Heatup Method Preparation of [(’PfylnSbfSiMesjJx Oligomer in Squalane A 50 mL amber Schott bottle was dried in an oven and taken into a glovebox. InCh (0.111 g) was weighed into the vial and suspended in degassed squalane (18 mL). 'Phln solution in squalane (0.5 M; 2 mL) was added via a syringe and the mixture was stirred overnight, forming a white solid. Sb(SiMes)3 in squalane (0.5 M; 3 mL) was then added dropwise via a syringe. The white solid rapidly dissolved to form a pale straw coloured solution which was stirred overnight at room temperature inside a glovebox. The final solution was filtered using a 1 pm syringe filter prior to use. Synthesis of InSb Colloidal QDs 1-octadecene (25 mL), indium carboxylate (4.87 g), and oleic acid (2.7 mL) were degassed at 110°C for 90 minutes, before cooling to 40°C under N2. Then the above prepared [('Pr)2lnSb(SiMe3)2]x oligomer in squalane (19.5 mL) was added over 15 minutes, then the mixture was degassed at room temperature for 30 minutes and backfilled with N2. 4 mL of trioctylphosphine was then added to the mixture. The final mixture was transferred into a syringe, leaving 5 mL in the flask for nucleation. The flask was heated to 230°C and the contents from the syringe were added to the flask at 7.5 mL / h at that temperature. After the addition of 21 mL, the temperature was increased to 250°C, and after 32 mL the temperature was further increased to 280°C. After the addition of a total of 41 mL, the reaction was cooled to room temperature for isolation. To isolate the QDs, 20 mL of the reaction mixture was added to 10 mL of octane and transferred to the glovebox and precipitated with three equivalent of isopropanol, followed by centrifugation at 6,000 rpm for 10 minutes. The clear supernatant was discarded and the solids were dispersed in octane (5 mL) and precipitated with three equivalents isopropanol, followed by centrifugation at 6,000 rpm for 10 minutes. The final solids were washed twice with acetone and dried before re-dispersing in octane (5 mL). After centrifugation at 6,000 rpm for 10 minutes the product was filtered through a 0.1 pm syringe filter. The absorption spectrum (Fig. 18A) shows an absorption peak centred on 1288 nm with a PA / ratio of 1.56, a % Trough of 36.0, and a HWHM of 69.6 meV. STEM imaging (Fig. 18B) shows an average particle size of 5.22 nm with a standard deviation of 9.74 %. Example 15: Synthesis of InSb Colloidal Quantum Dots using InSb Oligomer, via Heatup Method Preparation of [(lPr)2lnSb(SiMe3)2]x Oligomer in Squalane [(Et)2lnSb(SiMe3)2]x oligomer in squalane was prepared according to Example 11. Synthesis of InSb Colloidal QDs 1-octadecene (25 mL), indium carboxylate (2.70 g), and oleic acid (1.5 mL) were degassed at 110°C for 90 minutes, before cooling to 40°C under N2. 6.65 mL of trioctylphosphine was then added to the mixture. Then the above prepared [Et2lnSb(SiMe3)2]x oligomer in squalane (19.5 mL) was added over 5 minutes, then the mixture was degassed at 40°C for 30 minutes and backfilled with N2. The total volume at this stage was 54 mL. 51 mL of the mixture was transferred into syringes and the remaining 3 mL was heated to 230°C. When the temperature was reached, the contents from the syringe were added to the flask at 7.75 mUh. After the addition of 51 mL the reaction was cooled to room temperature for isolation. To isolate the QDs, 49 mL of the reaction mixture was heated to 45°C, transferred into a Schlenk tube, transferred to the glovebox and split into two pots, to each of which octane (3 mL) was added, followed by centrifugation at 6,000 rpm for 10 minutes. The insoluble solids were discarded. Of the remaining material, 20 mL was taken forward and precipitated with 3.5 volume equivalents of isopropanol, followed by centrifugation at 6,000 rpm for 10 minutes. The pale yellow supernatant was discarded and the solids were precipitated with isopropanol (90 mL), followed by centrifugation at 6,000 rpm for 10 minutes. The colourless supernatant was discarded. The solids were dissolved in octane (5 mL) and precipitated with isopropanol (40 mL), followed by centrifugation at 6,000 rpm for 10 minutes. The pale supernatant was discarded, then the solid was washed with acetone and centrifuged at 6,000 rpm for 10 minutes. The solid was redispersed in octane (3 mL) and filtered through a 0.2 pm syringe filter. The absorption spectrum (Fig. 19A) shows an absorption peak centred on 1723 nm with a PA / ratio of 1.22, a % Trough of 18.0, and HWHM of 41.8 meV. STEM imaging (Fig. 19B) shows an average particle size of 7.29 nm with a standard deviation of 15.95 %. Clauses of the Invention Clause 1. A method for the production of InSb colloidal quantum dots comprising the steps of: a) providing a reaction solution comprising a solvent and a single-source precursor; and b) heating the reaction solution to a reaction temperature for a reaction period such that the single-source precursor thermally decomposes to form InSb quantum dots, wherein the single-source precursor is selected from InSb adducts, InSb oligomers, and combinations thereof. Clause 2. A method according to clause 1, wherein heating the reaction solution to the reaction temperature comprises increasing the temperature of the reaction solution. Clause 3. A method according to clause 2, further comprising heating the reaction solution to a second reaction temperature for a second reaction period, wherein the second reaction temperature is greater than the first reaction temperature. Clause 4. A method according to clause 3, further comprising heating the reaction solution to a third reaction temperature for a third reaction period, wherein the third reaction temperature is greater than the second reaction temperature. Clause 5. A method according to any one of clauses 1 to 4, further comprising the addition of an additional solution, the additional solution comprising single-source precursor and a solvent. Clause 6. A method according to clause 1, wherein heating the reaction solution to the reaction temperature comprises adding the reaction solution to a hot solvent that is at the reaction temperature. Clause 7. A method according to any one of clauses 1 to 6, wherein the solvent is a non-coordinating organic solvent, optionally the solvent is selected from squalane, squalene, 1-octadecene, and combinations thereof. Clause 8. A method according to any one of clauses 1 to 7, wherein the singlesource precursor is an InSb oligomer having the formula [R22lnSb(SiR33)2]x or [R22lnSb(GeR33)2]x, wherein: each of R2 and R3 is an alkyl group; and x is from 2 to 3. Clause 9. A method according to clause 8, , wherein the InSb oligomer is a mixture of dimer and trimer when in the reaction solution. Clause 10. A method according to clause 8 or clause 9, wherein the InSb oligomer has the formula [Et2lnSb(SiMe3)2]x or ['Pr2lnSb(SiMe3)2]x. Clause 11. A method according to any one of clauses 1 to 10, wherein the InSb oligomer is the product of the reaction of an In organoindium halide having the formula lnXR22 with an Sb trialkylsilyl having the formula Sb(SiR33)3, wherein: each of R2 and R3 is an alkyl group; and X is selected from I, Br, and Cl. Clause 12. A method according to any one of clauses 1 to 7, wherein the singlesource precursor is an In-Sb adduct having the formula Raln<—Sb(SiR13)3 or Rsln*—Sb(GeR1s)3, wherein each of R and R1 is an alkyl group. Clause 13. A method according to clause 12 wherein the In-Sb adduct has the formula Et3ln<-Sb(SiMe3)3 or iPr3ln<-Sb(SiMe3)3. Clause 14. A method according to any one of clauses 1 to 13, wherein at least one of the reaction solution, the hot solvent, and the additional solution further comprise additional sources of In, additional sources of Sb, and / or additives, such as ligands. Clause 15. A method according to clause 14, wherein the additives are selected from zinc salts, such as zinc chloride, zinc oleate, zinc halides, zinc carboxylates (e.g. zinc isostearate or zinc acetate), amines such as oleylamine, hexadecylamine, and dodecylamine, PR43 compounds where R4 is selected from alkyl or aryl groups (such as trioctylphosphine or triphenylphosphine), acids (such as oleic acid) and combinations thereof. Clause 16. A method according to any one of clauses 1 to 15, wherein the reaction solution comprises the solvent, the single-source precursor, an additional source of In, an acid, and a PR43 compound. Clause 17. A method according to clause 16, wherein the reaction solution is formed by providing a first solution comprising the solvent, the single-source precursor, the additional source of In, and the acid, adding a solution of the single source precursor, and then adding the PR43 compound. Clause 18. A method according to clause 16 or clause 17, wherein a first portion of the reaction solution is heated to the reaction temperature by increasing the temperature of the reaction solution. Clause 19. A method according to clause 18, wherein a second portion of the reaction solution is gradually added to the first portion at the reaction temperature. Clause 20. A method according to any one of clauses 1 to 19, wherein the reaction temperature is from 180 to 280°C, preferably from 200 to 250°C, most preferably about 230°C. Clause 21. A method according to clause 19 or clause 20, wherein the reaction solution is heated to a second reaction temperature during addition of the second portion, optionally wherein the reaction solution is subsequently heated to a third reaction temperature during addition of the second portion.. Clause 22. A method according to clause 21, wherein the first reaction temperature is from 180 to 240°C, such as about 230°C, the second reaction temperature is from 240 to 260°C, such as about 250°C, the third reaction temperature, if used, is from 260 to 300°C, such as about 280°C. Clause 23. A method according to any one of clauses 1 to 22, wherein: (i) the solvent is 1-octadecene; (ii) the single-source precursor is an oligomer, such as [(Et)2lnSb(SiMe3)2]x or [fPrHnS^SiMeaM; (iii) the additional source of In, if present, is indium carboxylate; (iv) the acid, if present, is oleic acid; and / or (v) the PRS compound, if present, is trioctylphosphine. Clause 24. The use of an InSb oligomer in the synthesis of InSb colloidal quantum dots, preferably the InSb oligomer having the formula [R22lnSb(SiR33)2]x or [R22lnSb(GeR33)2]x, wherein: each of R2 and R3 is an alkyl group; and x is from 2 to 3. Clause 25. The use of clause 24, wherein the InSb oligomer is a mixture of dimer and trimer when in the reaction solution. Clause 26. The use of clause 24 or clause 25, wherein the InSb oligomer has the formula [Et2lnSb(SiMe3)2]x or ['Pr2lnSb(SiMe3)2]x. Clause 27. The use to any one of clauses 24 to 26, wherein the InSb oligomer is the product of the reaction of an In organoindium halide having the formula lnXR22 with an Sb trialkylsilyl having the formula Sb(SiR33)3, wherein: each of R2 and R3 is an alkyl group; and X is selected from I, Br, and Cl. Clause 28. A plurality of InSb colloidal quantum dots. Clause 29. The plurality of InSb colloidal quantum dots of clause 28, wherein the plurality of InSb colloidal quantum dots are formed by the method of any one of clauses 1 to 23. Clause 30. The plurality of InSb colloidal quantum dots of clause 28 or clause 29, wherein the plurality of InSb colloidal quantum dots has an average particle size of from 1.5 to 12 nm, preferably from 2 to 10 nm, more preferably from 4 to 9 nm, further preferably from 5 to 8 nm, yet further preferably from 5.5 to 7.5 nm, most preferably from 6 to 7 nm, such as about 6.5 nm. Clause 31. The plurality of InSb colloidal quantum dots of any one of clauses 28 to 30, wherein the average particle size of the plurality of InSb colloidal quantum dots dot has a standard deviation of from 1 to 20%, optionally from 5 to 15%, optionally from 8 to 12%, such as about 10%. Clause 32. The plurality of InSb quantum dots of any one of clauses 28 to 31, wherein the plurality of InSb colloidal quantum dots have a peak absorption centred on from 700 to 3000 nm, preferably from 800 to 1800 nm, more preferably from 900 to 1600 nm, further preferably from 1000 to 1500, nm, yet further preferably from 1100 to 1400 nm, most preferably from 1200 to 1300 nm. Clause 33. The plurality of InSb quantum dots of any one of clauses 28 to 32, wherein the plurality of InSb colloidal quantum dots have a peak-to-valley ratio of from 1.1 to 3, preferably from 1.2 to 2, more preferably from 1.3 to 1.8, further preferably from 1.4 to 1.6, most preferably about 1.5. Clause 34. The plurality of InSb colloidal quantum dots of any one of clauses 28 to 33, wherein the plurality of InSb colloidal quantum dots have a % Trough of from 9 to 67, preferably from 16 to 50, more preferably from 23 to 44, further preferably 28 to 38, most preferably about 33. Clause 35. The plurality of InSb colloidal quantum dots of any one of clauses 28 to 34, wherein the plurality of InSb colloidal quantum dots have a HWHM of from 10 to 200 meV, preferably from 20 to 160 meV, more preferably from 30 to 120 meV, further preferably from 40 to 100 meV, most preferably from 50 to 80 meV, such as about 60 meV.

Claims

1. A method for the production of InSb colloidal quantum dots comprising the steps of:a) providing a reaction solution comprising a solvent and a single-source precursor; andb) heating the reaction solution to a reaction temperature for a reaction period such that the single-source precursor thermally decomposes to form InSb quantum dots,wherein the single-source precursor is selected from InSb adducts, InSb oligomers, and combinations thereof.

2. A method according to claim 1, wherein heating the reaction solution to the reaction temperature comprises increasing the temperature of the reaction solution.

3. A method according to claim 2, further comprising heating the reaction solution to a second reaction temperature for a second reaction period, wherein the second reaction temperature is greater than the first reaction temperature.

4. A method according to claim 3, further comprising heating the reaction solution to a third reaction temperature for a third reaction period, wherein the third reaction temperature is greater than the second reaction temperature.

5. A method according to any one of claims 1 to 4, further comprising the addition of an additional solution, the additional solution comprising single-source precursor and a solvent.

6. A method according to claim 1, wherein heating the reaction solution to the reaction temperature comprises adding the reaction solution to a hot solvent that is at the reaction temperature.

7. A method according to any one of claims 1 to 6, wherein the solvent is a noncoordinating organic solvent, optionally the solvent is selected from squalane, squalene, 1-octadecene, and combinations thereof.

8. A method according to any one of claims 1 to 7, wherein the single-source precursor is an InSb oligomer having the formula [R22lnSb(SiR33)2]x or [R22lnSb(GeR33)2]x, wherein:each of R2 and R3 is an alkyl group; and x is from 2 to 3.

9. A method according to claim 8, wherein the InSb oligomer is a mixture of dimer and trimerwhen in the reaction solution.

10. A method according to claim 8 or claim 9, wherein the InSb oligomer has the formula [Et2lnSb(SiMe3)2]x or ['Pr2lnSb(SiMe3)2]x.

11. A method according to any one of claims 1 to 10, wherein the InSb oligomer is the product of the reaction of an In organoindium halide having the formula lnXR22 with an Sb trialkylsilyl having the formula Sb(SiR33)3, wherein:each of R2 and R3 is an alkyl group; andX is selected from I, Br, and Cl.

12. A method according to any one of claims 1 to 7, wherein the single-source precursor is an In-Sb adduct having the formula Rain<—Sb(SiR13)s or R3ln«-Sb(GeR13)3, wherein each of R and R1 is an alkyl group.

13. A method according to claim 12, wherein the In-Sb adduct has the formula Et3ln<-Sb(SiMe3)3 or iPr3ln<-Sb(SiMe3)3.

14. A method according to any one of claims 1 to 13, wherein at least one of the reaction solution, the hot solvent, and the additional solution further comprise additional sources of In, additional sources of Sb, and / or additives, such as ligands.

15. A method according to claim 14, wherein the additives are selected from zinc salts, such as zinc chloride, zinc oleate, zinc halides, zinc carboxylates (e.g. zinc isostearate or zinc acetate), amines such as oleylamine, hexadecylamine, and dodecylamine, PR43 compounds where R4 is selected from alkyl or aryl groups (such astrioctylphosphine or triphenylphosphine), acids (such as oleic acid) and combinations thereof.

16. The use of an InSb oligomer in the synthesis of InSb colloidal quantum dots.

17. A plurality of InSb colloidal quantum dots.

18. The plurality of InSb colloidal quantum dots of claim 17, wherein the plurality of InSb colloidal quantum dots are formed by the method of any one of claims 1 to 12.

19. The plurality of InSb colloidal quantum dots of claim 17 or claim 18, wherein the plurality of InSb colloidal quantum dots has an average particle size of from 1.5 to 12 nm, preferably from 2 to 10 nm, more preferably from 4 to 9 nm, further preferably from 5 to 8 nm, yet further preferably from 5.5 to 7.5 nm, most preferably from 6 to 7 nm, such as about 6.5 nm.

20. The plurality of InSb colloidal quantum dots of any one of claims 17 to 19, wherein the average particle size of the plurality of InSb colloidal quantum dots dot has a standard deviation of from 1 to 20%, optionally from 5 to 15%, optionally from 8 to 12%, such as about 10%.

21. The plurality of InSb quantum dots of any one of claims 17 to 20, wherein the plurality of InSb colloidal quantum dots have a peak absorption centred on from 700 to 3000 nm, preferably from 800 to 1800 nm, more preferably from 900 to 1600 nm, further preferably from 1000 to 1500, nm, yet further preferably from 1100 to 1400 nm, most preferably from 1200 to 1300 nm.

22. The plurality of InSb quantum dots of any one of claims 17 to 21, wherein the plurality of InSb colloidal quantum dots have a peak-to-valley ratio of from 1.1 to 3, preferably from 1.2 to 2, more preferably from 1.3 to 1.8, further preferably from 1.4 to 1.6, most preferably about 1.5.

23. The plurality of InSb colloidal quantum dots of any one of claims 17 to 22, wherein the plurality of InSb colloidal quantum dots have a % Trough of from 9 to 67,preferably from 16 to 50, more preferably from 23 to 44, further preferably 28 to 38, most preferably about 33.

24. The plurality of InSb colloidal quantum dots of any one of claims 17 to 23, 5 wherein the plurality of InSb colloidal quantum dots have a HWHM of from 10 to 200 meV, preferably from 20 to 160 meV, more preferably from 30 to 120 meV, further preferably from 40 to 100 meV, most preferably from 50 to 80 meV, such as about 60 meV.10

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