Synthesis of small inas qds

Abstract

The present invention relates to a method of synthesising small colloidal InAs quantum dots, the method comprising: providing an initial In-Zn-As feedstock in a reaction vessel; heating the reaction vessel to a reaction temperature; and maintaining the reaction temperature for a reaction period while gradually adding a further In-Zn-As feedstock, as well as to pluralities of colloidal InAs quantum dots and inks and devices incorporating colloidal InAs quantum dots.

Description

[0001] Synthesis of Small InAs QDs

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to the synthesis of colloidal InAs quantum dots and the colloidal InAs quantum dots themselves.

[0004] BACKGROUND

[0005] 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. Quantum dots 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.

[0006] IR photodetectors based on quantum dots have shown exceptional promise, offering numerous benefits such as solution processability, wavelength tunability, high responsivity and lower cost. Current state-of-the-art focuses on the use of PbS quantum dots in a photodiode structure that can be monolithically integrated onto CMOS read-out integrated circuits. InAs has a bandgap of 0.35 eV at room temperature and quantum dots formed from this material with sizes of from 3 to 7 nm will have peak absorptions of from 900 to 1600 nm. However, due to restrictions in conventional syntheses, these bandgaps are restricted from 940 to 1400 nm, with attempts to synthesise InAs quantum dots outside of this window resulting in pluralities of quantum dots with low quality.

[0007] It is an object of the present invention to address the foregoing challenges with the provision of high quality pluralities of InAs quantum dots able absorb at lower bandgaps.

[0008] SUMMARY OF THE INVENTION

[0009] A first aspect of the present invention relates to a method of synthesising small colloidal InAs quantum dots, the method comprising: providing an initial In-Zn-As feedstock in a reaction vessel; heating the reaction vessel to a reaction temperature; and maintaining the reaction temperature for a reaction period while gradually adding a further In-Zn-As feedstock.The initial In-Zn-As feedstock and / or further In-Zn-As feedstock may be formed by: providing a mixture of In carboxylate and Zn carboxylate; providing an As feedstock; heating the mixture of In carboxylate and Zn carboxylate to an As addition temperature; and adding the As feedstock to the mixture of In carboxylate and Zn carboxylate while maintaining the As addition temperature.

[0010] Providing the initial In-Zn-As feedstock and / or the further In-Zn-As feedstock may comprise: providing an In carboxylate; providing a Zn-As feedstock; heating the In carboxylate to a Zn-As addition temperature; and adding the Zn-As feedstock to the In carboxylate while maintaining the Zn-As addition temperature.

[0011] Providing the initial In-Zn-As feedstock and / or the further In-Zn-As feedstock may comprise: providing a Zn carboxylate; providing an As feedstock; heating the Zn carboxylate to an As addition temperature; and adding the As feedstock to the Zn carboxylate while maintaining the As addition temperature.

[0012] The method may further comprise monitoring the peak absorption wavelength of the colloidal InAs quantum dots within the reaction vessel and ceasing addition of the further In-Zn-As feedstock when a target peak absorption wavelength is achieved.

[0013] The ln:As molar ratio in the initial In-Zn-As feedstock and / or the further In-Zn-As feedstock may be from 1:1 to 10: 1 , preferably from 1.5:1 to 8: 1 , more preferably from 2: 1 to 6: 1 , most preferably from 3:1 to 4: 1.

[0014] The Zn:As molar ratio in the initial In-Zn-As feedstock and / or the further In-Zn-As feedstock may be from 1:5 to 5:1, preferably from 1:3 to 3:1, more preferably from 1:2 to 2: 1 , most preferably about 1:1.

[0015] The ln:Zn:As molar ratio in the initial In-Zn-As feedstock and / or the further In-Zn-As feedstock may be expressed as x:y:z, wherein: x is the quantity of In and has a value from 1 to 10; y is the quantity of Zn and has a value from 0.2 to 5; and z is the quantity of As and has a value of about 1.

[0016] The method may further comprise providing additives to the reaction vessel, optionally the additives being selected from carboxylic acids (such as myristic, isostearic, or oleicacids), amines (such as octadecylamine or trioctylamine), additional sources of In (such as In carboxylates as described herein), additional sources of Zn (such as Zn carboxylates as described herein), and sources of chloride (such as tetrachloroethylene and zinc chloride).

[0017] The reaction temperature may be from 220 to 380 °C, preferably from 240 to 360 °C, more preferably from 260 to 340 °C, most preferably from 280 to 320°C, such as about 300 °C.

[0018] The method may further comprise the step of cooling the reaction vessel and / or the contents thereof.

[0019] The method may further comprise the step of isolating the small colloidal InAs quantum dots.

[0020] A second aspect of the present invention relates to a plurality of colloidal InAs quantum dots having a peak absorbance of between 750 nm and 1000 nm, preferably between 775 nm and 975 nm, more preferably between 800 nm and 950 nm, further preferably between 820 nm and 920 nm, most preferably between 850 nm and 900 nm, optionally being obtained or obtainable by the method of the first aspect of the present invention.

[0021] The plurality of colloidal InAs quantum dots may have a HWHM of less than 100 meV, preferably less than 90 meV, more preferably less than 80 meV, further preferably less than 70 meV, most preferably less than 65 meV.

[0022] The plurality of colloidal InAs quantum dots may have a peak:valley ratio of greater than 1 , preferably greater than 1.3, more preferably greater than 1.6, further preferably greater than 2, yet further preferably greater than 2.2, still further preferably greater than 2.4, or most preferably greater than 2.7.

[0023] The plurality of colloidal InAs quantum dots may have isotropic morphology.

[0024] A third aspect of the present invention relates to an ink comprising a plurality of colloidal InAs quantum dots according to the second aspect of the present invention.The ligands of the colloidal InAs quantum dots may be selected from inorganic halides, organic halides, and combinations thereof.

[0025] A fourth aspect of the present invention relates to an infrared photodetector comprising a plurality of colloidal InAs quantum dots according to the second aspect of the present invention, optionally being formed using an ink according the third aspect of the present invention.

[0026] DESCRIPTION OF THE DRAWINGS

[0027] Fig. 1 is of a typical photoabsorption spectrum annotated to show the derivation of Peak:Valley ratio (P / V), % Trough, and HWHM.

[0028] Fig. 2 shows overlain photoabsorption spectra for the exemplary pluralities of colloidal InAs quantum dots, along with a comparative spectrum for a plurality of larger colloidal InAs quantum dots with peak absorption around 1100 nm. The inset indicates the target wavelength for each of the pluralities of colloidal InAs quantum dots.

[0029] Fig. 3 shows a photoabsorption spectrum for the In-Zn-As Feedstock (ln:Zn:As ratio of 3.4: 1.1: 1) for comparison.

[0030] Fig. 4 shows representative TEM images of the colloidal InAs quantum dots, which can be seen to be uniform in both size and shape

[0031] DEFINITIONS AND ABBREVIATIONS

[0032] By “InAs quantum dots” it is meant colloidal InAs quantum dots that are formed in solution using a ‘bottom up’ approach and typically having surface ligands. The InAs quantum dots may comprise indium and arsenic, but may include further elements as dopants. Alternatively, the InAs quantum dots may consist essentially of, or consist of, indium and arsenic. It will be understood that the ratio of indium to arsenic 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:As of from 3:1 to 1:2, optionally from 2:1 to 1:1, from 1.7:1 to 1.2:1, or from 1.6:1 to 1.4:1, such as about 1.5:1.

[0033] By small InAs quantum dots it is meant InAs quantum dots that have a peak absorbance below 1000 nm, below 975 nm, below 950 nm, below 920 nm, below 900 nm, below 850nm, below 820 nm, or below 800 nm. For example, the small InAs quantum dots may have a peak absorbance of between 750 nm and 1000 nm, preferably between 775 nm and 975 nm, more preferably between 800 nm and 950 nm, further preferably between 820 nm and 920 nm, most preferably between 850 nm and 900 nm.

[0034] References to “NIR” herein are references to “near infrared”, corresponding to light with a wavelength below 1 pm (e.g. from 0.7 to 1 pm).

[0035] References to “SWIR” herein are references to “short wavelength infrared”, corresponding to light with a wavelength of 1 to 3 pm.

[0036] References to “room temperature” herein will be understood to be references to ordinary temperatures, such as a temperature of about 20°C.

[0037] Due to the shape of the quantum dots’ first excitonic absorption peak, it is 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.

[0038] 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.

[0039] % Trough is a measure of the depth of the valley behind the first excitonic absorption peak. A higher % Trough indicates the presence of fewer smaller-than-median quantum dots having a smaller-than-median absorption wavelength and can be calculated as follows:

[0040] %Trough = 1-(V / P) x 100

[0041] Half-width-at-half-maximum (HWHM) is a measure of the width of the first excitonic absorption peak at half its maximum, taken towards higher 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.

[0042] DETAILED DESCRIPTION

[0043] Synthesis of Small InAs Quantum Dots

[0044] The present invention relates to a method of producing small InAs quantum dots with improved control over particle size and size distribution. The method comprises the steps of providing an initial In-Zn-As feedstock in a reaction vessel; heating the reaction vessel to a reaction temperature; and maintaining the reaction temperature for a reaction period while gradually adding a further In-Zn-As feedstock.

[0045] Any reaction vessel suitable for the materials used and the temperatures and pressures applied during the synthesis may be used. Preferably the synthesis is performed under an inert atmosphere, such as nitrogen or argon. Preferably, the synthesis is performed under anhydrous conditions.

[0046] The further In-Zn-As feedstock may be added at a rate of from 0.1 to 20 mL / min, preferably from 0.5 to 15 mL / min, more preferably from 0.85 to 12 mL / min, most preferably from 1 to 10 mL / min. The further In-Zn-As feedstock may be added at a rate of at least 0.1 mL / min, at least 0.5 mL / min, at least 0.85 mL / min, at least 1 mL / min, at least 10 mL / min, at least 12 mL / min, or of at least 15 mL / min. The further In-Zn-As feedstock may be added at a rate of at most 20 mL / min, at most 15 mL / min, at most 12 mL / min, at most 10 mL / min, at most 1 mL / min, at most0.85 mL / min, or of at most 0.5 mL / min. In embodiments, the further In-Zn-As feedstock is added at a rate exceeding 0.84 mL / min, such as between 0.84 and 20 mL / min, between 0.84 and 15 mL / min, between 0.84 and 12 mL / min, between 0.84 and 10 mL / min. Alternatively, or additionally, the rate at which the further In-Zn-As feedstock is added may be described in terms of the mmol of As added to the reaction vessel. In such embodiments, the rate of addition of the further In-Zn-As feedstock may be defined as from 0.01 to 2 mmol / min of As, preferably from 0.1 to 1.5 mmol / min of As, more preferably from 0.2 to 1.2 mmol / min of As, most preferably from 0.5 to 1 mmol / min of As. The further In-Zn-As feedstock maybe added at a rate of at least 0.01 mmol / min of As, at least 0,1 mmol / min of As, at least 0.2 mmol / min of As, at least 0.5 mmol / min of As, at least 1 mmol / min of As, at least 1.2 mmol / min of As, or of at least 1.5 mmol / min of As. The further In-Zn-As feedstock may be added at a rate of at most 2 mmol / min of As, at most 1.5 mmol / min of As, at most 1.2 mmol / min of As, at most 1 mmol / min of As, at most 0.5 mmol / min of As, or at most 0.2 mmol / min of As. In embodiments, the further In-Zn-As feedstock is added at a rate exceeding 0.1 mmol / min such as between 0.1 and 2 mmol / min, between 0.1 and 1.5 mmol / min, between 0.1 and 1.2 mmol / min, or between 0.1 and 1 mmol / min.

[0047] It will be understood that the ratio, whether molar or volume, of the initial In-Zn-As feedstock and the further In-Zn-As feedstock is proportionate to the size of the InAs quantum dots that are formed. In some embodiments the initial In-Zn-As feedstock and the further In-Zn-As feedstock have the same concentration and molar ratios of In, Zn, and As, for example, they may be portions of the same In-Zn-As feedstock. In such embodiments, the initial In-Zn-As feedstock present and the further In-Zn-As feedstock added may be in a volume ratio of from 1 :0.2 to 1 :2, preferably from 1 :0.3 to 1 : 1.5, more preferably from 1:0.4 to 1:1.2. In other embodiments, the initial In-Zn-As feedstock and the further In-Zn-As feedstock may be different in terms of their concentration and molar ratios of In, Zn, and As. In such embodiments, the ratio of moles of As in the initial In-Zn-As feedstock used to moles of As in the further In-Zn-As feedstock added may be from 1:0.2 to 1:2, preferably from 1:0.3 to 1:1.5, more preferably from 1:0.4 to 1:1.2.

[0048] The reaction temperature is any suitable to induce nucleation and growth of InAs quantum dots from the In-Zn-As feedstock. The reaction temperature may be from 220 to 380 °C, preferably from 240 to 360 °C, more preferably from 260 to 340 °C, most preferably from 280 to 320°C, such as about 300 °C. It will be understood that the reaction temperature may vary within the range during the course of the synthesis.

[0049] The reaction period may be from 5 to 120 minutes, optionally from 10 to 90 minutes, further optionally from 20 to 80 minutes, such as from 30 to 60 minutes.

[0050] Further additives may be included in the reaction vessel. For example, carboxylic acids (such as myristic, isostearic, or oleic acids), amines (such as octadecylamine or trioctylamine), additional sources of In (such as In carboxylates as described herein), additional sources of Zn (such as Zn carboxylates as described herein), and sources ofchloride (such as tetrachloroethylene and zinc chloride). Preferred additives are zinc isostearate and sources of chlorides (such as tetrachloroethylene and zinc chloride). Without wishing to be bound by theory, these additives appear to stabilise the growing nuclei, thereby improving the quality of the resulting quantum dots. It will be understood that the additional sources of In and Zn are additional to the In-Zn-As feedstock (i.e. are not further portions of the In-Zn-As feedstock).

[0051] The method may further comprise monitoring the peak absorption wavelength of the InAs quantum dots within the reaction vessel and ceasing addition of the In-Zn-As feedstock when a target peak absorption wavelength is achieved. Monitoring may involve in-line sampling or the periodic removal and analysis of aliquots of the contents of the reaction vessel.

[0052] The method may comprise cooling the reaction vessel and / or the contents thereof. It will be understood that cooling may comprising passive cooling and / or active cooling. It will be understood that passive cooling is simply allowing heat energy to pass to the environment from the reaction vessel and / or contents thereof, while active cooling includes actions to accelerate the loss of heat from the reaction vessel and / or contents thereof. Any suitable cooling means may be used. Passive cooling may be achieved by ceasing to heat the reaction vessel (e.g. switching off or removing the heating means) and / or removing the reaction vessel from any heated media into which it has been placed. Active cooling may be achieved by addition of relatively cool solvent to the reaction vessel, the flowing of relatively cool gas (such as an inert gas (e.g. nitrogen or argon)) through the reaction vessel, removal of the contents of the reaction vessel to a relatively cool vessel, or the application of relatively cool media to the exterior of the reaction vessel (for example, relatively cool gas (e.g. air), a flow of relatively cool gas (e.g. inert gas or compressed air), ora relatively cool gas (e.g. water, ice water)). Cooling the reaction vessel may proceed immediately on ceasing addition of the In-Zn-As feedstock. Cooling the reaction vessel, and the contents thereof, halts growth of the small InAs quantum dots such that the small particle size and low polydispersity is maintained.

[0053] The method may further comprise isolation of the small InAs quantum dots. Any suitable isolation technique, or combination of techniques, may be used, such as precipitation, centrifugation, and filtration.Provision of In-Zn-As Feedstocks

[0054] In-Zn-As feedstocks, both initial and further, may be provided by providing a mixture of In carboxylate and Zn carboxylate; providing an As feedstock; heating the mixture of In carboxylate and Zn carboxylate to an As addition temperature; and adding the As feedstock to the mixture of In carboxylate and Zn carboxylate while maintaining the As addition temperature.

[0055] The In carboxylate may be any suitable In carboxylate. Particular carboxylates are In myristate, In isostearate, In acetate, and mixed In carboxylates, such as In myristate:acetate. In embodiments, the In carboxylate may comprise ln(Ma)3-x(Ac)x, wherein 0 < x < 3, such as x being about 1.5. The Zn carboxylate may be any suitable Zn carboxylate. Particular carboxylates are Zn myristate, Zn isostearate, Zn acetate, and mixed Zn carboxylates. The In carboxylate and / or Zn carboxylate may be dissolved in a solvent. Any suitable high-boiling solvent that is able to dissolve the feedstocks and disperse the small InAs quantum dots that are formed may be used. Typical solvents include Lewis base type coordinating solvents, such as a phosphine (e.g. trioctylphopsphine (TOP)), a phosphine oxide (e.g. trioctylphosphine oxide (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 (such as hydrogenated terphenyl (e.g. Therminol® 66), mixtures of biphenyl and diphenyl oxide (e.g. Dowtherm™), ethers, and xylene). Preferred solvents are squalane and 1 -octadecene. Preferably, the boiling point of the solvent is high so as to permit the use of higher temperatures. Without wishing to be bound by theory, it is believed that the use of higher temperatures provides the plurality of small InAs quantum dots with improved size distribution. Preferably, the boiling point of the solvent is in excess of 200 °C, in excess of 220 °C, in excess of 240 °C, in excess of 260 °C, in excess of 280 °C, or in excess of 300 °C. 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 feedstocks by heating the solvent to an intermediate temperature, such as 120°C, under a reduced pressure. Further additives may be included, for example, carboxylic acids (such as myristic, isostearic, or oleic acids) or amines (such as octadecylamine or trioctylamine).The As feedstock may comprise any suitable As compound. Suitable As compounds include As trialkylsilyls having the formula As(SiR13)3 and As trialkylgermanium compounds having the formula As(GeR13)3. R1may be any suitable alkyl group, for example -Ci-ealkyl or -Cs-ecycloalkyl, optionally with substitutions. In embodiments, R1may be selected from methyl, ethyl, n-propyl, / so-propyl, n-butyl, / so-butyl, sec-butyl, tert-butyl, and combinations thereof. Preferably, R1is — Ci-3alkyl. Most preferably, R1is a methyl group. The As compound may be dissolved in a solvent to form the As feedstock. Particular solvents that may be used are those defined herein.

[0056] The As addition temperature may be in the range of from room temperature to 140 °C, preferably from 40 to 120 °C, more preferably from 50 to 100 °C, most preferably from 60 to 80 °C. In embodiments, the As addition temperature may be greater than room temperature, greater than 40 °C, greater than 50 °C, greater than 60 °C, greater than 80 °C, greater than 100 °C, or greater than 120 °C. In embodiments, the As addition temperature may be less than 140 °C, less than 120 °C, less than 100 °C, less than 80 °C, less than 60 °C, less than 50 °C, or less than 40 °C.

[0057] The As feedstock may be added to the In carboxylate and Zn carboxylate instantaneously. Alternatively, the As feedstock may be added to the In carboxylate and Zn carboxylate over a period of from 10 seconds to 240 minutes, preferably from 1 minute to 120 minutes, more preferably from 10 to 90 minutes, yet more preferably from 45 to 75 minutes, most preferably about 60 minutes.

[0058] Alternatively, the In-Zn-As feedstock may be provided by providing an In carboxylate; providing a Zn-As feedstock; heating the In carboxylate to a Zn-As addition temperature; and adding the Zn-As feedstock to the In carboxylate while maintaining the Zn-As addition temperature.

[0059] The In carboxylate may be any suitable In carboxylate. Particular carboxylates are In myristate, In isostearate, In acetate, and mixed In carboxylates, such as In myristate:acetate. In embodiments, the In carboxylate may comprise ln(Ma)3-x(Ac)x, wherein 0 < x < 3, such as x being about 1.5. The In carboxylate may be dissolved in a solvent. Particular solvents that may be used are those defined herein. Further additives may be included, for example, carboxylic acids (such as myristic, isostearic, or oleic acids) or amines (such as octadecylamine or trioctylamine).The Zn-As feedstock may be as described herein under “Provision of ZnAs Feedstocks”.

[0060] The Zn-As addition temperature may be in the range of from room temperature to 140 °C, preferably from 40 to 120 °C, more preferably from 50 to 100 °C, most preferably from 60 to 80 °C. In embodiments, the Zn-As addition temperature may be greater than room temperature, greater than 40 °C, greater than 50 °C, greater than 60 °C, greater than 80 °C, greater than 100 °C, or greater than 120 °C. In embodiments, the Zn-As addition temperature may be less than 140 °C, less than 120 °C, less than 100 °C, less than 80 °C, less than 60 °C, less than 50 °C, or less than 40 °C.

[0061] The Zn-As feedstock may be added to the In carboxylate instantaneously. Alternatively, the Zn-As feedstock may be added to the I n carboxylate over a period of from 10 seconds to 240 minutes, preferably from 1 minute to 120 minutes, more preferably from 10 to 90 minutes, yet more preferably from 15 to 60 minutes, most preferably about 30 minutes.

[0062] The ln:As ratio in the In-Zn-As feedstock, either initial or further, may be from 1:1 to 10:1, preferably from 1.5:1 to 8:1, more preferably from 2:1 to 6:1, most preferably from 3:1 to 4: 1 , such as about 3.4: 1.

[0063] The Zn:As ratio in the In-Zn-As feedstock, either initial or further, may be from 1:5 to 5:1, preferably from 1:3 to 3:1, more preferably from 1:2 to 2:1, most preferably about 1:1.

[0064] The ln:Zn:As ratio in the In-Zn-As feedstock, either initial or further, may be expressed as x:y:z, wherein:

[0065] x is the quantity of In and has a value from 1 to 10;

[0066] y is the quantity of Zn and has a value from 0.2 to 5; and

[0067] z is the quantity of As and has a value of about 1.

[0068] Alternatively, x is from 1.5 to 8, y is from 0.33 to 3, and z is about 1. Further alternatively, x is from 2 to 6, y is from 0.5 to 2, and z is about 1. Yet further alternatively, x is from 3 to 4 (such as about 3.4), y is 1 , and z is about 1.The In-Zn-As feedstock, either initial or further, may have an As concentration of from 0.01 to 1 M, preferably from 0.05 to 0.5 M, more preferably from 0.05 to 0.2 M, most preferably from 0.08 to 0.15 M, such as about 0.1 M.

[0069] In embodiments, the initial In-Zn-As feedstock and the further In-Zn-As feedstock are the same in terms of concentration and ln:Zn:As ratio, for example, they may be different portions of the same In-Zn-As. Alternatively, the initial In-Zn-As feedstock and further In-Zn-As feedstock may be different.

[0070] Without wishing to be bound by theory, it is believed that these ratios of In to As and Zn to As lead to improved size distribution at small InAs quantum dot sizes.

[0071] Provision of Zn-As Feedstocks

[0072] Providing the Zn-As feedstock may comprise: providing a Zn carboxylate; providing an As feedstock; heating the Zn carboxylate to an As addition temperature; and adding the As feedstock to the Zn carboxylate while maintaining the As addition temperature. Without wishing to be bound by theory, it is believed that combination of the Zn and As to form the Zn-As feedstock prior to mixing with the In carboxylate moderates the reactivity of these precursors, thereby improving the quality of the resulting plurality of small InAs quantum dots.

[0073] The Zn carboxylate may be any suitable Zn carboxylate. Particular carboxylates are Zn myristate, Zn isostearate, Zn acetate, and mixed Zn carboxylates. The Zn carboxylate may be dissolved in a solvent. Particular solvents that may be used are those defined herein. Further additives may be included, for example, carboxylic acids (such as myristic, isostearic, or oleic acids) or amines (such as octadecylamine or trioctylamine).

[0074] The As feedstock may comprise any suitable As compound. Suitable As compounds include As trialkylsilyls having the formula As(SiR13)3 and As trialkylgermanium compounds having the formula As(GeR13)3. R1may be any suitable alkyl group, for example -Ci-ealkyl or -Cs-ecycloalkyl, optionally with substitutions. In embodiments, R1may be selected from methyl, ethyl, n-propyl, / so-propyl, n-butyl, / so-butyl, sec-butyl, tert-butyl, and combinations thereof. Preferably, R1is — Ci-3alkyl. Most preferably, R1is a methyl group. The As compound may be dissolved in a solvent to form the As feedstock. Particular solvents that may be used are those defined herein.The As addition temperature may be in the range of from room temperature to 140 °C, preferably from 40 to 120 °C, more preferably from 50 to 100 °C, most preferably from 60 to 80 °C. In embodiments, the As addition temperature may be greater than room temperature, greater than 40 °C, greater than 50 °C, greater than 60 °C, greater than 80 °C, greater than 100 °C, or greater than 120 °C. In embodiments, the As addition temperature may be less than 140 °C, less than 120 °C, less than 100 °C, less than 80 °C, less than 60 °C, less than 50 °C, or less than 40 °C.

[0075] The As feedstock may be added to the In carboxylate and Zn carboxylate instantaneously. Alternatively, the As feedstock may be added to the In carboxylate and Zn carboxylate over a period of from 10 seconds to 240 minutes, preferably from 1 minute to 120 minutes, more preferably from 10 to 90 minutes, yet more preferably from 20 to 60 minutes, most preferably about 30 minutes.

[0076] Pluralities of InAs Quantum Dots

[0077] The present invention also relates to pluralities of InAs quantum dots obtained or obtainable by the foregoing methods.

[0078] The pluralities of InAs quantum dots may have a peak absorbance of between 750 nm and 1000 nm, preferably between 775 nm and 975 nm, more preferably between 800 nm and 950 nm, further preferably between 820 nm and 920 nm, most preferably between 850 nm and 900 nm.

[0079] The peak absorbance may be greater than 750 nm, optionally greater than 775 nm, optionally greater than 800 nm, optionally greater than 820 nm, optionally greater than 850 nm, optionally greater than 920 nm, optionally greater than 950 nm, or optionally greater than 975 nm. The peak absorbance may be less than 1000 nm, optionally less than 975 nm, optionally less than 950 nm, optionally less than 920 nm, optionally less than 900 nm, optionally less than 850 nm, optionally less than 820 nm, optionally less than 800 nm, or optionally less than 775 nm. In embodiments, the peak absorbance is between 800 nm and 900 nm, such as from 810 nm to 890 nm. In embodiments, the peak absorbance is between 900 nm and 915 nm. In embodiments, the peak absorbance is between 920 nm and 950 nm. In some embodiments, the peak absorbance is as described herein on the proviso that it is not 750 nm. In some embodiments, the peakabsorbance is as described herein on the proviso that it is not 800 nm. In some embodiments, the peak absorbance is as described herein on the proviso that it is not 900 nm. In some embodiments, the peak absorbance is as described herein on the proviso that it is not 919 nm. In some embodiments, the peak absorbance is as described herein on the proviso that it is not 932 nm. In some embodiments, the peak absorbance is as described herein on the proviso that it is not 1000 nm.

[0080] The pluralities of InAs quantum dots may have a HWHM of less than 100 meV, preferably less than 90 meV, more preferably less than 80 meV, further preferably less than 70 meV, or most preferably less than 65 meV. The pluralities of InAs quantum dots may have a HWHM of more than 65 meV, optionally more than 70 meV, optionally more than 80 meV, or optionally more than 90 meV. The pluralities of InAs quantum dots may have a HWHM in the range of 65 to 100 meV, optionally in the range of 70 to 90 meV.

[0081] The pluralities of InAs quantum dots may have a first peak:valley ratio of greater than 1, preferably greater than 1.3, more preferably greater than 1.6, further preferably greater than 2, yet further preferably greater than 2.2, still further preferably greater than 2.4, or most preferably greater than 2.7. The pluralities of InAs quantum dots may have a peak:valley ratio of less than 3, less than 2.7, less than 2.4, less than 2.2, less than 2, less than 1.6, or less than 1.3. The pluralities of InAs quantum dots may have a peak:valley ratio in the range of from 1 to 3, from 1.3 to 2.7, from 1.6 to 2.4, or from 2 to 2.2.

[0082] In embodiments, the InAs quantum dots have isotropic morphology.

[0083] Inks Comprising Pluralities of InAs Quantum Dots

[0084] The present invention also relates to inks comprising pluralities of InAs quantum dots as described herein. A key advantage of colloidal InAs quantum dots is that they may be processed in solution in the form of inks (e.g. when producing devices). The pluralities of InAs quantum dots may be converted to inks by dissolution in a suitable solvent. The solubility of the InAs quantum dots may be altered by exchanging their surface ligands, allowing the use of different solvents as required.

[0085] For example, InAs quantum dots with carboxylic acid ligands are soluble in non-polar solvents, such as octane. To render the InAs quantum dots soluble in polar solvents,such as dimethylformamide (DMF), the carboxylic acid ligands may be exchanged for more polar ligands such as inorganic halides or organic halides. Suitable inorganic halides include indium halides (such as indium fluoride, indium chloride, and indium bromide), zinc halides (such as zinc fluoride, zinc chloride, and zinc, bromide) tin halides (such as tin chloride and tin bromide), and nitrosonium tetrafluoroborate. Suitable organic halides include quaternary ammoniums, such as ammonium chloride, ammonium bromide, ammonium acetate, and cetrimonium bromide.

[0086] Ligand exchange may be effected by any suitable process. For example, the initial InAs quantum dots may be dissolved in a first solvent and the resulting solution mixed with a solution of the ligands in a second solvent, the first and second solvents being immiscible. The two phases are mixed thoroughly to enable ligand exchange and transfer of the InAs quantum dots to the second solvent. After being allowed to settle, the first solvent is removed. The ligand-exchanged InAs quantum dots in the second solvent may then be washed and / or filtered to provide the ink.

[0087] IR Photodetectors and Other Devices Comprising Pluralities of InAs Quantum Dots The present invention also relates to IR photodetectors comprising a plurality of InAs quantum dots as described herein. The present invention also relates to other optoelectronic devices comprising a plurality of InAs quantum dots as described herein. In embodiments, the devices comprise a single plurality of InAs quantum dots (e.g. all of the same size or morphology). Alternatively, the devices comprise two or more pluralities of InAs quantum dots (e.g. a mixture of InAs quantum dots having two or more peak absorbances).

[0088] EXAMPLES

[0089]

[0090] A mixed indium carboxylate is used in the following syntheses of InAs 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.

[0091] 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 addedand the mixture degassed for 2 hours while stirring at 200 rpm. 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.

[0092] Reaction

[0093]

[0094] Aliquots for absorption spectroscopy were obtained as follows. Using a syringe flushed with nitrogen and equipped with a suitable needle, 0.2-0.3 mL of tetrachloroethylene (TCE) was taken into the syringe, followed by approx. 0.1 mL of the reaction solution. The contents of the syringe were then expelled into a glass vial containing 3 mL TCE. The contents were then drawn up into a syringe and expelled via a 0.1 micron syringe filter into a 1 cm pathlength cuvette. TCE was added to make the contents the appropriate fill level for measurement. Unless stated otherwise, the formation of quantum dots in the following examples was tracked using this methodology.

[0095] Preparation of ZnAs Feedstock

[0096] Zinc isostearate (52 g) and trioctylamine (TOA; 34.67 mL) were degassed in a 500 mL 3-necked round bottomed flask (RBF) for 2 hours at 130 °C under vacuum. The RBF was cooled to 60 °C and fr / s-trimethylsilyl arsine ((TMS)As) (156 mL; 0.5 M in squalane) was added over 30 mins using a syringe pump at a rate of 312 mL / hr.

[0097] The reaction was heated at 60 °C for 30 mins then left to cool naturally to room temperature while stirring. The resulting ZnAs feedstock had a 1.1 :1 ratio of Zn to As.

[0098] Preparation of In-Zn-As Feedstock (ln:Zn:As ratio of 3.4:1.1:1)

[0099] Indium carboxylate (142.83 g), isostearic acid (93.6 mL), TOA (60.67 mL), and squalane (303.33 mL) were degassed in a 2 L 3-necked RBF for 2 hours at 130 °C under vacuum. The temperature was decreased to 60 °C and, when the solution had cooled to 70 °C,ZnAs feedstock (242.67 mL) was added over 30 mins using a syringe pump at a rate of 485.34 mL / hr.

[0100] The reaction was heated at 60 °C for 30 mins, after which the temperature was raised to 100 °C and degassed for 2 hours and 30 mins at 100 °C under vacuum. The reaction was then placed under nitrogen and allowed to cool to room temperature. The resulting In-Zn-As feedstock had an ln:Zn:As ratio of 3.4:1.1 :1.

[0101] Preparation of In-Zn-As Feedstock (ln:Zn:As ratio of 5.2:1.1:1)

[0102] Indium carboxylate (61.92 g), oleic acid (39 mL), TOA (25 mL), and squalane (130 mL) were degassed in a 1 L 3-necked RBF for 2 hours at 120 °C under vacuum and allowed to cool to room temperature. The solution was heated to 80 °C under nitrogen and ZnAs feedstock (80 mL) was added over 30 mins using a syringe pump at a rate of 160 mL / hr.

[0103] The reaction was heated at 80 °C for 30 mins, after which it was allowed to cool to room temperature. The reaction was heated to 80 °C and degassed for 5 hours at 80 °C under vacuum. The reaction was then placed under nitrogen and allowed to cool to room temperature. The resulting In-Zn-As feedstock had an ln:Zn:As ratio of 5.2:1.1:1.

[0104] Example 1: Synthesis of InAs Quantum Dots with a Target Peak Absorbance of 850 nm Indium carboxylate (59 g), zinc isostearate (73.7 g), isostearic acid (40.6 mL), and squalane (150 mL) were degassed in a 2 L flange reactor for 1 hour at 130 °C under vacuum. The reactor was cooled to 120 °C, octadecylamine (35.6 g) was charged under nitrogen and the reactor contents were degassed for a further 1 hour at 120 °C before cooling to 100 °C.

[0105] At 100 °C, In-Zn-As feedstock (ln:Zn:As ratio of 3.4:1.1:1, 421.2 mL) was added using a peristaltic pump set at a rate of 12.2 g / min, and the temperature was then increased to 310 °C.

[0106] When the temperature reached 295 °C, further In-Zn-As feedstock (ln:Zn:As ratio = 3.4:1.1:1, 177.9 mL) was added using a gear pump at a rate of 8 g / min. The reaction was monitored and when the peak absorption maximum reached 850 nm, the reaction was quickly cooled to 280 °C with compressed air to stop the growth of the quantum dots and then left cooling naturally to room temperature while stirring.For the isolation, the reaction mixture was diluted with dry chloroform (0.75 vols w.r.t. crude reaction solution) at 65 °C and spun in a centrifuge (4000 rpm, 15 mins) inside a glovebox to remove any solid particulates from the quantum dot solution. The quantum dot solution from the first spin (240 g) was treated with isopropanol (1440 g) to precipitate the quantum dots and the resulting mixture was centrifuged (4000 rpm, 15 mins) to obtain a pellet which was rinsed with a mixture of acetone and isopropanol (1:1 mass ratio, 1,920 g) and centrifuged again (4000 rpm, 15 mins). The pellets were washed a second time with acetone (800 g) and centrifuged (4000 rpm, 15 mins), after which they were dissolved in octane (176 g). The resulting quantum dot solution was treated with acetone (1,440 g) to precipitate the quantum dots and again centrifuged (4000 rpm, 15 mins) and the resulting pellet was re-suspended in octane (216 g). The resulting quantum dot solution was centrifuged (4000 rpm, 15 mins) to remove any residual particulates and filtered through a 0.1 pm filter.

[0107] The final mass yield was 31.4 g. The residual inorganic content at 600 °C determined by thermogravimetric analysis was 39 wt%.

[0108] A portion of the InAs quantum dots formed in Example 1 were subjected to ligand substitution with octanoic acid, to provide InAs quantum dots with octanoate ligands in place of isostearate.

[0109] Example 2: Synthesis of InAs Quantum Dots with a Target Peak Absorbance of 900 nm Indium carboxylate (59 g), zinc isostearate (73.7 g), isostearic acid (40.6 mL), and squalane (150 mL) were degassed in a 2 L flange reactor for 1 hour at 130 °C under vacuum. The reactor was cooled to 120 °C, octadecylamine (35.6 g) was charged under nitrogen and the reactor contents were degassed for a further 1 hour at 120 °C before cooling to 100 °C.

[0110] At 100 °C, In-Zn-As feedstock (ln:Zn:As ratio = 3.4:1.1:1, 421.2 mL) was added using a peristaltic pump set to add at 12.2 g / min, and the temperature was then increased to 320 °C.

[0111] When T = 295 °C, In-Zn-As feedstock (ln:Zn:As ratio = 3.4:1.1:1, 340.8 mL) was added using a gear pump at a rate of 8 g / min. The reaction was monitored and when theabsorption maximum reached 900 nm, the reaction was quickly cooled to 270 °C with compressed air to stop the growth of the quantum dots and then left to cool naturally to room temperature while stirring. For the isolation, the reaction mixture was diluted with chloroform (0.75 vols w.r.t. the squalane and feedstock used for growth during the reaction) at 65 °C and spun in a centrifuge (4000 rpm, 15 mins) inside a glovebox to remove any solid particulates from the quantum dot solution. The quantum dot solution from the first spin (240 g) was treated with isopropanol (1,440 g) to precipitate the quantum dots and the resulting mixture was centrifuged (4000 rpm, 15 mins) to obtain a pellet which was re-dissolved in octane (168 g). The resulting quantum dot solution was treated with acetone (760 g) to re-precipitate the quantum dots and the resulting mobile pellets were washed with acetone (840 g) and centrifuged (4000 rpm, 15 mins) to reduce the oiliness. This process was repeated using isopropanol (840 g) followed by centrifuging (4000 rpm, 15 mins) and the firmer pellets were dried under nitrogen and resuspended in octane (148 g). The resulting quantum dot solution was centrifuged (4000 rpm, 15 mins) to remove any residual particulates and filtered through a 0.1 pm filter.

[0112] The final mass yield was 21.4g. The residual inorganic content at 600 °C determined by thermogravimetric analysis was 52 wt%.

[0113] Example 3: Synthesis of InAs Quantum Dots with a Target Peak Absorbance of 920 nm Zinc isostearate (8.6 g), octadecylamine (3.7 g), and squalane (65 mL) were degassed in a 1 L 3-neck RBF for 1 hour at 130 °C under vacuum. The flask was cooled to 70 °C, then In-Zn-As feedstock (ln:Zn:As ratio = 5.2:1.1 :1; 60.25 mL) was added over 6 mins using a syringe pump set at a rate of 602.5 mL / hr and the resulting reaction mixture was stirred for 15 min at 70 °C before the temperature was increase to 320 °C.

[0114] When the temperature reached 290 °C, In-Zn-As feedstock (ln:Zn:As ratio = 5.2:1.1:1; 66.5 mL) was added at a rate of 108.6 mL / hr. The reaction was monitored and when the absorption maximum reached 920 nm, the reaction was quickly cooled 280 °C with compressed air to stop the growth of the quantum dots and then left to cool naturally to room temperature while stirring.

[0115] For the isolation, the reaction mixture was diluted with chloroform (0.75 vols w.r.t. crude reaction solution) at 60 °C and centrifuged (4000 rpm, 10 mins) inside a glovebox to remove any solid particulates from the quantum dot solution. The quantum dot solutionfrom the first spin (264 g) was treated with isopropanol (364 g) to precipitate the particles, the resulting suspension was centrifuged (4000 rpm, 10 mins) to obtain a pellet which was re-dissolved in octane (92 g). The resulting quantum dot solution was treated with acetone (206 g) to reprecipitate the dots and centrifuged (4000 rpm, 10 mins). The resulting pellet was rinsed with acetone (8 g) and dried under nitrogen, after which it was finally re-suspended in octane (40 g). The resulting quantum dot solution was centrifuged (6000 rpm, 10 mins) to remove any residual particulates and filtered through a 0.1 pm filter.

[0116] The final mass yield was 1.9 g. The residual inorganic content at 600 °C determined by thermogravimetric analysis was 65 wt%.

[0117] Example 3 was repeated using the alternative In-Zn-As feedstock (3.4:1.1:1) in the presence of indium carboxylate and isostearic acid.

[0118] Example 4: Synthesis of InAs Quantum Dots with a Target Peak Absorbance of 950 nm Indium carboxylate (4.94 g), zinc isostearate (6.14 g), isostearic acid (3.4 mL), and squalane (130 mL) were degassed in a 500 mL 3-neck RBF for 1 hour at 130 °C under vacuum. The flask was cooled to 120 °C, octadecylamine (2.96 g) was charged under nitrogen and the flask contents were degassed for a further 1 hour at 120 °C before being cooled to 100 °C. At 100 °C, In-Zn-As feedstock (ln:Zn:As ratio = 3.4:1.1:1, 35.1 mL) was added over 30 mins using a syringe pump at a rate of 70.2 mL / hr, after which the temperature was increased to 320 °C.

[0119] When the temperature reached 295 °C, In-Zn-As feedstock (ln:Zn:As ratio = 3.4: 1.1:1, 41 mL) addition was commenced at a rate of 46.8 mL / hr . The reaction was monitored and when the absorption maximum reached 950 nm, the reaction was quickly cooled to 280 °C with compressed air to stop the growth of the quantum dots and then left to cool naturally to room temperature while stirring.

[0120] For the isolation, the reaction mixture was diluted with chloroform (0.75 vols w.r.t. the squalane and feedstock used for growth during the reaction) at 65 °C and centrifuged (4000 rpm, 10 mins) inside a glovebox to remove any solid particulates from the quantum dot solution. The quantum dot solution from the first spin (392 g) was treated with isopropanol (976 g) to precipitate the quantum dots and the resulting mixture wascentrifuged (4000 rpm, 10 mins) to obtain a pellet which was re-dissolved in octane (112 g). The quantum dot solution was then treated with acetone (660 g) to re-precipitate the quantum dots and the mixture centrifuged (4000 rpm, 10 mins) to obtain a pellet which was re-dissolved in octane (110 g). The resulting quantum dot solution was treated once more with isopropanol (366 g) to re-precipitate the dots and the pellet was finally resuspended in octane (78 g). The resulting quantum dot solution was centrifuged (4000 rpm, 10 mins) to remove any residual particulates and filtered through a 0.1 pm filter.

[0121] The final mass yield was 1.8 g. The residual inorganic content at 600 °C determined by thermogravimetric analysis was 61 wt%.

[0122] of Results

[0123] The absorption spectra of the exemplary quantum dots (and a comparative example of larger InAs quantum dots with maximum absorption around 1100 nm) are displayed in Fig. 2, with the inset identifying which spectrum corresponds to which target wavelength. It can be seen from the spectra that each of the exemplary syntheses produced a high quality plurality of InAs quantum dots with features indicating a narrow polydispersity. For each, the first and second excitonic peaks are observable, with good, quantifiable P:V ratios (and corresponding high % Trough), as well as a low HWHM. The spectra also show that the synthetic protocol was effective for producing InAs quantum dots at very low peak absorbance values (e.g. below 900 nm) while maintaining a high quality. In addition, the spectra for Examples 1 and 2 show that the synthesis is amenable to operation on larger scales (i.e. 10’s of grams or greater). The numerical analysis of the spectra are provided in the below table, along with additional details (i.e. yield, wt% organics, In-Zn-As feedstock used, and ligands used).

[0124] An absorption spectrum for the In-Zn-As Feedstock (ln:Zn:As ratio of 3.4: 1.1: 1) is provided for reference in Fig. 3.

[0125] The exemplary pluralities of quantum dots were also imaged using TEM to determine average particle sizes. Fig. 4 displays representative TEM images of the quantum dots, which can be seen to be uniform in both size and shape.

[0126]

[0127]

Claims

CLAIMS:

1. A method of synthesising small colloidal InAs quantum dots, the method comprising:providing an initial In-Zn-As feedstock in a reaction vessel;heating the reaction vessel to a reaction temperature; andmaintaining the reaction temperature for a reaction period while gradually adding a further In-Zn-As feedstock.

2. The method of claim 1, wherein the initial In-Zn-As feedstock and / or further In-Zn-As feedstock is formed by:providing a mixture of In carboxylate and Zn carboxylate;providing an As feedstock;heating the mixture of In carboxylate and Zn carboxylate to an As addition temperature; andadding the As feedstock to the mixture of In carboxylate and Zn carboxylate while maintaining the As addition temperature.

3. The method of claim 1, wherein providing the initial In-Zn-As feedstock and / or the further In-Zn-As feedstock comprises:providing an In carboxylate;providing a Zn-As feedstock;heating the In carboxylate to a Zn-As addition temperature; andadding the Zn-As feedstock to the In carboxylate while maintaining the Zn-As addition temperature.

4. The method of claim 3, wherein providing the initial In-Zn-As feedstock and / or the further In-Zn-As feedstock comprises:providing a Zn carboxylate;providing an As feedstock;heating the Zn carboxylate to an As addition temperature; andadding the As feedstock to the Zn carboxylate while maintaining the As addition temperature.

5. The method of any preceding claim, further comprising monitoring the peak absorption wavelength of the colloidal InAs quantum dots within the reaction vessel andceasing addition of the further In-Zn-As feedstock when a target peak absorption wavelength is achieved.

6. The method of any preceding claim, wherein the ln:As molar ratio in the initial In-Zn-As feedstock and / or the further In-Zn-As feedstock is from 1 : 1 to 10: 1 , preferably from 1.5:1 to 8:1, more preferably from 2:1 to 6:1, most preferably from 3:1 to 4:1.

7. The method of any preceding claim, wherein the Zn:As molar ratio in the initial In-Zn-As feedstock and / or the further In-Zn-As feedstock is from 1:5 to 5:1, preferably from 1:3 to 3:1, more preferably from 1:2 to 2:1, most preferably about 1:1.

8. The method of any preceding claim, wherein the ln:Zn:As molar ratio in the initial In-Zn-As feedstock and / or the further In-Zn-As feedstock is expressed as x:y:z, wherein:x is the quantity of In and has a value from 1 to 10;y is the quantity of Zn and has a value from 0.2 to 5; andz is the quantity of As and has a value of about 1.

9. The method of any preceding claim, further comprising providing additives to the reaction vessel, optionally the additives being selected from carboxylic acids (such as myristic, isostearic, or oleic acids), amines (such as octadecylamine or trioctylamine), additional sources of In (such as In carboxylates as described herein), additional sources of Zn (such as Zn carboxylates as described herein), and sources of chloride (such as tetrachloroethylene and zinc chloride).

10. The method of any preceding claim, wherein the reaction temperature is from 220 to 380 °C, preferably from 240 to 360 °C, more preferably from 260 to 340 °C, most preferably from 280 to 320°C, such as about 300 °C.

11. The method of any preceding claim, further comprising the step of cooling the reaction vessel and / or the contents thereof.

12. The method of any preceding claim, further comprising the step of isolating the small colloidal InAs quantum dots.

13. A plurality of colloidal InAs quantum dots having a peak absorbance of between 750 nm and 1000 nm, preferably between 775 nm and 975 nm, more preferably between 800 nm and 950 nm, further preferably between 820 nm and 920 nm, most preferably between 850 nm and 900 nm, optionally being obtained or obtainable by the method of any one of claims 1 to 12.

14. The plurality of colloidal InAs quantum dots of claim 13, wherein the plurality of InAs quantum dots has a HWHM of less than 100 meV, preferably less than 90 meV, more preferably less than 80 meV, further preferably less than 70 meV, most preferably less than 65 meV.

15. The plurality of colloidal InAs quantum dots of claim 13 or claim 14, wherein the plurality of InAs quantum dots has a peak:valley ratio of greater than 1 , preferably greater than 1.3, more preferably greater than 1.6, further preferably greater than 2, yet further preferably greater than 2.2, still further preferably greater than 2.4, or most preferably greater than 2.7.

16. The plurality of colloidal InAs quantum dots of any of claims 13 to 15, wherein the quantum dots have isotropic morphology.

17. An ink comprising a plurality of colloidal InAs quantum dots according to any one of claims 13 to 16.

18. The ink of claim 17, wherein the ligands of the colloidal InAs quantum dots are selected from inorganic halides, organic halides, and combinations thereof.

19. An infrared photodetector comprising a plurality of colloidal InAs quantum dots according to any one of claims 13 to 16, optionally being formed using an ink according to claim 17 or claim 18

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