Infrared-absorbing quantum dot, and method for producing infrared-absorbing quantum dot

Abstract

An infrared-absorbing quantum dot according to an embodiment of the present invention includes silver (Ag) and tellurium (Te), and has an absorbance peak in the range of 1,400 nm to 1,800 nm, wherein the peak-to-trough ratio (peak / trough) of the absorbance peak is at least 1.0.

Description

Infrared absorbing quantum dots and method for producing the same

[0001] The present invention relates to infrared-absorbing quantum dots and methods for producing infrared-absorbing quantum dots. This application claims priority to U.S. Provisional Application No. 63 / 369,804, filed July 29, 2022, the contents of which are incorporated herein by reference.

[0002] Many optoelectronic devices, such as photovoltaic devices, telecommunications devices, sensor devices, and in vivo bioimaging materials, use materials that absorb light in the infrared (IR) region of the electromagnetic spectrum. In some cases, it can be advantageous to utilize materials with an absorbance peak in the range above 1400 nm. This can increase the signal-to-noise ratio of light absorbed by the device. For example, this region overlaps with the emission peak of IR light sources (e.g., 1450 nm lasers).

[0003] Zhen-Ya Liu, et al., “Breaking through the Size Control Dilemma of Silver Chalcogenide Quantum Dots via Trialkylphosphine-Induced Ripening: Leading to Ag2Te Emitting from 950 to 2100 nm” Journal of the American Chemical Society, vol. 143, issue 32, 2021, pp12867-12877Jianying Ouyang, et al. al., “Ag2Te Colloidal Quantum Dots for Near-Infrared-II Photodetectors” ACS Applied Nano Materials, vol. 4, issue 12, 2021, pp13587-13601

[0004] In some cases, single-crystal semiconductors such as gallium arsenide are utilized as IR-absorbing materials. However, it can be difficult to fabricate some devices using single-crystal semiconductors. For example, a detector for an IR camera can include an array of pixels, each of which includes a single-crystal semiconductor disposed on a silicon backplane. However, cutting the single-crystal semiconductor into portions corresponding to pixels and disposing each portion on the backplane of the array can be technically challenging, costly, and time-consuming. Furthermore, it can be difficult to fabricate silicon-based detectors that selectively absorb light in the range above 1400 nm.

[0005] In another example, quantum dots (QDs) can be used to absorb IR light. For example, lead-based QDs, cadmium-based QDs, and mercury-based QDs can absorb strongly in the 1400 nm to 1500 nm range. However, heavy metal-based QDs can be difficult to use in biological and medical applications. Heavy metals can also pose environmental hazards upon disposal.

[0006] As mentioned above, quantum dots (hereinafter also referred to as "QDs") based on heavy metals such as lead, cadmium, and mercury can absorb strongly in the range above 1400 nm. However, heavy metal-based QDs may pose environmental and health hazards. Conventional silver chalcogenides (e.g., Ag ２ S, Ag ２ Se, and Ag ２ Silver chalcogenide QDs can be used as less toxic alternatives to heavy metal-based QDs. However, silver chalcogenide QDs may have shorter absorption peak wavelengths (e.g., less than 1400 nm), larger absorption peak half-widths at half maximum (HWHM), and / or smaller peak-to-valley ratios (e.g., less than 1.0) than heavy metal-based QDs (e.g., PbS). This can result in poor absorption and / or a smaller or undetectable signal-to-noise ratio at target wavelengths (e.g., in the range of 1400 nm to 1800 nm) compared to the use of heavy metal-based QDs.

[0007] Therefore, an object of the present invention is to provide quantum dots that can absorb infrared light of 1400 nm or more and that are substantially free of heavy metals.

[0008] Infrared absorbing quantum dots according to an embodiment of the present invention are infrared absorbing quantum dots comprising silver (Ag) and tellurium (Te), wherein the infrared absorbing quantum dots have an absorbance peak in the range of 1400 nm to 1800 nm, and the peak-to-valley ratio (peak / valley) of the absorbance peak is 1.0 or more.

[0009] A method for producing infrared absorbing quantum dots according to an embodiment of the present invention is a method for producing infrared absorbing quantum dots according to the above embodiment of the present invention, comprising: forming a quantum dot seed core comprising silver (Ag) and tellurium (Te); and adding a chalcogen precursor to grow the quantum dot seed, thereby forming infrared absorbing quantum dots having an absorbance peak in the range of 1400 nm to 1800 nm, wherein the peak-to-valley ratio (peak / valley) of the absorbance peak is 1.0 or greater, and the chalcogen precursor comprises tellurium (Te).

[0010] Another embodiment of the present invention provides infrared absorbing quantum dots comprising a core comprising silver (Ag) and tellurium (Te) and a shell comprising silver (Ag), tellurium (Te), and selenium (Se), wherein the infrared absorbing quantum dots comprise an absorbance peak in the range of 1400 nm to 1800 nm, and the peak-to-valley ratio (peak / valley) of the absorbance peak is 1.0 or greater.

[0011] According to an embodiment of the present invention, it is possible to provide quantum dots that are capable of absorbing infrared light of 1400 nm or more and that are substantially free of heavy metals.

[0012] FIG. 1 shows an example of infrared-absorbing quantum dots comprising silver and tellurium according to an exemplary embodiment of the present disclosure. FIG. 2 shows a transmission electron microscope (TEM) image of a plurality of infrared-absorbing quantum dots comprising silver and tellurium according to an exemplary embodiment of the present disclosure. FIG. 3 shows a plot of absorbance spectra for a population of infrared-absorbing quantum dots formed with different silver-to-telluride molar ratios according to an exemplary embodiment of the present disclosure. FIG. 4 shows an example of infrared-absorbing quantum dots comprising silver, tellurium, and selenium according to another exemplary embodiment of the present disclosure. FIG. 5 shows a TEM image of a plurality of infrared-absorbing quantum dots comprising silver, tellurium, and selenium according to an exemplary embodiment of the present disclosure. FIG. 6 shows a plot of absorbance spectra for a population of infrared-absorbing quantum dots comprising, for example, a Se—Te-based shell. FIG. 7 shows an X-ray fluorescence spectrum for a sample of infrared-absorbing quantum dots according to an exemplary embodiment of the present disclosure. FIG. 8 shows a flowchart of an exemplary method for preparing infrared-absorbing quantum dots according to an exemplary embodiment of the present disclosure.

[0013] Disclosed herein are examples of infrared (IR)-absorbing quantum dots comprising silver (Ag) and tellurium (Te), and methods for making the same. The infrared-absorbing quantum dots comprise an absorbance peak in the range of 1400 nm to 1800 nm, and the peak-to-valley ratio (peak / valley) of the absorbance peak is 1.0 or greater. Advantageously, the infrared-absorbing quantum dots are substantially free of heavy metal elements. The term "substantially free of heavy metal elements" may generally refer to quantum dots that are free of heavy metal elements other than potential trace impurities present in the reactants used to make the quantum dots.

[0014] This Summary is provided to introduce a selection of concepts in a simplified form that are further described in the Detailed Description. It is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0015] Figure 1 shows an example of an infrared-absorbing quantum dot 100. As shown in Figure 1, the infrared-absorbing quantum dot 100 is formed in a two-step (e.g., seed growth) process in which a QD seed 102 is cored (nucleated) using a silver precursor 104 and a chalcogen precursor 106, and then additional chalcogen precursor 106 is added to grow the QD seed.

[0016] The QD seeds 102 include silver and tellurium. For example, the QD seeds 102 may be in the form of an Ag—Te system. In some examples, the QD seeds are nucleated using a hot injection method. In the hot injection method, a chalcogen precursor 106 is rapidly added to a hot (e.g., 150° C.) solution of a silver precursor 104. The silver precursor 104 and the chalcogen precursor 106 can include any suitable material. An example of a suitable chalcogen precursor 106 is trioctylphosphine telluride (TOPTe). An example of a suitable silver precursor 104 is silver acetate. Any suitable solvent can be used for the reaction. In some examples, silver acetate can be dissolved in octanethiol.

[0017] In some examples, the chalcogen precursor 106 is added to a solution containing excess silver. This allows the amount of chalcogen precursor 106 to control the size and distribution of the resulting QD seeds, as well as the stoichiometric ratio of silver and tellurium in the solution. The molar ratio of Ag:Te (Ag / Te) is described in more detail below with reference to FIG. 3.

[0018] In some instances, the QD seeds 102 are grown in the reaction mixture for up to one hour. For example, the QD seeds 102 can be grown for 40 minutes. In other instances, the QD seeds 102 are grown for more than one hour. In some instances, the QD seeds 102 are grown at a temperature ranging from 80°C to 200°C. In other instances, the QD seeds 102 are grown at a temperature ranging from 120°C to 180°C. In yet other instances, the QD seeds 102 are grown at a temperature ranging from 140°C to 160°C. With longer reaction times, the absorbance peak shifts to longer wavelengths and can also reduce the peak-to-valley ratio (peak / valley). Without wishing to be bound by theory, this may be due to particle growth occurring at different times and / or rates, resulting in a wider range of particle sizes and a corresponding broader absorbance peak. This may additionally or alternatively be due to a loss of ligand coating around the infrared-absorbing quantum dots.

[0019] The QD seeds 102 are used as a basis for growing infrared-absorbing quantum dots 100. Referring again to FIG. 1 , additional chalcogen precursor 106 is added to the reaction mixture containing the QD seeds 102. In some instances, growth of the QD seeds 102 is quenched before the chalcogen precursor 106 is added. For example, the reaction mixture containing the QD seeds 102 can be reacted at a growth temperature (e.g., 150° C. for 40 minutes) and then cooled to ambient temperature (e.g., 25° C.). Quenching can prevent uneven growth and agglomeration of the QD seeds 102. In other instances, the chalcogen precursor 106 is added to the reaction mixture without quenching the growth of the QD seeds 102. For example, quenching can be omitted when the additional chalcogen precursor used to grow the infrared-absorbing quantum dots 100 from the QD seeds 102 is substantially the same as the chalcogen precursor used to form the QD seeds 102.

[0020] As introduced above, in some examples, infrared-absorbing quantum dots 100 are formed by adding an additional amount of chalcogen precursor 106 to the reaction mixture containing the QD seeds 102. In some examples, additional TOPTe is added to the reaction mixture containing the QD seeds 102. In some examples, the reaction mixture is heated for up to an additional hour. For example, the reaction mixture can be heated for 40 minutes to grow infrared-absorbing quantum dots 100 from the QD seeds 102. In other examples, the reaction mixture is heated for longer than one hour.

[0021] In some examples, the infrared-absorbing quantum dots 100 are grown at temperatures ranging from 80°C to 200°C. In other examples, the infrared-absorbing quantum dots 100 are grown at temperatures ranging from 120°C to 180°C. In yet other examples, the infrared-absorbing quantum dots 100 are grown at temperatures ranging from 140°C to 160°C. Growing the infrared-absorbing quantum dots 100 from QD seeds 102 enables the formation of infrared-absorbing quantum dots 100 with a distinct absorbance peak (e.g., having a peak-to-valley ratio (peak / valley) ≥ 1.0) in the range of 1400 nm to 1800 nm, which is difficult to achieve via a single-step process. Figure 2 shows a transmission electron microscope (TEM) image of Ag—Te-based infrared-absorbing quantum dots prepared as described herein.

[0022] An additional amount of chalcogen precursor 106 is added to achieve an appropriate Ag:Te molar ratio (Ag / Te) in the infrared-absorbing quantum dots 100. In some examples, the infrared-absorbing quantum dots 100 include an Ag:Te molar ratio (Ag / Te) ranging from 2 to 6. In other examples, the infrared-absorbing quantum dots 100 include an Ag:Te molar ratio (Ag / Te) ranging from 2.1 to 5.8. In still other examples, the infrared-absorbing quantum dots 100 include an Ag:Te molar ratio (Ag / Te) ranging from 2.1 to 2.7, where the Ag:Te molar ratio (Ag / Te) can be calculated by ICP optical emission spectroscopy. FIG. 3 shows a plot of the absorbance spectra for multiple quantum dot populations formed using different Ag:Te molar ratios (Ag / Te). The absorbance peak values ​​are also listed in Table 1. As shown in Figure 3 and Table 1, a population of quantum dots with an Ag:Te molar ratio of 3.4 had a distinct absorbance peak centered at approximately 1150 nm, with a peak-to-valley ratio (peak / valley) of 1.6. The peak-to-valley ratio (peak / valley) described herein refers to the ratio of the maximum absorbance value at the absorbance peak to the minimum absorbance value adjacent to the absorbance peak. When an absorbance peak is adjacent to two valleys, the peak-to-valley ratio (peak / valley) is calculated using the larger absorbance value of the two valleys. Quantum dots with Ag:Te molar ratios of 3.2, 3.1, 2.5, and 2.1 were also prepared. The quantum dots with an Ag:Te ratio (Ag / Te) of 3.2 exhibited a broader absorbance peak in the range of 1100 nm to 1200 nm than the quantum dots with an Ag:Te molar ratio (Ag / Te) of 3.4. Quantum dots with Ag:Te molar ratios (Ag / Te) of 3.1, 2.5, and 2.1 did not exhibit a clear absorbance peak in the 1100 nm to 1200 nm range. In some examples, the infrared-absorbing quantum dots 100 have an absorbance peak in the 1400 nm to 1800 nm range, and the peak-to-valley ratio (peak / valley) of the absorbance peak is 1.0 or greater. A higher peak-to-valley ratio (peak / valley) indicates greater infrared absorption. A peak-to-valley ratio (peak / valley) of 1.0 or greater can be considered to have sufficient infrared absorption properties. From these perspectives, the upper limit of the peak-to-valley ratio (peak / valley) is not particularly limited, and may be, for example, 10.0 or less.For example, as shown in Figure 3 and Table 1, quantum dots with an Ag:Te molar ratio of 2.5 exhibited an absorbance peak above 1400 nm, with a peak-to-valley ratio (peak / valley) greater than 1.0. The absorbance peak was red-shifted by decreasing the Ag:Te molar ratio (Ag / Te) to 2.1. Table 1 shows the absorbance peak wavelength (λmax), half-width at half maximum (HWHM), and peak-to-valley ratio (peak / valley) for quantum dot populations formed with different Ag:Te molar ratios (Ag / Te). (The Ag:Te molar ratios were measured by ICP analysis.)

[0023]

[0024] In some examples, the infrared-absorbing quantum dots additionally or alternatively include another chalcogen. For example, FIG. 4 shows another example of an infrared-absorbing quantum dot 108 further including selenium (Se). Similar to the infrared-absorbing quantum dot 100 of FIG. 1, the infrared-absorbing quantum dot 108 of FIG. 4 is formed in a two-step seed growth process in which the QD seeds 102 serve as a base for growing the infrared-absorbing quantum dots 108. An additional amount of the chalcogen precursor 106 of FIG. 1 (e.g., TOPTe) is added to a reaction mixture containing the silver precursor 104 and the QD seeds 102 along with a selenium precursor 110. The selenium precursor 110 can include any suitable material. An example of a suitable selenium precursor 110 includes, but is not limited to, diphenylphosphine selenide (DPPSe). In this manner, the resulting infrared-absorbing quantum dots 108 comprise a core comprising Ag and Te (e.g., in the form of an Ag—Te-based QD seed 102) and a shell 112 comprising Ag, Te, and Se (e.g., in the form of an Ag—Se—Te-based shell).

[0025] The infrared-absorbing quantum dots 108 are grown in the reaction mixture for up to one hour. For example, the infrared-absorbing quantum dots 108 can be grown for 40 minutes. In other examples, the infrared-absorbing quantum dots 108 are grown for more than one hour. In some examples, the infrared-absorbing quantum dots 108 are grown at a temperature ranging from 80° C. to 200° C. In other examples, the infrared-absorbing quantum dots 108 are grown at a temperature ranging from 120° C. to 180° C. In still other examples, the infrared-absorbing quantum dots 108 are grown at a temperature ranging from 140° C. to 160° C. Growing the infrared-absorbing quantum dots 108 from the QD seeds 102 allows the infrared-absorbing quantum dots 108 to be formed with a distinct absorbance peak (e.g., having a peak-to-valley ratio (peak / valley) ≥ 1.0) in the range of 1400 nm to 1800 nm. A higher peak-to-valley ratio (peak / valley) indicates greater infrared absorption. A peak-to-valley ratio (peak / valley) of 1.0 or greater can be considered to be sufficient infrared absorption characteristics. From these perspectives, the upper limit of the peak-to-valley ratio (peak / valley) is not particularly limited, and may be, for example, 10.0 or less. Figure 5 shows a TEM image of Ag-Se-Te infrared-absorbing quantum dots prepared as described herein.

[0026] The selenium precursor 110 is added to achieve an appropriate Se:Te molar ratio (Se / Te). In some examples, infrared-absorbing quantum dots 108 are prepared with a Se:Te molar ratio (Se / Te) of 0.20 or less and greater than 0.00. In some examples, the Se:Te molar ratio (Se / Te) ranges from 0.01 to 0.20. In other examples, the Se:Te molar ratio (Se / Te) ranges from 0.05 to 0.15. In still other examples, the Se:Te molar ratio (Se / Te) ranges from 0.077 to 0.135. As an example, quantum dot samples with Se:Te molar ratios (Se / Te) of 0.077 and 0.135 were prepared. FIG. 6 shows plots of absorbance spectra for multiple quantum dot populations formed using different Se:Te molar ratios (Se / Te). The absorbance peak values ​​are also listed in Table 2. In the absence of Se, an absorbance peak centered at 1522 nm was obtained. Addition of Se to a Se:Te molar ratio (Se / Te) of 0.077 resulted in a blue shift of the absorbance peak to 1481 nm. At a Se:Te molar ratio (Se / Te) of 0.135, an absorbance peak centered at 1409 nm with a peak-to-valley ratio (peak / valley) of 1.2 was obtained. Therefore, Se doping can be used to tune the absorbance of infrared-absorbing quantum dots. Introducing S in addition to or as a substitute for Se can result in a more blue shift of the absorbance relative to the Ag-Te-Se system. In some instances, increasing the Se:Te molar ratio (Se / Te) above 0.20 can further blue-shift the absorbance toward 1200 nm. It will also be appreciated that infrared-absorbing quantum dots can be prepared using a Te-free Ag—Se-based shell. In some instances, the shell can include ZnS, ZnSe, and / or other suitable materials with suitably low environmental and health concerns. Table 2 shows the λmax, HWHM, and peak-to-valley ratio (peak / valley) of a population of quantum dots formed using different Se:Te molar ratios (Se / Te).

[0027]

[0028] X-ray fluorescence (XRF) analysis can also confirm the presence of Se in the infrared-absorbing quantum dots 108. Figure 7 shows the XRF spectrum obtained for a sample of infrared-absorbing quantum dots 108. A sample was prepared in tetrachloroethylene (TCE) solvent with a Se:Te molar ratio (Se / Te) of 0.135, which confirms the incorporation of Se into the infrared-absorbing quantum dots 108. Table 3 shows the actual Se:Te molar ratio (Se / Te) measured by XRF analysis, as well as the theoretical molar ratio.

[0029]

[0030] In some instances, the prepared infrared-absorbing quantum dots can be dispersed in a non-polar solvent. For example, the infrared-absorbing quantum dots 100, 108 can be purified from the reaction mixture and redispersed in a non-polar solvent. One suitable example of a non-polar solvent includes, but is not limited to, tetrachloroethylene (TCE).

[0031] In another example, the infrared-absorbing quantum dots can be dispersed in a polar solvent. For example, a ligand exchange reaction can be performed to provide the infrared-absorbing quantum dots with ligands that make the quantum dots dispersible in the polar solvent. The polar solvent can include any suitable solvent. The solvent can have a viscosity and surface tension suitable for inkjet printing. In this way, the infrared-absorbing quantum dots can be used to rapidly and cost-effectively manufacture IR-absorbing devices, such as pixels of an IR detector.

[0032] 8, a flowchart illustrating an exemplary method 800 for fabricating infrared-absorbing quantum dots is shown. The following description of method 800 is provided with reference to the components described above and shown in FIGS. 1-7, and the method steps in method 800 are described with reference to corresponding portions of FIGS. 1-7 below. It will be appreciated that method 800 may also be performed in other contexts, using other suitable hardware and software components.

[0033] It will be understood that the following description of method 800 is provided by way of example and is not meant to be limiting. It will be understood that various steps of method 800 may be omitted or performed in a different order than that described, and that method 800 may include additional and / or alternative steps to those shown in FIG. 8 without departing from the scope of the present disclosure.

[0034] The method 800 includes, at 802, nucleating QD seeds comprising Ag and Te. For example, the QD seeds 102 of FIG. 1 are nucleated using a silver precursor 104 and a chalcogen precursor 106 comprising Te to form Ag—Te-based QD seeds. The QD seeds 102 are used as a basis for growing the infrared-absorbing quantum dots 100 of FIG. 1 and the infrared-absorbing quantum dots 108 of FIG. 4.

[0035] In some examples, the method 800 includes providing excess Ag at 804. For example, the QD seeds 102 may be nucleated in the presence of excess Ag. Providing excess Ag allows for fine control of the size and distribution of the QD seeds, as well as the stoichiometric ratio of Ag and Te in the QD seeds.

[0036] The method 800 includes, at 806, adding a chalcogen precursor to grow QD seeds, thereby forming infrared-absorbing quantum dots having an absorbance peak in the range of 1400 nm to 1800 nm. The infrared-absorbing quantum dots have an absorbance peak with a peak-to-valley ratio (peak / valley) of 1.0 or greater, and the chalcogen precursor includes Te. For example, the infrared-absorbing quantum dots 100 of FIG. 1 are produced by adding an additional amount of chalcogen precursor 106 to a reaction mixture containing QD seeds 102. Growth of the infrared-absorbing quantum dots 100 from the QD seeds 102 results in an absorbance peak in the range of 1400 nm to 1800 nm, and the absorbance peak has a peak-to-valley ratio (peak / valley) of 1.0 or greater.

[0037] In some examples, adding the chalcogen precursor further includes adding Se, as shown at 808 in Figure 8. For example, the infrared-absorbing quantum dots 108 of Figure 4 are formed by adding Se precursor 110 to a reaction mixture containing QD seeds 102. This results in the incorporation of Se into the infrared-absorbing quantum dots 108, as shown by XRF in Figure 7.

[0038] In some examples, the method 800 includes forming quantum dots at 810 with a Se:Te molar ratio (Se / Te) of 0.20 or less and greater than 0.00. As described above with reference to FIG. 6 , Se doping can be used to tailor the absorbance of infrared-absorbing quantum dots. Using a Se:Te molar ratio (Se / Te) of 0.20 or less results in an absorbance peak in the 1400 nm to 1800 nm range with a peak-to-valley ratio (peak / valley) of 1.0 or greater. A higher peak-to-valley ratio (peak / valley) indicates greater infrared absorption. A peak-to-valley ratio (peak / valley) of 1.0 or greater can be considered to have sufficient infrared absorption properties. From these perspectives, the upper limit of the peak-to-valley ratio (peak / valley) is not particularly limited, and may be, for example, 10.0 or less.

[0039] In some examples, the method 800 includes forming the quantum dots at 812 with a molar ratio of Ag:Te (Ag / Te) ranging from 2.1 to 2.7. As described above with reference to Figure 3, the molar ratio of Ag:Te (Ag / Te) can be used to tailor the absorbance of the infrared-absorbing quantum dots. Utilizing a molar ratio of Ag:Te (Ag / Te) ranging from 2.1 to 2.7 results in an absorbance peak in the range of 1400 nm to 1800 nm, with a peak-to-valley ratio (peak / valley) of ≥ 1.0.

[0040] In some examples, forming the quantum dots at 814 includes forming a core including Ag and Te and forming a shell including Ag, Te, and Se. For example, forming the infrared-absorbing quantum dots 108 of FIG. 4 includes forming a core including Ag and Te and forming a shell including Ag, Te, and Se. As shown at 816, in some examples, forming the core includes forming an Ag—Te-based core and forming the shell includes forming an Ag—Se—Te-based shell. For example, the infrared-absorbing quantum dots 108 include a core that is Ag—Te-based and a shell that is Ag—Se—Te-based. As described above, this results in an absorbance peak in the range of 1400 nm to 1800 nm.

[0041] The above-described method can be used to produce infrared-absorbing quantum dots. The infrared-absorbing quantum dots include an absorbance peak in the range of 1400 nm to 1800 nm. This allows the infrared-absorbing quantum dots to detect IR light in the range of 1400 nm to 1800 nm (e.g., light emitted by a 1450 nm laser) with a high signal-to-noise ratio. The peak-to-valley ratio (peak / valley) of the absorbance peak is 1.0 or greater. This also increases the signal-to-noise ratio compared to using materials with smaller peak-to-valley ratios. Furthermore, the infrared-absorbing quantum dots include silver and tellurium, and optionally selenium. In this manner, the infrared-absorbing quantum dots may be substantially free of heavy metal elements.

[0042] Another example provides infrared-absorbing quantum dots comprising silver and tellurium, wherein the infrared-absorbing quantum dots comprise an absorbance peak in the range of 1400 nm to 1800 nm, and a peak-to-valley ratio (peak / valley) of the absorbance peak is 1.0 or greater. In some such examples, the infrared-absorbing quantum dots are substantially free of heavy metal elements. In some such examples, the infrared-absorbing quantum dots alternatively or additionally comprise a molar ratio of Ag:Te (Ag / Te) in the range of 2.1 to 2.7. In some such examples, the infrared-absorbing quantum dots alternatively or additionally further comprise selenium. In some such examples, the infrared-absorbing quantum dots alternatively or additionally comprise a molar ratio of Se:Te (Se / Te) less than or equal to 0.20 and greater than 0.00. In some such examples, the infrared-absorbing quantum dots according to embodiments of the present invention alternatively or additionally comprise a core comprising Ag and Te and a shell comprising Ag, Te, and Se. In some such examples, the core alternatively or additionally comprises an Ag—Te-based morphology and the shell alternatively or additionally comprises an Ag—Se—Te-based morphology. In some such examples, the infrared-absorbing quantum dots alternatively or additionally further comprise a core comprising Ag and Te and a shell comprising Ag and Se. In some such examples, the infrared-absorbing quantum dots alternatively or additionally are dispersible in non-polar solvents. In some such examples, the infrared-absorbing quantum dots alternatively or additionally further comprise a ligand that renders the quantum dots dispersible in polar solvents.

[0043] Another example provides a method for producing infrared-absorbing quantum dots, the method including nucleating QD seeds including Ag and Te and adding a chalcogen precursor to grow the QD seeds, thereby forming infrared-absorbing quantum dots having an absorbance peak in a range of 1400 nm to 1800 nm, wherein the peak-to-valley ratio (peak / valley) of the absorbance peak is 1.0 or greater, and the chalcogen precursor includes Te. In some such examples, adding the chalcogen precursor further includes adding Se. In some such examples, the method alternatively or additionally includes forming infrared-absorbing quantum dots having a Se:Te molar ratio (Se / Te) of 0.20 or less and greater than 0.00. In some such examples, the method alternatively or additionally includes providing excess Ag. In some such examples, the method alternatively or additionally includes forming infrared-absorbing quantum dots having an Ag:Te molar ratio (Ag / Te) in a range of 2.1 to 2.7. In some such examples, forming the infrared absorbing quantum dots alternatively or additionally includes forming a core comprising Ag and Te and forming a shell comprising Ag, Te, and Se. In some such examples, forming the core alternatively or additionally includes forming an Ag—Te based core and forming the shell includes forming an Ag—Se—Te based shell.

[0044] Another example provides infrared absorbing quantum dots comprising a core comprising Ag and Te and a shell comprising Ag, Te, and Se, wherein the infrared absorbing quantum dots comprise an absorbance peak in the range of 1400 nm to 1800 nm, and the peak-to-valley ratio (peak / valley) of the absorbance peak is 1.0 or greater. In some such examples, the molar ratio of Ag:Te (Ag / Te) is in the range of 2.1 to 2.7. In some such examples, the molar ratio of Se:Te (Se / Te) is 0.20 or less and greater than 0.00.

[0045] Infrared absorbing quantum dots and a method for manufacturing infrared absorbing quantum dots according to embodiments of the present invention include the following: (1) Infrared absorbing quantum dots comprising silver (Ag) and tellurium (Te), wherein the infrared absorbing quantum dots comprise an absorbance peak in the range of 1400 nm to 1800 nm, and wherein the peak-to-valley ratio (peak / valley) of the absorbance peak is 1.0 or greater. (2) The infrared absorbing quantum dots according to (1), wherein the infrared absorbing quantum dots are substantially free of heavy metal elements. (3) The infrared absorbing quantum dots according to (1) or (2), wherein the molar ratio of Ag:Te (Ag / Te) is in the range of 2.1 to 2.7. (4) The infrared absorbing quantum dots according to any one of (1) to (3), further comprising selenium (Se). (5) The infrared absorbing quantum dots according to (4), wherein the molar ratio of Se:Te (Se / Te) is 0.20 or less and greater than 0.00. (6) The infrared absorbing quantum dots according to any one of (1) to (5) above, further comprising a core comprising Ag and Te and a shell comprising Ag, Te, and Se. (7) The infrared absorbing quantum dots according to any one of (1) to (5) above, further comprising a core comprising Ag and Te and a shell comprising Ag and Se. (8) The infrared absorbing quantum dots according to any one of (1) to (7) above, which are dispersible in a non-polar solvent. (9) The infrared absorbing quantum dots according to any one of (1) to (7) above, further comprising a ligand that makes the infrared absorbing quantum dots dispersible in a polar solvent. (10) A method for producing infrared absorbing quantum dots, comprising: forming a quantum dot seed core containing silver (Ag) and tellurium (Te); and adding a chalcogen precursor to grow the quantum dot seed, thereby forming infrared absorbing quantum dots having an absorbance peak in the range of 1400 nm to 1800 nm, wherein a peak-to-valley ratio (peak / valley) of the absorbance peak is 1.0 or greater, and the chalcogen precursor contains tellurium (Te). (11) The method for producing infrared absorbing quantum dots according to (10), wherein the step of adding a chalcogen precursor further comprises adding selenium (Se).(12) The method for producing infrared absorbing quantum dots according to (11) above, further comprising forming the infrared absorbing quantum dots so that the molar ratio of Se:Te (Se / Te) is 0.20 or less and exceeds 0.00. (13) The method for producing infrared absorbing quantum dots according to any one of (10) to (12) above, further comprising providing excess Ag. (14) The method for producing infrared absorbing quantum dots according to any one of (10) to (13) above, further comprising forming the infrared absorbing quantum dots so that the molar ratio of Ag:Te (Ag / Te) is in the range of 2.1 to 2.7. (15) The method for producing infrared absorbing quantum dots according to any one of (11) to (14) above, further comprising forming a core containing Ag and Te, and forming a shell containing Ag, Te, and Se. (16) Infrared absorbing quantum dots comprising a core containing silver (Ag) and tellurium (Te) and a shell containing silver (Ag), tellurium (Te), and selenium (Se), wherein the infrared absorbing quantum dots have an absorbance peak in the range of 1400 nm to 1800 nm, and the peak-to-valley ratio (peak / valley) of the absorbance peak is 1.0 or more. (17) The infrared absorbing quantum dots according to (16) above, wherein the molar ratio of Ag:Te (Ag / Te) is in the range of 2.1 to 2.7. (18) The infrared absorbing quantum dots according to (16) or (17) above, wherein the molar ratio of Se:Te (Se / Te) is 0.20 or less and exceeds 0.00.

[0046] It will be understood that the configurations and / or approaches described herein are exemplary in nature and are susceptible to numerous variations, and therefore, these specific embodiments or examples should not be considered in a limiting sense. The specific routines or methods described herein may represent one or more of any number of strategies. Thus, the various operations shown and / or described may be performed in the order shown and / or described, in other orders, in parallel, or in omitted orders. Similarly, the order of steps described above may be changed.

[0047] The subject matter of the present disclosure includes all novel and non-obvious combinations and subcombinations of the various processes, systems, and configurations, as well as other features, functions, acts, and / or properties disclosed herein, and any and all equivalents thereof.

[0048] Furthermore, the words "includes," "including," "has," "contains," variations thereof, and other similar terms used in either the detailed description or the claims are intended to be as inclusive as the term "comprising" as an open transitional term, without excluding any additional or other elements.

[0049] As used herein, "and / or" is defined as inclusive or as follows, as specified by the truth table below (Table 4):

[0050]

[0051] The following paragraphs describe examples of infrared-absorbing quantum dots prepared as described herein and comparative quantum dots. Table 5 summarizes the composition and optical properties (λmax, HWHM, peak / valley) of each quantum dot population.

[0052]

[0053] Examples 1 to 3: Ag—Te QD seeds were nucleated using the hot injection method described above. Specifically, TOPTe was injected into a solution of Ag(acetate) mixed with octanethiol at 150°C. The temperature was maintained at 150°C for 40 minutes, after which the reaction mixture was cooled to ambient temperature. The molar ratio of Ag:Te (Ag / Te) at the time of charging was 5.8. The resulting QD seeds had an absorbance peak at 1150 nm with a peak-to-valley ratio (peak / valley) of 1.6.

[0054] The IR-absorbing quantum dots in Example 1 were prepared using the Ag-Te QD seeds synthesized as described above. Growth of the IR-absorbing quantum dots was continued for an additional 40 minutes at 150°C with the addition of TOPTe to adjust the Ag:Te molar ratio (Ag / Te). The IR-absorbing quantum dots were purified using acetone as an antisolvent and precipitated by centrifugation. The IR-absorbing quantum dots were then recovered, redispersed in TCE, and centrifuged again to remove undissolved particles. The IR-absorbing quantum dots were then analyzed using an ultraviolet-visible-near-infrared (UV-Vis-NIR) spectrophotometer. Furthermore, elemental analysis was performed on the resulting IR-absorbing quantum dots. Elemental analysis was performed as follows: 0.05 g to 0.2 g of IR-absorbing quantum dots in an organic solvent was mixed with 10 mL of concentrated nitric acid and heated to 200°C for 15 minutes. The infrared-absorbing quantum dots were then decomposed using a microwave digester (CEM Mars6), and the sample was diluted to 50 mL with deionized water to obtain the sample for elemental analysis. Further analysis was performed using an ICP-OES (Agilent 5800) with an external calibration curve based on commercially available certified elemental standards. An internal standard was used in the calibration standards and samples to correct for instrument drift.

[0055] In Examples 1 and 2, infrared-absorbing quantum dots were prepared with an Ag:Te molar ratio (Ag / Te) of 2.4. These resulted in an absorbance peak longer than 1500 nm with a peak-to-valley ratio (peak / valley) greater than 1.0. In Example 3, the absorbance peak was red-shifted to 1726 nm by decreasing the Ag:Te molar ratio (Ag / Te) to 2.1.

[0056] Examples 4 and 5: Infrared-absorbing quantum dots in Examples 4 and 5 were prepared using the Ag—Te-based QD seeds synthesized in Example 1. Specifically, a mixture of TOPTe and DPPSe was injected into the Ag—Te-based QD seed mixture at 150°C. The TOPTe and DPPSe mixture was adjusted to a Se:Te molar ratio (Se / Te) of 0.077 in Example 4 and a Se:Te molar ratio (Se / Te) of 0.135 in Example 5. The temperature of the mixture was maintained for 40 minutes to form an Ag—Se—Te (Te doped with Se) shell on the Ag—Te-based QD seeds. The mixture was then cooled to ambient temperature, and the infrared-absorbing quantum dots were purified and characterized as described above. An absorbance peak at 1481 nm was observed with a peak-to-valley ratio (peak / valley) of greater than 1.2 in Example 4 (Se / Te = 0.077). The absorbance peak was blue-shifted to 1409 nm in Example 5 by increasing the Se:Te molar ratio (Se / Te) to 0.135.

[0057] In Comparative Example 1, Ag—Te quantum dots were prepared with an Ag:Te molar ratio (Ag / Te) of 3.4. The quantum dots of Comparative Example 1 had an absorbance peak at 1149 nm, similar to the Ag—Te QD seeds described above, with a peak-to-valley ratio (peak / valley) of 1.6.

[0058] In Comparative Example 2, the molar ratio of Ag:Te (Ag / Te) was reduced to 3.2, resulting in an absorbance peak at 1156 nm similar to that of Comparative Example 1, but with a peak-to-valley ratio less than 1.3.

[0059] Comparative Example 3 In Comparative Example 3, the molar ratio of Ag:Te (Ag / Te) was reduced to 3.1, and no discernible absorbance peak was observed.

[0060] Comparative Example 4 In Comparative Example 4, Ag—Se quantum dots were prepared as described above, except that DPPSe was used instead of TOPTe. The resulting Ag—Se quantum dots had an absorbance peak at 960 nm.

[0061] Comparative Example 5 The Ag—S quantum dots prepared in Comparative Example 5 were blue-shifted compared to the Ag—Se quantum dots prepared in Comparative Example 4, and had an absorbance peak at 800 nm.

[0062] 100 Infrared absorbing quantum dot 102 QD seed 104 Silver precursor 106 Chalcogen precursor 108 Infrared absorbing quantum dot 110 Selenium precursor 112 Shell

Claims

1. An infrared absorbing quantum dot containing silver (Ag) and tellurium (Te), The infrared absorbing quantum dots include absorbance peaks in the range of 1400 nm to 1800 nm. The ratio of peaks to troughs (peak / trough) of the absorbance peak is 1.0 or greater. Infrared absorbing quantum dots.

2. The infrared absorbing quantum dots substantially contain no heavy metal elements. The infrared absorbing quantum dot according to claim 1.

3. The molar ratio of Ag:Te (Ag / Te) is in the range of 2.1 to 2.

7. The infrared absorbing quantum dot according to claim 1 or 2.

4. Further containing selenium (Se), The infrared absorbing quantum dot according to claim 1 or 2.

5. The molar ratio of Se to Te (Se / Te) is 0.20 or less and greater than 0.

00. The infrared absorbing quantum dot according to claim 4.

6. A shell containing Ag and Se, further comprising The infrared absorbing quantum dot according to claim 1 or 2.

7. The infrared-absorbing quantum dots are dispersible in a nonpolar solvent. The infrared absorbing quantum dot according to claim 1 or 2.

8. The infrared-absorbing quantum dots further include a ligand that enables dispersibility in a polar solvent. The infrared absorbing quantum dot according to claim 1 or 2.

9. A method for manufacturing infrared absorbing quantum dots, A process for forming the nucleus of a quantum dot seed containing silver (Ag) and tellurium (Te), A step of adding a chalcogen precursor to grow quantum dot seeds, thereby forming infrared absorbing quantum dots having absorbance peaks in the range of 1400 nm to 1800 nm, Includes, The ratio of peaks to troughs (peak / trough) of the absorbance peak is 1.0 or greater. The chalcogen precursor contains Te. A method for manufacturing infrared-absorbing quantum dots.

10. The step of adding the chalcogen precursor further includes adding Se. A method for producing an infrared-absorbing quantum dot according to claim 9.

11. The infrared absorbing quantum dot is formed such that the molar ratio of Se:Te (Se / Te) is 0.20 or less and greater than 0.

00. A method for producing an infrared-absorbing quantum dot according to claim 10.

12. Further includes providing an excess of Ag, A method for producing an infrared-absorbing quantum dot according to claim 9 or 10.

13. The infrared absorbing quantum dots are formed such that the molar ratio of Ag:Te (Ag / Te) is in the range of 2.1 to 2.

7. A method for producing an infrared-absorbing quantum dot according to claim 9 or 10.

14. The process further includes forming a core containing Ag and Te, and forming a shell containing Ag, Te and Se. A method for producing an infrared-absorbing quantum dot according to claim 9 or 10.

15. An infrared absorbing quantum dot comprising a core containing silver (Ag) and tellurium (Te), and a shell containing silver (Ag), tellurium (Te), and selenium (Se), The infrared absorbing quantum dots include absorbance peaks in the range of 1400 nm to 1800 nm. The ratio of peaks to troughs (peak / trough) of the absorbance peak is 1.0 or greater. Infrared absorbing quantum dots.

16. The molar ratio of Ag:Te (Ag / Te) is in the range of 2.1 to 2.

7. The infrared absorbing quantum dot according to claim 15.

17. The molar ratio of Se to Te (Se / Te) is 0.20 or less and greater than 0.

00. The infrared absorbing quantum dot according to claim 15 or 16.