Method for producing a nanocrystal, nanocrystal, and light-emitting device

Abstract

A method for producing a nanocrystal (1) is specified. The method comprises providing a core (2) surrounded by a first shell (3), wherein the first shell (3) comprises a first semiconductor material comprising a first chalcogen, and forming an outer shell (4) around the first shell (3), wherein the outer shell (4) comprises a second semiconductor material which is free of the first chalcogen. Furthermore, a nanocrystal (1) and a light-emitting device (10), in particular comprising a micro-LED, are specified.

Description

[0001] December 17, 2025

[0002] - 1 -

[0003] Description

[0004] METHOD FOR PRODUCING A NANOCRYSTAL, NANOCRYSTAL, AND LIGHTEMITTING DEVICE

[0005] A method for producing a nanocrystal, a nanocrystal, and a light-emitting device are specified.

[0006] It is an obj ect of the present disclosure to provide a method for producing a nanocrystal having improved longevity.

[0007] Furthermore, a nanocrystal with improved longevity shall be provided. It is an additional obj ect to provide a lightemitting device with improved efficiency.

[0008] A method for producing a nanocrystal is provided. In particular, the method is used to provide a plurality of nanocrystals . Here and in the following, a nanocrystal is a structure with an extension of at most 200 nanometers . In particular, an extension of the nanocrystal is between and including 2 nanometers and 60 nanometers . Compared to a bulk material comprising the same material as the nanocrystal, the nanocrystal can have significantly different properties . For instance, the properties of the nanocrystal depend on the size of the nanocrystal . In particular, the nanocrystal is a distinct species . The nanocrystal can also be referred to as a quantum dot .

[0009] According to at least one embodiment of the method, a core is provided. The core is surrounded by a first shell . In particular, the core is a nanocrystalline core . In other words, the core is crystalline and has an extension in the nanometer range . For example, the core has a diameter of between and including 2 nanometers and 10 nanometers . InDecember 17, 2025

[0010] - 2 -

[0011] particular, the first shell is in direct mechanical contact with the core . For instance, the first shell completely surrounds the core . For example, the first shell has a thickness of between and including 2 nanometers and 20 nanometers .

[0012] According to at least one embodiment of the method, the first shell comprises a first semiconductor material . In particular, the first semiconductor material comprises a first chalcogen. In other words, the first semiconductor material can comprise a II-VI semiconductor material . Here and in the following, a chalcogen is an element of group 16 of the periodic table . For example, the first chalcogen is selected from the group consisting of oxygen, sulfur, selenium, and tellurium. For instance, the first chalcogen is present as chalcogenide in the first semiconductor material .

[0013] Here and in the following, a semiconductor material is a material which has semiconducting properties . Semiconducting properties are the ability to conduct electrical current in a way between a conductor and an insulator .

[0014] According to at least one embodiment of the method, an outer shell is formed around the first shell . In particular, the outer shell completely surrounds the first shell . Thus, it is possible that the outer shell also completely surrounds the core . For example, the outer shell has a thickness of between and including 2 nanometers and 40 nanometers . For instance, the outer shell is configured for protecting the first shell and the core from environmental influences . The outer shell can be the outermost shell of the nanocrystal . It is possible, however, that the nanocrystal is further surroundedDecember 17, 2025

[0015] - 3 -

[0016] by a protective shell, in particular comprising an oxide such as silica .

[0017] According to at least one embodiment of the method, the outer shell comprises or consists of a second semiconductor material which is free of the first chalcogen. In particular, the outer shell is free of the first chalcogen. It is possible to determine the concentration of the first chalcogen in the second semiconductor material by inductively coupled plasma mass spectrometry ( ICP-MS) . For example, the second semiconductor material is a II-VI semiconductor material .

[0018] According to at least one embodiment, the method for producing a nanocrystal comprises providing a core surrounded by a first shell, wherein the first shell comprises or consists of a first semiconductor material comprising a first chalcogen, and forming an outer shell around the first shell, wherein the outer shell comprises a second semiconductor material which is free of the first chalcogen. In particular, the method steps are carried out in the given order .

[0019] It is an idea of the present application to provide a method for producing a nanocrystal which leads to a more reliable nanocrystal . This means, for example, that the nanocrystal has an improved operating lifetime . It is possible that a longevity of the nanocrystal is dependent on the first chalcogen and in particular on the distribution of the first chalcogen throughout the nanocrystal . For example, if the first chalcogen is present in the outer shell of the nanocrystal, a drop in a photoluminescence quantum yield retention can be observed. The nanocrystal provided by theDecember 17, 2025

[0020] - 4 -

[0021] method described above, however, does not show this photoluminescence quantum yield retention drop .

[0022] According to at least one embodiment of the method, the first chalcogen is selenium and / or tellurium. In other words, the first chalcogen is selected from the group of selenium, tellurium, and combinations thereof . In particular, the first semiconductor material is a selenide semiconductor material and / or a telluride semiconductor material . However, it is possible that the first semiconductor material comprises a second chalcogen such as sulfur .

[0023] In particular, the first chalcogen is selenium.

[0024] Advantageously, selenium improves electronic and structural properties of the nanocrystal if present as the first chalcogen. The improved electronic and structural properties can lead to improved optical properties . However, if selenium is present in the outer shell of the nanocrystal, it has been observed that the longevity of the nanocrystal was reduced. Advantageously, with the method described herein it is possible to provide a nanocrystal which is free of the first chalcogen in the outer shell of the nanocrystal . Thus, the improved electronic, structural, and optical properties attributed to selenium can be combined with an improved longevity of the nanocrystal .

[0025] According to at least one embodiment of the method, providing the core surrounded by the first shell comprises providing the core, and forming the first shell around the core . In particular, a reagent containing the first chalcogen is used for forming the first shell . For example, the reagent containing the first chalcogen is a first precursor of the first semiconductor material . For instance, the reagentDecember 17, 2025

[0026] 5

[0027] containing the first chalcogen is a selenium- or tellurium-containing, in particular selenium-containing reagent .

[0028] For forming the first shell, the reagent containing the first chalcogen can be reacted with a second precursor of the first semiconductor material . For example, the second precursor of the first semiconductor material comprises a metal such as Zn. For instance, the second precursor of the first semiconductor material is selected from the group consisting of ZnX2, wherein X is Cl, Br, and / or I, diethyl zinc, zinc carboxylic acid salts such as zinc palmitate, zinc oleate, zinc stearate, and combinations thereof . The carboxylic acid in the zinc carboxylic acid salt can have a carbon chain length between and including 1 to 20 carbon atoms . The carbon chain can also comprise or be free of double bonds .

[0029] According to at least one embodiment of the method, washing is performed after the use of the reagent containing the first chalcogen, in particular selenium and / or tellurium. In other words, the core with the first shell is purified after forming the first shell . For example, the washing is performed with a solvent selected from the group consisting of cyclohexane, toluene, acetone, methyl acetate, ethyl acetate, MeOH, EtOH, isopropyl alcohol ( IPA) , butanol, hexane, pentane, toluene, acetonitrile, and combinations thereof . For instance, one solvent, in particular having a higher polarity, for example IPA, is used for precipitation followed by a centrifugation spin to obtain a solid. Then the solid is dispersed in another solvent, in particular having a lower polarity, such as cyclohexane . The steps of precipitations and re-dispersion can be repeated for washing.December 17, 2025

[0030] 6

[0031] Advantageously, due to the washing, an excess of the reagent containing the first chalcogen is removed. Thus, the incorporation of the first chalcogen into the outer shell of the nanocrystal can be prevented. In particular, washing is a simple and efficient method to remove the excess of the reagent containing the first chalcogen.

[0032] According to at least one embodiment of the method, no chalcogenide-coordinating reagent is used in a step performed after forming the first shell, which in particular is a step directly performed after forming the first shell . In other words, the step performed after forming the first shell is free of a chalcogenide-coordinating reagent . The step after forming the first shell is, for example, forming the outer shell .

[0033] Here and in the following, a chalcogenide-coordinating reagent is a reagent which comprises a reactive site suitable for coordinating or reacting with the first chalcogen. For instance, the chalcogenide-coordinating reagent is an electrophile . For example, the chalcogenide-coordinating reagent is selected from the group consisting of tri-n-octylphosphine (TOP) , tri-n-octylphosphine oxide (TOPO) , ethylenediaminetetraacetic acid (EDTA) , mixtures of thiols and amines such as dodecanethiol (DDT) and oleylamine, imidazolium ionic liquids, phosphonium ionic liquids, and mixtures thereof .

[0034] In particular, the chalcogenide-coordinating reagents can remove the first chalcogen from the first shell .

[0035] Advantageously, not using the chalcogenide-coordinating reagent in the step performed after forming the first shell ensures that the first chalcogen is not removed from theDecember 17, 2025

[0036] - 7 -

[0037] first shell . In other words, it can be prevented that the first chalcogen, in particular selenium, is pulled off the core / first shell structure and into solution. Thus, an incorporation of the first chalcogen into a shell following the first shell such as the outer shell can be avoided.

[0038] According to at least one embodiment of the method, forming the outer shell is performed without the chalcogenide-coordinating reagent . In other words, during forming the outer shell no chalcogenide-coordinating reagent is present . Thus, advantageously, removing the first chalcogen from the first shell is prevented during forming the outer shell . In this way it is possible to also prevent the incorporation of the removed first chalcogen into the second semiconductor material .

[0039] According to at least one embodiment of the method, the second semiconductor material is a sulfide semiconductor material . The sulfide semiconductor material is particularly effective in protecting the structure of core and first shell from environmental influences . Furthermore, the sulfide semiconductor material has a large bandgap such that electronic confinement in the nanocrystal is improved. The sulfide semiconductor material is also chemically stable .

[0040] According to at least one embodiment of the method, the second semiconductor material is zinc sulfide (ZnS) .

[0041] Advantageously, ZnS is a semiconductor material having a large bandgap . Additionally, ZnS can be easily prepared under various conditions which are tolerated by the structure of the core and the first shell .December 17, 2025

[0042] 8

[0043] According to at least one embodiment of the method, forming the outer shell is performed with a sulfur-providing reagent . In particular, the sulfur-providing reagent does not react with the first chalcogen of the first semiconductor material . The missing reactivity of the sulfur-providing reagent with the first chalcogen can advantageously prevent that the first chalcogen is removed from the first shell . Thus, it can be avoided that the first chalcogen is then incorporated in the second semiconductor material, that is the outer shell .

[0044] According to at least one embodiment of the method, the outer shell is formed using a thiourea and / or a thioacetamide . In particular, the second semiconductor material is formed using the thiourea and / or the thioacetamide . The thiourea and the thioacetamide both advantageously do not react with the first semiconductor material such that the first chalcogen is removed therefrom.

[0045] In particular, the thiourea and / or the thioacetamide comprise organic substituents . For example, the amide groups of the thiourea and / or the amide group of the thioacetamide comprise (s) an organic substituent . Here and in the following, an organic substituent is a substituent comprising at least one carbon atom. The organic substituent is, for example, selected from the group consisting of methyl, ethyl, propyl, butyl, hexyl, and dodecyl . The substituents on the amide groups can be selected independently. It is also possible that the methyl group of the thioacetamide is substituted with an organic substituent . General formulas of the thiourea and the thioacetamide are shown below:

[0046]

[0047] December 17, 2025

[0048] - 9 -

[0049] wherein R is independently selected from an organic substituent .

[0050] According to at least one embodiment of the method, the core comprises a third semiconductor material . In particular, the third semiconductor material has a smaller bandgap than the first semiconductor material . Thus, the first semiconductor material can advantageously be used for confining excitons in the third semiconductor material .

[0051] According to at least one embodiment of the method, the core consists of the third semiconductor material . In this way, it is possible that the whole core is configured to absorb and emit electromagnetic radiation.

[0052] According to at least one embodiment of the method, the core comprises a non-emissive center surrounded by an emissive region. In particular, the emissive region is a shell which surrounds the non-emissive center . The emissive region can comprise or consist of the third semiconductor material . The emissive region is configured to absorb and emit electromagnetic radiation. The non-emissive center comprises or consists of a fourth semiconductor material . The fourth semiconductor material is identical to or different from the first semiconductor material and / or the second semiconductor material .

[0053] According to at least one embodiment of the method, the third semiconductor material is a III-V semiconductor material or a II-VI semiconductor material .

[0054] According to at least one embodiment of the method, the third semiconductor material is selected from the group consistingDecember 17, 2025

[0055] - 10 -

[0056] of InP, In (Zn) P, CdSe, PbS, and ZnSeTe . Advantageously, these semiconductor materials have a small bandgap .

[0057] According to at least one embodiment of the method, the first semiconductor material is ZnSe or ZnSeS . In particular, the ZnSeS can be a homogenous alloy. It is also possible, however, that ZnSeS as the first semiconductor material comprises a gradient of sulfur . For example, the sulfur content increases in a direction from the core towards the outer shell . Advantageously, with such a gradient it can be additionally prevented that the first chalcogen, presently selenium, is incorporated in the outer shell .

[0058] Furthermore, a nanocrystal is specified. In particular, the nanocrystal is provided by the method described herein. Thus, all embodiments, features, and advantages described in combination with the method also apply to the nanocrystal and vice versa .

[0059] According to at least one embodiment, the nanocrystal comprises a core . In particular, the core is configured to absorb electromagnetic radiation of a first wavelength range and emit electromagnetic radiation of a second wavelength range . The first wavelength range and the second wavelength range can be at least partially different from each other . The second wavelength range comprises wavelengths corresponding to a lower energy than the wavelengths of the first wavelength range, for example . For instance, the nanocrystal has wavelength-converting properties . This means that the nanocrystal is configured to convert electromagnetic radiation of the first wavelength range into electromagnetic radiation of the second wavelength range .December 17, 2025

[0060] 11

[0061] According to at least one embodiment, the nanocrystal comprises a first shell . The first shell comprises or consists of a first semiconductor material which comprises a first chalcogen. In particular, the first shell at least partially, for example completely, surrounds the core . The first shell can be configured to confine excitons in the core . Thus, the first shell improves electronic properties of the nanocrystal . In this way, the optical properties are also improved .

[0062] According to at least one embodiment, the nanocrystal comprises an outer shell . The outer shell comprises or consists of a second semiconductor material . The second semiconductor material is in particular free of the first chalcogen. In other words, the second semiconductor material is not contaminated with the first chalcogen. Thus, detrimental effects which can be attributed to the first chalcogen in the outer shell are avoided. For instance, the outer shell at least partially, in particular completely, surrounds the first shell .

[0063] According to at least one embodiment, the nanocrystal comprises a core, a first shell comprising a first semiconductor material comprising a first chalcogen, and an outer shell comprising a second semiconductor material which is free of the first chalcogen, wherein the first shell at least partially surrounds the core, and wherein the outer shell at least partially surrounds the first shell . In particular, the first shell is in direct mechanical contact with the core and / or the outer shell .

[0064] The nanocrystal described herein has the advantage that the beneficial aspects of the first chalcogen in the first shellDecember 17, 2025

[0065] 12

[0066] can be captured while harmful effects of the first chalcogen in the outer shell are avoided. In this way, the lifetime and the optical properties of the nanocrystal are improved at the same time .

[0067] Furthermore, a light-emitting device is specified. In particular, the light-emitting device comprises the nanocrystal described herein. Thus, embodiments and features described in combination with the nanocrystal also apply to the light-emitting device and vice versa .

[0068] According to at least one embodiment, the light-emitting device comprises a light-emitting semiconductor chip . In particular, the light-emitting semiconductor chip is configured to emit electromagnetic radiation of a first wavelength range . For example, the first wavelength range is in the ultraviolet to blue range of the electromagnetic spectrum.

[0069] In particular, the light-emitting semiconductor chip comprises an epitaxially grown semiconductor layer sequence . The epitaxially grown semiconductor layer sequence can comprise an active layer . In particular, the electromagnetic radiation of the first wavelength range is generated in the active layer . The electromagnetic radiation of the first wavelength range is, for example, emitted via a radiation exit surface of the light-emitting semiconductor chip .

[0070] According to at least one embodiment, the light-emitting device comprises a conversion element . In particular, the conversion element comprises a plurality of the nanocrystals described herein. For example, the conversion element is arranged on or above the radiation exit surface of the light-December 17, 2025

[0071] 13

[0072] emitting semiconductor chip . The conversion element is, for instance, a layer comprising the plurality of nanoparticles . The plurality of nanoparticles can be embedded in a matrix material .

[0073] According to at least one embodiment of the light-emitting device, the conversion element converts the electromagnetic radiation of the first wavelength range into electromagnetic radiation of a second wavelength range . In other words, the conversion element has radiation-converting properties . In particular, the conversion element has its radiationconverting properties due to the presence of the nanocrystals . The electromagnetic radiation of the second wavelength range can comprise wavelengths having a lower energy than the wavelengths of the first wavelength range .

[0074] According to at least one embodiment, the light-emitting device comprises the light-emitting semiconductor chip configured to emit the electromagnetic radiation of the first wavelength range and the conversion element comprising the plurality of nanoparticles described herein. The conversion element converts the electromagnetic radiation of the first wavelength range into electromagnetic radiation of the second wavelength range .

[0075] Advantageously, the light-emitting device described herein can be used in automotive applications, display applications, and for illumination purposes . It is also possible that the light-emitting device is used for virtual reality and augmented reality applications .

[0076] According to at least one embodiment of the light-emitting device, the light-emitting semiconductor chip comprises or isDecember 17, 2025

[0077] 14

[0078] a micro-LED. Here and in the following, "LED" is the abbreviation for light-emitting diode .

[0079] As a broad definition, a micro-LED could be seen as any light-emitting diode (LED) with a particularly small size . Micro-LEDs may comprise a width, a length, a thickness and / or a diameter smaller than or equal to 100 micrometers, in particular smaller than or equal to 70 micrometers, for example smaller than or equal to 50 micrometers . In particular, micro-LEDs, for example rectangular micro-LEDs, have an edge length, in particular in plan view of layers of the semiconductor layer sequence, of a radiation exit surface smaller than or equal to 70 micrometers, for example smaller than or equal to 50 micrometers . For example, a micro-LED is a light-emitting diode with its growth substrate removed, such that a thickness of the micro-LED is in the range between and including, for example, 1.5 micrometers and 10 micrometers . For example, the micro-LED is provided on a wafer having releasable retaining structures . The micro-LED can be detached from the wafer in a non-destructive manner .

[0080] In particular, micro-LEDs are mainly used in displays . The micro-LEDs form pixels or subpixels and emit light of a defined color . Small pixel size and a high density with close distances make micro-LEDs suitable, among others, for small monolithic displays for augmented reality applications, especially data glasses . In addition, other applications are being developed, in particular regarding the use in data communication or pixelated lighting applications .

[0081] Advantageous embodiments and developments of the method for producing a nanocrystal, the nanocrystal, and the light-December 17, 2025

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[0083] emitting device will become apparent from the exemplary embodiments described below in conjunction with the figures .

[0084] In the figures :

[0085] Figure 1 schematically shows steps of a method for producing a nanocrystal according to an exemplary embodiment .

[0086] Figures 2 to 4 show schematic cross sections during a method for producing a nanocrystal according to an exemplary embodiment .

[0087] Figure 4 shows a schematic cross section of a nanocrystal according to an exemplary embodiment .

[0088] Figure 5 shows a schematic cross section of a core .

[0089] Figure 6 shows a schematic cross section of a light-emitting device according to an exemplary embodiment .

[0090] In the exemplary embodiments and figures, similar or similarly acting constituent parts are provided with the same reference signs . The elements illustrated in the figures and their size relationships among one another should not be regarded as true to scale . Rather, individual elements may be represented with an exaggerated size for the sake of better representability and / or for the sake of better understanding.

[0091] In a first step SI of a method for producing a nanocrystal 1 according to the exemplary embodiment shown in Figure 1, a core 2 is provided. The core 2 comprises or consists of a third semiconductor material . The core is configured to absorb and emit electromagnetic radiation. TheDecember 17, 2025

[0092] - 16 -

[0093] electromagnetic radiation absorbed corresponds to a higher energy than the electromagnetic radiation emitted. In other words, the core 2 has down-converting properties . The third semiconductor material is selected from the group consisting of InP, In (Zn) P, CdSe, PbS, and ZnSeTe .

[0094] In a second step S2, a first shell 3 is formed around the core 2. The first shell 3 comprises a first semiconductor material comprising a first chalcogen. The first chalcogen is, for example, selenium or tellurium. The first shell 3 is formed using a reagent comprising the first chalcogen. The reagent comprising the first chalcogen is a precursor of the first semiconductor material . For example, the first semiconductor material is ZnSe or ZnSeS .

[0095] In a third step S3, an outer shell 4 is formed around the first shell 3 and thus also around the core 2. The outer shell 4 comprises or consists of a second semiconductor material . The first, second, and third semiconductor materials are different from each other . The third semiconductor material has a smaller bandgap than the first semiconductor material and the second semiconductor material . The second semiconductor material and / or the outer shell is free of the first chalcogen. In other words, the second semiconductor material and the outer shell are not contaminated with the first chalcogen. In particular, the second semiconductor material is ZnS, which is free of selenium and / or tellurium.

[0096] To obtain the outer shell 4 comprising or consisting of the second semiconductor material which is free of the first chalcogen, at least one of, in particular all of, the following method steps are preferably carried out .December 17, 2025

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[0098] After the use of the reagent containing the first chalcogen, that is after the formation of the first shell 3, a washing step is performed. The following solvents can be used for washing: cyclohexane, toluene, acetone, methyl acetate, ethyl acetate, MeOH, EtOH, isopropyl alcohol ( IPA) , butanol, hexane, pentane, toluene, acetonitrile, and combinations thereof . For instance, a first solvent, in particular having a higher polarity, for example IPA, is used for precipitation followed by a centrifugation spin to obtain a solid. Then the solid is dispersed in a second solvent, in particular having a lower polarity, such as cyclohexane . The steps of precipitations and re-dispersion can be repeated for washing. Due to the washing, an excess of the reagent containing the first chalcogen is removed such that the reagent containing the first chalcogen is not present during forming the outer shell 4. In this way, the incorporation of the first chalcogen in the outer shell 4 is prevented.

[0099] Additionally or alternatively, in a step performed after forming the first shell 3, for example during the formation of the outer shell 4, no chalcogenide-coordinating reagent such as TOP, TOPO, EDTA, a mixture of DDT and oleylamine, imidazolium ionic liquids, and phosphonium ionic liquids is used. Avoiding the use of the chalcogenide-coordinating reagent avoids pulling out the first chalcogen from the first shell 3 in a subsequent step . In this way, it can be prevented that pulled-out first chalcogen is incorporated in the outer shell 4.

[0100] Additionally or alternatively, forming the outer shell 4 is performed with a sulfur-providing reagent which does not react with the first chalcogen of the first semiconductorDecember 17, 2025

[0101] - 18 -

[0102] material . For example, a thiourea and / or a thioacetamide are used as the sulfur-providing reagent . These reagents do not react with the first chalcogen of the first semiconductor material in the first shell 3, for example at an outer surface of the first shell 3. Thus, an incorporation of the first chalcogen in the outer shell 4 or a deposition of the first chalcogen on the outer shell 4 is prevented.

[0103] The nanocrystal 1 is obtained after forming the outer shell 4 .

[0104] In Figure 2 a core 2 is shown, which is a starting point of a method for producing a nanocrystal according to a further exemplary embodiment . The core 2 comprises or consists of a third semiconductor material . For example, the core is based on InP . The core 2 is configured to absorb and emit electromagnetic radiation. The core 2 presently substantially consists of the third semiconductor material .

[0105] By adding precursors for a first semiconductor material, a first shell 3 is formed around the core 2, as is shown in Figure 3. The first semiconductor material comprises a first chalcogen. Thus, one of the precursors is a reagent containing the first chalcogen. The first chalcogen can be selenium. In other words, the first semiconductor material is a selenide semiconductor material . It is possible that the first semiconductor material further comprises sulfur .

[0106] Another one of the precursors is a precursor for a metal contained in the first semiconductor material . The metal is Zn, for example . In other words, the first semiconductor material can be ZnSe or ZnSeS . The first shell 3 comprising ZnSeS as the first semiconductor material can comprise the ZnSeS as a homogenous alloy. However, it is also possibleDecember 17, 2025

[0107] - 19 -

[0108] that the ZnSeS has a gradient of sulfur . In particular, the sulfur content in the ZnSeS increases from the core 2 to an outer surface of the first shell 3.

[0109] After forming the first shell 3, an outer shell 4 is formed as shown in Figure 4. Figure 4 also shows the finished nanocrystal 1 obtained by the method according to the presently described exemplary embodiment . The outer shell 4 comprises a second semiconductor material which is free of the first chalcogen. The outer shell 4 is presently formed with ZnS . Between forming the first shell 3 and forming the outer shell 4 a washing step is performed to remove an excess of the reagent containing the first chalcogen. Furthermore, with the washing step species re-solvating the first chalcogen, that is chalcogenide-coordinating reagents, are removed. The outer shell 4 is formed using precursors for the second semiconductor material . One of the precursors is present in the form of a zinc precursor . The other precursor is a sulfur precursor . The sulfur precursor is a sulfur-providing reagent which does not react with the first semiconductor material such that the first chalcogen is removed therefrom. In this way, an exchange of the sulfur with the first chalcogen in the second semiconductor material is prevented. The sulfur precursor is for example a thiourea or a thioacetamide as specified in the general part of the description. For example, the sulfur precursor is N-hexyl-N' -dodecyl thiourea .

[0110] As can be seen from Figure 4, the nanocrystal 1 comprises the core 2, the first shell 3, and the outer shell 4. The first shell 3 is in direct mechanical contact with the core 2 and the outer shell 4. In other words, no further layers are arranged between the core 2 and the first shell 3 or betweenDecember 17, 2025

[0111] 20

[0112] the first shell 3 and the outer shell 4. The first shell 3 completely surrounds the core 2, and the outer shell 4 completely surrounds the first shell 3. The nanocrystal 1 is configured to convert electromagnetic radiation of a first wavelength range into electromagnetic radiation of a second wavelength range . The electromagnetic radiation of the first wavelength range is absorbed by the core 2, whereas the electromagnetic radiation of the second wavelength range is emitted by the core 2. The first wavelength range and the second wavelength range are at least partially different from each other .

[0113] In the previous exemplary embodiments, the core 2 was configured as a whole to absorb and emit electromagnetic radiation. It is also possible, however, that the core 2 comprises a non-emissive center 21 and an emissive region 22 as shown in Figure 5. The non-emissive center 21 comprises a fourth semiconductor material . The fourth semiconductor material comprises a larger bandgap than a third semiconductor material contained in the emissive region 22. The emissive region 22 of the core 2 may also be referred to as an emissive shell . The third semiconductor material contained in the emissive region 22 is selected from the group consisting of InP, In (Zn) P, CdSe, PbS, and ZnSeTe . The fourth semiconductor material can be identical to or different from the first semiconductor material or the second semiconductor material .

[0114] Figure 6 shows an exemplary embodiment of a light-emitting device 10. The light-emitting device 10 comprises a lightemitting semiconductor chip 11 having a semiconductor layer sequence 111. The light-emitting semiconductor chip 11 emits electromagnetic radiation of a first wavelength range, whichDecember 17, 2025

[0115] - 21 -

[0116] is for example in the blue region of the electromagnetic spectrum. The electromagnetic radiation of the first wavelength range is generated in an active layer 112 of the semiconductor layer sequence 111. The light-emitting semiconductor chip 11 is a micro-LED, for example .

[0117] The light-emitting device 10 further comprises a conversion element 12, which is arranged on a radiation exit surface of the light-emitting semiconductor chip 11. The conversion element 12 comprises a plurality of nanocrystals 1, for example as described in combination with Figures 4A and 4B . The nanocrystals 1 can be embedded in a matrix material . The conversion element 12 can be a thin film.

[0118] The nanocrystals 1 in the conversion element 12 convert the electromagnetic radiation of the first wavelength range into electromagnetic radiation of a second wavelength range . For example, the electromagnetic radiation of the second wavelength range comprises wavelengths in the green to red wavelength range of the electromagnetic spectrum.

[0119] The features and exemplary embodiments described in connection with the figures can be combined with each other according to further exemplary embodiments, even if not all combinations are explicitly described. Furthermore, the exemplary embodiments described in connection with the figures may have alternative or additional features as described in the general part .

[0120] This patent application claims the priority of US provisional patent application 63 / 741, 139, the disclosure content of which is hereby incorporated by reference .December 17, 2025

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[0122] The invention is not restricted to the exemplary embodiments by the description on the basis of said exemplary embodiments . Rather, the invention encompasses any new feature and also any combination of features, which in particular comprises any combination of features in the patent claims and any combination of features in the exemplary embodiments, even if this feature or this combination itself is not explicitly specified in the patent claims or exemplary embodiments .December 17, 2025

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[0124] References

[0125] 1 nanocrystal

[0126] 2 core

[0127] 21 non-emissive center

[0128] 22 emissive region

[0129] 3 first shell

[0130] 4 outer shell

[0131] 10 light-emitting device

[0132] 11 light-emitting semiconductor chip 111 semiconductor layer sequence

[0133] 112 active layer

[0134] 12 conversion element

Claims

December 17, 2025- 24 -Claims1. A method for producing a nanocrystal ( 1 ) , comprising- providing a core (2 ) surrounded by a first shell (3) , wherein the first shell (3) comprises a first semiconductor material comprising a first chalcogen, and- forming an outer shell (4 ) around the first shell (3) , wherein the outer shell (4 ) comprises a second semiconductor material which is free of the first chalcogen.

2. The method according to claim 1, wherein the first chalcogen is selenium and / or tellurium.

3. The method according to any of the previous claims, wherein providing the core (2 ) surrounded by the first shell (3) comprises :- providing the core (2 ) , and- forming the first shell (3) around the core (2 ) , wherein a reagent containing the first chalcogen is used for forming the first shell (3) .4 . The method according to the previous claim, wherein washing is performed after the use of the reagent containing the first chalcogen.

5. The method according to any of claims 3 to 4, wherein in a step performed after forming the first shell (3) no chalcogenide-coordinating reagent is used.

6. The method according to any of the previous claims, wherein forming the outer shell (4 ) is performed without a chalcogenide-coordinating reagent .December 17, 2025- 25 -7. The method according to any of the previous claims, wherein the second semiconductor material is a sulfide semiconductor material .

8. The method according to any of the previous claims, wherein the second semiconductor material is ZnS .

9. The method according to any of the previous claims, wherein forming the outer shell (4 ) is performed with a sulfur-providing reagent which does not react with the first chalcogen of the first semiconductor material .

10. The method according to any of the previous claims, wherein the outer shell (4 ) is formed using a thiourea and / or a thioacetamide .

11. The method according to any of the previous claims, wherein the core (2 ) comprises a third semiconductor material having a smaller bandgap than the first semiconductor material .

12. The method according to the previous claim, wherein the third semiconductor material is a III-V semiconductor material or a II-VI semiconductor material .

13. The method according to any of claims 11 to 12, wherein the third semiconductor material is selected from the group consisting of InP, In (Zn) P, CdSe, PbS, and ZnSeTe .

14. The method according to any of the previous claims, wherein the first semiconductor material is ZnSe or ZnSeS .

15. A nanocrystal ( 1 ) comprisingDecember 17, 202526- a core ( 2 ) ,- a first shell (3) comprising a first semiconductor material comprising a first chalcogen, and- an outer shell (4 ) comprising a second semiconductor material which is free of the first chalcogen, wherein- the first shell (3) at least partially surrounds the core ( 2 ) , and- the outer shell (4 ) at least partially surrounds the first shell (3) .

16. A light-emitting device ( 10) comprising:- a light-emitting semiconductor chip ( 11 ) configured to emit electromagnetic radiation of a first wavelength range, and - a conversion element ( 12 ) comprising a plurality of nanocrystals ( 1 ) according to claim 15, wherein the conversion element ( 12 ) converts the electromagnetic radiation of the first wavelength range into electromagnetic radiation of a second wavelength range .

17. The light-emitting device ( 10) according to the previous claim, whereinthe light-emitting semiconductor chip ( 11 ) is a micro-LED.

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