Nanoparticle and light-emitting device

Abstract

A nanoparticle (1) comprising an emissive region (2) comprising a first semiconductor material, and a confining shell (3) is specified, wherein the confining shell (3) at least partially surrounds the emissive region (2), and the confining shell (3) comprises a material selected from the group consisting of MgS, MgSe, and combinations thereof. Furthermore, a light-emitting device (10) is specified. In particular, the light-emitting device is a micro-LED.

Description

[0001] 2024PF00564 July 15, 2025P2024,0559 WO N -1 –Description NANOPARTICLE AND LIGHT-EMITTING DEVICE A nanoparticle and a light-emitting device are specified. It is an object to provide a nanoparticle having an increased efficiency and / or stability. Furthermore, a light-emitting device having an improved efficiency shall be provided.According to at least one embodiment, a nanoparticle isspecified. In particular, the nanoparticle has wavelength- converting properties. In other words, the nanoparticle converts electromagnetic radiation of a first wavelength range into electromagnetic radiation of a second wavelength range. For instance, the first wavelength range comprises wavelengths corresponding to a higher energy compared to the wavelengths of the second wavelength range. For example, the first wavelength range is in the ultraviolet to blue range and / or the second wavelength range is in the green to infrared range of the electromagnetic spectrum. In particular, the nanoparticle is a discrete particle. The nanoparticle may comprise materials which show different properties when in a bulk. For example, the nanoparticle is a quantum dot. According to at least one embodiment, the nanoparticle comprises an emissive region. In particular, the emissiveregion comprises or consists of a first semiconductormaterial. Here and in the following, “emissive” means that the region is able to emit electromagnetic radiation, in particular of the second wavelength range.2024PF00564 July 15, 2025P2024,0559 WO N -2 –According to at least one embodiment, the nanoparticle comprises a confining shell. In particular, the confining shell acts as a physical barrier for the emissive region.Furthermore, the confining shell can confine excitons in theemissive region, for example by decreasing a likelihood for an exciton to reach an outer surface of the nanoparticle. According to at least one embodiment of the nanoparticle, the confining shell at least partially, in particular completely, surrounds the emissive region. In particular, the confiningshell is in direct mechanical contact with the emissiveregion. However, it is also possible that a further layer, such as an intermediate layer, is arranged between the emissive region and the confining shell. According to at least one embodiment of the nanoparticle, the confining shell comprises or consists of a material selected from the group consisting of MgS, MgSe, and combinations thereof. Advantageously, these materials have a higher bandgap compared to the first semiconductor material of the emissive region. Thus, excitons can be efficiently confined by the confining shell. The confining shell may have a thickness of 1 monolayer of the material selected from the group consisting of MgS, MgSe, and combinations thereof. According to at least one embodiment, the nanoparticle comprises the emissive region comprising the first semiconductor material and the confining shell, wherein the confining shell at least partially surrounds the emissive region, and the confining shell comprises the material selected from the group consisting of MgS, MgSe, and combinations thereof.2024PF00564 July 15, 2025P2024,0559 WO N -3 –In particular, MgS, MgSe, and combinations thereof have a lattice constant similar to that of the first semiconductormaterial. Thus, the confining shell has a low latticemismatch to the first semiconductor material of the emissiveregion. In this way, a more stable nanoparticle can beprovided. Furthermore, MgS, MgSe, and combinations thereof have a higher bandgap compared to other shelling materials for emissive regions. This improves confinement of the excitons in the emissive region. This leads to a nanoparticle which advantageously has a higher reliability of photoluminescence quantum yield (PLQY). According to at least one embodiment, the nanoparticle further comprises a gradient shell. In particular, the gradient shell at least partially, for example completely, surrounds the confining shell. For instance, the confining shell and the gradient shell are in direct mechanical contact. The gradient shell can comprise or consist of a semiconductor material alloy. In other words, the gradient shell comprises or consists of a mixture of at least two semiconductor materials.Advantageously, due the gradient shell the material of theemissive region can be further protected. Additionally or alternatively, interfacial strain between the emissive region and an outer shell can be reduced. According to at least one embodiment of the nanoparticle, the gradient shell comprises or consists of Mg1-xZnxS and / or Mg1-xZnxSe, wherein 0 ≤ x ≤ 1, in particular 0 < x < 1, andwherein x varies depending on a distance from the emissive region. The distance from the emissive region can be2024PF00564 July 15, 2025P2024,0559 WO N -4 –determined from an outer surface of the emissive region. In particular, x varies along a radius of the nanoparticle. Forinstance, x is such that the confining shell comprises agradient from MgS and / or MgSe to ZnS and / or ZnSe.Advantageously, Mg1-xZnxS and Mg1-xZnxSe have a higher bandgapthan ZnSe and ZnS while at the same time Mg1-xZnxS and / or Mg1-xZnxSe have a similar lattice constant compared to thematerial of the emissive region, for example InP. The gradient alloy from MgS and / or MgSe to ZnS and / or ZnSe enables interfacial lattice strain relief, serving to bolster desirable emission qualities such as a higher PLQY, a lower lifetime of the excitons, lower rates of non-radiative exciton recombination, and a higher multi-exciton quantum yield. Additionally, the gradient shell allows for an increased thickness of an outer shell. According to at least one embodiment of the nanoparticle, the gradient shell has a maximum value of x at a surface of the gradient shell facing away from the emissive region. In otherwords, x of Mg1-xZnxS and / or Mg1-xZnxSe has a maximum value ata surface of the gradient shell facing away from the emissiveregion. x can have a maximum value at an outer surface of thegradient shell. The gradient shell can have a minimum value of x at a surface of the gradient shell facing the emissiveregion. x of Mg1-xZnxS and / or Mg1-xZnxSe can have a minimumvalue at a surface of the gradient shell facing the emissiveregion. Advantageously, in this way the gradient efficientlyreduces interfacial strain between the emissive region and an outer shell. According to at least one embodiment, the nanoparticle comprises an outer shell. In particular, the outer shell at2024PF00564 July 15, 2025P2024,0559 WO N -5 –least partially, for example completely, surrounds the confining shell and / or the gradient shell. For instance, the outer shell is in direct mechanical contact with the confining shell or the gradient shell. Advantageously, the outer shell further protects the emissive region of the nanoparticle from environmental influence. Additionally, the outer shell contributes to the confining of the excitons in the emissive region.According to at least one embodiment, the outer shellcomprises or consists of a material selected from the groupconsisting of ZnS, ZnSe, ZnSeS, CdS, CdZnS, and combinationsthereof. These materials are particularly useful to protectthe emissive region. According to at least one embodiment, the nanoparticlefurther comprises an intermediate shell. In particular, theintermediate shell is arranged between the emissive region and the confining shell and / or the gradient shell. For example, the intermediate shell is in direct mechanical contact with the emissive region and / or the confining shell. Advantageously, the intermediate shell is used for further confinement of the excitons in the emissive region and / or for further protection of the emissive region. The intermediate shell can also be used to attenuate a lattice mismatch between the emissive region and the confining shell and / or the gradient shell. According to at least one embodiment of the nanoparticle, the intermediate shell comprises or consists of a second semiconductor material. In particular, the second semiconductor material is different from the first2024PF00564 July 15, 2025P2024,0559 WO N -6 –semiconductor material, the material of the confining shell and / or the material of the gradient shell. According to at least one embodiment of the nanoparticle, thesecond semiconductor material that has a larger bandgap thanthe first semiconductor material of the emissive region. Thelarger bandgap of the second semiconductor material comparedto the first semiconductor material improves a confinement ofthe excitons in the emissive region. According to at least one embodiment of the nanoparticle, the second semiconductor material has a smaller bandgap than thematerial of the confining shell and / or the gradient shell. Inother words, the bandgap of the material of the confining shell and / or the gradient shell has a higher bandgap than the second semiconductor material. Advantageously, this improves confinement of the excitons in the emissive region. According to at least one embodiment of the nanoparticle, the second semiconductor material is a II-VI compound semiconductor material. II-VI compound semiconductor materials comprise at least one element from group 2 or group 12 of the periodic table, for example Mg, Ca, Sr, Ba, Zn, Cd, and at least one element from group 16 of the periodic table,for example O, S, Se. In particular, the second semiconductormaterial is selected from the group consisting of ZnSe, CdSe, CdS, CdZnSe, CdZnS, and combinations thereof. According to at least one embodiment of the nanoparticle, the second semiconductor material is a III-V compound semiconductor material. III-V compound semiconductor materials comprise at least one element from group 13 of the periodic table, for example B, Al, Ga, In, and at least one2024PF00564 July 15, 2025P2024,0559 WO N -7 –element from group 15 of the periodic table, for example N, P, As, Sb. In particular, the second semiconductor material is selected from the group consisting of GaP, InP, and combinations thereof. According to at least one embodiment of the nanoparticle, the emissive region comprises a dopant. In other words, the emissive region comprises or consist of the first semiconductor material doped with the dopant. In particular,the dopant is homogeneously or heterogeneously distributed inthe first semiconductor material. The dopant is advantageously used to adjust the emission properties of the emissive region. For example, the dopant is selected from the group consisting of Cu, In, Ga, Al, and combinations thereof. According to at least one embodiment of the nanoparticle, the first semiconductor material is a II-VI compound semiconductor material or a III-V compound semiconductor material. For example, the first semiconductor material is selected from the group consisting of CdSe, CdS, CdSeS, CdZnS, CdZnSeS, CdZnSe, InP, InAs, PbS, PbSe, CuInSe2, CuInS2, ZnSe, and combinations thereof. According to at least one embodiment of the nanoparticle, the emissive region comprises or consists of an emissive core. In other words, the nanoparticle is a type I quantum dot. According to at least one embodiment of the nanoparticle, the emissive region comprises or consists of an emissive shell. In particular, the nanoparticle comprises a non-emissive core which is surrounded by the emissive shell. For example, the nanoparticle comprises a quantum well structure.2024PF00564 July 15, 2025P2024,0559 WO N -8 –According to at least one embodiment, the nanoparticle has a shape selected from the group consisting of a sphere, a rod, a cube, and a tetrahedron. In particular, the nanoparticle is a spherical nanoparticle. It is possible that a shape of the core, such as the emissive or the non-emissive core, is different from the shape of the nanoparticle. Furthermore, a light-emitting device is specified. In particular, the light-emitting device comprises the nanoparticle described herein. Thus, embodiments, features, and advantages of the nanoparticle also apply to the light- emitting device and vice versa. 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. 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. According to at least one embodiment, the light-emitting device comprises a conversion element. In particular, the conversion element comprises a plurality of the nanoparticles2024PF00564 July 15, 2025P2024,0559 WO N -9 –described herein. For example, the conversion element is arranged on or above the radiation exit surface of the light- 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. 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 radiation- converting properties due to the presence of the nanoparticles. The electromagnetic radiation of the second wavelength range can comprise wavelengths having a lower energy than the wavelengths of the first wavelength range. 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. Advantageously, the light-emitting device described herein can be used in display applications, for example for mobiles and / or in the automotive area, or in lighting products. The light-emitting device can be used for applications including virtual reality, augmented reality, near-to-eye displays, and other displays.2024PF00564 July 15, 2025P2024,0559 WO N -10 –Due to the use of the nanoparticle described herein in the conversion element, a higher resilience of the light-emitting device is observed. According to at least one embodiment, the light-emitting device is a micro-LED. Here and in the following, LED is the abbreviation for light-emitting diode. As a broad definition, a micro-LED could be seen as any light-emitting diode 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, forexample smaller than or equal to 50 micrometers. Inparticular, 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 a 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. 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 sizes 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 are2024PF00564 July 15, 2025P2024,0559 WO N -11 –being developed, in particular regarding their use in data communication or pixelated lighting applications. Advantageous embodiments and developments of the nanoparticle and the light-emitting device will become apparent from the exemplary embodiments described below in conjunction with the figures. In the figures: Figures 1 to 3 show schematic cross-sections of nanoparticles according to exemplary embodiments.Figures 4 and 5 show the photoluminescence quantum yield(PLQY) of nanoparticles according to exemplary embodiments and comparative examples depending on an illumination time. Figures 6 to 8 show schematic cross-sections of nanoparticles according to exemplary embodiments. Figure 9 shows bandgaps of various semiconductor materials. Figure 10 schematically shows a composition of a nanoparticle according to an exemplary embodiment. Figure 11 shows a lattice mismatch trend of a nanoparticle according to an exemplary embodiment. Figure 12 shows a schematic cross-section of a light-emitting device according to an exemplary embodiment. In the exemplary embodiments and figures, similar or similarly acting constituent parts are provided with the same2024PF00564 July 15, 2025P2024,0559 WO N -12 –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 betterrepresentability and / or for the sake of better understanding.Figure 1 shows a first exemplary embodiment of a nanoparticle 1. The nanoparticle 1 presently comprises an emissive region 2 which is an emissive core 21. The emissive core 21 comprises or consists of a first semiconductor material, which is InP, for example. The emissive core 21 is surroundedby a confining shell 3. The emissive core 21 and theconfining shell 3 are in direct mechanical contact. In otherwords, a material of the confining shell 3 is directly grownonto the emissive core 21. The confining shell 3 comprises orconsists of a material selected from the group consisting of MgS, MgSe, and combinations thereof. For example, theconfining shell 3 comprises or consists of MgS. The confiningshell 3 is completely surrounded by an outer shell 5,presently comprising ZnS. The material of the outer shell 5is directly grown onto the confining shell 3. Thus, theconfining shell 3 and the outer shell 5 are in directmechanical contact. The first semiconductor material has asmaller bandgap than the material of the confining shell 3 and the outer shell 5. Figure 2 shows a second exemplary embodiment of a nanoparticle 1. The structure of the nanoparticle 1 is similar to the structure of the nanoparticle 1 according toFigure 1. However, presently, an intermediate shell 6 isarranged between the emissive core 21 and the confining shell 3. The intermediate shell 6 comprises a second semiconductormaterial, which is different from the materials of the2024PF00564 July 15, 2025P2024,0559 WO N -13 –emissive core 21, the confining shell 3, and the outer shell 5. The bandgap of the second semiconductor material is larger than the bandgap of the first semiconductor material. Thesecond semiconductor material is ZnSe, for example.Furthermore, as an alternative to the above describedmaterial combinations, the nanoparticle 1 of figures 1 and 2can have one of the following compositions: CdSe / MgS / ZnS,CdS / MgS / ZnS, CdSeS / MgS / ZnS, CdSe / CdS / MgS / ZnS, CdZnSe / MgS / ZnS,CdZnSeS / MgS / ZnS, ZnSe / MgS / ZnS, ZnSeS / MgS / ZnS,CdSe / ZnSe / MgS / ZnS, CdZnSe / CdS / MgS / ZnS, CdZnSeS / CdS / MgS / ZnS,CdZnS / MgS / ZnS, CdZnSe / MgS / ZnS, CdSe / CdZnSe / MgS / ZnS, CdS / CdZnS / MgS / ZnS, InP / MgS / ZnS, InP / GaP / MgS / ZnS,InAs / MgS / ZnS, InAs / InP / MgS / ZnS, PbS / MgS / ZnS, PbSe / MgS / ZnS,PbSe / ZnSe / MgS / ZnS, CuInSe2 / MgS / ZnS, CuInS / MgS / ZnS,AgInGaS / MgS / ZnS. In the above compositions, the materials arelisted in the following order: emissive core 21 / ifapplicable, intermediate shell 6 / confining shell 3 / outershell 5. The emissive core 21 may also comprise a dopant such as Cu, In, Ga, Al, and combinations thereof. In this case, the nanoparticle 1 can have one of the following compositions: Cu:ZnSe / MgS / ZnS, Cu,In:ZnSe / MgS / ZnS, Cu,Ga:ZnSe / MgS / ZnS, Cu,Al:ZnSe / MgS / ZnS. In the above compositions, the materials are listed in the following order: emissive core 21 / confining shell 3 / outer shell 5. Figure 3 shows a third exemplary embodiment of a nanoparticle1. In contrast to the exemplary embodiments of figures 1 and2, the emissive region 2 is presently an emissive shell 22.The emissive shell 22 comprises or consists of a first semiconductor material, for example InP. The emissive shell2024PF00564 July 15, 2025P2024,0559 WO N -14 –22 surrounds a non-emissive core 7. The non-emissive core 7, for example, comprises or consists of ZnS. The emissive shell 22 is surrounded by a confining shell 3, comprising or consisting of a material selected form the group consisting of MgS, MgSe, and combinations thereof. The confining shell 3 is further surrounded by an outer shell 5, for example comprising or consisting of ZnS. The emissive shell 22 is directly grown onto the non-emissive core 7. The confining shell 3 is directly grown onto the emissive shell 22. The outer shell 5 is directly grown onto the confining shell 3.As an alternative to the above-described composition, thenanoparticle shown in figure 3 can have one of the following compositions: ZnS / ZnSe / MgS / ZnS, CdS / CdSe / MgS / ZnS, ZnS / CdSe / MgS / ZnS, ZnS / CdS / MgS / ZnS, ZnSe / CdSe / MgS / ZnS, CdZnSe / CdSe / MgS / ZnS, CdS / InP / MgS / ZnS, ZnSe / InP / MgS / ZnS,ZnS / InP / MgS / ZnS, ZnSe / InAs / MgS / ZnS, GaP / InP / MgS / ZnS. In theabove compositions, the materials are listed in the following order: non-emissive core 7 / emissive shell 22 / confining shell 3 / outer shell 5. In the exemplary embodiments of figures 1 to 3, the nanoparticle 1 has a spherical shape. However, it is also possible that the nanoparticle 1 has a tetrahedral shape or a rod shape. Figure 4 shows the retention of the photoluminescence quantum yield (PLQY) of nanoparticles 1 on a light-emitting semiconductor chip 11. The light-emitting semiconductor chip 11 is operated constantly at 5 W / cm2for the duration in hours shown on the x-axis. The corresponding PLQY is plotted on the y-axis. The composition of the nanoparticles 12024PF00564 July 15, 2025P2024,0559 WO N -15 –resulting in graphs 4-1 to 4-4 and further irradiationconditions are given in Table 1. Table 1: emissive intermediate confining outer graph condition core 21 shell 6 shell 3 shell 5 4-1 InP ZnSe MgS Zns air4-2 InP ZnSe - ZnS air4-3 InP ZnSe MgS ZnS argon4-4 InP ZnSe - ZnS argonThe emissive core 21 and the intermediate shell 6 of all samples were obtained from the same batch. As can be seen from figure 4, the nanoparticles 1 comprising the confining shell 3 show a superior PLQY retention during irradiation. This effect is even observable for an irradiation under air. Figure 5 further demonstrates the superior properties of thenanoparticles 1 having a confining shell 3 comprising MgS.The nanoparticles 1 are provided as thin films. The thinfilms were irradiated in air with a light-emittingsemiconductor chip 11 emitting electromagnetic radiationhaving an emission maximum at about 450 nanometers. The PLQYis plotted against the duration of the irradiation inminutes. Graph 5-1 results from a thin film withnanoparticles 1 comprising an emissive core 21 of InP, an intermediate shell 6 of ZnSe, the confining shell 3 of MgS,and an outer shell of ZnS. Graph 5-2 results from a thin filmwith nanoparticles 1 comprising an emissive core 21 of InP, an intermediate shell 6 of ZnSe, and an outer shell of ZnS.2024PF00564 July 15, 2025P2024,0559 WO N -16 –Figure 6 shows a fourth exemplary embodiment of ananoparticle 1. The nanoparticle 1 comprises an emissive core 21 as the emissive region 2. The emissive core 21 is surrounded by a confining shell 3, a gradient shell 4, and an outer shell 5. The gradient shell 4 is arranged between the confining shell 3 and the outer shell 5. The emissive core 21 comprises a first semiconductor material, for example InP. The confining shell 3 comprises a material selected from the group consisting of MgS, MgSe, and combinations thereof. The outer shell 5 comprises ZnS and / or ZnSe. A bandgap of the first semiconductor material is smaller than a bandgap of the materials of the confining shell 3, the gradient shell 4, and the outer shell 5. The gradient shell 4 comprises Mg1-xZnxS and / or Mg1-xZnxSe,wherein 0 ≤ x ≤ 1, in particular 0 < x < 1, and wherein xvaries depending on a distance from the emissive core 21. Amaximum value of x is reached at a surface of the gradient shell 4 facing away from the emissive core 21. In other words, a proportion of Zn in the gradient shell increases towards the outer shell 5. A proportion of Mg in the gradientshell decreases towards the outer shell 5. This means that aproportion of Mg is higher in the vicinity of the emissive region 2 than in the vicinity of the outer shell 5. In the gradient shell 4, the composition changes from pure MgS and / or MgSe to pure ZnS and / or ZnSe. A gradient of x canbe uniform and / or steady. In other words, the gradient isfree of steps. However, it is also possible for the gradient of x to have one or more steps. Figure 7 shows a fourth exemplary embodiment of a nanoparticle 1. In contrast to the exemplary embodiment of2024PF00564 July 15, 2025P2024,0559 WO N -17 –figure 6, the confining shell 3 is not in direct mechanical contact with the emissive region 2. Presently, an intermediate shell 6 comprising a second semiconductor material is arranged between the emissive region 2 and the confining shell 3. The second semiconductor material is ZnSe, for example. The other elements of the nanoparticle 1 shown in figure 7 are configured as described in combination with figure 6. Furthermore, as an alternative to the above describedmaterial combinations, the nanoparticle 1 of figures 6 and 7can have one of the following compositions: CdSe / MgS / Mg1-xZnxS / ZnS, CdS / MgS / Mg1-xZnxS / ZnS, CdSeS / MgS / Mg1-xZnxS / ZnS,CdSe / CdS / MgS / Mg1-xZnxS / ZnS, CdZnSe / MgS / Mg1-xZnxS / ZnS,CdZnSeS / MgS / Mg1-xZnxS / ZnS, ZnSe / MgS / Mg1-xZnxS / ZnS, ZnSeS / MgS / Mg1-xZnxS / ZnS, CdSe / ZnSe / MgS / Mg1-xZnxS / ZnS, CdZnSe / CdS / MgS / Mg1-xZnxS / ZnS, CdZnSeS / CdS / MgS / Mg1-xZnxS / ZnS, CdZnS / MgS / Mg1-xZnxS / ZnS, CdZnSe / MgS / Mg1-xZnxS / ZnS,CdSe / CdZnSe / MgS / Mg1-xZnxS / ZnS, CdS / CdZnS / MgS / Mg1-xZnxS / ZnS,InP / MgS / Mg1-xZnxS / ZnS, InP / GaP / MgS / Mg1-xZnxS / ZnS, InAs / MgS / Mg1-xZnxS / ZnS, InAs / InP / MgS / Mg1-xZnxS / ZnS, PbS / MgS / Mg1-xZnxS / ZnS, PbSe / MgS / Mg1-xZnxS / ZnS, PbSe / ZnSe / MgS / Mg1-xZnxS / ZnS, CuInSe2 / MgS / Mg1-xZnxS / ZnS, CuInS / MgS / Mg1-xZnxS / ZnS,AgInGaS / MgS / Mg1-xZnxS / ZnS. In the above compositions, thematerials are listed in the following order: emissive core 21 / if applicable, intermediate shell 6 / confining shell 3 / gradient shell 4 / outer shell 5. The emissive core 21 may also comprise a dopant such as Cu, In, Ga, Al, and combinations thereof. In this case, the nanoparticle 1 can have one of the following compositions: Cu:ZnSe / MgS / Mg1-xZnxS / ZnS, Cu,In:ZnSe / MgS / Mg1-xZnxS / ZnS,Cu,Ga:ZnSe / MgS / Mg1-xZnxS / ZnS, Cu,Al:ZnSe / MgS / Mg1-xZnxS / ZnS. In2024PF00564 July 15, 2025P2024,0559 WO N -18 –the above compositions, the materials are listed in the following order: emissive core 21 / confining shell 3 / gradient shell 4 / outer shell 5. Figure 8 shows a sixth exemplary embodiment of a nanoparticle 1. The nanoparticle 1 has a quantum well structure. The nanoparticle 1 comprises a non-emissive core 7 which is surrounded by an emissive shell 22. The emissive shell 22 corresponds to an emissive region 2. The emissive shell 22 isfurther surrounded by, and in direct mechanical contact with,a confining shell 3. A material of the emissive shell 22 has a smaller bandgap than a material of the non-emissive core 7 and / or the confining shell 3. The confining shell 3 comprises a material selected from the group consisting of MgS, MgSe, and combinations thereof. The confining shell 3 is surrounded by, and in direct mechanical contact with, a gradient shell 4. The gradient shell 4 comprises a material selected from the group consisting of Mg1-xZnxS, Mg1-xZnxSe, and combinations thereof, wherein 0 ≤ x ≤ 1, in particular 0 < x < 1, and wherein xvaries depending on a distance from the emissive shell 22. Inparticular, x decreases towards the emissive region 2. Thegradient shell 4 is further surrounded by, and in directmechanical contact with, an outer shell 5. For example, the outer shell 5 comprises ZnS and / or ZnSe. The gradient shell 4 comprises a mixture of the material of the confining shell 3 and a material of the outer shell 5, wherein the gradient shell 4 comprises a gradient such that the proportion of the material of the confining shell 3 decreases towards the outer shell 5.2024PF00564 July 15, 2025P2024,0559 WO N -19 –As an alternative to the above-described composition, the nanoparticle shown in figure 8 can have one of the following compositions: ZnS / ZnSe / MgS / Mg1-xZnxS / ZnS, CdS / CdSe / MgS / Mg1-xZnxS / ZnS, ZnS / CdSe / MgS / Mg1-xZnxS / ZnS, ZnS / CdS / MgS / Mg1-xZnxS / ZnS, ZnSe / CdSe / MgS / Mg1-xZnxS / ZnS, CdZnSe / CdSe / MgS / Mg1-xZnxS / ZnS, CdS / InP / MgS / Mg1-xZnxS / ZnS, ZnSe / InP / MgS / Mg1-xZnxS / ZnS, ZnS / InP / MgS / Mg1-xZnxS / ZnS, ZnSe / InAs / MgS / Mg1-xZnxS / ZnS, GaP / InP / MgS / Mg1-xZnxS / ZnS, ZnS / AgInGaS / MgS / Mg1-xZnxS / ZnS, GaP / AgInGaS / MgS / Mg1-xZnxS / ZnS. In the abovecompositions, the materials are listed in the following order: non-emissive core 7 / emissive shell 22 / confining shell 3 / gradient shell 4 / outer shell 5. In the exemplary embodiments of figures 6 to 8, the nanoparticle 1 has a spherical shape. However, it is also possible that the nanoparticle 1 has a tetrahedral shape or a rod shape. Figure 9 shows the bandgap energies E in eV and the lattice constant c of the semiconductor materials ZnS, ZnSe, and MgS. It can be seen from this figure that MgS has a higher bandgap than ZnS and ZnSe, while also having a lattice constant close to ZnSe. Thus, a lattice mismatch between a shell comprising ZnSe and a shell comprising ZnS can be smoothly compensated by a shell comprising Mg1-xZnxS and / or Mg1-xZnxSe. Figure 10 shows the atomic composition of a nanoparticle 1 according to an exemplary embodiment. The nanoparticle 1 comprises an emissive region 2 comprising InP, an intermediate shell 6 comprising ZnSe, a confining shell 3 comprising MgS, a gradient shell 4 comprising Mg1-xZnxS, and an outer shell 5 comprising ZnS. The x in Mg1-xZnxS variesdepending on a distance to the emissive region 2. Presently,2024PF00564 July 15, 2025P2024,0559 WO N -20 –x increases with increasing distance to the emissive region2. In other words, the gradient shell 4 comprises more Zn and less Mg towards the outer shell 5. Furthermore, the gradient shell 4 comprises more Mg and less Zn towards the emissiveregion 2.A trend of the lattice parameter P depending on the distanced from the emissive region 2 is shown in figure 11. The trendis shown for the nanoparticle 1 described in combination with figure 10. The confining shell 3 and the gradient shell 4 offer a smooth transition of the lattice parameter from theemissive region 2 to the outer shell 5. In particular, thevarying x in the gradient shell 4 contributes to this effect. In contrast, if the confining shell 3 and the gradient shell 4 are not part of the nanoparticle 1, there would be a steep step in the lattice parameter from the intermediate shell 6 to the outer shell 5. In case of an intermediate shell 6 comprising ZnSe and an outer shell 5 comprising ZnS, the lattice mismatch would be about 4%. In contrast, the steepest lattice parameter difference is presently the difference between the intermediate shell 6 and the confining shell 3, which is about 1%. Thus, the nanoparticle 1 has an increased stability. Figure 12 shows an exemplary embodiment of a light-emitting device 10. The light-emitting device 10 is a micro-LED, for example. The light-emitting device 10 comprises a light- emitting semiconductor chip 11 having a semiconductor layer sequence 111. The light-emitting semiconductor chip 11 emits electromagnetic radiation of a first wavelength range, which is for example in the blue region of the electromagnetic spectrum. The electromagnetic radiation of the first2024PF00564 July 15, 2025P2024,0559 WO N -21 –wavelength range is generated in an active layer 112 of the semiconductor layer sequence 111. The light-emitting device 10 further comprises a conversion element 12 which is arranged on a radiation exit surface ofthe light-emitting semiconductor chip 11. The conversionelement 12 comprises a plurality of nanoparticles 1, forexample as described in combination with figures 1 to 3 and 6to 8. The nanoparticles 1 can be embedded in a matrix material. However, it is also possible that the nanoparticles1 form the conversion element 12. The conversion element 12can be a thin film. Due to the nanoparticles 1, the conversion element 12 has a higher effectivity as the nanoparticles 1 are more stable compared to other nanoparticles 1. The higher effectivity can be explained by relieved interfacial lattice strain in the nanoparticles 1 due to the confining shell 3 and / or the gradient shell 4. This effect increases the PLQY, lowers thelifetime of excitons in the emissive region 2, lowers ratesof non-radiative exciton recombination in the emissive region 2, and increases multi-exciton quantum yield in the emissive region 2. The nanoparticles 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 secondwavelength range comprises wavelengths in the green to red orinfrared region of the electromagnetic spectrum. The features and exemplary embodiments described in connection with the figures can be combined with each other2024PF00564 July 15, 2025P2024,0559 WO N -22 –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. This patent application claims the priority of US provisional patent application 63 / 688,264, the disclosure content of which is hereby incorporated by reference. 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.

[0002] 2024PF00564 July 15, 2025P2024,0559 WO N -23 –Reference signs1 nanoparticle2 emissive region21 emissive core22 emissive shell3 confining shell4 gradient shell5 outer shell6 intermediate shell7 non-emissive core10 light-emitting device11 light-emitting semiconductor chip111 semiconductor layer sequence112 active layer12 conversion element

Claims

2024PF00564 July 15, 2025P2024,0559 WO N -24 –Claims 1. A nanoparticle (1) comprising- an emissive region (2) comprising a first semiconductormaterial, and- a confining shell (3), wherein- the confining shell (3) at least partially surrounds theemissive region (2), and- the confining shell (3) comprises a material selected fromthe group consisting of MgS, MgSe, and combinations thereof.

2. The nanoparticle (1) according to claim 1, further comprising a gradient shell (4), wherein the gradient shell (4) comprises Mg1-xZnxS and / or Mg1-xZnxSe, wherein 0 ≤ x ≤ 1 and wherein x varies depending on a distance from the emissive region (2).

3. The nanoparticle (1) according to claim 2, whereinthe gradient shell (4) has a maximum value of x at a surfaceof the gradient shell (4) facing away from the emissiveregion (2).

4. The nanoparticle (1) according to any of the previous claims, further comprising an outer shell (5), wherein the outer shell (5) comprises a material selected from the group consisting of ZnS, ZnSe, ZnSeS, CdS, CdZnS, and combinations thereof.

5. The nanoparticle (1) according to any of the previous claims, further comprising an intermediate shell (6),2024PF00564 July 15, 2025P2024,0559 WO N -25 –wherein the intermediate shell (6) comprises a secondsemiconductor material having a larger bandgap than the first semiconductor material of the emissive region (2).

6. The nanoparticle (1) according to claim 5, wherein the second semiconductor material has a smaller bandgap thanthe material of the confining shell (3) and / or the gradientshell (4).

7. The nanoparticle (1) according to any of claims 5 or 6, wherein the second semiconductor material is a II-VI compound semiconductor material.

8. The nanoparticle (1) according to any of claims 5 or 6, wherein the second semiconductor material is a III-V compound semiconductor material.

9. The nanoparticle (1) according to any of the previous claims, wherein the emissive region (2) comprises a dopant.

10. The nanoparticle (1) according to any of the previous claims, wherein the first semiconductor material is a II-VI compound semiconductor material or a III-V compound semiconductor material.

11. The nanoparticle (1) according to any of the previous claims, whereinthe emissive region (2) comprises an emissive core (21).2024PF00564 July 15, 2025P2024,0559 WO N -26 –12. The nanoparticle (1) according to any of claims 1 to 11, wherein- the emissive region (2) comprises an emissive shell (22),and- the emissive shell (22) surrounds a non-emissive core (7).

13. The nanoparticle (1) according to any of the previous claims, wherein the nanoparticle (1) has a shape selected from the groupconsisting of a sphere, a rod, a cube, and a tetrahedron.

14. A light-emitting device (10) comprising- a light-emitting semiconductor chip (11) configured to emitelectromagnetic radiation of a first wavelength range, and- a conversion element (12) comprising a plurality ofnanoparticles (1) according to any of claims 1 to 12, wherein the conversion element (12) converts the electromagnetic radiation of the first wavelength range into electromagnetic radiation of a second wavelength range.

15. The light-emitting device (10) according to claim 14, wherein the light-emitting device (10) is a micro-LED.

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