High-crystallinity near-infrared emission wurtzite CdS quantum dot / Zn < 2 + > modified CdS quantum dot as well as preparation method and application thereof

Abstract

The invention provides a high-crystallinity near-infrared emission wurtzite CdS quantum dot / Zn < 2 + > modified CdS quantum dot as well as a preparation method and application thereof, and belongs to the technical field of semiconductor quantum dots. The preparation method comprises the following steps: mixing cadmium oxide, a very small amount of zinc acetate, oleic acid and octadecene, heating for degassing, heating to a reaction temperature, and adding an S-ODE precursor for reaction to obtain the zinc-modified wurtzite CdS quantum dot. The CdS quantum dots synthesized under the condition of high concentration are of a wurtzite structure and have high crystallinity, the particle size is remarkably increased, a small amount of zinc acetate is added, disordered nucleation and growth processes under a high-concentration reaction system are effectively separated through a surface adsorption process, and the monodispersed wurtzite CdS quantum dots are obtained. According to the invention, the LED device is prepared by integrating the optimized CdS quantum dots and the 450nm purple light chip, and the dual functions of visible light illumination and night vision application are realized.

Description

Technical Field

[0001] This invention relates to the field of semiconductor quantum dot technology, and more particularly to a highly crystalline wurtzite CdS / Zn quantum dot with near-infrared emission. 2+ Modified CdS quantum dots, their preparation methods, and applications. Background Technology

[0002] Group II-VI semiconductor quantum dots (represented by CdSe and CdS) were the first colloidal quantum dot systems to achieve high-quality synthesis, laying the foundation for subsequent research on various colloidal quantum dots. Among them, CdS, as a wide-bandgap semiconductor (Eg=2.42eV), has been widely used in optoelectronic devices such as displays, lighting, solar cells, and photocatalysis due to its size-tunable photoelectric properties and excellent nonlinear optical behavior. As a luminescent material, wide-bandgap CdS is often used as a shell material in core-shell structures or as a seed in heterojunctions to improve the luminescence efficiency of quantum dots through carrier confinement effects (e.g., CdSe / CdS systems). When used as a luminescent core, CdS quantum dots exhibit unique dual-mode luminescence characteristics: intrinsic narrowband emission in the violet-blue light region, and broadband defect state emission induced by intrinsic defects such as sulfur vacancies (VS) or cadmium interstitials (Cdi). Current research mainly focuses on controlling its intrinsic narrowband emission (through size / morphology control), while systematic research on the control and application of defect state emission remains limited. In fact, these defect-related broadband emissions have great potential in advanced optoelectronic device applications.

[0003] Recent studies have shown that defect-induced emission in the visible region of zincblende CdS quantum dots can be effectively coupled with near-ultraviolet LEDs to achieve efficient single-phase white light emission. For example, Zou et al. developed a pressure-coordinated ligand engineering strategy to achieve white light emission in zincblende CdS quantum dots by combining band-edge emission and strong defect emission. Meanwhile, Huang et al. synthesized thiol-passivated CdS quantum dots at room temperature using ethanol as a solvent, which emitted bright white light covering the spectral range of 420 nm to 700 nm. Furthermore, researchers found that surface modification or size control can redshift the defect emission spectrum to the near-infrared region, thus expanding its application potential in near-infrared optoelectronic devices. However, research on the regulation of near-infrared emission mediated by CdS quantum dot defects remains relatively limited. Samuel et al. redshifted the defect emission peak of CdS quantum dots from ~600 nm to 760 nm by extending the growth time and significantly improved the near-infrared emission efficiency by modification with tri-n-octylphosphine oxide (TOPO). However, the reported CdS quantum dots still suffer from poor morphological characteristics (such as unclear lattice fringes). Simply increasing the quantum dot size to extend it beyond the strong confinement region to achieve a spectral redshift cannot achieve complete near-infrared spectral coverage. Crystal structure is considered to have a significant impact on the defect emission properties of quantum dots. It is speculated that the highly structurally symmetric zincblende phase may favor narrow-band edge emission, while the wurtzite structure, due to its ease of forming stacking faults and intrinsic point defects, may be more conducive to producing broader defect-related emission. Despite these potential structure-property relationships, the controllable synthesis of wurtzite-phase CdS quantum dots and the systematic engineering study of their defect states have not been fully explored, highlighting a significant gap in current research. Furthermore, intentionally introducing vacancy defects may be a feasible strategy to redshift the defect emission of CdS quantum dots into the near-infrared range. Summary of the Invention

[0004] The purpose of this invention is to provide a highly crystalline near-infrared emitting wurtzite CdS quantum dot / Zn 2+ Modified CdS quantum dots, their preparation methods, and applications are presented to address the aforementioned technical problems.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing highly crystalline near-infrared emitting wurtzite CdS quantum dots, comprising the following steps: Cadmium oxide, oleic acid and octadecene are mixed and degassed by heating, then heated to the reaction temperature, and then S-ODE precursor is added to react, thus obtaining highly crystalline wurtzite CdS quantum dots with near-infrared emission. The S-ODE precursor was prepared by dissolving sulfur powder in octadecene; The molar ratio of the S-ODE precursor to cadmium oxide is 0.5~2:1.

[0006] Furthermore, the ratio of cadmium oxide, oleic acid, and octadecene is 1 mmol: 1-3 mL: 3-5 mL.

[0007] Furthermore, the degassing temperature is 120~140℃, and the degassing time is 1~3h.

[0008] Furthermore, the reaction temperature is 300~330℃, and the reaction time is 1~15min.

[0009] Furthermore, in the preparation of the S-ODE precursor, the ratio of sulfur powder to octadecene is 1~3 mmol: 4 mL, and the dissolution is carried out at 110~130℃.

[0010] The present invention also provides highly crystalline near-infrared emitting wurtzite CdS quantum dots prepared by the above preparation method.

[0011] The present invention also provides a highly crystalline near-infrared emitting wurtzite Zn 2+ The method for preparing modified CdS quantum dots includes the following steps: Cadmium oxide, zinc acetate, oleic acid, and octadecene were mixed, degassed by heating, and then heated to the reaction temperature. An S-ODE precursor was then added to initiate the reaction, yielding highly crystalline wurtzite Zn with near-infrared emission. 2+ Modified CdS quantum dots; The ratio of cadmium oxide, zinc acetate, oleic acid and octadecene is 1 mmol: 0.05~0.2 mmol: 1~3 mL: 3~5 mL.

[0012] Furthermore, the molar ratio of the S-ODE precursor to cadmium oxide is 0.5~2:1; The degassing temperature is 120~140℃, and the degassing time is 1~3h; The reaction temperature is 300~330℃, and the reaction time is 1~15min.

[0013] This invention also provides highly crystalline near-infrared emitting wurtzite CdS quantum dots or highly crystalline near-infrared emitting wurtzite Zn. 2+ Application of modified CdS quantum dots in near-infrared LED devices.

[0014] The beneficial effects of this invention are: This invention synthesizes CdS quantum dots with a wurtzite structure under high concentration conditions, exhibiting high crystallinity and significantly increased particle size. Both intrinsic and defect emissions show a significant redshift. Further increasing the sulfur content further redshifts the defect emission of the wurtzite CdS quantum dots to the near-infrared region. Broadband near-infrared emission with a center wavelength of 740 nm is achieved when the Cd:S molar ratio is 1:1.25. Adding a very small amount of zinc oleate precursor effectively improves defect emission efficiency. As part of the carboxylate ligand system, zinc oleate adheres to the quantum dot surface without incorporating into the CdS lattice, thereby reducing nonradiative recombination at defect sites and improving the uniformity of quantum dot nucleation and morphology. Finally, this invention integrates the optimized CdS quantum dots with a 450nm violet light chip to fabricate an LED device, achieving dual functionality for visible light illumination and night vision applications. This invention provides a feasible path for developing high-quality near-infrared luminescent CdS quantum dots. Attached Figure Description

[0015] Figure 1 Characterization of the optical and structural properties of cadmium sulfide quantum dots synthesized from low-concentration precursors with different elemental ratios: (a) absorption and PL spectra; (b) TEM image, with inset showing the particle size distribution; (c) XRD pattern; (d) absorption and PL spectra; (e) XRD pattern.

[0016] Figure 2 The images show the optical and structural characteristics of CdS quantum dots synthesized in high precursor concentration systems with different Cd:S ratios: (a) absorption spectrum, (b) emission spectrum, (c) variations in intrinsic emission peak position, defect emission peak position and corresponding full width at half maximum (FWHM), (d) XRD pattern, (e) TEM image, and the inset is a statistical diagram of particle size distribution.

[0017] Figure 3 Optical and structural properties of CdS quantum dots synthesized at a Cd:S ratio of 1:1.25 and different nucleation times. (a) Absorption spectrum, (b) Emission spectrum, (c) XRD pattern, (d) TEM image, inset is particle size distribution statistical diagram, (e) HRTEM image, inset is FFT image.

[0018] Figure 4 Optical and structural properties of Zn-modified CdS quantum dots. (a) Absorption and emission spectra, (b) XRD patterns, (c) TEM and HRTEM images, with insets showing particle size distribution statistics and FFT images, respectively.

[0019] Figure 5The optical and structural characteristics of CdS quantum dots under different currents and light sources are shown. (a) Photoluminescence spectra of CdS LEDs driven by 50mA-460mA, with insets showing the actual LED and the device lit up at 310mA, respectively. (b) Images of CdS LEDs under different light sources. Detailed Implementation

[0020] This invention provides a method for preparing highly crystalline near-infrared emitting wurtzite CdS quantum dots, comprising the following steps: Cadmium oxide, oleic acid and octadecene are mixed and degassed by heating, then heated to the reaction temperature, and then S-ODE precursor is added to react, thus obtaining highly crystalline wurtzite CdS quantum dots with near-infrared emission. The S-ODE precursor was prepared by dissolving sulfur powder in octadecene; The molar ratio of the S-ODE precursor to cadmium oxide is 0.5~2:1.

[0021] In this invention, the molar ratio of the S-ODE precursor to cadmium oxide is preferably 0.5:1, 0.8:1, 1.25:1 or 1.5:1.

[0022] In this invention, the ratio of cadmium oxide, oleic acid and octadecene is 1 mmol: 1~3 mL: 3~5 mL, preferably 1 mmol: 1.5~2.5 mL: 3.5~5 mL, and more preferably 1 mmol: 2 mL: 5 mL.

[0023] In this invention, the degassing temperature is 120~140℃, preferably 125~135℃, and more preferably 130℃; the degassing time is 1~3h, preferably 2h.

[0024] In this invention, the reaction temperature is 300~330℃, preferably 310~320℃; the reaction time is 1~15min, preferably 3~12min, and more preferably 5~8min.

[0025] In this invention, the ratio of sulfur powder to octadecene in the preparation of the S-ODE precursor is 1~3 mmol:4 mL, preferably 2 mmol:4 mL; the dissolution is carried out at 110~130℃, preferably 120℃.

[0026] The present invention also provides highly crystalline near-infrared emitting wurtzite CdS quantum dots prepared by the above preparation method.

[0027] The present invention also provides a highly crystalline near-infrared emitting wurtzite Zn 2+ The method for preparing modified CdS quantum dots includes the following steps: Cadmium oxide, zinc acetate, oleic acid, and octadecene were mixed, degassed by heating, and then heated to the reaction temperature. An S-ODE precursor was then added to initiate the reaction, yielding highly crystalline wurtzite Zn with near-infrared emission. 2+ Modified CdS quantum dots; The ratio of cadmium oxide, zinc acetate, oleic acid and octadecene is 1 mmol: 0.05~0.2 mmol: 1~3 mL: 3~5 mL, preferably 1 mmol: 0.1~0.15 mmol: 1.5~2.5 mL: 3.5~5 mL, and more preferably 1 mmol: 0.1 mmol: 2 mL: 5 mL.

[0028] In this invention, the molar ratio of the S-ODE precursor to cadmium oxide is 0.5 to 2:1, preferably 0.5:1, 0.8:1, 1.25:1 or 1.5:1; The degassing temperature is 120~140℃, preferably 125~135℃, and more preferably 130℃; the degassing time is 1~3h, preferably 2h. The reaction temperature is 300~330℃, preferably 310~320℃; the reaction time is 1~15min, preferably 3~12min, and more preferably 5~8min.

[0029] This invention also provides highly crystalline near-infrared emitting wurtzite CdS quantum dots or highly crystalline near-infrared emitting wurtzite Zn. 2+ Application of modified CdS quantum dots in near-infrared LED devices.

[0030] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0031] Chemicals: Cadmium oxide (CdO, 99.98%, powder), zinc acetate (Zn(Ac)2, 99.99%, powder), sulfur powder (S, 99.99%, powder), oleic acid (OA, 90%), and 1-octadecene (1-ODE, industrial grade, 90%) were supplied by Sigma-Aldrich. UV-curable adhesive (AA 3491) was supplied by Hangaoda. n-Hexane and ethanol (both analytical grade) were purchased from China National Pharmaceutical Group Corporation. All materials were used directly without any purification.

[0032] Example 1

[0033] Preparation of highly crystalline near-infrared emitting wurtzite CdS quantum dots: 1 mmol CdO, 2 mL OA, and 5 m LODE (octadecene) were added to a three-necked flask. The mixture was first degassed at 130 °C for 2 h, and then heated to 310 °C under a nitrogen atmosphere. When the target temperature was reached, 1.25 mmol of the S-ODE precursor (prepared by dissolving 2 mmol of sulfur powder in 4 m LODE at 120 °C) was rapidly injected into the reaction flask. Subsequently, the reaction was annealed at 310 °C for 3 min, and the synthesized CdS quantum dots were purified using n-hexane and ethanol to obtain highly crystalline wurtzite CdS quantum dots with near-infrared emission.

[0034] Example 2

[0035] Same as Example 1, except that the molar ratio of CdO to S-ODE precursor is 1 mmol: 0.5 mmol.

[0036] Example 3

[0037] Same as Example 1, except that the molar ratio of CdO to S-ODE precursor is 1 mmol: 0.8 mmol.

[0038] Example 4

[0039] Same as Example 1, except that the molar ratio of CdO to S-ODE precursor is 1 mmol: 1.5 mmol.

[0040] Example 5

[0041] Same as Example 1, except that the annealing time is 0 min.

[0042] Example 6

[0043] Same as Example 1, except that the annealing time is 8 minutes.

[0044] Example 7

[0045] A highly crystalline wurtzite Zn with near-infrared emission 2+ Preparation of modified CdS quantum dots: 1 mmol CdO, 0.1 mmol zinc acetate, 2 mL OA, and 5 m LODE were added to a three-necked flask. The mixture was first degassed at 130 °C for 2 h, and then heated to 310 °C under a nitrogen atmosphere. When the target temperature was reached, 1.25 mmol of the S-ODE precursor (prepared by dissolving 2 mmol sulfur powder in 4 m LODE at 120 °C) was rapidly injected into the reaction flask. Subsequently, the reaction was annealed at 310 °C for 3 min. The synthesized CdS quantum dots were purified using n-hexane and ethanol to obtain highly crystalline wurtzite Zn with near-infrared emission. 2+ Modified CdS quantum dots.

[0046] Comparative Example 1

[0047] Preparation of CdS quantum dots with zincblende structure: Under a nitrogen atmosphere, 5 mmol of CdO was dissolved in a mixture of 10 mL of 1-ODE and 10 mL of oleic acid, and 0.25 M cadmium oleate (Cd(OA)) was prepared at 250 °C. Precursor. In the synthesis of typical zincblende structure CdS quantum dots, 1.2 mL of Cd(OA) precursor was used. The precursor (0.25 M) and 10 mLODE were added to a three-necked flask. The mixture was degassed at 130 °C for 2 h, and then heated to 310 °C under a nitrogen atmosphere. When the temperature reached 310 °C, 0.06 mmol of the S-ODE precursor (prepared by dissolving 3 mmol of sulfur powder in 10 mLODE at 120 °C) was rapidly injected into the reaction flask. Subsequently, the reaction mixture was annealed at this temperature for 8 min, and the synthesized CdS quantum dots were purified by hexane and ethanol to obtain zincblende structured CdS quantum dots.

[0048] Comparative Example 2

[0049] Similar to Comparative Example 1, the difference lies in Cd(OA) The molar ratio of the precursor to the S-ODE precursor is 0.3:0.3.

[0050] Comparative Example 3

[0051] Similar to Comparative Example 1, the difference lies in Cd(OA) The molar ratio of the precursor to the S-ODE precursor is 0.3:0.36.

[0052] Application examples

[0053] Preparation of near-infrared LED devices: The dried wurtzite Zn from Example 7 was used... 2+ Modified CdS quantum dot powder was thoroughly mixed with UV-curable adhesive at a mass ratio of 3:1 (quantum dot: adhesive) to prepare a device-grade quantum dot slurry. The mixture was stirred in the dark for 30 minutes to ensure homogeneity and prevent pre-curing. Subsequently, the resulting slurry was dotted onto a 450nm GaN LED chip and cured under 365nm UV light for 10 minutes to prepare the final near-infrared LED device.

[0054] Experimental Example 1

[0055] Characterization tests: UV-Vis absorption and photoluminescence spectra were obtained using a Horiba Duetta fluorescence-absorption spectrometer. The crystal structure was analyzed using an X-ray diffractometer on a Rigaku MiniFlexII system. Morphology and structural details were observed using a FEI Tecnai F20 ST transmission electron microscope (operating voltage 200 kV) and a high-resolution transmission electron microscope, respectively. The photoelectric properties of the obtained near-infrared LED devices were measured using a HAAS 2000 photoelectric testing system.

[0056] First, low-concentration precursor systems (comparative examples 1-3) were tested to investigate the effects of different Cd:S ratios (0.3:0.06, 0.3:0.3, and 0.3:0.36) on the luminescence properties and crystal structure of CdS quantum dots at 310℃. Figure 1 ).

[0057] When the Cd:S ratio is 0.3:0.06 (comparative Example 1, cadmium-rich conditions), the resulting CdS quantum dots exhibit a sharp exciton absorption peak. Figure 1 (a) indicates that it has good monodispersity. The corresponding fluorescence spectrum is dominated by strong intrinsic emission at 432 nm, accompanied by weak defect-related emission at 629 nm. This is attributed to the fact that the excess cadmium precursor eventually forms cadmium carboxylate species on the surface. These species act as effective ligands to passivate the quantum dot surface, thereby significantly suppressing nonradiative recombination pathways and enhancing intrinsic emission, while reducing defect emission related to surface dangling bonds.

[0058] When the Cd:S ratio was 0.3:0.3 (Comparative Example 2), the fluorescence spectrum changed significantly: intrinsic emission weakened and blue-shifted to 418 nm, while defect emission strengthened and shifted to 586 nm. Figure 1 (a below). This blue shift in the spectrum is mainly attributed to the decrease in quantum dot size. As the amount of injected sulfur precursor increased from 0.06 mmol to 0.3 mmol, the higher nucleation rate resulted in a decrease in the average particle size from approximately 2.23 nm to 2.02 nm. Figure 1 b). The XRD patterns confirmed this size difference, with the sample at a ratio of 0.3:0.3 showing broader diffraction peaks ( Figure 1 c). Both spectra are consistent with the zincblende structure (matching PDF cards #65-2887 and #75-0581, respectively). The enhanced defect emission can be attributed to the near-stoichiometric (1:1) reduction in the number of surface-passivated cadmium carboxylate ligands, thereby making the surface dangling bond-related radiative recombination pathway more significant.

[0059] When the sulfur precursor was further increased to an excess (Cd:S = 0.3:0.36, Comparative Example 3), the overall fluorescence intensity of the resulting CdS quantum dots decreased sharply. The intrinsic emission peak disappeared, and only a weak broadband defect emission with a center wavelength of approximately 700 nm could be observed. Figure 1 d). This is the result of multiple factors working together: excessive surface anions (S) generate severe surface defects, thus quenching intrinsic emission; simultaneously, the large number of sulfur vacancies introduced form deep-level defect states, leading to a redshift and broadened defect emission band. However, under these conditions, the quantum dot size is too small, and no obvious XRD diffraction peaks were detected. Figure 1 e).

[0060] In low-concentration precursor systems, the resulting CdS quantum dots primarily exhibit a zincblende structure and are relatively small in size, with both intrinsic and defect emissions confined to the visible light region. Notably, under sulfur-rich conditions, defect emission undergoes a significant redshift, approaching the near-infrared region. This phenomenon preliminarily suggests that introducing sulfur vacancies is a feasible strategy for achieving near-infrared defect emission in CdS quantum dots. Inspired by this, the inventors further explored the optical and structural properties of CdS quantum dots synthesized in high-precursor-concentration systems (exemplary embodiments of this invention).

[0061] Experiment Example 2

[0062] This invention increases the concentration of the cationic precursor to five times that of the low-concentration system and systematically adjusts the Cd:S ratio (1:1.25, 1:0.5, 1:0.8, and 1:1.5, corresponding to Examples 1 to 4, respectively). Four types of CdS quantum dots were synthesized under fixed nucleation conditions (reaction at 310°C for 3 minutes). The absorption spectra of all samples showed a broad band (…). Figure 2 a) indicates that the quantum dots have poor monodispersity. Furthermore, the fluorescence spectrum is dominated by defect emission, whose intensity exceeds that of intrinsic emission, especially under sulfur-rich conditions. Figure 2 b). This suggests the existence of high-density, unpassivated surface states. These phenomena are attributed to the additional energy levels introduced by the surface states: they can enhance defect emission as exciton traps, quench intrinsic emission as nonradiative recombination centers, and simultaneously cause exciton absorption peak broadening.

[0063] Compared to the sample with a Cd:S ratio of 1:0.5 (Example 2), the intrinsic and defect emission intensities of CdS quantum dots decreased significantly with increasing sulfur content. Intrinsic emission showed a slight redshift, while defect emission exhibited a significant redshift and band broadening. Under sulfur-rich conditions (ratios of 1:1.25 and 1:1.5), the defect emission peak was located at approximately 740 nm, with a full width at half maximum (FWHM) of 250 nm, indicating that the introduced sulfur vacancies created new deep-level defect states, extending luminescence into the near-infrared region. Figure 2c). Defect emission intensity peaks at a Cd:S ratio of 1:1.25, but significantly decreases at 1:1.5, where intrinsic emission completely disappears. This trend indicates that excess sulfur vacancies promote the formation of nonradiative recombination centers, thereby inhibiting radiative recombination. XRD analysis further reveals that the sulfur-rich samples have a pure wurtzite structure, while the samples with ratios of 1:0.8 and 1:0.5 contain a mixed phase of sphalerite and wurtzite. Figure 2 d). Therefore, it is concluded that the synergistic effect of a sulfur-rich environment and high precursor concentration successfully synthesized CdS quantum dots with a stable wurtzite structure and near-infrared emission. Furthermore, the average size of the CdS quantum dots synthesized at the four ratios remained above 5.5 nm, which is significantly larger than the size of the wurtzite quantum dots synthesized in the low-concentration system (~2.2 nm). This increased size caused a redshift of intrinsic emission to 490 nm and, to some extent, also promoted a redshift of defect emission and coverage of the near-infrared region. However, their monodispersity was poor, especially at the 1:1.5 ratio. Considering the requirement for effective near-infrared spectral coverage, 1:1.25 is currently the optimal choice among the four ratios for CdS quantum dots. Subsequently, the structure and luminescence properties of CdS quantum dots synthesized at the 1:1.25 ratio under different nucleation times were further investigated.

[0064] Experimental Example 3

[0065] In a high-concentration precursor system, a large number of CdS quantum dot nuclei are generated simultaneously within a very short time. Here, the present invention selects nucleation times of 0 minutes, 3 minutes, and 8 minutes, where the 0-minute nucleation time was experimentally achieved by immediately stopping heating and rapidly cooling after injecting the precursor. Figure 3 As shown in a and 3b, with the extension of nucleation time, the absorption and emission spectra of CdS quantum dots exhibit a redshift trend, especially within 0 to 3 minutes. The intrinsic emission peak and defect emission peak redshift from 480 nm and 700 nm to 491 nm and 740 nm, respectively, accompanied by a significant decrease in intrinsic emission and an enhancement in defect emission. Simultaneously, the half-width at half maximum (WHM) of the defect emission increases from 212 nm to 252 nm. When the nucleation time is extended to 8 minutes, the emission peaks further redshift to 495 nm and 747 nm, but the defect emission intensity decreases. The redshift trend of the defect emission peak is much greater than that of the intrinsic emission peak, indicating that the redshift of defect emission is not solely due to size increase, but is accompanied by the formation of S vacancies induced by excess S during the nucleation and growth of the quantum dots, introducing new defect emission and thus broadening its WHM. As can be seen from the XRD patterns (…), Figure 3 c) The X-ray diffraction peaks of the three CdS quantum dots are close to the CdS wurtzite phase, and with the extension of nucleation time, the diffraction peak widths significantly narrow, and the characteristic diffraction peaks of wurtzite gradually become more prominent. This is mainly attributed to the significant increase in quantum dot size. (Corresponding to TEM...) Figure 3 d) With increasing nucleation time, the size of CdS quantum dots significantly increased. At 0 min, the diameter of the CdS quantum dots was approximately 4.66 nm, increasing to about 5.74 nm at 3 min, and by 8 min, the particle diameter increased by an average of about 11.5 nm, with a size distribution ranging from a wide 5 nm to 16 nm. However, all three quantum dots exhibited excellent crystallinity, such as... Figure 3 eHRTEM images show that all three quantum dots exhibit clear wurtzite lattice fringes, especially at a 1:1.25 scale, where the crystal faces are exceptionally neat 100-planes. While this condition favors the formation of well-crystallized quantum dots, it severely sacrifices size uniformity. At high precursor concentrations, explosive nucleation occurs at the outset of the reaction, with a large number of CdS nuclei forming simultaneously within a very short time. Subsequently, the high concentration of precursor remaining in the system triggers continuous nucleation, resulting in a significant temporal overlap between nucleation and growth processes. Consequently, the earlier-formed nuclei have longer growth times and grow larger, while the later-formed nuclei are smaller, leading to a broad size distribution in the final product.

[0066] To overcome this size uniformity problem, the present invention further attempts to add 0.1 mmol of zinc acetate to the synthesis of CdS quantum dots (Example 7). Figure 4 As shown in Figure a, the addition of a very small amount of zinc acetate improved the defect emission intensity of the modified CdS quantum dots, while maintaining a relatively consistent full width at half maximum (FWHM). Meanwhile, the XRD pattern showed that the diffraction peaks remained consistent with the wurtzite CdS phase, consistent with pure CdS quantum dots. Notably, the size distribution uniformity of the Zn-modified CdS quantum dots was significantly improved, while maintaining good crystallinity. Figure 4 c) Under the same three-minute nucleation condition, the average size of the quantum dots was 5.71 nm, slightly smaller than the average size of pure CdS quantum dots (5.74 nm). We believe this is due to the solubility product of ZnS (Ksp≈1.6×10⁻⁶). -24 The solubility product of CdS (Ksp≈8.0×10) -27 It needs to be several orders of magnitude larger. This means that, in the same S... 2- At certain concentrations, the thermodynamic driving force for CdS formation is much greater than that for ZnS formation. Therefore, during CdS nucleation, S... It will be prioritized with Cd 2+ The reaction produces CdS crystal nuclei. However, a small amount of Zn... 2+ Ions competitively adsorb onto the surface of CdS quantum dots. This not only moderates the growth rate but, more importantly, significantly raises the energy barrier for secondary nucleation, forcing the reaction system to enter a pure crystal growth stage after the initial explosive nucleation, thus achieving temporal separation between "nucleation" and "growth." Secondly, Zn... 2+The surface adsorption of Zn is equivalent to a mild "surface passivation," stabilizing the quantum dot surface and preventing Ostwald ripening. Based on the high degree of uniformity in the crystal structure and optical properties of CdS quantum dots after Zn modification, the inventors believe that the addition of a "small amount" of zinc acetate means that the Zn element is mainly adsorbed on the surface or forms a very shallow surface doping layer, not enough to form a completely new ZnS phase or CdZnS alloy phase in the core. Therefore, the size distribution was successfully controlled while the wurtzite crystal structure of CdS quantum dots was perfectly preserved.

[0067] Experiment Example 4

[0068] The wurtzite Zn obtained in Example 7 2+ Modified CdS quantum dots were combined with a 450nm blue light chip to fabricate an LED device. Although the synthesized CdS quantum dots had a low luminous efficiency, they still achieved broadband visible and near-infrared light emission under high-power chip drive. Figure 5 The photoluminescence spectra of CdS LEDs driven by currents from 50 mA to 460 mA are presented, with insets showing actual LED images and the device illuminated at 310 mA. It was found that the intrinsic emission of the CdS quantum dots at 490 nm is completely quenched, while defect emission exhibits a broadband emission with a center wavelength of approximately 750 nm covering the 580-1100 nm range, and its intensity steadily increases with increasing driving current. Figure 5 Image b shows fruit illuminated by a CdS LED light source. In dark environments, clear images of the fruit can be effectively captured using both conventional and near-infrared cameras, achieving a preliminary dual function of visible light illumination and night vision. This invention provides a new material candidate for achieving both visible and near-infrared emission. Future research suggests that defect-induced near-infrared emission efficiency in wurtzite CdS quantum dots can be further improved through surface ligand passivation, potentially making it an excellent candidate material for NIR-LED light sources.

[0069] As can be seen from the above embodiments, the present invention provides a highly crystalline near-infrared emitting wurtzite CdS quantum dot / Zn 2+This invention relates to modified CdS quantum dots, their preparation methods, and applications. It observes that CdS quantum dots synthesized under high concentration conditions exhibit a wurtzite structure with high crystallinity and significantly increased particle size. Correspondingly, both intrinsic and defect emissions show a significant redshift. Further increasing the sulfur content further redshifts the defect emission of the wurtzite CdS quantum dots to the near-infrared region. When the Cd:S molar ratio is 1:1.25, broadband near-infrared emission with a center wavelength of 740 nm is achieved, which can be attributed to the regulatory effect of increased sulfur vacancies on the quantum dot surface on broadband defect emission. Adding a small amount of zinc oleate precursor effectively improves defect emission efficiency. Zinc oleate, as part of the carboxylate ligand system, adheres to the quantum dot surface without incorporating into the CdS lattice, thereby reducing nonradiative recombination at defect sites and improving the uniformity of quantum dot nucleation and morphology. Finally, this invention integrates the optimized CdS quantum dots with a 450 nm ultraviolet light chip to fabricate an LED device, achieving dual functionality for visible light illumination and night vision applications. This invention provides a feasible path for developing high-quality near-infrared luminescent CdS quantum dots.

[0070] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing highly crystalline near-infrared emitting wurtzite CdS quantum dots, characterized in that, Includes the following steps: Cadmium oxide, oleic acid and octadecene are mixed and degassed by heating, then heated to the reaction temperature, and then S-ODE precursor is added to react, thus obtaining highly crystalline wurtzite CdS quantum dots with near-infrared emission. The S-ODE precursor was prepared by dissolving sulfur powder in octadecene; The molar ratio of the S-ODE precursor to cadmium oxide is 0.5~2:

1.

2. The method for preparing highly crystalline near-infrared emitting wurtzite CdS quantum dots according to claim 1, characterized in that, The ratio of cadmium oxide, oleic acid, and octadecene is 1 mmol: 1-3 mL: 3-5 mL.

3. The method for preparing highly crystalline near-infrared emitting wurtzite CdS quantum dots according to claim 1 or 2, characterized in that, The degassing temperature is 120~140℃, and the degassing time is 1~3h.

4. The method for preparing highly crystalline near-infrared emitting wurtzite CdS quantum dots according to claim 3, characterized in that, The reaction temperature is 300~330℃, and the reaction time is 1~15min.

5. The method for preparing highly crystalline near-infrared emitting wurtzite CdS quantum dots according to claim 1, characterized in that, In the preparation of the S-ODE precursor, the ratio of sulfur powder to octadecene is 1~3 mmol: 4 mL, and the dissolution is carried out at 110~130℃.

6. Highly crystalline near-infrared emitting wurtzite CdS quantum dots prepared by the preparation method according to any one of claims 1 to 5.

7. A highly crystalline wurtzite Zn with near-infrared emission 2+ The method for preparing modified CdS quantum dots is characterized by, Includes the following steps: Cadmium oxide, zinc acetate, oleic acid, and octadecene were mixed, degassed by heating, and then heated to the reaction temperature. An S-ODE precursor was then added to initiate the reaction, yielding highly crystalline wurtzite Zn with near-infrared emission. 2+ Modified CdS quantum dots; The ratio of cadmium oxide, zinc acetate, oleic acid and octadecene is 1 mmol: 0.05~0.2 mmol: 1~3 mL: 3~5 mL.

8. The highly crystalline near-infrared emitting wurtzite Zn according to claim 7 2+ The method for preparing modified CdS quantum dots is characterized by, The molar ratio of the S-ODE precursor to cadmium oxide is 0.5~2:1; The degassing temperature is 120~140℃, and the degassing time is 1~3h; The reaction temperature is 300~330℃, and the reaction time is 1~15min.

9. The highly crystalline near-infrared emitting wurtzite Zn prepared by the preparation method according to claim 7 or 8 2+ Modified CdS quantum dots.

10. The highly crystalline near-infrared emitting wurtzite CdS quantum dots of claim 6 or the highly crystalline near-infrared emitting wurtzite Zn of claim 9 2+ Application of modified CdS quantum dots in near-infrared LED devices.

Images