CN103320133A - Water-phase preparation method of ZnSe:Ag quantum dots - Google Patents

Abstract

The invention relates to an aqueous phase preparation method of ZnSe:Ag quantum dots, and belongs to the technical field of composite nanocrystal materials. The preparation method of the present invention is as follows: firstly, sodium borohydride (NaBH ₄ ) and selenium powder are used to react to prepare sodium selenium hydride (NaHSe), and then sodium selenium hydride is injected into zinc nitrate/3-mercaptopropane whose pH has been adjusted with sodium hydroxide. In the acid solution, the two react to form a light yellow-brown transparent ZnSe:Ag quantum dot solution. The product obtained by the invention has uniform dispersion, good stability and less agglomeration; it can be applied to the fields of biological fluorescence labeling, drug separation and some photoelectric devices.

Description

Aqueous phase preparation method of ZnSe:Ag quantum dots

technical field

The invention relates to a water-phase preparation method of ZnSe:Ag quantum dots, belonging to the technical field of composite nano-microcrystalline materials.

Background technique

ZnSe is an important direct bandgap Ⅱ-Ⅵ group semiconductor luminescent material. It is a sphalerite structure and a face-centered cubic crystal with a wide bandgap (2.8eV) and a large binding energy (21meV). At room temperature, the band gap directly transitions to a luminescent wavelength in the range of blue-violet light. It has good transmission performance for light with a wavelength range of 0.5-22 μm, basically covers the visible-infrared range, and has low material toxicity. It is suitable for optoelectronic devices, biological detection, marking and imaging and other fields.

To realize the wide application of ZnSe in optoelectronic and biological fields, it is necessary to obtain ZnSe materials with high quantum yield and stable luminescence. ZnSe quantum dots have poor luminous intensity and low quantum yield. Doping can improve the luminous intensity of ZnSe quantum dots. Through effective doping, the energy band of the raw material can be changed, and the energy level of impurities can be introduced, thereby changing the fluorescence characteristics of the material, adjusting its fluorescence emission spectrum, and improving the fluorescence efficiency.

At present, the doping of ZnSe quantum dots mainly focuses on Cu and Mn elements, while the research on Ag doping is blank. However, the stability of ZnSe: Cu and ZnSe: Mn is poor, and precipitation usually occurs after about 7 days of storage. The patent of the present invention adopts the doping of Ag element, which fills the blank of Ag doping of ZnSe quantum dots at home and abroad, and effectively improves the stability of ZnSe doped quantum dots while improving the luminous intensity and quantum yield.

The Ag-doped nanomaterials synthesized in the aqueous phase are under the action of a dispersant, allowing Zn source, Se source and a certain amount of Ag source to react in an alkaline environment to form a ZnSe:Ag quantum dot solution. Compared with the traditional oil-phase preparation process, the water-phase process is simple to operate, easy to control, and has a low reaction temperature. The obtained samples are soluble in water and have good biocompatibility.

Contents of the invention

The object of the present invention is to provide a method for preparing ZnSe:Ag quantum dots with high fluorescence intensity, stable luminescence and low toxicity.

The invention relates to a water-phase preparation method of Ag-doped ZnSe quantum dots. The experiment adopts the growth doping method, and the dopant Ag is added to the zinc source. It is characterized in that it has the following preparation process and steps:

a. In a 100ml pear-shaped bottle, after passing nitrogen for about 30 minutes, add 0.8mmol NaBH ₄ , 0.2mmol selenium powder (Se) and 2ml deionized water in sequence; then react the pear-shaped bottle under nitrogen protection for 1 hour, and wait for the black selenium powder All disappear, forming a colorless transparent clear solution I, namely NaHSe solution; the chemical reaction equation is:

4NaBH ₄ + 2Se +7H ₂ O —— 2NaHSe + Na ₂ B ₄ O ₇ + 14H ₂ ↑

b. In a 250ml three-neck flask, add 0.8mmol zinc nitrate, 0.024mmol silver nitrate, 100ml deionized water and 200μL 3-mercaptopropionic acid in sequence, pass through nitrogen to remove oxygen in the solution, and then adjust the pH value to 9 with 1M NaOH, Heat the three-necked flask in an oil bath at 100°C for 1 hour to obtain a colorless and transparent solution II, namely Zn(NO ₃ ) ₂ (Ag) solution;

c. Use a syringe to quickly inject solution Ⅰ into solution Ⅱ, continue to pass nitrogen gas and maintain an oil bath at 100°C, and react for 3 hours to obtain a light yellow-brown transparent ZnSe:Ag quantum dot solution; the chemical reaction equation is:

Zn(NO ₃ ) ₂ (Ag) + NaHSe —— ZnSe(Ag) + NaNO ₃ + HNO ₃

The ZnSe:Ag quantum dot prepared by the invention has the characteristics of good stability, less agglomeration, etc., so that it shows great application prospects in the fields of bioluminescence labeling, photoelectric materials and the like.

The outstanding features of the present invention are: (1) ZnSe:Ag quantum dots are prepared for the first time, which emit blue-green light under ultraviolet light; The operation is simple, the process is easy to control, and the prepared quantum dots do not need secondary conversion, and can be directly applied to biomarkers; (3) The prepared quantum dots can be stored at low temperature and protected from light for four months, indicating their stability better. It solves the problem of poor stability of quantum dots and the inability to store them for a long time.

Description of drawings

The X-ray diffraction (XRD) figure of the sample that Fig. 1 present invention makes;

Fig. 2 is a high-magnification transmission electron microscope (HRTEM) photo of the sample prepared by the present invention;

The energy dispersive (EDS) energy spectrum of the sample that Fig. 3 present invention makes;

Fig. 4 is the ultraviolet-visible absorption (uv-vis) spectrum of the sample prepared by the present invention;

Fig. 5 is the PL (photoluminescence) spectrogram of samples ZnSe and ZnSe:Ag prepared by the present invention.

Fig. 6 PL (photoluminescence) spectra of samples ZnSe:Ag with different doping concentrations prepared by the present invention.

Detailed ways

a. In a 100ml pear-shaped bottle, after passing nitrogen gas for about 30 minutes, add 0.8mmol NaBH ₄ , 0.2mmol selenium powder (Se) and 2mL deionized water in sequence; then react the pear-shaped bottle under nitrogen protection for 1 hour, and wait for the black selenium powder All disappear, forming a colorless transparent clear solution Ⅰ, that is, NaHSe solution, ready for use;

b. In a 250ml three-neck flask, add 0.8mmol zinc nitrate, 0.024mmol silver nitrate, 100ml deionized water and 200μL 3-mercaptopropionic acid in sequence, pass through nitrogen to remove the oxygen in the solution, and then adjust the pH to 9 with 1M NaOH. The three-necked flask was heated in an oil bath at 100°C for 1 hour to obtain a colorless and transparent solution II, namely Zn(NO ₃ ) ₂ (Ag) solution;

c. Use a syringe to quickly inject solution Ⅰ into solution Ⅱ, continue to pass nitrogen gas and maintain an oil bath at 100 °C, and react for 3 hours to obtain a light yellow-brown transparent ZnSe:Ag quantum dot solution.

The present invention uses an X-ray diffractometer and a fluorescence indexer to analyze the structure and fluorescence properties of the experimental sample, uses an EDS energy spectrometer to analyze the composition of the prepared ZnSe:Ag quantum dots, and observes them through a high-resolution transmission electron microscope. Ultrastructure, the test results show that: as shown in Figure 1, the XRD diffraction characteristic peaks of ZnSe and ZnSe:Ag quantum dots are consistent, at about 27.2 ^o , 45.2 ^o and 53.6 ^o , which is similar to that of zinc blende structure ZnSe crystal The positions of (111), (220) and (311) crystal planes are consistent, indicating that the prepared quantum dots have a sphalerite structure, and Ag doping has no obvious effect on the structure of ZnSe crystals. Ag ₂ Se at 22.9° and 33.5° indicates the formation of Ag ₂ Se; Figure 2 is a high-magnification transmission electron micrograph (black spot) of ZnSe:Ag quantum dots. The particle size distribution of quantum dots is uniform and no agglomeration occurs. The size is around 3nm. Figure 3 is the EDS energy spectrum of ZnSe:Ag quantum dots. It can be seen that the product contains Ag, Zn, Se and other elements, which are consistent with the chemical composition of ZnSe:Ag quantum dots. The characteristic peak of the S element is because the 3-mercaptoacetic acid used in the experiment contains S ions; since the prepared sample is carried on the copper grid for observation, the characteristic peak of the Cu element is caused by the copper grid; the Ag content is obviously high, and its The main reason is the generation of Ag ₂ Se compound. Fig. 4 is the ultraviolet-absorption spectrum of ZnSe quantum dot and ZnSe:Ag quantum dot. Compared with the absorption edge of ZnSe quantum dots, the absorption edge of ZnSe:Ag quantum dots is wider. Combined with the XRD image of ZnSe:Ag quantum dots, it shows that the presence of Ag ₂ Se in the prepared samples leads to the broadening of the absorption edge. But the starting turning point is around 375nm. It shows that the ZnSe:Ag quantum dot structure has not changed relative to the ZnSe quantum dot structure, which is consistent with the conclusion obtained from the XRD image. Fig. 5 shows the fluorescence emission spectra of ZnSe and ZnSe:Ag quantum dots at an excitation wavelength of 325nm. As shown in the figure, ZnSe has two peak positions at about 375nm and 460nm, corresponding to the position of the absorption edge, it can be seen that the emission peak at 375nm is the band edge emission of ZnSe quantum dots, and the peak at 460nm is the defect peak. When ZnSe is doped with Ag ions, there is only one fluorescence emission peak at 475nm, which is red-shifted relative to ZnSe quantum dots. It may be that Ag interstitially doped Ag _i enters the ZnSe quantum dot forbidden band to form a new impurity energy level and become a carrier recombination center. A certain degree of Ag ion doping has been achieved, and because the impurity energy level and the surface state are in a "competition" state after doping, the carriers tend to recombine on the impurity energy level, resulting in the disappearance of the band-edge emission at 375nm and turning to 475nm At the impurity level, recombination emits light, and the luminous intensity is obviously enhanced. Figure 6 shows the PL (photoluminescence) spectra of quantum dots with different doping concentrations. It can be seen that the quantum dots with a doping concentration of 12.5% have the highest luminous intensity. Quantum dots with this concentration emit blue-green light under the irradiation of 365nm ultraviolet lamp. Quantum dots with a doping concentration lower than 12.5% also emit blue-green light, but the luminous intensity decreases as the doping concentration decreases. When the doping concentration is too high, reaching 15%, the emission peak is obviously weakened, and at this time, the luminescence is an inconspicuous khaki light. When the doping concentration is low, the emission peak of the quantum dots is not obvious, and a good impurity energy level cannot be formed at this time, resulting in the indistinct recombination of carriers at the impurity energy level, resulting in low luminous intensity. When the doping concentration reaches 12.5%, the impurity energy level is fully formed, and the carriers recombine on the impurity energy level, with high luminous intensity and obvious emission peak. However, when the doping concentration is too high, Ag ions combine with Se ions to form a large amount of Ag ₂ Se, and quantum dots may agglomerate, which affects the luminescence of impurity levels in quantum dots, resulting in a greatly reduced luminous intensity.

Claims (1)

1. a kind of ZnSe: the aqueous phase preparation method of Ag quantum dot is characterized in that having following preparation process and step: a. In a 100ml pear-shaped bottle, after passing nitrogen gas for about 30 minutes, add 0.8mmol NaBH ₄ , 0.2mmol selenium powder (Se) and 2ml deionized water in sequence; All the powders disappeared, and a colorless and transparent clear solution I was produced, that is, NaHSe solution, which was ready for use; b. In a 250ml three-neck flask, add 0.8mmol zinc nitrate, 0.024mmol silver nitrate, 100ml deionized water and 200μL 3-mercaptoacetic acid in sequence, pass through nitrogen to remove oxygen in the solution, then adjust the pH to 9 with 1M NaOH, and mix the three The neck flask was placed in an oil bath at 100°C and heated for 1 hour to obtain a colorless and transparent clear solution II, namely Zn(NO ₃ ) ₂ (Ag) solution; c. Use a syringe to quickly inject solution I into solution II, continue to pass nitrogen gas and maintain an oil bath at 100°C, and react for 3 hours to obtain a light yellow-brown transparent ZnSe:Ag quantum dot solution.

Images