How CdSe / ZnS Quantum Dots Work?

 Peter Rom
  Aug 07, 2018

What is a CdSe / ZnS quantum dot?

Quantum dots are inorganic semiconductor nanocrystals with excellent optical properties, and have the advantages of high fluorescence quantum yield, wide excitation spectrum, narrow emission spectrum, and good light stability. CdSe / ZnS quantum dots have been widely used in biomedical fields such as sensing, marking, imaging and tracing. The CdSe / ZnS quantum dot is one of the most important ones. It refers to a quantum dot with CdSe as the core and ZnS as the shell.

Several applications of CdSe / ZnS quantum dots

As a light-emitting layer material of QELD

Experiments show that the CdSe/ZnS core-shell quantum dots are used as the light-emitting layer material of quantum dot light-emitting diodes (QLED), which is a feasible method.

The quantum dot luminescent material has the characteristics of narrow emission peak, high luminous efficiency, adjustable spectrum, long fluorescence lifetime and good solution stability, and is suitable for use as a light-emitting display material. In order to further improve the luminous efficiency of quantum dot luminescent displays, many researchers have synthesized colloidal quantum dots of CdSe/ZnS core-shell structure, and the electron confinement effect on the core is very strong, and the electronic transition is limited and cannot reach the outer casing. Therefore, the quantum dot fluorescence effect of this structure is not affected by the surface state, and the performance is more stable.

Quantum dot LED displays have broad commercial applications and have a strong competitive advantage in next-generation display technologies. Its advantages are:

  • Self-luminous
  • Wide viewing angle
  • The reaction time is fast
  • High luminous efficiency
  • The working voltage is low
  • The thickness of the panel is thin
  • Large size and flexible panels can be made
  • The manufacturing process is simple

Application in dopamine fluorescence detection method

In recent years, quantum dots have become a new type of semiconductor nanoluminescent material, which provides a possibility for rapid determination of various analytes. Currently widely used quantum dots mainly include single-core quantum dots such as CdTe, CdSe, and CdS, but single-core quantum dots have many surface defects, low fluorescence efficiency, and poor photooxidation stability. Recent studies have shown that the formation of core-shell quantum dots by quantum dot coating on the basis of mononuclear quantum dots can effectively overcome the shortcomings of mononuclear quantum dots. Moreover, the optical performance is more stable, which can effectively increase the sensitivity to analyte detection. Using CdSe/ZnS quantum dots as fluorescent probes, based on the fluorescence quenching effect of dopamine on CdSe/ZnS quantum dots, a fluorescence detection method for rapid determination of dopamine was established.

Transition ion doped CdSe/ZnS quantum dots

The transition ion (Mn、Cu) doped CdSe/ZnS quantum dots first meet the needs of green environmental protection from the choice of matrix materials. In addition to its low toxicity, doping quantum dots can overcome many of the essential disadvantages of undoped quantum dots:

  • The luminescence mechanism of doped quantum dots is different from that of quantum dots. The large Stokes translation generated by it can prevent the self-quenching of quantum dot luminescence caused by or reabsorption in undoped quantum dots.
  • Doped quantum dots have better thermal stability and photochemical stability.
  • From the energy of the emitted light, the band gap of the quantum dot matrix semiconductor material has a large difference with the energy level of the doped transition ion excited state, and the luminescent energy of the quantum dot varies with the size of the particle. Therefore, it is entirely possible to obtain a series of luminescence (such as blue, green, yellow, and orange-red) below the band edge with ZnS as the matrix material.
  • In addition, the application of transition-ion doped quantum dots to biomarkers is a new idea that has emerged in the last two years. However, before quantum dots are used for biomarkers, they must have three characteristics under aqueous biological conditions: effective fluorescence, glial stability, and low non-specific absorption. For quantum dots used in biomarkers, the surface of quantum dots synthesized in organic systems is hydrophobic. However, quantum dots used as fluorescent labels must be water-soluble. Therefore, before coupling with biomolecules, the surface must be fixed. The bifunctional group is modified to provide certain water solubility while being coupled to biomolecules.

Problems and Challenges of CdSe/ZnS Quantum Dots

Degradation of light-induced function is one of the main challenges faced by colloidal quantum dots in applications. In other words, how can we improve the luminous stability of quantum dots? It is found that the SiO2 film can block the light-induced oxidation of the surface of the quantum dots because it can block the water and oxygen in the air, thus significantly improving the luminescence stability of the CdSe/ZnS quantum dots.

So why does SiO2 film have such a magical effect? This must be inseparable from the properties of the silica nanoparticles. The mystery of this is left to the reader to explore!

References

[1] Narayan P, David M B, Yong C L, et a1, Efficient and color-tunable Mn-doped ZnSe nanocrystal emitters: control of optical performane via greener synthetic chemistry [J]. Nano Lett, 2007, 129 : 3339 -3347.

[2]SHEN Chen-fan, ZHANG Zhi-feng, GUO Yuan, YAN Gui-qin. Research on Development of Dopamine Fluorescence Detection Method Based on CdSe/ZnS Quantum Dots. 1004 —4957(2016)08 —0949 —06.

How CdSe / ZnS Quantum Dots Work?

Peter Rom

Peter Rom is a material scientist from Creative Diagnostics. He has been working in this field for over five years, he loves this job and would like to share his knowledge with everyone.

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