The present group consists of chemical and materials engineers who have focused and conducted research on the synthesis of quantum dots (nanoparticles with the size of 5-10 nm whose properties are justifiable from the quantum perspective) with the capability of emission in the visible range since year 2009. The quantum dots generated in this collection have been introduced for medical applications, luminescent equipment such as LED and field emission displays.
Quantum dots can be divided into two general categories. The first one is core-shell quantum dot.These quantum dots have a core with a plasmonic compound which require a core-shell of a ceramic material with luminescence properties and suitable refractive index to stay stable. In this
regard, the group managed to synthesize CdSe and CdTe quantum dots with various core-shells including CdS, ZnS, and SiO2. These products can be mass produced up to a capacity of 40 liters/day. To date, these products have been used in the production of luminescent equipment of UV filters, several examples of which will be indicated in the following:
Plasmon plays a significant role in the optical properties of metals. Light is reflected with frequencies below plasma frequency, because metal electrons block the electric field of light. Light passes with frequencies higher than that of plasma, because the electrons cannot be fast enough to
fend off light like the electric field shield. Most of the metals, whose plasma frequency is in the ultraviolet range, are shiny (reflective) in the visible range. In fact, with excitation with UV radiation at this stage, a cloud of electrons frequently absorb and lose certain amounts of energy.
In this synthesized amount, the electromagnetic field has been locally compressed and improved.
The slight changes in the dielectric around the nanoparticles influences surface plasmon resonance so that these changes show in the amount of absorbed and scattered radiation and also variation in its wavelength. These variations can be measured using optical properties.
These quantum dots are composed of two base metals; due to their toxic properties and instability, a neutral ceramic core-shell needs to be created around it. Our group has been very successful in the synthesis of these quantum dots with high optical efficiency. In the synthesis of the CdSe sample, an extensive range of of synthesis parameters, such as temperature, time, type of regenerative and ceramic core-shell have been studied. A wide range of different emissions from the blue range to the red range have been obtained from this sample. The need for repeatability, and maintaining optical efficiency in mass production are among the advantages of synthesis with our method.
Maximum efficiency in the luminescence phenomenon in the core-shell quantum dots system is dependent on the thickness of the shell and layers of fewer than two atomic layers have desirable properties in CdS and CdSe in core-shell nanoparticles. Thicker shells lead to the formation of heterogeneous dislocations which result in recombination locations of radiation and consequently reduction in the optical performance of quantum dots. Generally, shell with larger energy gap to create a potential emission around the quantum dot core is related to limited excitons. This is schematically shown in the following figure. Entrapment charge carriers in the core area by the bond’s compensatory potential is effective and constant luminescence is achieved in quantum dots.
In order to have the best inactive shell, it is necessary to transfer materials with lattice parameter of 12% compared to the core in order to minimizing lattice strain and also reduce the thickness in order to have a good intersection. Core and shell quantum dots such as CdSe/ZnSe with a larger band gap for the core show interesting electroluminescence properties. Whether these semiconductors are of the first or second type depends on the thickness of the shell and core.
To date, this group has used quantum dots to create different items.
- Producing filters to absorb harmful UV light in LED and low consumption lamps to prevent skin cancer
This filter has been produced by stabilizing quantum dots in organic polymers; after being excited with UV radiation, the radiation is absorbed and we witness a different emission from this
- Producing luminescent composites using carbon nanotubes and quantum dots These composites are used to build sensors and electric supercapacitors. This collection can cover these composites using the electrophoretic deposition (EPD). This procedure can be used for the isolation of DNA from base solutions and connecting them to carbon nanotubes and quantum dots. Our group can synthesize quantum dots and connect them with carbon nanotubes. Moreover, quantum dots can be used for making DNA luminescent.
In this regard, biological modifiers can also be used.
- Producing CdTe quantum dots with different cores shells for the purpose of functionalization with biological and pharmaceutical compounds such as Curcumine and chitosan antihistamines for tissue identification applications. In order to connect biomolecules to luminescent quantum dots, a wide range of agents containing silane and amine and also biological compounds such as antihistamines and Curcumine can be used. These materials are used for staining and specifying cancer tissue cells and color imaging under UV excitation with fixed wavelength. In this regards, our researchers has managed to use these quantum dots to identify cancer cells.
- Labeling bioceramic materials with CdSe quantum dots.
In this case, the research group managed to label biological compounds such as SiO2 and forsterite (Mg2SiO4) by CdSe quantum dots via changing the surface charge of nanoparticles. This changes the emissions of these compounds so that they can be used for marking living tissues. On this basis, using a simple synthesis without creating a controlled atmosphere, this group has managed to deposit quantum dots on the substrate of bioceramic materials for the first time and in some cases, improve optical efficiency in these samples. These composites has been used in the treatment of industrial wastewater. In addition, it is also possible to deposit these materials using the electrophoretic process. One of the advantages of this synthesis is not controlling the atmosphere during the synthesis.
By creating shells of luminescent quantum dots on biomaterials, the absorption of these substances on bone tissues can be ensured. For example, in new research by our researchers, luminescent forsterite is used on porous substrates which can be deposite on bone tissues.
The second category of quantum dots produced in this collection can be divided into two oxide and sulphide categories. In this category, two important samples including zinc oxide and its sulfide have been taken into consideration and work on the synthesis of the quantum dots of CaO has been recently finished successfully. This category of materials with different antibodies and keys to enter the cell walls have been functionalized. Recent research has used them to eliminate breast cancer cells. Additionally, using polymer surface modifiers, ZnS:Cu quantum dots with green colored emissions and biologic properties have been synthesized for the first time. Our researchers have managed to synthesize zinc oxide quantum dots in antibacterial substrates. In the synthesis of quantum dots, zinc oxide has created a wide range of colors with different surface modifiers.
These quantum dots are also easily done on Graphene substrate using simple synthesis methods which has lead to the creation of special medical applications and anti-corrosion properties in this composite.
Synthesis of zinc sulfide quantum dots is one of the main achievements of the group. Using appropriate surface modifiers, the group has managed to dope manganese, copper and silver ions in the structure of zinc oxide quantum dots. This doping both changed the luminescence emission positions and created antibacterial properties in them.
All of the samples have been synthesized using nitrate sources with the same volume ratio of modifier and this makes comparison possible. In all samples, the peaks of the 480 nm range are due to the emission of zinc sulfide quantum dots. The strongest intensity belongs to the sample modified wtih PVP. Zn ions are normally absorbed by the negative pole in PVP. Zinc sulfide synthesized with copper and manganese dopents are other cases of synthesis by our group. Synthesis of zinc sulfide with copper dopent was done by our researchers for the first time and yielded a desirable efficiency. Manganese-doped zinc sulfide quantum dots are another product of this group. With increased amount of manganese dopent, the optical efficiency of these samples increased. Due to its biocompatibility, this sample can enter cancer cells.
The advantages of produced quantum dots:
- Synthesis of quantum dots on biological and magnetic nanoparticles such as iron oxide and SiO2
- Possibility of industrial scale production
- Appropriate production cost
- No sedimentation of particles in the long run
- Possibility of creating different CoreShells on quantum dots
- Possibility of absorbing polymer and biological modifiers on the surface of particles
- Labeling nanoparticles using quantum dots
- Production of copper and silver sulfide quantum dots for the first time
- Possibility of producing quantum dots on different substrates without the need for controlled atmospheres such as nitrogen
- Creation of antibacterial properties and penetration into live cells for these quantum dots.