Properties, Applications and Safety of Quantum Dots

By AZoNano

Table of Contents

Introduction - Zero-Dimensional Materials
Quantum Dots
Applications of Quantum Dots
Risk Assessment of Quantum Dots
Products from EMFUTUR Technologies
About EMFUTUR Technologies

Introduction - Zero-Dimensional Materials

In the large nanomaterials family, zero-dimensional (0D) materials are key building blocks of exotic artificial materials that have significant technological impact on a myriad of applications. 0D materials are ultra-small particles with size in nanoscale in all three space directions. Atom clusters and group of atomic clusters are examples of 0D nanostructures.

Materials demonstrate totally different properties at their nanoscale when compared to bulk form. At nanoscale, quantum effects govern the properties and behavior of particles. Hence, properties of materials rely on their size in this scale range. At nanoscale, material properties such as chemical reactivity, magnetic permeability, electrical conductivity, fluorescence, melting point vary as a function of the size of the particle.

Quantum Dots

Quantum dots are 0D materials that confine charge carriers in three dimensions. The confinement of charge carriers is a quantum phenomenon. The density of states for the confined particles is totally different from the density of states for particles in a larger part of the material. Discrete energy levels exist for an ideal isolated quantum dot corresponding to a delta-shaped density of states devoid of states in between the delta peaks.

This is a characteristic behavior of atoms. Hence, quantum dots can be considered as a type of artificial atoms that can change energy levels depending on their design. This can be done either by controlling the material composition or dimensions of the quantum dots. Actually, large clusters of quantum dots are generally utilized and their size distribution extends density of states distribution, which means inhomogeneous broadening.

Quantum dots can be manufactured from certain semiconductors. They exhibit an extremely narrow emission spectrum, which is directly related to their size. The larger the particle, the more its emission is red shifted, and conversely the smaller the particle size, the more its emission is blue shifted. This means the same material can emit the complete visible light spectra.

Applications of Quantum Dots

Quantum dots have found use in the following applications:

  • Achieving attractive colors in stained glasses is the oldest application
  • Composite applications
  • Production of laser diodes with low temperature sensitivity and/or very low threshold pump power
  • In white light-emitting diodes (LEDs): quantum dots emit green and red light when excited with a blue or near-ultraviolet LED, thus achieving overall a white color tone
  • In semiconductor saturable absorber mirrors (SESAMs)
  • As absorbers with very low saturation fluence
  • It is possible to contain quantum dot absorbers in a glass matrix
  • As single-photon emitters in the perspective of quantum nanophotonics and quantum cryptography
  • As components of solar cells (Gratzel cells) and highly sensitive photodetectors
  • As fluorescent biological labels in the biological field

Risk Assessment of Quantum Dots

The following key points are suggested by present literature:

  • All quantum dots are not same
  • It is not possible to consider engineered quantum dots as a uniform group of substances
  • Quantum Dots’ distribution, absorption, metabolism, excretion, and toxicity vary with environmental conditions and inherent physicochemical properties
  • Quantum dots’ toxicity is influenced by their concentration, charge, size, outer coating bioactivity, and mechanical, photolytic and oxidative stability
  • Although quantum dots are useful in applications such as in vivo biomedical imaging and drug targeting, they may also have negative impact on human health and environment under specific conditions.

Products from EMFUTUR Technologies

EMFUTUR Technologies offers many different quantum dots semiconductor materials such as cadmium telluride (CdTe), zinc cadmium selenide/zinc sulfide (ZnCdSe/ZnS), and cadmium selenide/zinc sulfide (CdSe/ZnS) with well-defined peak emission frequencies encompassing a wavelength range of 440-790 nm.

The following forms of quantum dots are offered by EMFUTUR Technologies:

  • CdTe quantum dots, powder, hydrophilic - CdTe quantum dots exhibit the broadest wavelength emission spectra range between 510 nm and up to 780 nm. It is easy to form colloidal solutions of them in water and terminate them with -COOH group. It is possible to couple -NH2 groups with them through EDC-mediated esterification. They are suitable for biologic labeling purposes.
  • CdSe/ZnS (core/shell) quantum dots, powder, hydrophobic - CdSe/ZnS quantum dots are core-shell structured inorganic nanocrystals wherein an outer core of wider band gap ZnS encapsulates an inner core of CdSe. They are highly luminescent semiconductor nanocrystals coated with hydrophobic organic molecules. They are insoluble in ethers, alcohols and water, but soluble in pyridine, tetrahydrofuran, chloroform, toluene, heptanes, and hexane. The wavelength emission spectra range between 530 and 650 nm.
  • ZnCdSe/ZnS (core/shell) quantum dots, powder, hydrophobic - ZnCdSe/ZnS quantum dots have the smallest available average particle size. Thus, they can emit the bluest to white light, making them suitable for use in solid state luminescent devices. Wavelengths range from 440 to 480 nm. They are highly luminescent semiconductor nanocrystals coated with hydrophobic organic molecules. They are soluble in pyridine, tetrahydrofuran, chloroform, toluene, heptanes, and hexane, but insoluble in ethers, alcohols and water.

About EMFUTUR Technologies

EMFUTUR Technologies is a high quality Nanomaterials supplier, offering nanoparticles, nanopowders, micron powders, and CNTs (carbon nanotubes) in small quantity for researchers and in bulk order for industry groups.

EMFUTUR Technologies product quality emphases the significance of purest Nanomaterials with uniform composition free of impurities for advanced research and production purposes.

With a portfolio of products targeting the needs of almost all Nanotechnology work groups, we help our customers by delivering best products with the assurance of quality.

This information has been sourced, reviewed and adapted from materials provided by EMFUTUR Technologies.

For more information on this source, please visit EMFUTUR Technologies.

Date Added: Apr 16, 2013 | Updated: Jun 11, 2013
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