Buying Guide: How to Choose Quantum Dots for Your Research

Here are a few things to consider when choosing quantum dots for your research:

What is your target emission or absorption peak? The range of emission and absorption peaks varies between different quantum dot formulations. For example, the range of emission and absorption peaks for our high efficiency cadmium sulfide zinc selenide (CdSe/ZnS) quantum dots fall within the visible light region of the electromagnetic spectrum while the range of emission and absorption peaks for our lead sulfide (PbS) quantum dots falls within the near infrared (near-IR) region.

Is cadmium (Cd) content a concern for your application? Cadmium-based quantum dots exhibit high quantum yield, narrow emission spectra, and excellent stability. For example, our high efficiency CdSe/ZnS (HECZ) quantum dots feature quantum yields greater than 70% and narrow FWHM between 20 to 30 nanometers as well as exceptional color purity and stability. However, the potential cytotoxicity of cadmium renders Cd-based quantum dots unsuitable for certain applications, particularly in biological research. Additionally, if your application must comply with cadmium-related environmental regulations, Cd-based quantum dots may or may not be suitable depending on the required concentration. Cadmium-free quantum dots such as InP/ZnS QDs or CuInS2/ZnS QDs are a lower toxicity alternative to Cd-based quantum dots that exhibit comparable optical and physical properties. Cd-free quantum dots are well-suited for research and applications requiring low toxicity or requiring compliance with cadmium-related environmental regulations.

Do you need organic-soluble or water-soluble quantum dots? Organic-soluble quantum dots are coated with hydrophobic ligands and dispersed in organic solvents such as toluene or octane while water-soluble quantum dots are coated with hydrophilic ligands and dispersed in deionized water. Many of our quantum dots are available in both organic-soluble and water-soluble forms. For example, our high efficiency CdSe/ZnS quantum dots are available in organic solvent with oleic acid ligands (HECZ) or in deionized water with carboxylic acid ligands (HECZW).

Do you need a specific type of quantum dot structure? Differences in the structure of core, core-shell, and type-II quantum dots bring about different physical and optical properties. Core quantum dots such as CdSe QDs are comprised of a single semiconductor crystal while core-shell quantum dots such as CdSe/ZnS QDs are comprised of a single semiconductor crystal encapsulated by a semiconductor shell. In the case of CdSe/ZnS QDs, there is a cadmium selenide core encapsulated by a zinc sulfide shell. The shell stabilizes the core and protects it from potentially damaging environment while reducing surface trap states. The addition of the ZnS shell significantly improves quantum yields, from greater than 30% for our CdSe QDs (CSE) to greater than 70% for our high efficiency CdSe/ZnS QDs (HECZ). Type-II quantum dots are also made up of a core and shell but with a staggered band alignment which separates the charge carriers, which is particularly useful for photovoltaic applications.

If you are looking to purchase quantum dots or nanoparticles for your research, check out our products here or contact us at contact@nn-labs.com for custom orders.