Quantum Dots and Nanoparticles
Investigation of Nano Materials
Quantum dots (QD) are semiconductor particles with sizes of a few nm. QD emit light of a specific wavelength when a current is applied or exposed to light. The emission wavelength can be tuned by changing either the size, shape, material, or by doping the QDs. Smaller QDs (2–3 nm) emit light at short wavelengths (blue-green spectral region), while larger QDs (5–6 nm) will emit light in the longer wavelengths (orange, red, or IR). Furthermore, it has been shown that their fluorescence lifetime is also tied to particle size. In larger dots, the lifetime is longer due to more closely spaced energy levels in which the electron-hole pair can be trapped.
Nanoparticles (NPs) are also very small structures but larger than QDs, usually ranging from 8 to 100 nanometers. Because of this, NPs exhibit behaviors between those bulk materials and atoms or molecules. NPs often possess unexpected optical properties as their size allows for quantum confinement effects. Additionally, the interfacial layers surrounding NPs play an important role in all of their physical properties. These layers typically consists of ions, inorganic material, or organic molecules.
By controlling their size, shape as well as composition, the absorption properties of NPs can be fine-tuned to fit the needs of photovoltaic or solar thermal applications. QDs are also of great interest for display or lighting applications where their stability and tunable emission properties are very desirable.
Both time-resolved as well as steady-state luminescence spectroscopy are excellent tools for investigating the excited state characteristics and dynamics of both NPs and QDs.
Typical application areas for such materials are:
- Solar cell
- Diode lasers and second-harmonic generation
- Quantum computing
- Medical applications as imaging markers, tumors detection or photodynamic therapy