Spray Coated Colloidal Quantum Dot Films for Broadband Photodetectors

Biofabrication of carbon quantum dots and their food packaging applications: a review

Carbon quantum dots (CQDs) are an emerging class of novel carbon nanomaterials (< 10 nm). These zero-dimensional CQDs have recently invoked significant interest due to their high fluorescence ability, strong electronic conductivity, biocompatibility, excellent chemical stability, non-toxicity, and environmental safety. Bio-fabrication of CQDs from organic resources remains attractive owing to their excellent functional properties. An emerging class of CQDs is fabricated by various conventional methods. However, these methods need many chemical agents and instrument facilities. Bio-fabrication of CQDs has a lot of benefits because of its simple fabrication and eco-friendly. Therefore, the green synthesized CQDs are considered optimistic candidates for developing novel functional materials for food packaging applications. Thus, it is important to investigate the latest update on green-based CQDs for food packaging applications. This current review paper discusses the physicochemical properties of CQDs, the bio-fabrication of CQDs, and the fluorescent properties of CQDs along with their food packaging applications.

Measuring the carrier diffusion length in quantum dot films using graphene as photocarrier density probe

The diffusion length of quantum dot (QD) films is a critical parameter to improve the performance of QD-based optoelectronic devices. The dot-to-dot hopping transport mechanism results in shorter diffusion lengths compared to bulk solids. Herein, we present an experimental method to measure the diffusion length in PbS QD films using single layer graphene as a charge collector to monitor the density of photogenerated carriers. By producing devices with different thicknesses, we can construct light absorption and photocarrier density profiles, allowing extracting light penetration depths and carrier diffusion lengths for electrons and holes. We realized devices with small (size: ∼2.5 nm) and large (size: ∼4.8 nm) QDs, and use λ = 532 nm and λ = 635 nm wavelength illumination. For small QDs, we obtain diffusion lengths of 180 nm for holes and 500 nm for electrons. For large QDs, we obtain diffusion lengths of 120 nm for holes and 150 nm for electrons. Our results show that films made of small QD films have longer diffusion lengths for holes and electrons. We also observe that wavelength illumination may have a small effect, with electrons showing a diffusion length of 500 and 420 nm under λ = 532 nm and λ = 635 nm illumination, respectively, which may be due to increased interactions between photocarriers for longer wavelengths with deeper penetration depths. Our results demonstrate an effective technique to calculate diffusion lengths of photogenerated electrons and holes and indicate that not only QD size but also wavelength illumination can play important roles in the diffusion and electrical transport of photocarriers in QD films.