Infrared Quantum Dots


  • The author acknowledges the contributions of Ahmed Maria, Ethan Klem, Fred Chang, Gerasimos Konstantatos, Ian Howard, Joe Salfi, Larissa Levina, Paul Cyr, Sam Cauchi, Scott Kuntze, Shiguo Zhang, Sjoerd Hoogland, Steve McDonald, and Vlad Sukhovatkin. Research presented herein was supported by Nortel Networks; the Ontario Centres of Excellence through Materials and Manufacturing Ontario, Photonics Research Ontario, Communications and Information Technology Ontario; the Ontario Research and Development Challenge Fund and the Ontario Innovation Trust; the Natural Sciences and Engineering Research Council of Canada through its Discovery Grant program, Collaborative Research and Development program, and Nano Innovation Platform; the Canada Foundation for Innovation; and the Canada Research Chairs Programme.


Colloidal nanocrystals are quantum-size-effect tunable; offer an abundance of available surface area for electronic and chemical interactions; and are processible from organic or aqueous solution onto substrates rigid or flexible, smooth or rough, flat or curved, inorganic or organic (including biological), crystalline or amorphous, conducting, semiconducting, or insulating. With the benefit of over a decade's progress in visible-light-emitting colloidal-quantum-dot synthesis, physical chemistry, and devices, significant progress has recently been made in infrared-active colloidal quantum dots and devices. This progress report summarizes the state-of-the-art in infrared colloidal quantum dots, with an emphasis on applications and devices. The applications of interest surveyed include monolithic integration of fiber-optic and free-space-communications photonic components with electronic substrates such as silicon and glass; in-vivo biological tagging in infrared spectral bands in which living tissue is optically penetrable to a depth of 5–10 cm; solar and thermal photovoltaics for energy conversion; and infrared sensing and imaging based on non-visible, including thermal, signatures. The synthesis and properties of quantum dots are first reviewed: photoluminescence quantum efficiencies greater than 50 % are achievable in solution, and stable luminescent dots are available in organic and aqueous solvents. Electroluminescent devices based on solution processing have been reported with external quantum efficiencies approaching 1 %. Photoconductive devices have been realized with 3 % internal quantum efficiencies, and a photovoltaic effect was recently observed. Electro-optic modulation achieved by either field- or charge-induced modification of the rate of optical absorption has been demonstrated based both on interband and intersubband (intraband) transitions. Optical gain from these processible materials with a threshold of 1 mJ cm–2 and an optical net modal gain coefficient of 260 ± 20 cm–1 have been reported.