Beyond the Bandgap Photoluminescence of Colloidal Semiconductor Nanocrystals

Abstract

Intraband transitions of colloidal semiconductor nanocrystals, or the electronic transitions occurring in either the conduction band or valence band, have recently received considerable attention because utilizing the intraband transitions provides new approaches for applications such as photodetectors, imaging, solar cells, lasers, and so on. In the past few years, it has been revealed that observing the intraband transition is not limited for temporal measurement such as ultrafast spectroscopy but available for steady-state measurement even under ambient conditions with the help of self-doped semiconductor nanocrystals. Considering the large absorption coefficient of the steady-state intraband transition comparable to that of the bandgap transition, the use of the intraband transition will be promising for both fundamental and application studies. Here, we summarize the recent progress in studies on intraband photoluminescence of self-doped semiconductor nanocrystals and discuss key questions to be addressed in future research.

Intraband Transitions of Nanocrystals Transforming from Lead Selenide to Self-doped Silver Selenide Quantum Dots by Cation Exchange

“…8 Furthermore, by virtue of manipulating the stoichiometry and surface dipole of the nanocrystals, higher electronic transitions such as intraband transitions are now available for mid-IR infrared optoelectronics. 9,10 The unique character of the selfdoped nanocrystal is the stand-alone intraband transition explicitly separated from the interband transition, allowing one to utilize the target frequency without an additional optical filter.…”

“…Conventionally, the infrared industries have widely used HgCdTe, InSb, and other II–V infrared superlattices as a source of narrow gap semiconductors, made by epitaxial or single-crystal growth methods with high manufacturing costs. , The preceding precursor chemistry has realized the colloidal synthesis of low-dimensional infrared nanocrystals where one can easily tune the optical and electrical properties . Furthermore, by virtue of manipulating the stoichiometry and surface dipole of the nanocrystals, higher electronic transitions such as intraband transitions are now available for mid-IR infrared optoelectronics. , The unique character of the self-doped nanocrystal is the stand-alone intraband transition explicitly separated from the interband transition, allowing one to utilize the target frequency without an additional optical filter.…”

Nanostructured Materials and Architectures for Advanced Optoelectronic Synaptic Devices

“…At the nanoscale, energy bands can be adjusted with size and geometry. Thanks to 3D tunability, 0D materials exhibit many unique electronic and optoelectronic properties, in particular for laser, [222][223][224] photodetectors, [225][226][227][228][229][230][231][232] photonic memories, [233,234] etc. Aside from the tunable bandgap, such materials have a large surface area, making them better suited for efficient light absorption than 1D and 2D nanostructured materials.…”

Toward Bright Mid-Infrared Emitters: Thick-Shell n-Type HgSe/CdS Nanocrystals

“… 4 − 6 Slow intraband relaxation is also required when intraband transitions, typically between the two lowest quantized conduction levels 1S e and 1P e , are utilized directly for light emission and detection such as in infrared optoelectronics. 7 − 12 It is therefore of broad practical importance to understand and control intraband relaxation rates.…”

“…The control of intraband carrier relaxation in semiconductor quantum dots (QDs) is a longstanding topic of interest due to its central role in QD optoelectronic technologies. − In applications utilizing the interband emission of light, such as conventional QD lasers and LEDs, fast intraband relaxation is desired. In contrast, other applications such as solar energy harvesting utilizing hot-carrier extraction and carrier multiplication are significantly aided when intraband relaxation is slow. − Slow intraband relaxation is also required when intraband transitions, typically between the two lowest quantized conduction levels 1S e and 1P e , are utilized directly for light emission and detection such as in infrared optoelectronics. − It is therefore of broad practical importance to understand and control intraband relaxation rates.…”