Fig. 1. Colloidal quantum dot technology^[4]

Fig. 2. Interband transition infrared detectors based on mercury chalcogenide CQDs by the University of Chicago. (a) Schematic of the device structure^[16]; (b) schematic of the detector structure^[21]; (c) cross-sectional scanning electron microscope of the fabricated detector^[21]; (d) illustration of the structure of a dual-band CQD imaging device, bias voltage is applied between the indium tin oxide (ITO) and the Au contact (grounded)^[22]; (e) spectral response of the dual-band detector under a bias voltage from positive (+500 mV) to negative (-300 mV) voltage at 85 K^[22]

Fig. 3. Interband transition infrared detectors based on mercury chalcogenide CQDs by Beijing Institute of Technology. (a) Schematic of spray-stencil lithography platform^[23]; (b) photograph of CQD films on a 4 inch substrate and a glass hemisphere^[23]; (c) detectivity as a function of wavenumber of detectors fabricated by spray-stencil lithography and drop-coated^[23]; (d) structure diagram of the dual-band device^[24]; (e) energy band structure diagram of the dual-band device^[24]; (f) response spectra of the dual-band device under positive and negative bias^[24]

Fig. 4. Interband transition infrared detectors based on mercury chalcogenide CQDs by Beijing Institute of Technology. (a) Illustration of dual-mode colloidal quantum-dot photodetector (inset: equivalent circuit of dual band infrared photodiode)^[25]; bias-dependent spectral response under (b) positive and (c) negative bias voltages^[25]; (d) cross-sectional scanning electron microscopy image of the dual-band photodetector (scale bar: 1 μm)^[26]; (e) spectral response of the dual-band detector under a positive (+800 mV) and negative (-200 mV) bias voltage at 80 K^[26]; (f) spectral responsivity of the short-wave infrared /mid-wave infrared mode with and without the cavity at 80 K^[26]; (g) schematic diagram of the spectrometer with a homojunction device^[27]; (h) transmission measured by homojunction device and Fourier transform spectrometers^[27]; (i) absorption with different hexane concentrations in the air^[27]

Fig. 5. Intraband transition infrared detectors based on mercury chalcogenide CQDs by representative groups. (a) Doping requirement for intraband conduction^[28]; (b) plot of the ratio of the intraband signal divided by the fitted magnitude of 1 s interband signal for two sizes of nanocrystals ^[31]; (c) Fermi energy with respect to the valence band as a function of the interband gap^[32]; (d) scheme of HgSe QDs capped with POM-SH ligands^[33]; (e) current as a function of decreasing temperature, V_DS = 1 V^[33]; (f) scheme of polarized band structure of a random colloidal quantum dot infrared photodetector consisting of HgSe nanocrystals as absorber material and HgTe nanocrystals as barrier material^[34]; (g) transient reflectivity signal as a function of time for the film made of HgSe (bottom), HgTe (middle), and HgSe/HgTe mixture (top)^[35]

Fig. 6. Intraband transition infrared detectors based on mercury chalcogenide CQDs by Beijing Institute of Technology. (a) Field effect transistor source-drain current for HgSe/Hybrid at 80 K^[36]; (b) field effect transistor mobility of HgSe/hybrid (black) and HgSe/EDT (red) as a function of temperature as well as Marcus theory fitting^[36]; (c) Hall voltage measured at 200 K of (7.5±0.5) nm diameter HgSe/Hybrid QD film with thickness (35±5) nm^[36]; (d) 1Se-1Pe exciton spectra of films of HgSe/EDT with different size distributions^[37]; (e)(f) size distribution effect on 0.25 eV interband and intraband gaps at 80 K^[37]; (g) schematic diagram of the mixed-phase ligand exchange process^[38]; (h) infrared hot images by a HgSe intraband CQD photodetector^[38]; (i) schematic of plasmonic disk arrays on SiO₂ /Si^[39]; (j) spectral responsivity of 4.2 μm samples, 6.4 μm samples, 7.2 μm samples, and 9.0 μm samples^[39]

Fig. 7. HgTe CQDs-based infrared-to-visible upconverters by Beijing Institute of Technology^[49]. (a) Operational mechanism of infrared-to-visible upconverters; (b) architecture schematic of infrared-to-visible upconverter; (c) images of an upconversion device without and with infrared light; (d) comparison between unmatched photodetector with light-emitting diode-coupled and optimally matched photodetector with light-emitting diode -coupled upconverters; (e) relative luminance variation with the dark condition of upconverters varying with infrared power densities at the applied voltage of 16 V; (f) infrared-to-visible upconversion efficiency of upconversion devices varying with infrared power densities

Fig. 8. Study on infrared focal plane array based on mercury chalcogenide CQDs. (a) Diagram of photoconduction in a CQD detector^[50]; (b) map of the dark current for the 320×256 mid-wave infrared CQDs focal plane array^[50]; (c) mid-wave infrared image of a person in a doorway^[50]; (d) scheme of the device that is plugged in the camera based on a film of HgTe CQDs, picture of the short-wave infrared camera with a Computar M1614-SW objective^[52]; (e) visible picture (smartphone camera) of a scene with four vials containing tetrachloroethylene (TCE), toluene, acetone, and water (H₂O), and an ITO covered glass slide and a 2 inch silicon wafer are placed^[52]; (f) same scene as in Fig. (e) taken with the HgTe QD based focal plane array^[52]

Fig. 9. Study on infrared focal plane array based on mercury chalcogenide CQDs^[53]. (a) Illustration of the working process of trapping-mode photodetectors; (b) energy band diagrams of the trapping-mode photodetectors; (c) 8 inch silicon readout integrated circuit wafer and zoomed view of the pixel region; (d) captured short-wave and mid-wave infrared images with CQD imagers

Fig. 10. Study on infrared focal plane array based on mercury chalcogenide CQDs^[54]. (a) Multispectral CQD imagers and periphery circuits; (b) imaging scene: a soldering iron, a silicon wafer, and an ultraviolet lamp; (c) captured ultraviolet, visible, and short-wave infrared images; (d) merged multispectral images with an ultraviolet image as the blue channel, visible light as the grayscale channel, and a short-wave infrared image as the red channel