Semiconductor nanocrystals possessing broadly size‐ and facet‐dependent optical properties

Abstract

Cu2O cubes, octahedra, and rhombic dodecahedra have been shown to exhibit continuous light absorption and emission band shifts with increasing particle sizes from 10 nm to sub‐microcrystals. They also possess clear facet‐dependent optical properties. Ag3PO4, Ag2O, SrTiO3, and CeO2 crystals show similar optical size and facet effects. Thus, spectral shifts over a broad size range far beyond the quantum‐size regime should be generally observable in many semiconductor materials. Facet‐dependent optical properties of a semiconductor can be understood to arise from the presence of an ultrathin surface layer with subtle bond and orbital level variations for different crystal faces. Although these optical features seem unexpected, they should be the general behaviors of semiconductor crystals. As more examples of these optical effects are available, we will find that these intrinsic properties of semiconductors have been ignored in the past. Furthermore, if valence and conduction band positions are broadly tunable by particle size, the knowledge should have tremendous impacts on the applications of semiconductors, where band energies are important to efficient interfacial charge transfer.

Current Rectification and Photo-Responsive Current Achieved through Interfacial Facet Control of Cu2O–Si Wafer Heterojunctions

“…Figure S3 offers diffuse reflectance spectra of the prepared Cu 2 O crystals and the corresponding Tauc plot for band gap determination. The synthesized Cu 2 O cubes, octahedra, and rhombic dodecahedra have band gaps of 1.61, 2.17, and 1.84 eV, respectively, showing again that band gap values are still tunable for very large Cu 2 O crystals, and light absorption by semiconductors includes both bulk and surface components . Using the band gap values and ultraviolet photoelectron spectroscopy (UPS) results previously obtained for Cu 2 O crystals synthesized by the same method for energies of valence band maximum (VBM), Fermi level, and work function, the band diagrams of the prepared Cu 2 O cubes, octahedra, and rhombic dodecahedra are presented in Figure S4 .…”

“…The synthesized Cu 2 O cubes, octahedra, and rhombic dodecahedra have band gaps of 1.61, 2.17, and 1.84 eV, respectively, showing again that band gap values are still tunable for very large Cu 2 O crystals, and light absorption by semiconductors includes both bulk and surface components. 34 Using the band gap values and ultraviolet photoelectron spectroscopy (UPS) results previously obtained for Cu 2 O crystals synthesized by the same method for energies of valence band maximum (VBM), Fermi level, and work function, the band diagrams of the prepared Cu 2 O cubes, octahedra, and rhombic dodecahedra are presented in Figure S4. 20 When the vacuum level is equalized, there are just small valence band energy differences among the three particle shapes and a small energy difference in the conduction band between octahedra and rhombic dodecahedra.…”

Size‐dependent Auger recombination in CdSe quantum dots studied by transient absorption spectroscopy

“…[ 9–15 ] Besides, AR is considered to be a prevailing reason for the efficiency droop effect of QD LEDs, especially at a high current density when the nonradiative recombination of electrically excited excitons occur more easily. [ 16–19 ] Also in the photocatalytic system, AR intrinsically prevents efficient charge extraction. [ 20–23 ] For multiexciton generation breaking the Shockley–Queisser limit, which is significant for efficiency improvement in solar energy conversion, the efficiency gains as well reduces due to the AR process.…”

Photocatalytic activity enhancement of Cu2O cubes functionalized with 2-ethynyl-6-methoxynaphthalene through band structure modulation

“…Band gap variation is observable in these samples because band gap value has both size and facet components. 39,40…”