The development of modern cutting-edge technology relies heavily on the huge success and advancement of nanotechnology, in which nanomaterials and nanostructures provide the indispensable material cornerstone. Owing to their nanoscale dimensions with possible quantum limit, nanomaterials and nanostructures possess a high surface-to-volume ratio, rich surface/interface effects, and distinct physical and chemical properties compared with their bulk counterparts, leading to the remarkably expanded horizons of their applications. Depending on their degree of spatial quantization, low-dimensional nanomaterials are generally categorized into nanoparticles (0D); nanorods, nanowires, and nanobelts (1D); and atomically thin layered materials (2D). This review article provides a comprehensive guide to low-dimensional nanomaterials and nanostructures. It begins with the classification of nanomaterials, followed by an inclusive account of nanofabrication and characterization. Both top-down and bottom-up fabrication approaches are discussed in detail. Next, various significant applications of low-dimensional nanomaterials are discussed, such as photonics, sensors, catalysis, energy storage, diverse coatings, and various bioapplications. This article would serve as a quick and facile guide for scientists and engineers working in the field of nanotechnology and nanomaterials.

We present studies of the compositional dependence of the optical properties of ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}\text{(0<x<0.22)}$ alloys by modulation spectroscopy and photoluminescence. The yellow luminescence, which is well known in GaN and is generally assigned to shallow donor–deep acceptor pair recombination has also been observed in ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}.$ As aluminum concentration increases, the color of the band changes from yellow (2.2 eV) to blue (2.6 eV). The shift was less than that of the band gap. Together with previously published studies, it implies that the deep acceptor level is pinned to a common reference level to both materials, thus the deep level responsible for the yellow emission is used as a common reference level to determine the band alignment in ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N/GaN}$ heterojunctions. Combining with the near-band-edge modulation spectra, the estimated ratio of conduction-to-valence band discontinuity is 65:35. Our results are close to the values obtained from PL measurements on ${\mathrm{Al}}_{\mathrm{0.14}}{\mathrm{Ga}}_{\mathrm{0.86}}\mathrm{N/GaN}$ quantum wells and those calculated by linear muffin-tin orbital method and linearized augmented plane wave method.

Vertically aligned ZnO nanorods (NRs) on aluminum-doped zinc oxide (AZO) substrates were fabricated by a single-step aqueous solution method at low temperature. In order to optimize optical quality, the effects of annealing on optical and structural properties were investigated by scanning electron microscopy, X-ray diffraction, photoluminescence (PL), and Raman spectroscopy. We found that the annealing temperature strongly affects both the near-band-edge (NBE) and visible (defect-related) emissions. The best characteristics have been obtained by employing annealing at 400°C in air for 2 h, bringing about a sharp and intense NBE emission. The defect-related recombinations were also suppressed effectively. However, the enhancement decreases with higher annealing temperature and prolonged annealing. PL study indicates that the NBE emission is dominated by radiative recombination associated with hydrogen donors. Thus, the enhancement of NBE is due to the activation of radiative recombinations associated with hydrogen donors. On the other hand, the reduction of visible emission is mainly attributed to the annihilation of OH groups. Our results provide insight to comprehend annealing effects and an effective way to improve optical properties of low-temperature-grown ZnO NRs for future facile device applications.