Green-Lighting the Sub-Band Gap Excitation in Two-Dimensional Zinc Oxide

Abstract

Solar spectrum and sensitivity of human eyes peak at green wavelength range of visible light, and the materials that can respond to a larger part of the visible spectrum are highly sought after. Two-dimensional graphene-like zinc oxide (gZnO) is a wide band gap semiconductor, but photogeneration of electron–hole pairs in it at visible wavelengths has not been achieved so far. Here, the sub-band gap excitation in 2D zinc oxide layers covered with gold nanoparticles is reported. The sub-band gap excitation and corresponding emission are correlated with oxygen interstitials introduced by AuNP deposition in the gZnO lattice. Attachment of AuNPs on gZnO also leads to increased electron availability at oxygen sites of the gZnO lattice, which translates into greater electron availability for sub-band gap excitation. The plasmonically enhanced trap level to conduction band transition constitutes sub-band gap excitation and manifests itself in local surface potential measurements carried out using a Kelvin probe force microscope.

Transiently controlled emission from ZnO surface

“…The transient control of the PL in ZnO was achieved by utilizing a second excitation source at 3.08 eV. Also, we observe a significant emission for the below band gap excitation at 532 nm in stark contrast to the literature [8,9,19,20]. It notable that ZnO and graphene oxide quantum dots have depicted excitation wavelength independent (280-430 nm) blue emission [19].…”

Ultrafast Infrared-to-Visible Photon Upconversion on Plasmon/TiO2 Solid Films

“…The proposed mechanisms are purely photonic, where the plasmonic gold nanoparticles enhance the optical absorption of the TiO 2 transitions. , This is distinct from the upconversion process via triplet–triplet annihilation in molecules and lanthanide emission through energy migration in hybrid materials. The most phenomenologically relatable system is the two-level single organolead halide perovskite nanocrystal in a resonance-adjustable plasmonic nanocavity reported by Lu et al Their upconversion plasmonic nanolaser system utilizes a near-infrared pump laser that excites electron–hole pairs in the perovskite nanocrystal through two-photon absorption.…”