Blue-shifted and picosecond amplified UV emission from aqueous chemical grown ZnO microrods

Abstract

a b s t r a c tRoom-temperature amplified spontaneous emission (ASE) has been observed from aqueous chemical grown zinc oxide (ZnO) microrods. The well-faceted microrods have only a single narrow ultraviolet (UV) emission at 390 nm (3.2 eV) with average lifetimes as fast as 85-100 ps. The characteristic ASE also exhibits blue-shifted peaks and shortened lifetimes. At present, the peak shifting and the lifetime shortening are attributed to the band filling and photo-induced screening effects and to the nonradiative relaxation process, respectively. Results indicate that the ZnO microrods have good structural and optical quality which leads to their suitable use for optoelectronic applications.

Conformable Nanowire-in-Nanofiber Hybrids for Low-Threshold Optical Gain in the Ultraviolet

“…In particular, the ASE peak is found to correspond to the spectral region of excitonic recombination, while ZnO surface states and defects contributing to the broader spontaneous emission do not appear to undergo SE assisted by waveguiding in the electrospun polymer fibers. We also find a blueshift (9 meV) of the ASE peak energy for very high excitation fluences (from 1.6 up to 2.2 mJ cm –2 ), which is a signature of the increasing screening of the exciton binding energy, as a consequence of the increased density of electron–hole pairs created upon photoexcitation. , Such effect competes with the band gap renormalization that typically red shifts the gain profile as the excitation intensity is increased, as here found for excitation fluences up to 1.6 mJ cm –2 . Correspondingly, the full width at half-maximum (FWHM) of the PL spectrum decreases from 25 nm to about 4 nm (triangles in Figure b) upon increasing the excitation fluence.…”

“…We also find a blueshift (9 meV) of the ASE peak energy for very high excitation densities (from 1.6 up to 2.2 mJ cm -2 ), which is a signature of the increasing screening of the exciton binding energy, as a consequence of the increased density of electron-hole pairs created upon photoexcitation. 54,55 Such effect competes with the band gap renormalization that typically red-shifts the gain profile as the excitation intensity is increased, 54 as here found for excitation Published in ACS Nano, doi: 10.1021/acsnano.0c00870 (2020). 16 fluences up to 1.6 mJ cm -2 .…”

Femtosecond Luminescence Imaging for Single Nanoparticle Characterization

“…The fluence dependence of the luminescence spectra is a clear indication of amplified spontaneous emission. , ASE is the process of amplification of spontaneously emitted photons by stimulated emission as light propagates in a medium. , This type of mirrorless lasing exhibits characteristics between that of a coherent laser and an incoherent light emitting source . These intermediate features are observed in the spectra (Figure d) integrated over the field of view of the microscope containing the single nanowire.…”

“…The dependence of the emission intensity on the fluence is shown Figure d (inset). At fluences above the threshold the emission intensity rises sharply with an increase in excitation fluence, which is indicative of the onset of ASE. , It should be pointed out that the sensitivity of the setup to ultrafast (sub 50 ps) and ultraviolet (360–420 nm) fluorescence precludes the detection of the well-known green emission from ZnO defect states that is commonly observed between 500 and 600 nm in the visible range with photoluminescence lifetime on the nanosecond time scale.…”