The presented work is dedicated to the study and comparison of scintillating properties of zinc oxide samples prepared in different morphologies: whiskers, nanowalls, multipods, and ceramics. It was shown that total transmittance, photo- and radioluminescence spectra, and radioluminescence kinetics can vary significantly depending on sample structure and preparation conditions. The highest total transmittance was registered for ZnO ceramics (>50% at 0.5 mm thickness). Differences in the transmittance of whiskers, nanowalls, and multipods can be attributed to their shape and thickness which affects the amount of light refraction and scattering. The study of radioluminescence demonstrated that all samples, except undoped ceramics and air annealed whiskers, have predominantly fast luminescence with a decay time <1 ns. High transmittance of ceramics opens the way for their use in the registration of high energy X-ray and gamma radiation, where a large volume of scintillators is required. In cases, where large scintillator thickness is not a necessity, one may prefer to use other ZnO structures, such as ensembles of whiskers and nanowalls. Studies of near-band-edge luminescence components at low temperatures showed that the structure is quite similar in all samples except Ga doped ceramics.

Microrod arrays of zinc oxide with copper have been grown by chemical vapor deposition on single-crystal sapphire substrates preliminarily covered with a nanoscale copper layer. The presence...

Whispering gallery mode (WGM) ZnO microlasers gain attention due to their high Q-factors and ability to provide low-threshold near-UV lasing. However, a detailed understanding of the optical gain mechanisms in such structures has not yet been achieved. In this work, we study the mechanisms of stimulated emission (SE) in hexagonal ZnO microrods, demonstrating high-performance WGM lasing with thresholds down to 10–20 kW/cm² and Q-factors up to ~3500. The observed SE with a maximum in the range of 3.11–3.17 eV at room temperature exhibits a characteristic redshift upon increasing photoexcitation intensity, which is often attributed to direct recombination in the inverted electron-hole plasma (EHP). We show that the main contribution to room-temperature SE in the microrods studied, at least for near-threshold excitation intensities, is made by inelastic exciton-electron scattering rather than EHP. The shape and perfection of crystals play an important role in the excitation of this emission. At lower temperatures, two competing gain mechanisms take place: exciton-electron scattering and two-phonon assisted exciton recombination. The latter forms emission with a maximum in the region near ~3.17 eV at room temperature without a significant spectral shift, which was observed only from weakly faceted ZnO microcrystals in this study.

Lasing in ZnO tetrapods produced by pyrolytic carbothermal synthesis is investigated. Since a tetrapod can have several optical cavities, which complicates analysis, emission from individual tetrapod legs is investigated. It is found that laser lines originate from optical cavities of different types. It is suggested that low-threshold lasing is due to whispering-gallery modes excited in the tips of the tetrapod legs.

The model for estimation of the amplitude modulation depth of photoplethysmographic (PPG) signal based on the modified Beer-Lambert law was developed. It was analytically confirmed that the modulation depth of PPG signal depends on the wavelength and illumination geometry. The modulation depth is directly proportional to the distance between the light source and the detector. The sensitivity of green light (525 nm) to blood volume changes is approximately 6-9 times greater than that for red (640 nm) and IR (805 nm) light. It was found that in case of green light, the main contribution to the modulation of PPG signal is made by absorption coefficient changes while in case of red and IR light, the modulation is mainly caused by scattering coefficient changes.