Ultraviolet Luminescence of ZnO Whiskers, Nanowalls, Multipods, and Ceramics as Potential Materials for Fast Scintillators

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.

Localized UV emitters on the surface of β-Ga2O3

Monoclinic gallium oxide (β-Ga2O3) is attracting intense focus as a material for power electronics, thanks to its ultra-wide bandgap (4.5–4.8 eV) and ability to be easily doped n-type. Because the holes self-trap, the band-edge luminescence is weak; hence, β-Ga2O3 has not been regarded as a promising material for light emission. In this work, optical and structural imaging methods revealed the presence of localized surface defects that emit in the near-UV (3.27 eV, 380 nm) when excited by sub-bandgap light. The PL emission of these centers is extremely bright—50 times brighter than that of single-crystal ZnO, a direct-gap semiconductor that has been touted as an active material for UV devices.

Рентгенолюминесценция тетраподов ZnO, выращенных в присутствии примеси Сu и Au в исходной шихте

The morphology and luminescent properties of ZnO tetrapod powders with Cu and Au impurities obtained by pyrolytic carbothermal synthesis were studied. The X-ray luminescence spectrum of the samples is dominated by a broad band in the range from 450 to 650 nm. A weak band-edge luminescence band with a maximum at 391 nm is also registered. Measurements of the decay kinetics showed the presence of both fast (~ 1 ns) and slow (~ 850 ns) luminescence components, where the fast one generally did not exceed 1% of the integrated intensity. It is shown that with the used doping method, the incorporation of Cu and Au impurities into the ZnO lattice does not occur. In this case, the presence of Cu with a concentration of up to 9% does not affect the morphology and luminescent properties of tetrapods, while Au has an effect even at a concentration close to 1%.