No abstract

We prepare InGaN/GaN multiple quantum well (MQW) structure by metal-organic vapour phase epitaxy and characterize it by fine XRD measurements. We demonstrate its suitability for scintillator application including a unique measurement of wavelength-resolved scintillation response under nanosecond pulse soft x-ray source in extended dynamical and time scales. The photoluminescence and radioluminescence were measured: we have shown that the ratio of the intensity of quantum well (QW) exciton luminescence to the intensity of the yellow luminescence (YL) band IQW/IYL depends strongly on the type and intensity of excitation. Slower scintillation decay measured at YL band maximum confirmed the presence of several radiative recombination centres responsible for wide YL band, which also partially overlap with the QW peak. Further improvements of the structure are suggested, but even the presently reported decay characteristics of the excitonic emission in MQW are better compared to the currently widely used single crystal YAP:Ce or YAG:Ce scintillators. Thus, such a type of a semiconductor scintillator is highly promising for fast detection of soft x-ray and related beam diagnostics.

Energetic ions represent an important tool for the creation of controlled structural defects in solid nanomaterials. However, the current preparative irradiation techniques in accelerators show significant limitations in scaling-up, because only very thin layers of nanoparticles can be efficiently and homogeneously irradiated. Here, we show an easily scalable method for rapid irradiation of nanomaterials by light ions formed homogeneously in situ by a nuclear reaction. The target nanoparticles are embedded in B2O3 and placed in a neutron flux. Neutrons captured by 10B generate an isotropic flux of energetic α particles and 7Li+ ions that uniformly irradiates the surrounding nanoparticles. We produced 70 g of fluorescent nanodiamonds in an approximately 30-minute irradiation session, as well as fluorescent silicon carbide nanoparticles. Our method thus increased current preparative yields by a factor of 102–103. We envision that our technique will increase the production of ion-irradiated nanoparticles, facilitating their use in various applications.

Six Mg co-doped Lu 3 Al 5 O 12 :Ce scintillating films were prepared by a liquid phase epitaxy method, having Mg concentration of 0−3000 ppm. The following luminescence and scintillation characteristics and their dependence on Mg concentration were studied: photoluminescence emission and excitation spectra, radioluminescence spectra, photoluminescence and scintillation decay curves, light yield, energy resolution, and afterglow. Light yield increases with Mg concentration until 700 ppm and becomes 15−20% higher than in the Mg-free sample. Further increase of Mg concentration leads to light yield decrease. Scintillation decay is getting faster with an increasing Mg concentration and the afterglow is significantly reduced. The results are compared to ceramics and crystals of very similar compositions.

No abstract

LiCaAlF6-based scintillators are studied under X- and soft gamma-ray excitations. Under nanosecond pulsed soft X-ray laser excitation the scintillation decay is measured with extremely high dynamical resolution and broad time scale. The undoped LiCaAlF6 shows complex temperature dependence of exciton luminescence and tunneling-driven energy transfer process in scintillation decay. In both the Ce and Eu-doped LiCaAlF6 the dominant part of measured scintillation decay is due to prompt recombination of electrons and holes at the doped emission centers. Nevertheless, the measured light yield value is considerably lower with respect to the derived upper limits. Possible origin of its deterioration is discussed.

The compositional dependence of luminescence properties and scintillation response were investigated in Ce3+-doped Y2Gd1Al5-xGaxO12 (x = 2, 3, 4) single crystals. The Gd3+ → Ce3+ energy transfer was evidenced by photoluminescence excitation spectra of Ce3+ emission. With increasing Ga content in the garnet host, the Ce3+ luminescence from the lowest 5d level (5d1) is shifted toward higher energy due to the decrease in the crystal field splitting of the 5d levels. Light yield (LY) and its dependence on the amplifier shaping time were measured under excitation with γ-rays. High LY value of ∼38 000 ph/MeV was obtained for a Y2Gd1Al3Ga2O12:Ce sample. Scintillation decay was measured with an extended dynamical and temporal scale under the nanosecond pulse soft X-ray excitation. The decrease of both LY value and relative contribution of slower decay component in the scintillation response was observed with increasing Ga content in the garnet host.

No abstract