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For the first time, hafnia (HfO2) nanoparticles have been produced by photochemical synthesis. The photochemical route has been proven to be scalable, affordable, and straightforward to create monoclinic HfO2 nanoparticles with a size of tens of nanometers. The exploitation of this route offers a chance to create large amounts of dense nanoparticles with reduced costs and time of production for future creation of large area composite scintillators for fast timing techniques. Specific annealing treatments from 450 °C to 1000 °C have been targeted to tune the structural and morphological properties and optimize the luminescence of the nanoparticles. Hafnia nanoparticles annealed at low temperature display an amorphous structure. After thermal treatment at 1000 °C, HfO2 nanoparticles crystallize into a monoclinic phase, as evidenced by thermal analyses and X-ray diffraction. Radioluminescence and photoluminescence of HfO2 have been investigated at room temperature and 77 K. The emission band of hafnia covers a range from 300 to 600 nm and it can be attributed to defects within the matrix. In particular, the highest radioluminescence intensity appears in the crystalline sample annealed at 1000 °C, thanks to the higher crystallinity degree and the reduction of non-radiative channels and quenching defects. Photoluminescence and scintillation decay have evidenced the presence of the fast decay in the nanosecond time range. Thus, due to their size, density, and spectroscopic and timing features, monoclinic hafnia nanoparticles obtained by photochemical synthesis are attractive for potential creation of large area scintillating composites. [ABSTRACT FROM AUTHOR]

Cs2HfCl6 (CHC) and Cs2ZrCl6 (CZC) single crystals were grown by a vertical Bridgman method. Luminescence and charge trapping properties were studied in CHC crystals by the correlated measurements of electron paramagnetic resonance (EPR), radioluminescence (RL) and thermally stimulated luminescence (TSL) techniques. CZC crystals were studied by the same set of measurements in order to find correlations between CHC and CZC crystals. EPR spectra measured before and after X-ray irradiation in both CHC and CZC samples were attributed with the typical signals of the Vk(a) hole trapping center (Cl2− pseudomolecular ion), which has recently been reported though the magnitude of the signal was much smaller in the CZC crystal. Besides the Vk(a) signal, another spectrum was observed in both samples; however, its intensity was at a very low level. It has been tentatively ascribed to the complex HCl-related hole trapping center. TSL glow curves measured in both CHC and CZC samples within the 10–500 K temperature range were composed of 6–8 complex peaks. The dominating peak at about 100–120 K originates from the de-trapping of holes at the Vk(a) trapping center. Scintillation characteristics of CHC crystal were studied over the temperature range of 9–295 K. Scintillation decay curves were fitted by three components. The CHC crystal demonstrated a much similar light yield of ca. 20 500 ph per MeV at room temperature and 9 K. The temperature dependence of the scintillation light output exhibits an unusual s-shaped character with the drop at around 100 K that correlates well with the decrease in the Vk(a) EPR signal, evidencing detrapping of holes trapped at the Vk(a) center in the CHC crystal. Therefore, the Vk(a) center was assumed to be the part of Hf3+–Cl2− self-trapped exciton (STE) that participates in the emission above 100 K becoming "frozen" below 100 K. RL and TSL spectra were complex in the CHC sample composed of two and three overlapping bands, respectively. One of the components peaking at 2.65 eV originated from the Zr-related STE. [ABSTRACT FROM AUTHOR]

In this study, we investigate the effects of Ho 3+ codoping on the luminescence and scintillation properties of GGAG:Ce, with a particular focus on timing properties and scintillator efficiency. The research reveals that Ho 3+ codoping and subsequent resonant energy transfer from Ce 3+ to Ho 3+ can significantly reduce the 5d 1 excited state decay time of Ce 3+ and shorten scintillation pulses of GGAG:Ce registered by using photomultipliers, although this reduces scintillator efficiency as well. The study presents a detailed analysis of the loss of scintillator efficiency due to Ho 3+ codoping, identifying the most significant loss pathways and estimating their impact. The findings suggest that Ho 3+ codoping is an effective method for accelerating the scintillation response of GGAG:Ce. Furthermore, the study presents a high level of consistency of the Ce 3+ kinetics with the Inokuti-Hirayama model and with results obtained in the previous studies on similar systems, demonstrating the predictability of the effect of RE 3+ codoping on scintillator properties., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)