Fast d-f emission in Ce, Pr and Nd activated RbCl

In the search for new scintillator materials, Ce³⁺ doped chlorides are a promising class of materials, combining a high efficiency and fast response time. Even shorter response times may be achieved by replacing Ce³⁺ by Pr³⁺ or Nd³⁺ as the lifetime of the d-f emission is substantially shorter for these ions. Here we report on the luminescence properties of Ce³⁺, Pr³⁺ and Nd³⁺ in RbCl and investigate the potential as a scintillator material. Under UV excitation Ce³⁺ shows d-f emission between 325 and 425 nm. The emission originates from multiple (differently charge compensated) Ce³⁺ sites. The luminescence lifetime varies with wavelength and is ∼40 ns for the longer wavelength emission. For RbCl:Pr³⁺ three d-f emission band are observed between 250 and 350 nm which can be assigned to transitions from the lowest energy fd state to different ³H_J (J = 4-6) states within the 4f² configuration of Pr³⁺. The decay time is ∼17 ns. For the Nd³⁺ activated sample a weak emission band around 220 nm is observed only at 8 K which may be due to d-f emission. The very short lifetime (4 ns) is faster than the radiative lifetime, indicating that the d-f emission is quenched by relaxation to lower lying 4f³ states or by the process of photoionization. Under VUV excitation at wavelengths below 175 nm (the bandgap of RbCl) the d-f emission is very weak for Ce³⁺, Pr³⁺ and Nd³⁺ doped RbCl and the emission spectra are dominated by defect related emission. This indicates that energy transfer from the host lattice to the fd states is inefficient which prevents application as a scintillator material.     

HfO2:Eu nanoparticles excited by X-rays and UV-visible radiation used in biological imaging

Europium doped hafnium dioxide nanoparticles were crystallized using biologically friendly microwave hydrothermal method and employed in observation of small rodents tissues.Main solvent in synthesis is water,in consequence nanoparticles are found surrounded by thin hydroxide layer.Size of the nanoparticles is controlled by temperature of calcination.1200℃heating causes drop of luminescence intensity,explained as damage of high symmetry surface emission centers in the nanocrystals.On the other hand,growth of crystallites increases intensity of X-ray and electron beam excited luminescence.This makes them promising activator in photodynamic therapy.     

Sol-gel synthesis and luminescent properties of nanocrystalline YAP:Mn

The work describes results of synthesis of Mn-doped YAP nanocrystalline samples by the sol-gel method and characterization of the material by X-ray powder diffraction, scanning electron microscopy and luminescence techniques. It was revealed that obtained in such a way YAP samples posses rather poor radiation storage properties that is interpreted by the uniform near-equilibrium synthesis conditions that does not allow formation of Y_Al antisite ions required for electrons trapping. On the other hand, the sol-gel method can be suggested as a suitable technique for obtaining of highly stoichiometric and not defected structure material without parasitic charge capturing and recombination processes that is very essential e.g. for scintillator materials.     

Large area microchannel plate detector with amorphous silicon pixel array readout for fast neutron radiography

Fast neutron radiography is a non-destructive testing technique with a variety of industrial applications and the capability for element sensitive imaging for contraband and explosives detection.

Commonly used position sensitive detectors for fast neutron radiography are based on charge coupled devices (CCDs) and scintillators. The limited format of CCDs implies that complex optical systems involving lenses and mirrors are required to indirectly image areas that are larger than 8.6 cm×11.05 cm. The use of optics reduces the light collection efficiency of the imaging system, while the efficiency of hydrogen rich scintillators exploiting the proton recoil reaction is limited by the hydrogen concentration and the magnitude of the neutron scattering cross-section.

The light conversion step inevitably involves a tradeoff in scintillator thickness between light yield and spatial resolution.

The development of large area amorphous silicon (a-Si) panel flat panel photodiode arrays and direct neutron-to-charge converters based on microchannel plates, provide an attractive new form of high resolution, large area, fast neutron imaging detector for the non-destructive imaging of large structures. This paper describes some recent results of both Monte Carlo simulations and measurements for such a detector.     

Silicon photomultipliers characterization for the EMR prototype of the MICE experiment

The SiPMs are excellent candidates for the replacement of PMTs in many experimental situations. In this article we describe the performances of different types of SiPMs from Hamamatsu and FBK-IRST before and after irradiation with photons and neutrons in terms of signal to noise ratio, time resolution and efficiency. The SiPMs are connected to a scintillation tracker/calorimeter, composed of eight layers (4x and 4y) of 10 scintillating bars each and have been tested at the CERN PS T9 beamline. The tracker/calorimeter is a small-size prototype of a bigger detector called EMR (Electron Muon Ranger), a particle identification system developed for the MICE experiment.     

A thermal neutron mini-detector with SiPM and scintillating fibers

We developed and tested a simple prototype of thermal neutron detector suitable for inexpensive deployment in the decommissioning and storage of radioactive waste, as well as for mapping the flux in the out-of-core regions of fission reactors. Though the prototype version we tested provides the neutron rate by subtracting the gamma background measured with a twin detector insensitive to neutrons, a simple geometrical improvement can strongly reduce the gamma contribution.     

Novel methods for measuring afterglow in developmental scintillators for X-ray and neutron detection

In this paper we discuss two novel methods of measuring afterglow in scintillators. One method is designed for X-ray detection and the other for neutron detection applications. In the first method a commercial fan-beam scanner of basic design similar to those seen at airports is used to deliver a typically 12 ms long X-ray pulse to a scintillator by passing the test equipment through the scanner on the conveyor belt. In the second method the thermal neutron beam from a research reactor is incident on the scintillator. The beam is cut-off in about 1 ms using a ¹⁰B impregnated aluminum pneumatic shutter, and the afterglow is recorded on a dual range storage oscilloscope to capture both the steady state intensity and the weak decay. We describe these measurement methods and the results obtained for a range of developmental ceramic and glass scintillators, as well as some standard scintillators such as NaI(Tl), LiI(Eu) and the plastic scintillator NE102A. Preliminary modeling of the afterglow is presented.     

Transparent glass ceramics containing Lu6O5F8:Tb3+ nano‐crystals: Enhanced photoluminescence and X‐ray excited luminescence

The development of scintillators is of fundamental and industrial meaning for their diverse applications. Despite the great advance in scintillating mono‐crystals, challenge remains to search for novel scintillating materials with low cost, large volume, and high efficiency. Here, Tb³⁺‐doped glass ceramics (GC) with crystallized Lu₆O₅F₈ nano‐crystals were prepared and characterized as potential X‐ray scintillators. Their structural, optical, and luminescent properties were explored systematically. After thermal treatment, X‐ray excited luminescence (XEL) intensity from Lu₆O₅F₈:Tb³⁺ GC is greatly increased and the relative intensity is about 64% of commercial BGO scintillator, benefiting from preferential enrichment of Tb³⁺ ions into Lu₆O₅F₈ nano‐crystals with low phonon energy. Moreover, unusual decay behaviors of Tb³⁺ emissions in GC sample are observed and discussed. Our results indicate that rare earth doped GC may offer a novel platform for designing and fabricating new scintillating materials in the future.     

Luminescence characteristics of LuAG:Pr and YAG:Pr single crystalline films

Emission and excitation spectra and luminescence decay kinetics were studied for Pr³⁺-doped Lu₃Al₅O₁₂ and Y₃Al₅O₁₂ single crystalline films (SCF) grown by the liquid phase epitaxy method from a PbO-based flux. The influence of lead-induced centers on their scintillation characteristics was clarified. It was found that the influence of single Pb²⁺-based centers on the characteristics of Pr³⁺ centers due to the Pb²⁺ → Pr³⁺ energy transfer was weak. However, an overlap of the emission spectra of single and dimer lead-induced centers with the emission spectrum of Pr³⁺ ions, and especially a strong overlap of the 4f–5d₁ absorption band of Pr³⁺ ions with the slow emission of localized excitons in the 290 nm band had a considerable influence on the scintillation characteristics of the Pr³⁺-doped SCF.     

Layered Y3Al5O12:Pr/Gd3(Ga,Al)5O12:Ce optical ceramics: Synthesis and photo-physical properties

We report a study of composite scintillating ceramics based on coupled layers of two different garnets, namely Ce-doped gadolinium gallium aluminium (GGAG:Ce) and Pr-doped yttrium aluminium (YAG:Pr), fabricated by hot isostatic pressing. Two samples were prepared, with different GGAG:Ce layer thickness, 120 µm and 690 µm respectively, but with a comparable overall thickness of 1.4 mm. The key finding is that the material architecture strongly determines the scintillation response. The radioluminescence is that expected from the irradiated material when a thick layer of ceramic is exposed to X-rays. Conversely, exposing a thin layer allows a non-null probability —about 0.3% for 120 µm of GGAG— of finding an X-ray photon in the underlying layer, and thus radioluminescence from both materials is recorded. We believe these results can extend the potential of layered optical ceramics for advanced devices, such as energy- and direction-sensitive X-ray detectors.