BaHfO3:Ce sintered ceramic scintillators

Raw powders of BaHfO₃:Ce were prepared with modified Pechini process and were calcined in the 650–1700 °C range of temperatures, at different atmospheres – air, vacuum and nitrogen–hydrogen mixture. The powders were converted into sintered ceramics by vacuum sintering. The materials were characterized by XRD, TEM, photoluminescence and radioluminescence spectroscopy. UV-VUV excitation spectra were recorded using synchrotron radiation. Excitation spectra proved that atmosphere of preparation significantly influences the host-to-activator energy transfer, which is the most efficient for materials made in reducing conditions. Also radioluminescence efficacy was found to be superior for materials prepared in such conditions.     

Neutron detection with LiCaAlF6 scintillator doped with 3d-transition metal ions

Capability of thermal neutron detection was examined for LiCaAlF₆ (LiCAF) scintillators doped with 3d-transition metal ions. Their radioluminescence spectra were measured with an 241-Am source to simulate ⁶Li(n, α)³H reaction. The sufficiently intense radioluminescence was observed for the Mn, Co and Cu dopants, while only a weak one was observed for Ti, V, Fe and Ni. A Mn doped LiCAF crystal, which showed the highest radioluminescence intensity, was coupled with a Si avalanche photodiode for the examination of its neutron response. It was confirmed that the average current of the photodiode clearly increased under excitation with 13.5 meV neutron flux.     

Optical and scintillation properties of Sr3BGa3Si2O14 (B = Nb,Ta) single crystals

Optical and scintillation properties of Sr₃NbGa₃Si₂O₁₄ [SNGS] and Sr₃TaGa₃Si₂O₁₄ [STGS] single crystals with the langasite-type crystal structure were investigated as a novel scintillator materials. In the transmittance spectra of the SNGS and STGS polished specimens, absorption peaks around 380 and 505 nm were observed and the absorptions are considered to be attributable to the excess oxygen in the crystals. An emission peak around 420 nm was observed in the X-ray radioluminescence spectrum of the SNGS crystal. On the other hand, there was an emission peak around 335 nm in the X-ray radioluminescence spectrum of the STGS crystal.     

Characterisation of a real-time fibre-coupled beryllium oxide (BeO) luminescence dosimeter in X-ray beams

For the first time the feasibility of using beryllium oxide (BeO) ceramics as a fibre-coupled radioluminescent dosimeter is investigated. BeO ceramic exhibits both radioluminescence (RL) and optically stimulated luminescence (OSL), and has the potential to be a near tissue equivalent alternative to Al₂O₃:C. A BeO fibre-coupled radioluminescence dosimeter is demonstrated and characterised for 6 MV X-rays and superficial X-ray energies, 150 kVp and 120 kVp. Based on the results, we demonstrate the capability of the RL BeO FOD for accurate and reproducible dose measurements with a linear dose rate and dose response. It has also been found that the percentage depth dose curves for 6 MV agreed with ion chamber measurements to within 2%, except in the build up region. For the 150 kVp and 120 kVp photon beams, the depth dose measurements agreed with ion chamber measurements to within 2.5% and 4%, respectively.     

Recombination luminescence in lead tungstate scintillating crystals

Room temperature radioluminescence and photoluminescence decay kinetics measurements of Ba-doped PbWO₄ crystals were compared with those of undoped and Mo-doped samples. Photoluminescence decay measurements focus on the coexistence of the immediate (fast) decay having a decay time of a few nanoseconds with slower delayed recombination decay processes. The radioluminescence emission peaking at 500 nm in Ba-doped crystals is similar to that observed in Mo-doped samples. However, photoluminescence of the Ba-doped crystals shows much faster decay kinetics with respect to that of PbWO₄:Mo. Wavelength-resolved thermally stimulated luminescence data (10–300 K) provides complementary information about trapping states and is correlated to photoluminescence decay kinetics.     

Real time dose rate measurements with fiber optic probes based on the RL and OSL of beryllium oxide

This work covers the examination of fiber optical probes based on the radioluminescence and real time optically stimulated luminescence of beryllium oxide. Experiments are carried out to determine the fundamental dosimetric and temporal properties of the system and evaluate its suitability for dose rate measurements in brachytherapy and other applications using non-pulsed radiation fields. For this purpose the responses of the radioluminescence and optically stimulated luminescence signal have been investigated in the dose rate range of 20 mGy/h to 3.6 Gy/h and for doses of 1 mGy up to 6 Gy. Furthermore, a new, efficient analysis procedure, the double phase reference summing, is introduced, leading to a real time optically stimulated luminescence signal. This method allows a complete compensation of the stem effect during the measurement. In contrast to previous works, the stimulation of the 1 mm cylindrical beryllium oxide detectors is performed with a symmetric function during irradiation. The investigated dose rates range from 0.3 to 3.6 Gy/h. The real time optically stimulated luminescence signal of beryllium oxide shows a dependency on both the dose rate and the applied dose. To overcome the problem of dose dependency, further experiments using higher stimulation intensities have to follow.     

Fiber-optic-coupled RbMgF3:Eu for remote radiation dosimetry

A portable fiber optic dosimeter has been developed that incorporates RbMgF₃:Eu²⁺ at the end of a multimode polymer fiber. It uses two stimulation sources and takes advantage of the range of stimulable traps in this compound. We observe radioluminescence (RL) during gamma ray irradiation and show that the low-dose RL increases linearly with increasing dose rate where the minimum detectible dose rate is ∼0.015 μSv/s. We show that pulsed infrared-stimulated (940 nm) optically stimulated luminescence (OSL) can be used for real time dose monitoring. The cumulative dose can be readout after irradiation where a linear OSL dose response was observed when stimulating at 505 nm and the minimum detectable dose is ∼50 μSv.     

Dose rate measurements with a ruby-based fiber optic radioluminescent probe

Fiber optic radioluminescence dosimetry allows real-time dose rate measurements in complex, narrow geometries and at places of high dose rates, without exposing the operator or the susceptible electronics. The keys are the spatial separation of radiation sensitive probe and electronic processing system and their optical connection by a flexible light guide. The small probes are capable of measuring fields of high dose rate gradients and the sealed probe-tip qualifies for applications in the fluid milieu and even for in-vivo-dosimetry. One problem of fiber optic dosimetry is the generation of Cherenkov radiation and fiber luminescence in the irradiated light guide, the so called stem effect. Ruby (Al₂O₃:Cr) has a narrow radioluminescent emission at 694 nm and is a potential luminophor for fiber optic radioluminescence dosimetry. In this work the influence of the stem effect on our ruby-based fiber optic dosimetry system is examined. The behavior of ruby probes under irradiation up to 0.5 kGy, as well as their luminescence decay characteristics and the applicability for measurements in radiotherapeutic fields are investigated.     

Radioluminescent dosimetry of α-quartz

The variation in the ultraviolet component of the radioluminescence intensity during X-ray excitation of α-quartz has been found to be dependent on the dose of previous ionizing irradiation. A new method of radiation dosimetry using UV radioluminescence is described. Radioluminescent dosimetry measurements of γ-rays produced by Chernobyl accident and background irradiation were made using natural and extracted crystalline quartz.     

Eu and Rb co-doped LiCaAlF6 scintillators for neutron detection

Eu and Rb co-doped LiCaAlF₆ (LiCAF) single crystals with different dopant concentrations were grown by the micro-pulling-down method for neutron detection. Their transmittance spectra showed strong absorption bands at 200–220 and 290–350 nm, and under ²⁴¹Am alpha-ray excitation, their radioluminescence spectra exhibited an intense emission peak at 373 nm that was attributed to the Eu²⁺ 5d–4f transition. These results were consistent with those for the Rb-free Eu:LiCAF. The highest light yield among the grown crystals was 36,000 ph/n, which was 20% greater than that of the Rb-free crystal. In addition, the neutron-excited scintillation decay times were 650–750 ns slower than that of the Rb-free Eu:LiCAF.     

Growth and radioluminescence of metal elements doped LiCaAlF6 single crystals for neutron scintillator

The ns²-type metal elements (Pb and Sn) doped LiCaAlF₆ single crystals were grown by a micro-pulling-down (μ-PD) method. Pb doped LiCaAlF₆ [Pb:LiCAF] crystals showed high transparency and single phase of the LiCAF structure. However, we could not obtain Sn:LiCAF crystals due to the evaporation of SnF₂ during the crystal growth. There was an absorption peak around 193 nm in the transmittance spectrum of Pb:LiCAF crystal. In the radioluminescence spectrum of the Pb:LiCAF crystal under X-ray irradiation, two emission peaks around 200 and 830 nm were observed.     

Radioluminescence Properties of Copper- and Terbium-Implanted Strontium Titanate

In this study, the effects of Cu and Tb implantation on the radioluminescence (RL) properties of unimplanted and Cu- and Tb-implanted SrTiO₃ (STO) crystals were investigated. The changes induced by heavy ion implants of the surface clearly modify the initial strong RL signals seen near 400–750 nm. During heating there are step increases in intensity at the RL spectrum near 60, 40, and 82 K for unimplanted and Cu- and Tb-implanted samples, respectively.     

A systematic study of the radioluminescence properties of single feldspar grains

Spectral radioluminescence properties of a large number of single grains were measured. The main emission in K-feldspar grains occurs in the infrared range with the same dose characteristic as shown by multi-grain samples. For plagioclases, large differences in spectral radioluminescence between single-grains and multi-grain aliquots were detected. Differences in the saturation of the dose characteristics of the individual emissions have been observed. Consequences for dating application are discussed.     

Crystal growth and luminescence properties of Pr-doped LuLiF4 single crystal

0.1, 1, and 3% Pr (with respect to Lu) doped LuLiF₄ (Pr:LuLiF₄) single crystals were grown by the micro-pulling-down (μ-PD) method. Transparency of the grown crystals was higher than 70% in the visible wavelength region with some absorption bands due to Pr³⁺ 4f-4f transitions. Intense absorption bands related with the Pr³⁺ 4f-5d transitions were observed at 190 and 215 nm. In radioluminescence spectra, Pr³⁺ 5d-4f emissions were observed at 220, 240, 340, and 405 nm. In the pulse height spectra recorded under ¹³⁷Cs γ-ray excitation, the Pr 3% doped sample showed the highest light yield of 2050 photons/MeV and the scintillation decay time of it exhibited 23 and 72 ns also excited by ¹³⁷Cs γ-ray.     

Photochemical preparation of ZnO nanoparticles

Preparation of zinc oxide nanoparticles from aqueous solutions containing zinc nitrate or formate using UV irradiation was investigated. Analysis of solid phase formed during irradiation confirmed the presence of zinc oxide or zinc peroxide nanoparticles ranging in size from 1 to 70 nm, depending on initial precursors. Annealing at temperatures 650–1000 °C results in forming of rice-like zinc oxide particles, up to hundreds of nm in size. Photochemical method yields material with high chemical purity and uniform particle size distribution. In addition, photo-induced doping of zinc oxide with lanthanum was studied. Presence of lanthanum in zinc oxide crystal lattice and post-preparation treatment in reduction atmosphere significantly increase the UV excitonic luminescence at 395 nm in radioluminescence spectra.     

Luminescence properties of Pr3+-doped transparent oxyfluoride glass–ceramics containing BaYF5 nanocrystals

Transparent oxyfluoride glass–ceramics containing BaYF₅ nanocrystals were successfully synthesized by appropriate heat-treatment on the SiO₂–Al₂O₃–Na₂O–BaF₂–Y₂O₃–Pr₆O₁₁ precursor glass. The structure and luminescence properties of the precursor glass and glass–ceramics were investigated by DSC, XRD, TEM, optical transmission, photoluminescence, decay time and radioluminescence spectra. The XRD results indicate that the BaYF₅ nanocrystals can percitated in the precursor glass and the sharper emission peaks of Pr³⁺ in glass ceramic suggests that Pr³⁺ ions are incorporated into the BaYF₅ nanocrystals. The higher the heat-treatment temperature is, the more the Pr³⁺ ions are centered into BaYF₅ nanocrystals, which results in the optimal concentration of Pr³⁺ in glass ceramic changes on heat-treatment temperature. It is notable that the emission intensity of both photoluminescence and radioluminescence for 0.1 mol% Pr³⁺ in the glass ceramic (GC665) are stronger than those in the precursor glass. The mechanism of enhanced luminescence is also discussed.     

Monoclinic HfO2:Eu X-ray phosphor

HfO₂ and HfO₂:Eu powders were synthesized with Pechini method at temperatures in the range of 600–1500 °C. Structural, radioluminescence and photoluminescence properties of the powders were investigated. The highest light output of about 20% of the efficiency of commercial GOS:Eu was found for materials containing 0.5% of Eu and prepared at 1500 °C. The data shows, that further improvement of light output could be obtained if materials are processed at yet higher temperatures. Emission spectra indicate that Eu³⁺ experiences variety of symmetries of its surroundings. Undoped materials produce broad band emission peaking at 480 nm and showing a significant afterglow.     

Preparation and properties of Ce-doped Na–Gd phosphate glasses

Rare earth-doped sodium–gadolinium phosphate glasses with increased luminescence efficiency are promising materials for the detection of neutrons, γ- and X-rays. Their main advantages are low cost, high radioluminescence light output, high quality and chemical durability. The glasses were prepared by a rapid quenching technique in air. The radioluminescence intensity maximum was achieved for a Ce concentration of 3 mol% and that of Gd around 30%. Glass transition temperatures were above 300°C for the tested samples and this guarantees that the glass can be utilised in a sufficiently broad temperature range. The glass-forming ability of this glass system is high. However, until now high-quality glass has been only prepared with a Gd concentration of 40 mol% in the starting batch. The glasses containing at least 30 mol% Gd were moisture resistant, while those with lower Gd concentrations were slightly hygroscopic.     

Thermoluminescent properties of HfO2:Ti after exposure to X-rays

Radio- and thermoluminescent properties of HfO₂:Ti sintered ceramics were investigated in the temperature range of 10–300 K. Fabrication atmosphere altered somewhat the efficiency of radioluminescence but did not affect the spectral distribution of the broad scintillation band covering the 380–570 nm range of wavelengths and peaking at 522 nm at 10 K and about 490 nm at 300 K. The analogous shift was seen in photoluminescence. Scintillation efficiency was continuously growing from 10 K to 300 K, while photoluminescence intensity was stable in the 10–250 K range of temperatures and was reduced by about 30% at 300 K. Analysis of these observations allowed to conclude that diffusion of carriers generated upon the impact of high-energy photons towards the Ti emitting center is strongly temperature-dependent and inferior at lower temperatures. Upon exposure to X-rays at 10 K the ceramics stored more than 50% of the absorbed energy. This energy could be recovered later upon thermal stimulation of the ceramics. Four main thermoluminescent peaks were then produced at 95, 140, 243 and 278 K. This effect was tentatively associated with theoretically predicted self-trapping of holes in HfO₂. The so-called partial cleaning and T_max–T_stop experiments indicated that some fraction of traps shows a continuous distribution of their depths.     

Photoluminescence and radioluminescence study of NaMgF3:Eu nanoparticles

Photoluminescence (PL) and radioluminescence (RL) measurements were made on small (∼25 nm) NaMgF₃ nanoparticles doped with Eu concentrations ranging from 0.1% to 5%. We find that they contained Eu³⁺, Eu²⁺, and an additional unidentified defect with a broad PL emission ∼470 nm. Similar to previous measurements on larger (57 nm–77 nm) NaMgF₃:Eu nanoparticles with 1% Eu and 5% Eu, we find that the PL lifetime decreases with increasing Eu concentration that can be attributed to Eu energy transfer to non-radiative recombination sites. However, there is no change in the fraction of Eu³⁺ distorted sites. The ∼470 nm PL defect peak was also reported for larger nanoparticles, which suggests that this peak arises from similar unidentified point defects. However, the activated non-radiative decay for the small nanoparticles has a significantly lower activation energy. The Eu³⁺ RL decreases by only 2.3% at 10 kGy for low Eu concentrations.