T. Zorenko

Scintillating Screens for Micro-Imaging Based on the Ce-Tb Doped LuAP Single Crystal Films

Single Crystal Film (SCF) scintillators are key-components of todays high-resolution 2D X-ray detectors used at synchrotrons for applications such as X-ray Radiography, Computed Tomography (CT), laminography, full-field XANES, and topography. Due to its high density and effective atomic number, LuAlO3 (LuAP) perovskite has a great potential to replace or complement the currently used Eu-doped Gd3Ga5O12 (GGG:Eu) and Tb-doped Lu2SiO5 (LSO:Tb) SCFs. In this article we present the growth of LuAP single crystalline films on undoped YAlO3 (YAP) by the vertical dipping isothermal Liquid Phase Epitaxy (LPE) growth method. For the comparison of the light output of Ce and Tb doped LuAP SCF screens both cathodoluminescence (CL) and X-ray excited luminescence (RL) measurements were used. For investigations of Ce-Tb energy transfer in the afore mentioned oxide hosts, in addition to using traditional spectroscopic methods, we made time-resolved luminescent spectroscopy of Ce-Tb doped LuAP SCFs under excitation by pulsed synchrotron radiation at the Superlumi station (HASYLAB at DESY). Recently we have demonstrated the strong quenching influence of Pb2+ flux related impurity on the Ce3+ emission in the Ce-doped LuAP SCF screens. However our present investigation shows that Tb-doped LuAP SCFs are efficient X-ray scintillators, whose light output can be significantly increased by co-doping with Ce3+ ions. Namely, we demonstrate the efficient Ce→ Tb energy transfer in LuAP:Tb,Ce SCFs. Finally, as-grown LuAP:Tb and LuAP:Tb,Ce films were evaluated for high-resolution X-ray imaging using a spatial resolution target at the European Synchrotron Radiation Facility (ESRF), and displayed promising results.

Thermoluminescent Properties of Undoped and Ce-Doped Lutetium Orthosilicate and Yttrium Orthosilicate Single Crystals and Single Crystalline Films Scintillators

In this work the comparative analysis of thermoluminescent properties of undoped and Ce-doped single crystals (SC) and single crystalline films (SCF) of Lu₂SiO₅ (LSO) and Y₂SiO₅ (YSO) orthosilicates were performed. The SC samples were prepared with the Czochralski method, and SCF were grown by the liquid phase epitaxy technique. We show that such different methods of material preparation resulted in different thermoluminescent properties of undoped and Ce³⁺ doped LSO and YSO SC and SCF caused by the presence host defects (first of all, oxygen vacancies) as trapping centers in SC and formation of Pb²⁺-Ce⁴⁺ pair centers in SCF.

Luminescence centers in Y3Al5O12:La single crystals

The nature of luminescence centers created by La3+ isoelectronic impurities (IIs) in Y3Al5O12 (YAG) crystals has been considered. The La3+ dopant in YAG crystals gives rise to intensive UV luminescence in the complex band peaked at 4.28 eV at 300 K with a decay time of the main component of 575 ns. It has been shown that the complex UV emission band in YAG:La crystals in the 10–300 K range is a superposition of the luminescence of excitons localized near La dopants (LE(La) centers), the recombination luminescence of La3+ ions in the positions of Y3+ cations (LaY centers) and the low-intensive recombination luminescence of YAl antisite defects in the bands peaked at 4.65–4.62, 4.29–4.25 and 3.86–3.84 eV, respectively. In the visible range the emission spectra of YAG:La crystals also consist of the luminescence of F+ and F-centers in the bands peaked at 3.1 and 2.69 eV with a decay time of the main components of 2.3 ns and in the μs-ms range, respectively. It has been shown that the luminescence of F+ and F-centers in YAG:La crystals can be excited by emission of LE(LaY) and LaY centers.

High pressure spectroscopy study of SCF Tb3Al5O12:Mn

Single crystal film of Tb3Al5O12:Mn, with concentration of Mn approximately equal to 0.07 at%, has been grown by liquid phase epitaxy on Y3Al5O12 substrate. We have measured the absorption, luminescence, luminescence excitation spectra and luminescence kinetics of the film. To analyze the energetic structure and to estimate the crystal field strength we have measured the photoluminescence spectra under high hydrostatic pressure applied in diamond anvil cell up to 110 kbar. The Mn emission was consisted with the band peaked at 16800 cm−1 that shifts toward the lower energy with increasing pressure with the rate −9 cm−1/kbar. To characterize the Mn charge state we performed calculations of Tanabe -Sugano diagrams for 3d5, 3d4 and 3d3 system. The negative pressure shift of the 16800 cm−1 band yields attribution of this band to the 4T1 →6A1 transition in dodecahedrally coordinated Mn2+ ion. We have estimated quantity of Dq/B equal to 1.8 ±0.2. The configurational coordinate diagram of the Mn2+(3d5) has been calculated to analyze the nonradiative deexcitation processes 4T1 → 2T2 →6A1.

Novel Scintillating Screens Based on the Single Crystalline Films of Ce Doped Multi-Component

The paper is dedicated to development of the novel scintillating screens based on single crystalline films of Ce doped multi-component (Gd,Y,Lu)₃(Al,Sc)₅O₁₂ garnets onto Gd₃Ga₅O₁₂ substrates using the liquid phase epitaxy method.

({\rm Gd},{\rm Y},{\rm Lu})_{3}({\rm Al},{\rm Sc})_{5}{\rm O}_{12}

UV emitting scintillating screens based on single crystalline films (SCFs) of Lu3Al5−xGaxO12:Pr garnet have been developed by the liquid phase epitaxy (LPE) growth method onto Y3Al5O12 (YAG) substrates using a lead-free BaO based flux. The absorbance, luminescence and scintillation properties of these SCFs have been investigated depending on the Ga content in the x = 0–1.9 range. We have found that the absorption and luminescence spectra of Pr3+ ions as well as the scintillation light yield (LY) and decay kinetics of Lu3Al5−xGaxO12 SCFs are non-linearly affected by the gallium concentration x in the mentioned solid solution due to preference for the distribution of Ga3+ and Al3+ ions between the tetrahedral and octahedral positions of the garnet host, respectively. The best scintillation properties of Lu3Al5−xGaxO12:Pr SCFs are achieved at the Ga content in the x = 1.0–1.2 range. The LY of the Lu3Ga1.2Al3.8O12:Pr SCF is comparable with the LY of the best reference LuAG:Pr single crystal counterpart and significantly (up to 3 times) overcomes the LY of LuAG:Pr and Lu3Al4–3.5Ga1.0–1.5O12 SCFs, grown onto the YAG substrates from the conventional PbO–B2O3 flux.