This work is devoted to examining the influence of energy transfer processes between Ce3+ and Pr3+ ions on the luminescent and scintillation properties of LuAG:Ce and LuAG:Ce,Pr scintillators, grown by liquid phase epitaxy onto undoped LuAG substrates with a PbO-B2O3-based flux. To characterize them, measurements of the absorption, cathodoluminescence, photoluminescence emission and excitation spectra as well as the photoluminescence decay kinetics of the SCFs under study were performed. The investigation confirmed simultaneous energy transfer processes between d-f and f-f states of Pr3+ ions and between Pr3+ (d-f) and Ce3+ (d-f) ions, as well as from Ce3+ (d-f) to Pr3+ (f-f) ions in LuAG host. Furthermore, the energy transfer from Pb2+ flux-related impurity to Ce3+ (d-f) and Pr3+ (f-f) ions also were found in the LuAG:Ce and LuAG:Ce,Pr SCFs. An energy diagram of the Pb2+, Pr3+ and Ce3+ ion levels was constructed, which provides a deeper overview of the mentioned energy transfer processes.

The study is dedicated to investigation of the structural, luminescent and photoconversion properties of epitaxial converters based on the single crystalline films of Ce3+ doped Ca3Sc2Si3O12 (CSSG:Ce) garnet. These SCFs with different thicknesses were grown using the liquid phase epitaxy method onto: (i) undoped Gd3Ga2.5Al2.5O12 (GAGG (2.5)) substrates; (ii) Ce3+ doped Gd3Ga2.5Al2.5O12 (GAGG:Ce (2.5) and Gd3Ga3Al2O12 (GAGG:Ce (3) substrates. For the first time, we have examined the phosphor conversion properties of the mentioned film and film-crystal converters under the excitation of a blue LED. We have established a trend line in the color coordinate diagram by systematically varying the film thickness in the 2-30 μm, 17-22 μm and 7-22 μm ranges for CSSG:Ce film/GAGG (2.5) crystal, CSSG:Ce film/GAGG:Ce (2.5) crystal and CSSG:Ce film/GAGG:Ce (3) crystal composite converters, respectively.

This work is dedicated to investigation of the luminescent properties of the prospective photoconversion material based on the crystal of Ce3+ doped Ca3Sc2Si3O12 (CSSG) garnet. The GSSG:Ce crystal was grown using the micropulling-down (mu PD) method. The CSSG:Ce crystal exhibited an intensive photoluminescence (PL) emission band with two sub-bands peaked at 504 and 545 nm, corresponding to 5d-4f (2F5/2;7/2) transitions. Furthermore, we have investigated also the formation of cerium multicenters in the GSSG:Ce crystal using analyses of the structure of Ce3+ photoluminescence emission and excitation spectra under excitation of the luminescence of this crystal by synchrotron radiation. The formation of Ce3+-multicenters in CSSG:Ce garnet is caused by the local inhomogeneity of the dodecahedral sites of garnet lattice due to localization of the hetero-valent Sc3+ and Si4+ cations in the octahedral and tetrahedral positions of the garnet host. The existence of Ce3+ multicenters resulted in a significant enhancement of the Ce3+ emission band in the red range and improving the performance of conventional YAG:Ce phosphor. The next task of our work was to evaluate the possibility of application of the GSSG:Ce crystal as a light phosphor-converter (pc) for white light-emitting diodes (WLEDs). In the frame of this task, we have successfully developed a prototype of WLED by employing the CSSG:Ce crystal as a phosphorconverter (pc) with blue 450 emitting LED as well as investigated the color characteristics of this pc-WLED.

In this study, Ce3+-doped Lu3Al5O12 garnet (LuAG) crystal detectors, with a density of ρ = 6 g/cm3 and an effective atomic number Zeff = 62, are proposed as promising materials for radiotherapy applications. This type of detector demonstrates excellent uniformity of structural and optical properties, high thermoluminescence (TL) light yield, optimal position of main TL glow peaks at temperatures around 245–295 °C, and high radiation stability. The set of TL detectors made from LuAG:Ce single crystal was used to evaluate the uniformity of dose and energy spectra of X-ray radiation from a clinical accelerator with 6 MV and 15 MV beams at the Department of Medical Physics, Oncology Center in Bydgoszcz, Poland, and γ-rays from a 60Co source at the National Institute of Oncology in Warsaw. The LuAG:Ce crystal detectors demonstrated highly promising results for registering X-ray radiation from accelerators with both 6 MV and 15 MV electron beams, as well as γ-rays from a 60Co source with energies of 1.17 and 1.33 MeV.

Introduction: In vivo verification of the delivered dose in brachytherapy remains an unsolved dosimetric problem. Conventional detectors based on ionization chambers, semiconductors or thermoluminescent (TL) materials based on LiF or Al2O3:C compounds cannot be used for this purpose. The first way to solve this problem is to use dosimetric materials that can be placed in the patient's body to record the delivered radiation dose in-situ using the OSL and/or scintillation phenomena.Material and Methods: In this work, it was proposed to use a known scintillation crystal of Ce3+ doped Ga3Ga3Al2O12:Ce garnet (GAGG:Ce) attached with a long optical fiber to measure in situ the radiation dose during brachytherapy treatment. The measurements were first performed in a phantom, and then on patients in the clinical conditions of the Oncology Center in Bydgoszcz.Results: The obtained results are very encouraging. Luminescence spectra from scintillators were recorded using a long optical fiber and a sensitive spectrometer, which can be placed in a safe place. Measurements on the phantom showed the perfect linear correlation between the dose and signal registered by the detector based on the GAGG:Ce crystal. Meanwhile, clinical measurements are subject to some uncertainty regarding the accuracy of detector placement in the treatment planning system and the possible passive emission response of the optical fiber.Conclusion: Scintillation crystals combined with optical fibers and very sensitive luminescence spectrometers create an ideal measurement system for in situ determining the dose of various ionizing radiations. However, their use in clinical practice requires the development of procedures for precisely positioning the detector in relation to the radiation target.

In this study, we propose novel three-layer composite scintillators designed for the simultaneous detection of different ionizing radiation components. These scintillators are based on epitaxial structures of LuAG and YAG garnets, doped with Ce3+ and Sc3+ ions. Samples of these composite scintillators, containing YAG:Ce and LuAG:Ce single crystalline films with different thicknesses and LuAG:Sc single crystal substrates, were grown using the liquid phase epitaxy method from melt solutions based on PbO-B2O3 fluxes. The scintillation properties of the proposed composites, YAG:Ce film/LuAG:Sc film/LuAG:Ce crystal and YAG:Ce film/LuAG:Ce film/LuAG:Sc crystal, were investigated under excitation by radiation with α-particles from a 239Pu source, β-particles from 90Sr sources and γ-rays from a 137Cs source. Considering the properties of the mentioned composite scintillators, special attention was paid to the ability of simultaneous separation of the different components of mixed ionizing radiation containing the mentioned particles and quanta using scintillation decay kinetics. The differences in scintillation decay curves under α- and β-particle and γ-ray excitations were characterized using figure of merit (FOM) values at various scintillation decay intensity levels (1/e, 0.1, 0.05, 0.01).

This work demonstrates current progress of our group in developing of two- and three-layered composite for radiation monitoring of various components of mixed ionization radiation fluxes based on the epitaxial structures of Ce3+ doped garnet compounds using the Liquid Phase Epitaxy growth technique. These scintillators contain one or two single crystalline films, dedicated for registration of low-penetrating particles, and bulk single crystal substrates used for detection of high-penetrating γ-rays. For creation of two- and three-layered epitaxial structures, the single crystalline films of Ce3+ doped Y3Al5O12, Tb3Al5O12 and Tb2GdAl5O12 garnets were used. The single crystal of mixed Gd3GaxAl5-xO12:Ce garnet with fixed Ga concentrations of x = 2.3 and 3.0 are utilized as substrates. To assess the scintillation properties of these epitaxial structures, the pulse height spectra, light yield and scintillation decay kinetics were measured under excitation by α–particles (239Pu), β-particles (90Sr + 90Y) and γ–rays (137Cs). Finally, the figure-of merit of composite scintillators under study were calculated for selection of the best epitaxial structures for simultaneous registration α– and β-particles and γ–rays.

Ce3+ doped Al2O3-YAG eutectics were successfully grown by the horizontal directional crystallization method. The crystallization rate of eutectic growth was changed in the 1–7.5 mm/h range at a growth temperature of 1835 ℃. The microstructure of eutectic samples was investigated using scanning electron microscopy and X-ray microtomography. The intrinsic morphology of eutectic represents the stripe-like channel structure with a random distribution of the garnet Y3Al5O12 (YAG) and Al2O3 (sapphire) phases. The content of these phases in the stripes changes in the 52.9–55.3% and 46.1–47.1% ratios, respectively, depending on the growth rate of the crystallization of the eutectic samples. The luminescent properties of the eutectic demonstrated the dominant Ce3+ luminescence in the garnet phase. The luminescence of the Ce3+ ions in Al2O3 has also been observed and the effective energy transfer processes between Ce3+ ions in the Al2O3 and YAG garnet phases were revealed under high-energy excitation and excitation in the UV Ce3+ absorption bands of sapphire. The phosphor conversion properties and the color characteristics (Al2O3-YAG):Ce eutectic with different thicknesses were investigated under excitation by a blue LED. We have also tested the prototypes of white LEDs, prepared using a blue 450 nm LED chip and (Al2O3-YAG):Ce eutectic photoconverters with 0.15 to 1 mm thicknesses. The results of the tests are promising and can be used for the creation of photoconverters for high-power white LEDs.

The luminescent properties of the single crystals of Ce3+ doped (Gd1−x−yLuxYy)3Al5O12:Ce (x = 0.1; y = 1.5) and Gd3GaxAl5-xO12:Ce (x = 2.7) garnets (GLYAG:Ce and GGAG:Ce) were investigated in this work. Both crystals were grown by the micropulling down method. The conventional absorption and luminescence spectral measurements together with the luminescent spectroscopy under excitation by synchrotron radiation were performed to characterize the optical properties of crystals. It has been found that cumulative effects of reducing the ion radius from Gd3+ to Y3+ and Lu3+ in the dodecahedral sites of the garnets host and alloying of Al3+ ions in octahedral positions instead Ga3+ ions increases the crystal field strength and causes the respective redshift of the Ce3+ emission spectra in GLYAG:Ce crystals in comparison with GAGG:Ce garnet. The energy transfer from Gd3+ cations to Ce3+ has also been registered at the emission spectra and excitation spectra of both crystals. The energies of creation of the excitons bound with the Ce3+ ions in GLYAG:Ce and GAGG:Ce hosts were found to be equal to 6.415 ± 0.15 eV and 6.22 ± 0.15 eV, respectively. Both crystals show well-distinguished thermo- and optically stimulated luminescence (TSL and IR OSL) after α- and β-particle irradiation. Meanwhile, GAGG:Ce crystals show significantly higher TSL and IR OSL intensities (by 3–4 times) and faster OSL decay kinetics in comparison with GLYAG:Ce counterpart.

In this work, three sets of single crystalline films (SCF) of Al2O3:Mn sapphire, YAlO3:Mn perovskite (YAP:Mn), and Y3Al5O12:Mn garnet (YAG:Mn), with a nominal Mn content of 0.1%, 1%, and 10 atomic percent (at.%) in the melt-solutions, were crystallized by the liquid phase epitaxy (LPE) method onto sapphire, YAP and YAG substrates, respectively. We have also calculated the average segregation coefficient of Mn ions for Al2O3:Mn, YAP:Mn and YAG:Mn SCFs with Mn content in the melt-solution in the 0.1–10% concentration range, which was equal to 0.1, 0.14 and 0.2, respectively. The main goal of the conducted research was the spectroscopic determination of the preferable valence states of manganese ions which were realized in the SCFs of sapphire, perovskite and garnet depending on the Mn content. For this purpose, the absorption, cathodoluminescence (CL), photoluminescence (PL) emission/excitation spectra and PL decay kinetics of Al2O3:Mn, YAP:Mn and YAG:Mn SCFs with different Mn concentrations were studied. Based on the CL and PL spectra, we showed that Mn ions, depending on the Mn content in the melt-solution, are incorporated in Al2O3:Mn, YAP:Mn and YAG:Mn SCFs in the different charged states and are located in the different crystallographic positions of the mentioned oxide lattices. We have observed the presence of the luminescence of Mn4+, Mn3+ and Mn2+ valence states of manganese ions in CL spectra in all SCFs under study with 0.1 and 1% Mn concentrations. Namely, the Mn4+ ion valence state with the main sharp emission bands peaked at 642 and 672 nm, related to the 2E → 4A2 transitions, was found in the luminescence spectra of the all studied Al2O3:Mn SCFs. The luminescence of the Mn2+ valence state was found only in YAP:Mn and YAG:Mn SCFs, grown from melt solution with 1% Mn content, in the emission bands peaked at 525 and 560 nm, respectively, related to the 4T1 → 6A1 transitions. The PL and CL spectra of YAP:Mn and YAG:Mn SCFs with the Mn content in the 0.1–1% range show that the main valence state of manganese ions in these films is Mn3+ with the main emission bands peaking at 655 and 608 nm, respectively, related to the 1T2 → 5E transitions. Meanwhile, higher than 1% Mn content in the melt solution causes a strong concentration quenching of luminescence of all Mn centers in Al2O3:Mn, YAP:Mn and YAG:Mn SCFs.

The luminescent properties of the single crystals of Ce3+ doped (Gd1_x_yLuxYy)3Al5O12:Ce (x = 0.1; y = 1.5) and Gd3GaxAl5-xO12:Ce (x = 2.7) garnets (GLYAG:Ce and GGAG:Ce) were investigated in this work. Both crystals were grown by the micropulling down method. The conventional absorption and luminescence spectral measurements together with the luminescent spectroscopy under excitation by synchrotron radiation were performed to characterize the optical properties of crystals. It has been found that cumulative effects of reducing the ion radius from Gd3+ to Y3+ and Lu3+ in the dodecahedral sites of the garnets host and alloying of Al3+ ions in octahedral positions instead Ga3+ ions increases the crystal field strength and causes the respective redshift of the Ce3+ emission spectra in GLYAG:Ce crystals in comparison with GAGG:Ce garnet. The energy transfer from Gd3+ cations to Ce3+ has also been registered at the emission spectra and excitation spectra of both crystals. The energies of creation of the excitons bound with the Ce3+ ions in GLYAG:Ce and GAGG:Ce hosts were found to be equal to 6.415 & PLUSMN; 0.15 eV and 6.22 & PLUSMN; 0.15 eV, respectively. Both crystals show well-distinguished thermo- and optically stimulated luminescence (TSL and IR OSL) after & alpha;- and fl-particle irradiation. Meanwhile, GAGG:Ce crystals show significantly higher TSL and IR OSL intensities (by 3-4 times) and faster OSL decay kinetics in comparison with GLYAG:Ce counterpart.

Growth technologies of oxide crystals in W/Mo crucibles have been developed as a low-cost alternative to conventional processes involving Ir crucibles. Carbon-containing atmosphere needed to protect crucibles from oxidation leads to the introduction of carbon into the crystal lattice and creation of carbon-related defects, which affect the scintillation performance. Meanwhile, a search for fast scintillators for the new generation of positron-emission tomographs and high-energy physics experiments at colliders is under way. Codoping with divalent cations has become an efficient way to suppress long components of scintillation decay in Ce-doped scintillators. This work addresses Y 3 Al 5 O 12 (YAG) crystals codoped with carbon, cerium activator, and divalent cations. Optical and scintillation properties of YAG:Ce,C, $\text{A}^{2+}$ crystals (A = Ca $^{2+}$ , Mg $^{2+}$ , Ba $^{2+}$ , Sr $^{2+}$ ) are systematically studied. Among all the studied garnet compounds, YAG:Ce,C,Ca $^{2+}$ crystals demonstrated the fastest scintillation decay times, which are promising for the mentioned applications. Mechanisms of scintillation process in the studied materials are discussed. The Ce $^{3+}$ /Ca $^{2+}$ ratio in YAG:Ce,C,Ca $^{2+}$ was optimized to minimize slow components in scintillation decay.

Sesquioxides of lanthanides, yttrium, and scandium are promising hosts for laser and scintillation materials; however, the crystallization of such compounds is complicated by very high melting temperatures, as well as polymorph transitions. This work reports for the first time the growth of Y2O3 and Y2−xScxO3 crystals by the Vertical Gradient Freezing method from tungsten crucibles, proposing an alternative to extremely expensive rhenium and iridium crucibles. Translucent Y2O3 samples are obtained, and their luminescent and scintillation parameters are evaluated. The main issues of Y2O3 crystallization under the proposed conditions are discussed, as well as ways of enhancing the crystal quality. Finally, polymorph transitions are avoided by decreasing the average radius of the rare earth cation by Y3+/Sc3+ substitution, providing transparent Y2−xScxO3 crystals with a cubic structure.

This work was dedicated to the development of novel types of composite phosphor converters of white LED, based on the epitaxial structures containing Y3Al5O12:Ce (YAG:Ce) and Tb3Al5O12:Ce (TbAG:Ce) single crystalline films, steeply grown, using the liquid-phase epitaxy method, onto LuAG:Ce single crystal substrates. The influence of Ce3+ concentration in the LuAG:Ce substrate, as well as the thickness of the subsequent YAG:Ce and TbAG:Ce films, on the luminescence and photoconversion properties of the three-layered composite converters were investigated. Compared to its traditional YAG:Ce counterpart, the developed composite converter demonstrates broadened emission bands, due to the compensation of the cyan-green dip by the additional LuAG:Ce substrate luminescence, along with yellow-orange luminescence from the YAG:Ce and TbAG:Ce films. Such a combination of emission bands from various crystalline garnet compounds allows the production of a wide emission spectrum of WLEDs. In turn, the variation in the thickness and activator concentration in each part of the composite converter allows the production of almost any shade from green to orange emission on the chromaticity diagram.

This work is dedicated to the development of new types of composite thermoluminescent detectors based on the single crystalline films of Ce-doped GdAlO3 perovskite and Mn-doped YAlO3 and (Lu0.8Y0.2)AlO3:Mn perovskites as well as Ce and Pr-doped YAlO3 single crystal substrates. These detectors were obtained using the Liquid Phase Epitaxy growth method from the melt solution based on the PbO-B2O3 fluxes. Such composite detectors can by applied for the simultaneous registration of different components of mixed ionization fluxes using the differences between the thermoluminescent glow curves, recorded from the film and crystal parts of epitaxial structures. For creation of the new composite detectors, we considered using, for the film and crystal components of epitaxial structures (i) the different perovskite matrixes doped with the same type of activator or (ii) the same perovskite host with various types of activators. The thermoluminescent properties of the different types of epitaxial structures based on the abovementioned films and crystal substrates were examined in the conditions of β-particles and X-ray excitation with aim of determination of the optimal combination of perovskites for composite detectors. It was shown that, among the structures with all the studied compositions, the best properties for the simultaneous thermoluminescent detection of α- and X-rays were the GdAlO3:Ce film/YAlO3:Ce crystal epitaxial structure.

This manuscript summarizes recent results on the development of composite luminescent materials based on the single-crystalline films and single crystals of simple and mixed garnet compounds obtained by the liquid-phase epitaxy growth method. Such composite materials can be applied as scintillating and thermoluminescent (TL) detectors for radiation monitoring of mixed ionization fluxes, as well as scintillation screens in the microimaging techniques. The film and crystal parts of composite detectors were fabricated from efficient scintillation/TL materials based on Ce3+-, Pr3+-, and Sc3+-doped Lu3Al5O12 garnets, as well as Ce3+-doped Gd3−xAxAl5−yGayO12 mixed garnets, where A = Lu or Tb; x = 0–1; y = 2–3 with significantly different scintillation decay or positions of the main peaks in their TL glow curves. This work also summarizes the results of optical study of films, crystals, and epitaxial structures of these garnet compounds using absorption, cathodoluminescence, and photoluminescence. The scintillation and TL properties of the developed materials under α- and β-particles and γ-quanta excitations were studied as well. The most efficient variants of the composite scintillation and TL detectors for monitoring of composition of mixed beams of ionizing radiation were selected based on the results of this complex study.

Results of spectroscopic studies at ambient and high pressures of a LuAlO3:Ce3+ (LuAP:Ce) single crystalline film (SCF) as well as LuAP:Ce and YAlO3:Ce (YAP:Ce) single crystals are reported. Room temperature absorption measurements of the single crystals in the vacuum UV region allowed establishing the bandgap energies of 7.63 eV for YAP and 7.86 eV for LuAP, with an assumption of the direct band-gaps. Luminescence of Ce3+ in LuAP and YAP bulk crystals was measured as a function of temperature from 6 K up to 873 K. Temperature quenching of the Ce3+ luminescence in YAP:Ce was observed above 650 K, which is related to the location of the lowest Ce3+ 5d level at 1.27 eV below the conduction band minimum. No temperature quenching occurred in LuAP:Ce up to 873 K, mostly due to the lower energy of the 4f levels with respect to the valence band maximum. The barycenter energies and splittings of Ce3+ 5d states in YAP and LuAP at room temperature were precisely established. Theoretical calculations of the Ce3+ 5d states energy structure under pressure revealed a discrepancy between the obtained experimental results and the prediction of Dorenbos' theoretical model. The discrepancy can be removed if instead of the 5d state of the free Ce3+ ion the bandgap of the compound is taken as reference energy for the red-shift of the 5d level. This hypothesis also allows us to take into account the pressure-induced increase of the bandgap energy, expected for the studied compounds. Pressure dependences of LuAP:Ce luminescence spectra suggest that a certain type of phase transition occurs above 15 GPa.