The work presents the results of optical and electron paramagnetic resonance (EPR) investigations of Ce3+ incorporation into Lu2SiO5 single crystalline films (LSO:Ce SCFs), grown using the liquid phase epitaxy method. It also examines the conversion of Ce valence state as a result of the LSO:Ce SCF thermal treatment in reducing and oxygen-rich atmospheres. The EPR study revealed the presence of only one type of Ce3+ center (Ce1), corresponding to the localization of Ce3+ ions in 7-fold coordinated positions within the Lu2SiO5 host. No spectra of Ce2 centers (6-fold coordinated Ce3+ positions) were detected in the LSO:Ce SCF films, indicating their negligibly small concentration. High-temperature annealing of the as-grown films in air reduces the concentration of Ce3+ ions to a level undetectable by EPR due to the Ce3+ -> Ce4+ conversion. In contrast, thermal treatment in a 95%N2 + 5%H2 reducing atmosphere results in the opposite Ce4+ -> Ce3+ conversion, substantially increasing the concentration of Ce3+. The oxidation/reduction treatment and Ce3+/Ce4+ valence state change lead to notable variations in the scintillation light yield and decay kinetics of the LSO:Ce SCFs, offering a method to tune their scintillation figure of merit.

In this work, we present a study of newly developed two-layered composite scintillators based on epitaxial structures of garnet compounds for the simultaneous registration of different components of mixed radiation fluxes, and we evaluate their α/β/γ discrimination performance. The composite scintillators under study were doubly layered structures composed of TbAG:Ce or TbAG:Ce,Mg single-crystalline film grown onto Czochralski-grown GAGG:Ce single-crystal substrates using the liquid-phase epitaxy (LPE) method. The spectrometry measurements were performed with four different radioactive sources: 137Cs (emitting 661.6-keV γ rays), 241Am (5.5-MeV α particles and 59.5-keV γ rays), 90Sr (β particles with energies up to 2 MeV), and 14C (β particles with energies up to 156 keV). The pulse-height spectra (PHS) were recorded with a shaping time of 10 μs in an amplifier due to the presence of long scintillation components in the tested samples. Scintillation time profiles were measured under excitation of 661.6-keV γ rays, 5.5-MeV α particles, and β particles from 90Sr/90Y and 14C. Both types of TbAG:Ce film/GAGG:Ce substrate and TbAG:Ce,Mg film/GAGG:Ce substrate composites show good ability for the simultaneous registration of the mentioned components in the mixed radiation field with very reasonable Figure-of-Merit values: FoM(τ) greater than 0.2 and FoM(PSD) greater than 1.0.

In this work, we report the fabrication and characterization of single-film and double-film composite epitaxial garnet structures based on single-crystalline films (SCFs) and bulk single-crystal (SC) scintillators for enhanced α-γ discrimination in mixed radiation fields. These composite scintillators consist of TbAG:Ce and YAG:Ce SCFs grown by liquid-phase epitaxy (LPE) on Czochralski-grown Gd3Ga2.5Al2.5O12 (GAGG:Ce) bulk SC substrates. Single- and double-film architectures were designed to optimize the energy absorption and pulse-shape discrimination (PSD) performance for low-penetrating α-particles and high-energy γ-rays. Energy calibration was performed using different γ-ray sources (57Co, 51Cr, and 137Cs), enabling the conversion of detector signals to a calibrated electron-equivalent energy scale (keVee). Integration gates were systematically optimized, yielding maximum figures of merit (FOM) of 1.4 for the GAGG:Ce SC substrate, 1.9 for the single-film composite, and 5.0 for the double-film composite, demonstrating a progressive improvement in α-γ discrimination with increasing structural complexity. Two-dimensional PSD density maps reveal well-separated α and γ events, with the highest separation observed for the double-film composite. These results indicate that the engineering of LPE-grown composites provides tunable scintillation decay profiles, enhanced temporal separation, and increased light yields, making them promising candidates for applications such as mixed radiation field detection, dosimetry, and radiation monitoring.

This study investigates the structural, luminescent, and photoconversion properties of composite converters based on epitaxial structures containing single-crystalline films of Ce³⁺-doped Ca₂₋ₓY₁₊ₓMg₁₊ₓSc₁₋ₓSi₃O₁₂:Ce (x=0–0.25) (CYMSSG:Ce) garnet, and Y₃Al₅O₁₂ (YAG) or YAG:Ce substrates, grown using the Liquid Phase Epitaxial (LPE) method. The research focuses on a detailed analysis of the properties of film-crystal composite converters to achieve a deeper understanding of their photoconversion performance, providing an innovative approach to designing a new type of film/ substrate converters for white LEDs. This was accomplished by systematically varying the Y/Sc/Mg cation content in the film and adjusting the film thickness within the range of 19–67 µm for CYMSSG:Ce/YAG structures and 10–22 µm for CYMSSG:Ce/YAG:Ce structures. A significant emphasis of this research was placed on mapping the performance of these converters using a color coordinate diagram, a key tool for visualizing the relationship between film composition, thickness, and photoconversion efficiency. The resulting data revealed clear and distinct trends, offering valuable insights into the tunability of the luminescent properties of white LEDs through precise control of content and film thickness.

This work presents a comprehensive study of the structural, luminescent, and photoconversion properties of epitaxial composite phosphor converters based on single crystalline films of Ce3+-activated Ca2−xY1+xMg1+xSc1−xSi3O12:Ce (x = 0–0.25) (CYMSSG:Ce) garnet, grown using the liquid phase epitaxy (LPE) method on single-crystal Y3Al5O12 (YAG) and YAG:Ce substrates. The main goal of this study is to elucidate the structure–composition–property relationships that influence the photoluminescence and photoconversion efficiency of these film–substrate composite converters, aiming to optimize their performance in high-power white light-emitting diode (WLED) applications. Systematic variation in the Y3+/Sc3+/Mg2+ cationic ratios within the garnet structure, combined with the controlled tuning of film thickness (ranging from 19 to 67 µm for CYMSSG:Ce/YAG and 10–22 µm for CYMSSG:Ce/YAG:Ce structures), enabled the precise modulation of their photoconversion properties. Prototypes of phosphor-converted WLEDs (pc-WLEDs) were developed based on these epitaxial structures to assess their performance and investigate how the content and thickness of SCFs affect the colorimetric properties of SCFs and composite converters. Clear trends were observed in the Ce3+ emission peak position, intensity, and color rendering, induced by the Y3+/Sc3+/Mg2+ cation substitution in the film converter, film thickness, and activator concentrations in the substrate and film. These results may be useful for the design of epitaxial phosphor converters with tunable emission spectra based on the epitaxially grown structures of garnet compounds.

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.

Excitation with synchrotron radiation has provided a powerful means to study the intrinsic and dopant-related luminescent phenomena of wide bad -gap dielectrics. In this study, the luminescent properties of Mn- and Crdoped single crystalline films of alpha-Al 2 O 3 (sapphire), grown using the liquid phase epitaxy method from PbO -B 2 O 3 flux onto C plane-oriented sapphire crystal substrates, were systematically investigated using absorption and cathodoluminescence spectra as well as the conventional and advanced photoluminescent spectroscopy under synchrotron radiation excitation. The emission and excitation spectra have shown characteristic bands corresponding to Mn 4 + and Cr 3 + impurities as well as Pb 2 + flux-related dopants and indicated the participation of these metal ions in the luminescence process. The influence of the excitation energy in the transparency region and exciton range of the Al 2 O 3 host on the intensity and spectral shape of the emissions bands of these dopants is discussed in detail. The obtained results contribute to understanding the application potential of Al 2 O 3 :Mn and Al 2 O 3 :Mn single crystalline films in optoelectronic devices and luminescent sensors.

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.

This work is dedicated to investigating the structural, luminescence and photocurrent characteristics of LuAG:Ce single crystalline films grown using the liquid phase epitaxy method on both LuAG and YAG substrates. The primary objective is to analyze the influence of different growth modes, namely homoepitaxial and quasi-homoepitaxial, on the structural and luminescence properties of Ce3+ ions in these films under ambient and high-pressure conditions. Based on the results of X-ray diffraction measurements, we can conclude that both epitaxial structures are fully relaxed. However, a slight deformation of the garnet lattices is observed, manifesting the inequality of the in-plane and out-of-plane lattice constants of substrates and films. The difference in the energy gap values between positions of 4f-5d1,2 Ce3+ absorption bands (6-12 meV) and the positions of the Ce3+ emission band (6 meV) was observed for both LuAG:Ce films and caused by the small differences in local perturbations of garnet hosts for epitaxial structures, grown in homoepitaxial and quasi-homoepitaxial modes. The Ce3+ emission intensity in both LuAG:Ce films decreases with temperature in the 10-300 K range. The decay time of the Ce3+ luminescence in the LuAG:Ce homoepitaxially-grown film demonstrates a weak temperature dependence in the mentioned range. However, in the LuAG:Ce quasi-homoepitaxially-grown film, the decay time of the Ce3+ emission shows notable temperature dependences in the 10-300 K range, probably due to the formation of Ce4+-Pb2+ pair centers. The non-monotonical redshift of the Ce3+ emission band and the increase of the Ce3+ decay time are observed in both LuAG:Ce films under increasing external pressure from ambient to 19 GPa due to the compression and distortion of the crystal lattice. The redshift changes of the Ce3+ emission band on pressure are significantly more complicated for the LuAG:Ce quasi-homoepitaxially-grown film than the homoepitaxially-grown counterpart. The outcomes of this study contribute to the fundamental understanding of epitaxial growth processes and their impact on the luminescence characteristics of rare-earth-doped materials in the single crystalline film form.

Thermal management poses a significant challenge for conventional phosphor-converted white LEDs (pc-WLEDs), thereby affecting their overall efficiency. Single crystal phosphors (SCPs), such as Y3Al5O12:Ce (YAG:Ce), exhibit enhanced efficiency and thermal stability in comparison to conventional powder phosphors. The garnet Lu3Al5O12:Ce (LuAG) has been characterized as a green phosphor with even higher than YAG:Ce temperature stability, making it suitable for use in high-power WLEDs. However, there are some difficulties in obtaining suitable components with longer emission wavelengths in LuAG:Ce phosphors. As a way to solve this issue, the article suggests the growth of LuAG:Ce single crystalline films onto YAG:Ce substrates, thereby producing a composite color converter that possesses adjustable parameters. This paper presents a comprehensive analysis of the fabrication process as well as the characteristics of a two-layered LuAG:Ce film/YAG:Ce substrate composite color converter. The results of investigations of the structural, luminescence and photoconversion characteristics of composite color converters were presented as well. This study includes also consideration of the effect of varying LuAG:Ce film thicknesses and concentrations of Ce3+ in YAG:Ce substrates on photoconversion characteristics of composite converters.

The development of innovative high-power lighting sources is urgently required to design and investigate the new high structural quality and high-temperature stable converters in the form of single crystals and single crystalline films. This research deals with the growth and investigation of structural, luminescence, and photoconversion properties (color coordinates, color temperature and color rendering index) of the single crystalline films of Ce3+ doped (Lu, Y, Tb, Gd)3Al5O12 garnets, grown using the Liquid Phase Epitaxy method onto undoped Y3Al5O12 substrates. The combination of Ce3+ doped Lu3Al5O12, Y3Al5O12, Tb3Al5O12, Gd2.9Lu0.1Al5O12 film converter with respective thickness with commercial blue LED allows for obtaining green-yellow-orange-emitting pc-WLEDs. The application of the mentioned film converters results in the formation of four basic trends on the color diagram depending on the thickness of the converter.

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.

The work is dedicated to the investigation of the luminescent properties of Tris (8-hydroxyquinoline) aluminium (Alq3) thin layers using the conventional spectral methods (cathodoluminescence and photoluminescence), as well as the advanced time-resolved luminescent spectroscopy under excitation by the synchrotron radiation in the fundamental absorption edge of this material. The Alq3 films with a thickness of 100-300 nm were deposited by the PVD (Physical Vapor Deposition) method on silicon substrates. The structural properties of Alq3 layers were studied using scanning electronic microscopy and X ray diffraction. The structure of the luminescence spectra of the Alq3 layer in the green-yellow range at 10 K and 300 K confirms the complex structure of the emission centers of this material, associated with the internal fast radiation transitions in the Al3+ molecule surrounded by three 8-hydroxynoline ligands. It has been determined the energy of creation of excitons asso-ciated with Alq3 green emission centers, which has been equal to 6.78 eV and 6.86 eV at 10 K and 300 K, respectively.

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.