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.

This work is dedicated to investigating the spatially-resolved Raman and optical properties of Eu3+-doped Gd1-xLuxAlO3 (x = 0.0, 0.4, 1.0) single-crystalline mixed perovskite compounds prepared using the liquid phase epitaxy method. The films were grown onto YAlO3 single crystal substrates in a quasi-homoepitaxial mode. Particular attention is given to the Gd1-xLuxAlO3 mixed composition with lattice parameters close to YAlO3, ensuring the best film-substrate compatibility. Vibrational properties were studied using micrometer-step Raman probing across the samples’ cross-sections, revealing distinct features of the films, substrates, and the interface regions (transition layers). The observed Raman bands were assigned to characteristic ionic motions of AlO6 octahedra, and their frequency evolution with increasing Lu content was correlated with changes in A-site cation mass and pseudo-lattice parameter.Micro-luminescence spectroscopy was employed to evaluate the dopant 5D0 → FJ (J = 0–4) transitions as a function of cross-section depth and host composition. The results provide new insights into melt-material migration toward the substrate, a critical issue in flux-assisted growth. The characteristic 4f-4f bands of Eu3+ were analyzed and fitted using site-symmetry considerations and Judd–Ofelt theory, enabling clarification of the interplay between lattice structure, phonon dynamics, and activator-site symmetry in Gd1-xLuxAlO3 perovskites. These findings offer valuable guidance for the development of high-density, Eu3+-doped single-crystalline film scintillators for next-generation micro-imaging detectors.

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.

Raman spectroscopy, high spectral resolution luminescence, and X-ray diffraction techniques were employed to study two Ce3+ doped Y3Al5O12 single crystalline films grown by liquid phase epitaxy method onto Y3Al5O12 and Lu3Al5O12 single crystal substrates. Optical spectra were obtained with a micrometer step along the cross-sections of epitaxial structures, allowing excellent differentiation of the film, the transition layer, and the substrate of each sample. X-ray measurements demonstrate the mismatch between the lattice constants of the Y3Al5O12:Ce3+ film and its Lu3Al5O12 substrate, an effect related to different compositions. Consequently, the film grown onto Lu3Al5O12 exhibits higher residual stresses than its counterpart grown onto Y3Al5O12. This was confirmed by a mutual comparison of the Raman bands positions of the films. The luminescence spectra of both samples consist mainly of cerium 5d-4f emission, the intensity of which allows for additional study of epitaxial cross section and estimation of the size of transition layer.

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 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.

The SC-YAG:Tb@YAG:Pr-SCF composite epitaxial structure consisting of a 1 mm thick single crystal substrate of YAG:Tb garnet and a thin (9 mu m) single crystalline film of YAG:Pr garnet is fabricated, and its luminescent properties are examined toward luminescence thermometry. The possibility to efficiently excite, individually or simultaneously, the Tb3+ and Pr3+ dopants by their intense allowed 4f -> 5d transitions is executed to reach relative thermal sensitivity higher than 1% K-1 over the range of temperatures as wide as 100-625 K and above 0.5% K-1 over 13-650 K. The obtained results demonstrate that using intra- and inter-configurational emission transitions of Pr3+ and other lanthanides makes it possible to design wide-range luminescence thermometers with high sensitivity spanning the entire operating limits.

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.